Driving forces of evolution. The driving forces of evolution: hereditary variability and natural selection The driving forces of evolution are hereditary variability
Living organisms are capable of “compensatory phenotypic modifications,” that is, such intravital changes that compensate for the effects of various injuries (a typical example is regeneration). This ability, which arises during evolution, can itself influence further evolution, since compensatory modifications arise not only in response to injury, but also in response to mutations that disrupt the normal course of development of the organism. Compensatory modifications can contribute to the consolidation of such mutations, which leads to rapid evolutionary transformations.
Two types of variability. Biological evolution is based on the famous “Darwinian triad”: heredity, variability and selection. Today, behind each of these three concepts are well-developed, complex and highly detailed theories, supported by countless facts, experiments and observations. Far from being static, these theories continue to evolve rapidly as new data emerge (and old ones are understood).
With regard to variation, the focus of evolutionary biology has traditionally been on so-called heritable (that is, genetically determined) variation. Hereditary variability is determined by differences in the genotype of individuals, it is transmitted from parents to offspring, and it is with this that natural selection “works” directly. However, there is also so-called modification variability, which is not hereditary in the strict sense of the word. Modification variability is a change in structure (phenotype) that occurs in response to changes in the conditions in which the organism develops (for one of the striking examples, see the note “A caterpillar has been bred that changes color when heated.” “Elements”, 02/9/06).
Modification variability is one of those natural phenomena that exist as if on purpose in order to confuse theorists. An erroneous understanding of the nature of modification variability and its cause-and-effect relationships with the evolutionary process in the past often led to various misunderstandings and inadequate conclusions. The following key provisions are currently generally accepted:
- The genotype does not determine the phenotype as such, but the norm of reaction: a certain range of development possibilities. Which of these possibilities will be realized no longer depends on genes, but on the conditions in which the development of the organism will occur. Phenotype variations within the reaction norm are modification variability.
- Modifications are not inherited (they are not “written” in genes), however ability they are, of course, inherited, i.e. is genetically determined.
- Modifying variability is often expedient (adaptive). For example, tanning caused by sunlight protects us from the harmful effects of ultraviolet radiation. However, the ability for adaptive modifications did not “fall out of the sky” for us. There is nothing mystical in it, it is not a manifestation of some incomprehensible “internal purposiveness of nature” or the result of the intervention of supernatural forces. The ability for adaptive modifications develops under the influence of selection, based on the consolidation of certain hereditary changes (mutations), just like any other adaptive properties of the organism.
- The ability for modification variability, on the one hand, is the result of evolution, on the other hand, it can itself have a significant impact on evolution. In the article under discussion by N.N. Iordansky, we are talking about one of the aspects of this influence.
The evolutionary role of modification variability. Already at the end of the 19th century, some biologists began to think that the ability for modification variability arising during evolution (in a broad sense, including the ability for lifetime changes in behavior, learning, etc.) could have a reverse effect on the course of the evolutionary process, and the nature of this influence may vary.
On the one hand, the ability for adaptive modifications can slow down evolution. If an organism, without changing its genotype, can adapt to different living conditions during its life, this can lead to a weakening of the effect of selection when the latter change.
On the other hand, this ability may partly predetermine further paths of evolutionary transformations. If conditions have changed “seriously and for a long time”, so that organisms from generation to generation have to undergo the same modification transformations during their development, this can lead to the fact that mutations leading to a strict genetic “fixation” of these transformations will be supported selection, and then the modification will turn into a hereditary change. In this case, the illusion of Lamarck’s “inheritance of an acquired characteristic” may arise. This phenomenon is known as the “Baldwin effect” (see about it in the note “Genes control behavior, and behavior controls genes.” “Elements”, 11/12/08). In this way, for example, some skill acquired by an animal during its life as a result of training can eventually turn into a hereditary instinct. In addition, a new manner of behavior - it does not matter whether it is instinctive or “conscious”, the main thing is that this behavior is reproduced over many generations - creates new selection vectors and can lead to the fixation of mutations that “make life easier” precisely with this behavior. For example, the development of animal husbandry led to the spread of a specific mutation in “livestock” human populations that allows adults to digest the milk sugar lactose (initially, people had this ability only in infancy). Once again we see the illusion of Lamarckian inheritance: our ancestors spent a long time “training” to drink milk as adults, and eventually the “results of training” became hereditary. In fact, of course, the mechanism of this evolutionary change is completely different: changed behavior (drinking the milk of domestic animals) led to the fact that periodically occurring mutations that disable the mechanism for turning off (in order to save) the synthesis of the lactase enzyme in adults ceased to be harmful and On the contrary, they became useful. People with this mutation ate better and left more offspring. Therefore, these mutations began to spread in the population in strict accordance with the laws of population genetics.
Even at the beginning of the 20th century, it was established that for almost any modification it is possible to find a mutation that will lead to similar phenotypic consequences, only strictly determined, independent of external conditions. This is called "genocopying modifications". As N.N. Iordansky notes, this is essentially not surprising. The genotype determines the “reaction norm”, i.e. a set of possible paths of individual development. If there are variants of external conditions that lead to the choice of one of these paths, then there may also be mutations that will make this path the only possible (or most probable) regardless of external conditions. Ultimately, modifications are caused by changes in the activity (expression) of certain genes in certain cells of the body. It is well known that changes in gene expression can be caused by both fluctuations in external conditions and mutations. The evolutionary significance of "genocopy modifications" is discussed in detail in the works of Waddington, Kirpichnikov, Shishkin and other evolutionists; these ideas are used in Schmalhausen's theory of stabilizing selection; even an attempt was made to formulate a special “epigenetic theory of evolution” on this basis.
Compensatory modifications. N.N. Iordansky draws attention to a special group of adaptive modifications, namely, compensatory reactions of organisms to various disturbances of ontogenetic processes and traumatic injuries to adult organisms. For example, many cases have been described in which an amphibian, reptile, bird or mammal lost one of its limbs, but compensated for the effects of the injury through behavioral changes and successfully produced offspring year after year. Fish have been repeatedly observed that have completely lost the caudal fin (sometimes along with part of the spine), but are in good physical shape. In such fish, the dorsal and anal fins often grow back, which form around the damaged area something like the dorsal and ventral lobes of the caudal fin.
This suggests that in natural biocenoses the struggle for existence and selection are not always so severe. In any case, selective “survival of the fittest” is a statistical process, and injured individuals often have a chance to survive and even leave offspring.
The main idea of N.N. Iordansky’s article is that the ability for compensatory modifications can lead to rapid evolutionary transformations due to the fact that the effect of many harmful mutations can be smoothed out thanks to compensatory modifications. As a result, such mutations can sometimes persist and even spread throughout the population. The fact is that compensatory modifications can compensate not only for injuries, but also for the consequences of harmful mutations.
Let's imagine that a fish has a mutation, as a result of which it does not develop a caudal fin. It is quite possible that during the ontogeny of such a fish, the same mechanism of compensatory modification that is activated when the tail is lost as a result of injury will “work.” In other words, the dorsal and anal fin will begin to grow back and form a kind of lost caudal fin. Of course, this will lead to a serious change in the structure of the fish. But this change will not necessarily be completely incompatible with life, because it is based on an “expedient” compensatory modification, the ability for which has been honed by selection in millions of previous generations of fish.
Perhaps this is how the sunfish and its relatives arose, whose fin structure is very similar to that obtained in other fish as a result of the traumatic loss of the caudal fin.
Thus, the ability to undergo compensatory modifications increases the likelihood of the fixation of large mutations, the evolutionary significance of which is usually considered to be extremely insignificant (because the likelihood that a large mutation will be beneficial or even not very harmful) is extremely small. However, taking into account compensatory modifications forces us to reconsider this assessment of probabilities.
N.N. Iordansky emphasizes that the idea he proposes is not an argument in favor of the so-called. saltationist model of evolution. Saltationists see saltations (abrupt changes in structure) as the main mechanism of evolution, ensuring the emergence of evolutionary innovations without the participation of selection. In contrast, N.N. Iordansky suggests that large changes in the organism that have arisen through mutations “along with more frequently occurring small variations can serve as elementary evolutionary material from which, under the influence of selection, new adaptations and new types of organization are formed.”
It should be noted that the evolutionary role of compensating mechanisms (including all kinds of negative feedbacks) is clearly manifested at the molecular genetic level. This is reflected in the concept of “evolutionary swing”, developed by N.A. Kolchanov and his colleagues from the Novosibirsk Institute of Cytology and Genetics (see: N.A. Kolchanov, V.V. Suslov, K.V. Gunbin. Modeling of biological evolution: Regulatory genetic systems and coding the complexity of biological organization). According to researchers, in networks of intergenic interactions, as a result of the action of stabilizing selection under relatively constant conditions, the development of compensatory mechanisms based on the principle of negative feedback occurs. In essence, these mechanisms provide the ability for compensatory modifications at the molecular level. They make the system more stable, better able to compensate for fluctuations in external conditions. But the development of compensatory mechanisms also leads to the fact that many mutations that could be harmful and throw the system out of balance actually do not cause harm, because their effects are compensated in the same way as external influences. As a result, such mutations are not eliminated by selection and can accumulate. This continues until some very large changes (for example, a transition to a new habitat) disable the compensating mechanisms - and then “latent” mutations can suddenly appear, leading to an explosive increase in the variability of organisms.
Thus, the ability for compensatory modifications that arises during evolution is an important factor that directs (limites, “channels”) possible paths of further evolution.
Hereditary variability
Random (non-directional) storage of features
Population waves- periodic fluctuations in population size. For example: the number of hares is not constant, every 4 years there are a lot of them, then a decline in number follows. Meaning: During decline, genetic drift occurs.
Genetic drift: if the population is very small (due to disaster, disease, decline of the pop wave), then traits persist or disappear regardless of their usefulness, by chance.
Struggle for existence
Cause: Many more organisms are born than can survive, so there is not enough food and territory for them all.
Definition: the totality of relationships of an organism with other organisms and with the environment.
Shapes:
- intraspecific (between individuals of the same species),
- interspecific (between individuals of different species),
- with environmental conditions.
Consequence: natural selection
Natural selection
This is the main, leading, directing factor of evolution, leading to adaptability, to the emergence of new species.
Insulation
Gradual accumulation of differences between populations isolated from each other can lead to the fact that they will not be able to interbreed - there will be biological containment, two different views will appear.
Types of isolation/speciation:
- Geographical - if there is an insurmountable barrier between populations - a mountain, river or a very large distance (occurs with rapid expansion of the range). For example, Siberian larch (in Siberia) and Daurian larch (in the Far East).
- Ecological - if two populations live in the same territory (within the same area), but cannot interbreed. For example, different populations of trout live in Lake Sevan, but they go to different rivers that flow into this lake to spawn.
Insert the missing terms from the proposed list into the text “Fluctuations in the number of individuals”, using numerical notations for this. The number of individuals in populations is not constant. Its periodic oscillations are called (A). Their significance for evolution lies in the fact that as the population grows, the number of mutant individuals increases as many times as the number of individuals increases. If the number of individuals in a population decreases, then it (B) becomes less diverse. In this case, as a result of (B), individuals with certain (D) may disappear from it.
1) population wave
2) struggle for existence
3) variability
4) gene pool
5) natural selection
6) genotype
7) phenotype
8) heredity
Answer
Choose one, the most correct option. Combinative variability is referred to as
1) the driving forces of evolution
2) directions of evolution
3) the results of evolution
4) stages of evolution
Answer
1. Establish the sequence of formation of adaptations in a plant population during the process of evolution. Write down the corresponding sequence of numbers.
1) consolidation of a new trait by stabilizing selection
2) the action of the driving form of selection on individuals in the population
3) change in the genotypes of individuals in the population under new conditions
4) change in the habitat conditions of the population
Answer
2. Establish the sequence of formation of plant fitness in the process of evolution. Write down the corresponding sequence of numbers.
1) reproduction of individuals with useful changes
2) the occurrence of various mutations in the population
3) struggle for existence
4) preservation of individuals with hereditary changes useful for given environmental conditions
Answer
3. Establish the sequence of microevolution processes. Write down the corresponding sequence of numbers.
1) the action of driving selection
2) the appearance of beneficial mutations
3) reproductive isolation of populations
4) struggle for existence
5) formation of a subspecies
Answer
4. Establish the sequence of action of the driving forces of evolution. Write down the numbers under which they are indicated.
1) struggle for existence
2) reproduction of individuals with useful changes
3) the appearance of various hereditary changes in the population
4) preservation of predominantly individuals with hereditary changes useful in given environmental conditions
5) formation of adaptation to the environment
Answer
5. Establish the sequence of formation of the population of the dark-colored birch moth butterfly in polluted industrial areas.
1) the appearance of differently colored butterflies in the offspring
2) an increase in the number of butterflies with darker colors
3) preservation as a result of natural selection of butterflies with dark colors and death with light colors
4) the emergence of a population of dark-colored butterflies
Answer
6n. Establish the sequence of processes during speciation. Write down the corresponding sequence of numbers.
1) distribution of useful traits in isolated populations
2) natural selection of individuals with useful traits in isolated populations
3) rupture of the species’ range due to changes in relief
4) the emergence of new traits in isolated populations
5) formation of new subspecies
Answer
1. Indicate the sequence of processes of geographic speciation. Write down the corresponding sequence of numbers
1) distribution of a trait in a population
2) the appearance of mutations in new living conditions
3) spatial isolation of populations
4) selection of individuals with useful changes
5) formation of a new species
Answer
2. Determine the sequence of processes characteristic of geographic speciation
1) formation of a population with a new gene pool
2) the appearance of a geographical barrier between populations
3) natural selection of individuals with characteristics adaptive to given conditions
4) the appearance of individuals with new characteristics in an isolated population
Answer
3. Indicate the sequence of processes during geographic speciation
1) accumulation of mutations in new conditions
2) territorial isolation of the population
3) reproductive isolation
4) formation of a new species
Answer
4. Indicate the sequence of stages of geographic speciation
1) divergence of traits in isolated populations
2) reproductive isolation of populations
3) the emergence of physical barriers in the range of the original species
4) the emergence of new species
5) formation of isolated populations
Answer
5. Establish the sequence of stages of geographic speciation. Write down the corresponding sequence of numbers.
1) the appearance of new random mutations in populations
2) territorial isolation of one population of a species
3) change in the gene pool of the population
4) preservation by natural selection of individuals with new characteristics
5) reproductive isolation of populations and formation of a new species
Answer
Establish the sequence of stages of ecological speciation. Write down the corresponding sequence of numbers.
1) ecological isolation between populations
2) biological (reproductive) isolation
3) natural selection in new environmental conditions
4) the emergence of ecological races (ecotypes)
5) the emergence of new species
6) development of new ecological niches
Answer
Choose one, the most correct option. In ecological speciation, as opposed to geographic speciation, a new species arises
1) as a result of the collapse of the original area
2) inside the old range
3) as a result of expansion of the original range
4) due to genetic drift
Answer
Choose one, the most correct option. An evolutionary factor contributing to the accumulation of various mutations in a population is
1) intraspecific struggle
2) interspecific struggle
3) geographical isolation
4) limiting factor
Answer
Choose one, the most correct option. Hereditary variability in the process of evolution
1) fixes the created attribute
2) is the result of natural selection
3) supplies material for natural selection
4) selects adapted organisms
Answer
Choose one, the most correct option. An example of ecological speciation
1) Siberian and Daurian larch
2) white hare and brown hare
3) European and Altai squirrel
4) populations of Sevan trout
Answer
Choose three correct answers out of six and write down the numbers under which they are indicated. Indicate the characteristics that characterize natural selection as the driving force of evolution
1) Source of evolutionary material
2) Provides a reserve of hereditary variability
3) The object is the phenotype of an individual
4) Provides selection of genotypes
5) Directional factor
6) Random factor
Answer
1. Establish a correspondence between the process occurring in nature and the form of struggle for existence: 1) intraspecific, 2) interspecific
A) competition between individuals of a population for territory
B) the use of one type by another
B) competition between individuals for the female
D) displacement of a black rat by a gray rat
D) predation
Answer
2. Establish a correspondence between an example of the struggle for existence and the form to which this struggle belongs: 1) intraspecific, 2) interspecific. Write numbers 1 and 2 in the correct order.
A) identification of nesting sites in the forest by crossbills
B) the bovine tapeworm uses cattle as a habitat
B) competition between males for dominance
D) displacement of a black rat by a gray rat
D) fox hunting for voles
Answer
3. Establish a correspondence between examples and types of struggle for existence: 1) intraspecific, 2) interspecific. Write numbers 1 and 2 in the order corresponding to the letters.
A) displacement of a black rat by a gray rat
B) behavior of male moose during the mating season
B) fox hunting mice
D) growth of beet seedlings of the same age in one bed
D) the behavior of a cuckoo in the nest of another bird
E) rivalry between lions in the same pride
Answer
4. Establish a correspondence between the processes occurring in nature and the forms of struggle for existence: 1) interspecific, 2) intraspecific. Write numbers 1 and 2 in the order corresponding to the letters.
A) marking of territory by a male field mouse
B) mating of male capercaillie in the forest
C) inhibition of seedlings of cultivated plants by weeds
D) competition for light between spruce trees in the forest
D) predation
E) displacement of the black cockroach by the red one
Answer
1. Establish a correspondence between the cause of speciation and its method: 1) geographical, 2) ecological. Write numbers 1 and 2 in the correct order.
A) expansion of the range of the original species
B) stability of the range of the original species
C) division of the species' range by various barriers
D) diversity of variability of individuals within the range
D) diversity of habitats within a stable range
Answer
2. Establish a correspondence between the features of speciation and their methods: 1) geographical, 2) ecological. Write numbers 1 and 2 in the order corresponding to the letters.
A) isolation of populations due to a water barrier
B) isolation of populations due to different timing of reproduction
B) isolation of populations due to the emergence of mountains
D) isolation of populations due to large distances
D) isolation of populations within the range
Answer
3. Establish a correspondence between the mechanisms (examples) and methods of speciation: 1) geographical, 2) ecological. Write numbers 1 and 2 in the order corresponding to the letters.
A) expansion of the range of the original species
B) preservation of a single original range of the species
C) the appearance of two species of gulls in the North and Baltic seas
D) formation of new habitats within the original range
E) the presence of populations of Sevan trout that differ in spawning periods
Answer
4. Establish a correspondence between the characteristics and methods of speciation: 1) geographical, 2) ecological. Write numbers 1 and 2 in the order corresponding to the letters.
A) long-term persistence of the existence of the range of the original species
B) division of the range of the original species by an insurmountable barrier
C) different food specializations within the original range
D) division of the area into several isolated parts
D) development of various habitats within the original range
E) isolation of populations due to different timing of reproduction
Answer
5. Establish a correspondence between the characteristics and methods of speciation: 1) geographical, 2) ecological. Write numbers 1 and 2 in the order corresponding to the letters.
A) habitat stability
B) the emergence of physical barriers
C) the emergence of populations with different periods of reproduction
D) isolation of populations in the forest by road
D) range expansion
Answer
1. Select three sentences from the text that describe the ecological method of speciation in the evolution of the organic world. Write down the numbers under which they are indicated. (1) Reproductive isolation causes microevolution. (2) Free crossing allows for the exchange of genes between populations. (3) Reproductive isolation of populations can occur within the same range for various reasons. (4) Isolated populations with different mutations adapt to the conditions of different ecological niches within the former range. (5) An example of such speciation is the formation of buttercup species that have adapted to life in the field, meadow, and forest. (6) The species serves as the smallest genetically stable supraorganismal system in living nature.
Answer
2. Read the text. Select three sentences that describe the processes of ecological speciation. Write down the numbers under which they are indicated. (1) During speciation, the range of a species is divided into fragments. (2) There are several populations in Lake Sevan, differing in spawning periods. (3) Speciation may be associated with a change in the ecological niche of a species. (4) If polyploid forms are more viable than diploid forms, they can give rise to a new species. (5) Several species of tits live in Moscow and the Moscow region, differing in their methods of obtaining food.
Answer
3. Read the text. Select three sentences that describe ecological speciation. Write down the numbers under which they are indicated. (1) Species in nature exist in the form of separate populations. (2) Due to the accumulation of mutations, a population can be formed under changed conditions in the original area. (3) Sometimes microevolution is associated with a gradual expansion of the range. (4) Natural selection consolidates persistent differences between plants of different populations of the same species, occupying the same habitat, but growing in a dry meadow or in a river floodplain. (5) For example, in this way the types of buttercups that grow in forests, meadows, and along river banks were formed. (6) Spatial isolation caused by mountain building may be a factor in speciation.
Answer
4. Read the text. Select three sentences that describe ecological speciation. Write down the numbers under which they are indicated. (1) Speciation can occur within a single contiguous range if organisms inhabit different ecological niches. (2) The causes of speciation are discrepancies in the timing of reproduction in organisms, the transition to new food without changing the habitat. (3) An example of speciation is the formation of two subspecies of the greater rattle growing in the same meadow. (4) Spatial isolation of groups of organisms can occur when the range expands and the population enters new conditions. (5) As a result of adaptations, South Asian and Eurasian subspecies of the great tit were formed. (6) As a result of isolation, endemic island species of animals were formed.
Answer
5. Read the text. Select three sentences that fit the description of ecological speciation. Write down the numbers under which they are indicated. (1) The result of the action of the driving forces of evolution is the spread of the species into new areas. (2) Speciation may be associated with an expansion of the range of the original species. (3) Sometimes it occurs as a result of the rupture of the original range of a species by physical barriers (mountains, rivers, etc.) (4) New species can master specific living conditions. (5) As a result of food specialization, several species of tits were formed. (6) For example, the great tit feeds on large insects, and the tufted tit eats the seeds of coniferous trees.
Answer
1. Read the text. Select three sentences that describe the features of geographic speciation. Write down the numbers under which the selected statements are indicated. (1) Associated with spatial isolation due to range expansion or fragmentation, as well as human activity. (2) Occurs in the event of a rapid increase in the chromosome set of individuals under the influence of mutagenic factors or errors in the process of cell division. (3) Occurs more often in plants than in animals. (4) Occurs through the dispersal of individuals to new territories. (5) In different living conditions, ecological races are formed, which become the ancestors of new species. (6) Polyploid viable forms can give rise to a new species and completely displace a diploid species from its range.
Answer
2. Select three sentences from the text that characterize the geographical method of speciation in the evolution of the organic world. Write down the numbers under which they are indicated. (1) The exchange of genes between populations during the reproduction of individuals preserves the integrity of the species. (2) If reproductive isolation occurs, crossing becomes impossible and the population takes the path of microevolution. (3) Reproductive isolation of populations occurs when physical barriers arise. (4) Isolated populations expand their range by maintaining adaptations to new living conditions. (5) An example of such speciation is the formation of three subspecies of the great tit, which colonized the territories of eastern, southern and western Asia. (6) The species serves as the smallest genetically stable supraorganismal system in living nature.
Answer
3. Read the text. Select three sentences that describe geographic speciation. Write down the numbers under which they are indicated. (1) Speciation is the result of natural selection. (2) One of the reasons for speciation is the discrepancy in the timing of reproduction of organisms and the occurrence of reproductive isolation. (3) An example of speciation is the formation of two subspecies of the greater rattle growing in the same meadow. (4) Spatial isolation of groups of organisms may be accompanied by range expansion, in which populations find themselves in new conditions. (5) As a result of adaptations, South Asian and Eurasian subspecies of the great tit were formed. (6) As a result of isolation, endemic island species of animals were formed.
Answer
4. Read the text. Select three sentences that describe geographic speciation. Write down the numbers under which they are indicated. (1) A species in nature occupies a certain area and exists in the form of separate populations. (2) Due to the accumulation of mutations, a population with a new gene pool can be formed within the original area. (3) Expansion of the species' range leads to the emergence of isolated new populations at its borders. (4) Within the new boundaries of the range, natural selection consolidates persistent differences between spatially separated populations. (5) Free interbreeding between individuals of the same species is disrupted as a result of the appearance of mountain barriers. (6) Speciation is gradual.
Answer
Choose three correct answers out of six and write down the numbers under which they are indicated. The processes leading to the formation of new species in nature include
1) mitotic cell division
2) spasmodic mutation process
4) geographic isolation
5) asexual reproduction of individuals
6) natural selection
Answer
Establish a correspondence between the example and the method of speciation that this example illustrates: 1) geographical, 2) ecological. Write numbers 1 and 2 in the correct order.
A) the habitat of two populations of common perch in the coastal zone and at great depths of the lake
B) the habitat of different populations of blackbirds in dense forests and near human habitation
C) disintegration of the May lily of the valley range into isolated areas due to glaciation
D) the formation of different types of tits based on food specialization
D) the formation of Dahurian larch as a result of the expansion of the range of Siberian larch to the east
Answer
Choose three options. Under the influence of what evolutionary factors does the process of ecological speciation occur?
1) modification variability
2) fitness
3) natural selection
4) mutational variability
5) struggle for existence
6) convergence
Answer
Choose three options. What factors are the driving forces of evolution?
1) modification variability
2) mutation process
3) natural selection
4) adaptability of organisms to their environment
5) population waves
6) abiotic environmental factors
Answer
1) crossing over
2) mutation process
3) modification variability
4) insulation
5) variety of species
6) natural selection
Answer
Choose three options. The driving forces of evolution include
1) isolation of individuals
2) adaptability of organisms to the environment
3) variety of species
4) mutational variability
5) natural selection
6) biological progress
Answer
Read the text. Select three sentences that indicate the driving forces of evolution. Write down the numbers under which they are indicated. (1) The synthetic theory of evolution states that species live in populations in which evolutionary processes begin. (2) It is in populations that the most intense struggle for existence is observed. (3) As a result of mutational variability, new characteristics gradually arise. Including adaptations to environmental conditions - idioadaptations. (4) This process of gradual emergence and retention of new characters under the influence of natural selection, leading to the formation of new species, is called divergence. (5) The formation of new large taxa occurs through aromorphosis and degeneration. The latter also leads to the biological progress of organisms. (6) Thus, the population is the initial unit in which the main evolutionary processes occur - changes in the gene pool, the appearance of new characteristics, the emergence of adaptations.
Answer
Establish a correspondence between the factors of speciation and its method: 1) geographical, 2) ecological, 3) hybridogenic. Write numbers 1-3 in the correct order.
A) polyploidization of hybrids from inbreeding
B) differences in habitats
B) division of the area into fragments
D) the habitat of different types of lily of the valley in Europe and the Far East
D) food specialization
Answer
Analyze the table “Struggle for Existence”. For each lettered cell, select the appropriate term from the list provided. Write down the selected numbers in the order corresponding to the letters.
1) combating environmental conditions
2) limited natural resources
3) combating unfavorable conditions
4) various ecological criteria of the species
5) seagulls in colonies
6) males during the mating season
7) birch and tinder
8) the need to choose a sexual partner
Answer
Choose one, the most correct option. Separation of populations of the same species according to the timing of reproduction can lead to
1) population waves
2) convergence of features
3) intensification of interspecies struggle
4) ecological speciation
Answer
Select two sentences that indicate processes NOT related to the intraspecific struggle for existence. Write down the numbers under which they are indicated.
1) Competition between wolves of the same population for prey
2) The fight for food between gray and black rats
3) Destruction of young animals with excess population size
4) The struggle for dominance in a pack of wolves
5) Reduction of leaves in some desert plants
Answer
© D.V. Pozdnyakov, 2009-2019
Darwin considered artificial selection to be the main mechanism responsible for the emergence and diversity of cultivated plants and domestic animals. In the process of studying artificial selection, the scientist came to the idea that a similar phenomenon exists in nature. What are the driving forces behind the evolution of species? Darwin saw the answer to this question in two components.
Firstly, he pointed out the presence of uncertain (individual) variability of organisms in their natural habitat.
Darwin determined the presence of individual variability in nature based on a number of facts. For example, bees distinguish bees from their own and neighboring hives. Plants grown from the acorns of one oak tree differ in many small external features, etc.
Secondly, Darwin came to the conclusion that the fitness of wild species, like cultivated forms, is the result of selection. But this selection is not made by man, but by the environment. Individual variability in nature is material for selection. Just as animal breeds and plant varieties are appropriately adapted to human needs, species adapt to life in certain environmental conditions.
As already mentioned, organisms tend to reproduce exponentially. However, not all born individuals survive to sexual maturity. The reasons for this are varied. The death of organisms may be observed from a lack of food resources, unfavorable environmental factors, diseases, enemies, etc. Based on this, Darwin came to the conclusion that there is a constant struggle for existence between organisms in nature.
The struggle for existence is a set of diverse and complex interactions of organisms with each other and with the environmental conditions surrounding them.
Darwin identified three forms of struggle for existence: intraspecific, interspecific, and struggle against unfavorable environmental conditions.
Intraspecific struggle- relationships between individuals of the same species. Darwin considered intraspecific struggle to be the most intense. Of course, organisms belonging to the same species have similar requirements for food, breeding conditions, shelters, etc. Such a struggle is most acute with a significant increase in the number of individuals of the species and a deterioration in living conditions. This leads to the death of some individuals or to their elimination from reproduction. For example, intraspecific struggle manifests itself in the form of competition for nesting sites in birds or for a sexual partner in animals of the same species. Germinated seeds of plants, such as birches, often die because the soil is already densely overgrown with seedlings of the same species. Young seedlings experience a lack of light, nutrition, etc. In the flour beetle, exceeding the permissible number of individuals per unit of food substrate leads to disruption of sexual cycles and cannibalism.
Combating adverse environmental conditions- survival of the most adapted individuals, populations and species in changed conditions of inanimate nature. This form of control is more acute when any of the abiotic environmental factors are in deficiency or excess. Such situations arise during severe droughts, floods, frosts, fires, volcanic eruptions, etc. For example, in deserts, the struggle for existence among plants is aimed at economical consumption of moisture. As a result, some plants have developed adaptations in the form of fleshy leaves or stems for storing water. Others have thorny leaves to reduce evaporation, deep-penetrating roots to use groundwater, etc. Another example of combating unfavorable environmental conditions is the migration of migratory birds to warm countries when cold weather sets in.
The natural result of all forms of struggle is a decrease in the number of the least adapted individuals from generation to generation. This is due both to their immediate death and to the smaller number of offspring produced. On the other hand, more adapted individuals increase their numbers. At the same time, in each next generation they take away from the less adapted more and more resources necessary for life. This gradually leads to the complete displacement of the latter from the biotope. Darwin called this process, which constantly occurs in nature, natural selection.
According to Darwin, natural selection is the process of survival and reproduction of individuals most adapted to living conditions and the death of those less adapted.
Selection occurs continuously over a number of generations and preserves predominantly those forms that are most adapted to given environmental conditions. Natural selection and the struggle for existence are inextricably linked and are the driving forces of the evolution of species. These driving forces contribute to the improvement of organisms, which results in their adaptability to their environment and the diversity of species in nature.
Main results of evolution
According to Darwin, the results of evolution are the adaptability of organisms to their environment and the diversity of species in nature. Fitness- a set of adaptations (features of the external and internal structure and behavior of organisms) that provide a given species with an advantage in survival and leaving offspring under certain environmental conditions.
Variety of species- the second important result of evolution. Firstly, indefinite variability and the natural selection proceeding on its basis lead to a variety of relationships between organisms. Secondly, our planet is characterized by many biotopes that differ in the strength of environmental factors. Based on the above, the diversity of species in nature is formed. In this case, the most highly organized and adapted to environmental conditions receive an advantage. Darwin emphasized that the simultaneous existence of species of living organisms with different levels of organization is explained by the fact that their evolution proceeded simultaneously in several directions.
The struggle for existence is a set of diverse and complex interactions of organisms with each other and with the environmental conditions surrounding them. The consequence of the struggle for existence is natural selection. As a result of the action of natural selection, the main results of evolution are achieved: the fitness of organisms and the diversity of species in nature.
Question 1
The main driving forces (factors) of the evolutionary process, according to Charles Darwin, are the hereditary variability of individuals, the struggle for existence and natural selection. Currently, research in the field of evolutionary biology has confirmed the validity of this statement and has identified a number of other factors that play an important role in the process of evolution.
Several English naturalists came to the idea of the existence of natural selection independently of each other and almost simultaneously: V.
Wells (1813), P. Matthew (1831), E. Blythe (1835, 1837), A. Wallace (1858), C. Darwin (1858, 1859); but only Darwin was able to reveal the significance of this phenomenon as the main factor in evolution and created the theory of natural selection. Unlike artificial selection carried out by humans, natural selection is determined by the influence of the environment on organisms.
According to Darwin, natural selection is the “survival of the fittest” organisms, as a result of which evolution occurs on the basis of uncertain hereditary variability over a series of generations.
Natural selection is the main driving force of evolution, and any type of living organism that has ever lived on Earth was, in one way or another, formed under the influence of natural selection
Evolutionary theory states that each species purposefully develops and changes in order to best adapt to its environment.
In the process of evolution, many species of insects and fish acquired protective colors, the hedgehog became invulnerable thanks to its needles, and man became the owner of a very complex nervous system.
We can say that evolution is the process of optimization of all living organisms and the main mechanism of evolution is natural selection. Its essence is that more adapted individuals have more opportunities for survival and reproduction and, therefore, produce more offspring than poorly adapted individuals.
Moreover, thanks to the transfer of genetic information ( genetic inheritance) descendants inherit their basic qualities from their parents. Thus, the descendants of strong individuals will also be relatively well adapted, and their share in the total mass of individuals will increase.
After a change of several tens or hundreds of generations, the average fitness of individuals of a given species increases noticeably.
Natural selection occurs automatically. From generation to generation, all living organisms undergo rigorous testing in all the smallest details of their structure and the functioning of all their systems in a variety of conditions.
Only those who pass this test are selected and give rise to the next generation. Darwin wrote: “Natural selection daily and hourly examines throughout the world the smallest variations, discarding the bad, preserving and adding up the good, working silently and imperceptibly, wherever and whenever the opportunity presents itself, to improve every organic being in relation to conditions his life, organic and inorganic.
We notice nothing of these slow changes in development until the hand of time marks the elapsed centuries.”
Thus, natural selection is the only factor that ensures the adaptation of all living organisms to constantly changing environmental conditions and regulates the harmonious interactions between genes within each organism.
Question 2
Any cell, like any living system, despite the continuous processes of decay and synthesis, intake and release of various chemical compounds, has the inherent ability to maintain its composition and all its properties at a relatively constant level.
This constancy is preserved only in living cells, and when they die, it is violated very quickly.
The high stability of living systems cannot be explained by the properties of the materials from which they are built, since proteins, fats and carbohydrates have little stability.
The stability of cells (as well as other living systems) is actively maintained as a result of complex processes of self-regulation or autoregulation.
The basis for the regulation of cell activity are information processes, i.e. processes in which communication between individual links of the system is carried out using signals. A signal is a change that occurs in some link of the system.
In response to the signal, a process is launched, as a result of which the resulting change is eliminated. When the normal state of the system is restored, this serves as a new signal to shut down the process.
How does the cell signaling system work, how does it ensure autoregulation processes in it? Reception of signals inside the cell is carried out by its enzymes. Enzymes, like most proteins, have an unstable structure. Under the influence of a number of factors, including many chemical agents, the structure of the enzyme is disrupted and its catalytic activity is lost.
This change is usually reversible, i.e., after eliminating the active factor, the structure of the enzyme returns to normal and its catalytic function is restored.
As a result of this interaction, the structure of the enzyme is deformed and its catalytic activity is lost.
Question 3
Artificial mutagenesis is a new important source of creating starting material in plant breeding. Artificially induced mutations are the starting material for obtaining new varieties of plants, microorganisms and, less commonly, animals.
Mutations lead to the emergence of new hereditary traits, from which breeders select those properties that are beneficial to humans.
In nature, mutations are observed relatively rarely, so breeders widely use artificial mutations. Impacts that increase the frequency of mutations are called mutagenic. The frequency of mutations is increased by ultraviolet and x-rays, as well as chemicals acting on DNA or the apparatus that ensures division.
The significance of experimental mutagenesis for plant breeding was not immediately understood.
L. Stadler, who was the first to obtain artificial mutations in cultivated plants under the influence of X-rays in 1928, believed that they would have no significance for practical selection.
He concluded that the likelihood of experimentally obtaining changes through mutagenesis that would be superior to the forms found in nature is negligible. Many other scientists also had a negative attitude towards mutagenesis.
A. A. Sapegin and L. N. Delaunay were the first researchers to show the importance of artificial mutations for plant breeding.
In their experiments conducted in 1928-1932. in Odessa and Kharkov, a series of economically useful mutant forms was obtained in wheat. In 1934, A. A. Sapegin published the article “X-ray mutation as a source of new forms of agricultural plants,” which indicated new ways of creating source material in plant breeding based on the use of ionizing radiation.
But even after this, the use of experimental mutagenesis in plant breeding continued to be viewed negatively for a long time.
It was only at the end of the 50s that increased interest was shown in the problem of using experimental mutagenesis in breeding. It was associated, firstly, with major successes in nuclear physics and chemistry, which made it possible to use various sources of ionizing radiation (nuclear reactors, particle accelerators, radioactive isotopes, etc.) and highly reactive chemicals to obtain mutations and, secondly, with these methods obtaining practically valuable hereditary changes on a wide variety of crops.
Work on experimental mutagenesis in plant breeding has developed especially widely in recent years.
They are carried out very intensively in Sweden, Russia, Japan, the USA, India, Czechoslovakia, France and some other countries.
Mutations that are resistant to fungal (rust, smut, powdery mildew, sclerotinia) and other diseases are of great value. The creation of immune varieties is one of the main tasks of breeding, and methods of radiation and chemical mutagenesis should play a large role in its successful solution.
With the help of ionizing radiation and chemical mutagens, it is possible to eliminate certain deficiencies in crop varieties and create forms with economically useful traits: non-lodging, frost-resistant, cold-resistant, early ripening, with a high content of protein and gluten.
There are two main ways of breeding use of artificial mutations: 1) direct use of mutations obtained from the best released varieties; 2) the use of mutations in the process of hybridization.
In the first case, the task is to improve existing varieties according to some economic and biological characteristics and correct their individual shortcomings.
This method is considered promising in breeding for disease resistance. It is assumed that resistance mutations can be quickly obtained from any valuable variety and its other economic and biological characteristics can be preserved intact.
The method of direct use of mutations is designed for the rapid creation of starting material with the desired characteristics and properties.
However, the direct and rapid use of mutations, given the high demands placed on modern breeding varieties, does not always give positive results.
To date, more than 300 mutant varieties of agricultural plants have been created in the world.
Some of them have significant advantages over the original varieties. Valuable mutant forms of wheat, corn, soybeans and other field and vegetable crops have been obtained in recent years in research institutions of our country.
Development of evolutionary concepts. Evidence of evolution.
Evolution is the process of historical development of the organic world.
The essence of this process is the continuous adaptation of living things to diverse and constantly changing environmental conditions, and the increasing complexity of the organization of living beings over time. In the course of evolution, the transformation of some species into others occurs.
The main ones in evolutionary theory– the idea of historical development from relatively simple forms of life to more highly organized ones.
The foundations of the scientific materialist theory of evolution were laid by the great English naturalist Charles Darwin. Before Darwin, biology was mainly dominated by the incorrect concept of the historical immutability of species, that there are as many of them as were created by God. However, even before Darwin, the most insightful biologists understood the inconsistency of religious views on nature, and some of them speculatively arrived at evolutionary ideas.
The most prominent natural scientist, predecessor of Ch.
Darwin was the famous French scientist Jean Baptiste Lamarck. In his famous book “Philosophy of Zoology” he proved the variability of species. Lamarck emphasized that the constancy of species is only an apparent phenomenon; it is associated with the short duration of observations of species. Higher forms of life, according to Lamarck, evolved from lower ones in the process of evolution.
Lamarck's evolutionary doctrine was not sufficiently conclusive and did not receive wide recognition among his contemporaries. Only after the outstanding works of Charles Darwin did the evolutionary idea become generally accepted.
Modern science has many facts that prove the existence of the evolutionary process.
This is data from biochemistry, genetics, embryology, anatomy, systematics, biography, paleontology and many other disciplines.
Embryological evidence– similarity of the initial stages of embryonic development of animals. While studying the embryonic period of development in various groups of vertebrates, K. M. Baer discovered the similarity of these processes in various groups of organisms, especially in the early stages of development. Later, based on these findings, E.
Haeckel expresses the idea that this similarity has evolutionary significance and on its basis the “biogenetic law” is formulated - ontogenesis is a brief reflection of phylogeny. Each individual in its individual development (ontogenesis) goes through the embryonic stages of ancestral forms. Studying only the early stages of development of the embryo of any vertebrate does not allow us to determine with accuracy which group they belong to. Differences are formed at later stages of development.
The closer the groups to which the studied organisms belong, the longer the common features will be preserved in embryogenesis.?
Morphological– many forms combine the characteristics of several large systematic units. When studying different groups of organisms, it becomes obvious that in a number of features they are fundamentally similar.
For example, the structure of the limb in all four-legged animals is based on a five-fingered limb. This basic structure in different species is transformed in connection with different living conditions: this is the limb of an equid animal, which rests on just one finger when walking, and the flipper of a marine mammal, and the burrowing limb of a mole, and the wing of a bat.
Organs built according to a single plan and developing from single rudiments are called homologous.
Homologous organs cannot in themselves serve as evidence of evolution, but their presence indicates the origin of similar groups of organisms from a common ancestor. A striking example of evolution is the presence of vestigial organs and atavisms. Organs that have lost their original function but remain in the body are called vestigial. Examples of rudiments include: the appendix in humans, which performs a digestive function in ruminant mammals; the pelvic bones of snakes and whales, which do not perform any function for them; coccygeal vertebrae in humans, which are considered to be the rudiments of the tail that our distant ancestors had.
Atavisms are the manifestation in organisms of structures and organs characteristic of ancestral forms. Classic examples of atavisms are multi-nipple and tailedness in humans.
Paleontological– the fossil remains of many animals can be compared with each other and similarities can be detected. Based on the study of fossil remains of organisms and comparison with living forms. They have their advantages and disadvantages. The advantages include the opportunity to see firsthand how a given group of organisms changed in different periods.
Disadvantages include that paleontological data are very incomplete due to many reasons. These include such as the rapid reproduction of dead organisms by animals that feed on carrion; soft-bodied organisms are extremely poorly preserved; and finally, that only a small fraction of the fossil remains are being discovered.
In view of this, there are many gaps in paleontological data, which are the main object of criticism by opponents of the theory of evolution.
Biogeographic– distribution of animals and plants across the surface of our planet. Comparison of the flora and fauna of different continents, showing that the differences between their flora and fauna are greater, the older and stronger their isolation from each other.
As is known, the state of the earth's crust is constantly undergoing changes, and the current position of the continents was formed in recent (geological) time.
Before this, all continents were brought closer together and united into one continent.
The separation of continents occurred gradually, some separated earlier, others later. Each new highly organized species sought to spread to the largest possible territory. The absence of more highly organized forms in any territory indicates that this territory separated earlier than some species were formed or had time to spread to it. This in itself does not explain the mechanism by which species emerged, but it does indicate that different species formed in different areas and at different times.
The modern classification of organisms was proposed by Linnaeus long before the theory of evolution proposed by Darwin.
Of course, it can be assumed that all the diversity of plant and animal species was created simultaneously, and each of them was created independently of each other.
However, taxonomy, based on the morphological similarities of organisms, unites them into groups. The existence of such groups (genera, families, orders) suggests that each taxonomic group is the result of adaptation of various species to specific environmental conditions.
Evolutionary doctrine of Charles Darwin.
Its main provisions and meaning.
Type, type criteria. Populations.
The preconditions of evolution by themselves cannot lead to evolution. For the evolutionary process to occur, leading to the appearance of adaptations and the formation of new species and other taxa, the driving forces of evolution are necessary.
Currently, the doctrine created by Darwin about the driving forces of evolution (the struggle for existence and natural selection) has been supplemented with new facts thanks to the achievements of modern genetics and ecology.
The struggle for existence and its forms
According to the concepts of modern ecology, individuals of the same species are united in populations, and populations of different species exist in certain ecosystems.
The relationships of individuals within populations and with individuals of populations of other species, as well as with environmental conditions in ecosystems, are considered as struggle for existence.
Darwin believed that the struggle for existence is the result of species multiplying exponentially and the emergence of an excess number of individuals with limited food resources.
That is, the word “fight” essentially meant competition for food in conditions of overpopulation.
According to modern ideas, elements of the struggle for existence can be any relationship - both competitive and mutually beneficial (caring for offspring, mutual assistance). Overpopulation is not a necessary condition for the struggle for existence. Consequently, at present the struggle for existence is understood more broadly than according to Darwin, and is not reduced to competitive struggle in the literal sense of the word.
There are two main forms of struggle for existence: direct struggle and indirect struggle.
Direct fight- any relationship in which there is physical contact to one degree or another between individuals of the same or different species within their populations.
The consequences of this struggle can be very different for the interacting parties. Direct struggle can be either intraspecific or interspecific.
Examples of direct intraspecific struggle can be: competition between rook families for nesting sites, between wolves for prey, and between males for territory.
This is also feeding the young with milk in mammals, mutual assistance in building nests in birds, protection from enemies, etc.
Indirect struggle- any relationship between individuals of different populations that use common food resources, territory, environmental conditions without direct contact with each other.
Indirect control can be intraspecific, interspecific and with abiotic environmental factors.
Examples of indirect struggle can be the relationship between individual birch trees in a dense birch grove (intraspecific struggle), between polar bears and arctic foxes, lions and hyenas for prey, and light-loving and shade-loving plants (interspecific struggle).
Also, indirect control is the different resistance of plants to the supply of soil with moisture and minerals, and of animals to temperature conditions (fight against abiotic environmental factors).
The result of the struggle for existence is the success or failure of these individuals in surviving and leaving offspring, i.e. natural selection, as well as changes in territories, changes in environmental needs, etc.
Natural selection and its forms
According to Darwin, natural selection is expressed in the preferential survival and leaving of offspring by the most fit individuals and the death of the less fit.
Modern genetics has expanded this idea. The diversity of genotypes in populations, arising as a result of the preconditions of evolution, leads to the appearance of phenotypic differences between individuals. As a result of the struggle for existence in each population, individuals with phenotypes and genotypes useful in the given environment survive and leave offspring.
Consequently, the action of selection is the differentiation (selective preservation) of phenotypes and the reproduction of adaptive genotypes. Since selection occurs according to phenotypes, this determines the significance of phenotypic (modification) variability in evolution.
The variety of modifications influences the degree of diversity of phenotypes analyzed by natural selection and allows a species to survive in changing environmental conditions. However, modification variability cannot be a prerequisite for evolution, since it does not affect the gene pool of the population.
Natural selection is a directed historical process of differentiation (selective preservation) of phenotypes and reproduction of adaptive genotypes in populations.
Depending on the environmental conditions of populations in nature, two main forms of natural selection can be observed: driving and stabilizing.
Driving selection operates in environmental conditions gradually changing in a certain direction.
It preserves useful deviant phenotypes and removes old and useless deviant phenotypes. In this case, there is a shift in the average value of the reaction norm of the characteristics and a shift in their variation curve in a specific direction without changing its limits.
If selection acts in this way in a series of generations (F1 → F2 → F3), then it leads to the formation of a new norm of reaction of characters.
It does not overlap with the previous reaction norm. As a result, new adaptive genotypes are formed in the population. This is the reason for the gradual transformation of the population into a new species. It was this form of selection that Darwin considered the driving force of evolution.
As a result of the action of driving selection, some characteristics may disappear in new conditions, while others may develop and improve.
The unidirectional action of natural selection leads to elongation of roots in sclerophytes, increased visual acuity, hearing, and smell in predators and their prey.
Stabilizing selection operates under constant and optimal environmental conditions for populations.
It maintains the same phenotype and removes any phenotypes that deviate from it. In this case, the average value of the reaction norm of the traits does not change, but the limits of their variation curve are narrowed. Consequently, the genotypic and phenotypic diversity that arises as a result of the preconditions of evolution is reduced.
This helps to consolidate previous genotypes and preserve the existing species. The result of this form of selection is the current existence of ancient (relict) organisms.
Relic(from Latin relictum - remainder) kinds- living organisms preserved in modern flora and fauna or in a certain region as a remnant of an ancestral group. In past geological eras they were widespread and played a large role in ecosystems.
The driving forces of evolution are natural selection and the struggle for existence.
There are two forms of struggle for existence: direct and indirect struggle. There are two main forms of natural selection in nature: driving and stabilizing.
The guiding factor of evolution according to Darwin
All our dignity lies in thought. It is not space or time, which we cannot fill, that elevates us, but it is she, our thought.
Let us learn to think well: this is the basic principle of morality.
Charles Darwin was born in the cold winter of 1809 in England. His father was Robert Waring, the son of the famous scientist and talented poet Erasmus Darwin.
Little Charles's mother died when he was not even 8 years old.
Soon Charles was sent to study at an elementary school, and after one year he was transferred to Dr. Beutler, the head of the gymnasium. C. Darwin studied very mediocrely, although his love for nature “awakened” very early, as well as a “living” interest in flora and fauna. The guiding factor of evolution according to Darwin He enjoyed collecting insects, various minerals, flowers and shells.
After graduating from high school in 1825, young Darwin brilliantly entered the University of Edinburgh. He studied there for only two years. After an unsuccessful attempt to become a doctor, Darwin decides to try his hand at being a priest. For this, the young man enters Cambridge. He completed his studies without standing out at all from the rest of the students. He was attracted by something completely different: societies of naturalists and botanists, excursions dedicated to the natural sciences. During these years, the scientist’s first work came out, which contained his notes and observations of the natural world.
In 1831, Darwin began a trip around the world, during which for 5 years he became acquainted with the nature of the most diverse parts of the planet. As a result of the observations he made during his travels, he wrote several works devoted to geological observations of volcanic islands and coral reefs.
They brought Darwin fame in scientific circles.
In 1839, Darwin got married, which forced him to stay in London. Charles' poor health leads to a move to Doane, where Darwin remains for the rest of his life. There he develops the question of the origin of species and formulates the idea of natural selection. The guiding factor of evolution according to Darwin The essay “The Origin of Species by Means of Natural Selection” is published, in which his theory is thoroughly proven and indisputable evidence is provided.
His name has gained recognition and fame throughout the world. All subsequent works of Darwin represent further developments of his teachings. For example, some explanations of the origin of man from monkeys.
After spreading his theory, C. Darwin received a number of awards for his work, becoming an honorary member of numerous scientific societies.
The scientist died in 1882, having lived to the age of 74. Darwin's teaching glorified his name for centuries, marking a new approach to the doctrine of the origin of mankind.
In order for the upbringing of children to be successful, it is necessary for the people raising them to continually educate themselves.
Elementary factors of evolution- factors that change the frequency of alleles and genotypes in a population (the genetic structure of the population). There are several basic elementary factors of evolution: mutation process, combinative variability, population waves and genetic drift, isolation, natural selection.
Mutation process leads to the emergence of new alleles (or genes) and their combinations as a result of mutations.
As a result of mutation, a transition of a gene from one allelic state to another (A→a) or a change in the gene in general (A→C) is possible. The mutation process, due to the randomness of mutations, has no direction and, without the participation of other evolutionary factors, cannot direct changes in the natural population.
It only supplies elementary evolutionary material for natural selection. Recessive mutations in the heterozygous state constitute a hidden reserve of variability that can be used by natural selection when conditions of existence change.
Combinative variability arises as a result of the formation in descendants of new combinations of already existing genes inherited from their parents.
The causes of combinative variability are: chromosome crossing (recombination); random segregation of homologous chromosomes in meiosis; random combination of gametes during fertilization.
Waves of life- periodic and non-periodic fluctuations in population size, both upward and downward.
The causes of population waves can be:
- periodic changes in environmental environmental factors (seasonal fluctuations in temperature, humidity, etc.);
- non-periodic changes (natural disasters);
- colonization of new territories by the species (accompanied by a sharp increase in numbers).
Population waves act as an evolutionary factor in small populations where genetic drift may occur.
Genetic drift- random non-directional change in allele and genotype frequencies in populations. In small populations, the action of random processes leads to noticeable consequences. If the population is small in size, then as a result of random events, some individuals, regardless of their genetic constitution, may or may not leave offspring, as a result of which the frequencies of some alleles can change significantly over one or several generations.
Thus, with a sharp reduction in population size (for example, due to seasonal fluctuations, reduction in food resources, fire, etc.), among the few surviving individuals there may be rare genotypes.
If in the future the population size is restored due to these individuals, this will lead to a random change in allele frequencies in the gene pool of the population. Thus, population waves serve as a supplier of evolutionary material.
Insulation is caused by the emergence of various factors that prevent free crossing.
The exchange of genetic information between the resulting populations ceases, as a result of which the initial differences in the gene pools of these populations increase and become fixed. Isolated populations can undergo various evolutionary changes and gradually turn into different species.
There are spatial and biological isolation. Spatial (geographical) isolation is associated with geographical obstacles (water barriers, mountains, deserts, etc.), and for sedentary populations, simply with long distances.
Biological isolation is caused by the impossibility of mating and fertilization (due to changes in the timing of reproduction, structure or other factors that prevent crossing), the death of zygotes (due to biochemical differences in gametes), and sterility of the offspring (as a result of impaired chromosome conjugation during gametogenesis).
The evolutionary significance of isolation is that it perpetuates and enhances genetic differences between populations.
Changes in the frequencies of genes and genotypes caused by the evolutionary factors discussed above are random and non-directional.
The guiding factor of evolution is natural selection.
Natural selection- a process as a result of which predominantly individuals with traits useful for the population survive and leave behind offspring. Selection operates in populations; its objects are the phenotypes of individual individuals. However, selection based on phenotypes is a selection of genotypes, since it is not traits, but genes that are passed on to descendants.
As a result, in a population there is an increase in the relative number of individuals possessing a certain property or quality. Thus, natural selection is the process of differential (selective) reproduction of genotypes.
Not only properties that increase the likelihood of leaving offspring are subject to selection, but also traits that are not directly related to reproduction. In some cases, selection may be aimed at creating mutual adaptations of species to each other (plant flowers and insects visiting them).
Signs may also appear that are harmful to an individual, but ensure the survival of the species as a whole (a bee that stings dies, but by attacking an enemy, it saves the family). In general, selection plays a creative role in nature, since from undirected hereditary changes those that can lead to the formation of new groups of individuals that are more perfect in given conditions of existence are fixed.
There are three main forms of natural selection: stabilizing, driving and disruptive.
Stabilizing selection is aimed at preserving mutations leading to less variability in the average value of the trait.
Operates under relatively constant environmental conditions, i.e. while the conditions that led to the formation of one or another sign (property) persist.
For example, the preservation of the size and shape of the flower in insect-pollinated plants, since the flowers must correspond to the body size of the pollinating insect.
Conservation of relict species.
Driving selection is aimed at preserving mutations that change the average value of a trait. Occurs when environmental conditions change. Individuals of a population have some differences in genotype and phenotype, and with long-term changes in the external environment, some individuals of the species with some deviations from the norm may gain an advantage in life activity and reproduction.
The variation curve shifts in the direction of adaptation to new conditions of existence. For example, the emergence of resistance to pesticides in insects and rodents, and resistance to antibiotics in microorganisms.
Or industrial melanism, for example, the darkening of the color of the birch moth butterfly in developed industrial areas of England. In these areas, tree bark becomes dark due to the disappearance of lichens sensitive to air pollution, and dark-colored butterflies are less visible on tree trunks.
Disruptive selection is aimed at preserving mutations that lead to the greatest deviation from the average value of a trait.
Discontinuous selection occurs when environmental conditions change in such a way that individuals with extreme deviations from the norm gain an advantage. As a result of discontinuous selection, population polymorphism is formed, i.e. the presence of several groups differing in some way. For example, with frequent strong winds on oceanic islands, insects either with well-developed wings or with vestigial ones are preserved.
Type, its criteria. A population is a structural unit of a species and an elementary unit of evolution. Microevolution. Formation of new species. Methods of speciation. Preservation of species diversity as the basis for the sustainability of the biosphere
Type, its criteria
The founder of modern taxonomy, C. Linnaeus, considered a species as a group of organisms similar in morphological characteristics that freely interbreed. As biology developed, evidence was obtained that the differences between species are much deeper and affect the chemical composition and concentration of substances in tissues, the direction and speed of chemical reactions, the nature and intensity of vital processes, the number and shape of chromosomes, i.e. the species is the smallest a group of organisms reflecting their close relationship. In addition, species do not exist forever - they arise, develop, give rise to new species and disappear.
View- this is a collection of individuals that are similar in structure and characteristics of life processes, have a common origin, freely interbreed with each other in nature and produce fertile offspring.
All individuals of the same species have the same karyotype and occupy a certain geographical area in nature - area
Signs of similarity between individuals of the same species are called type criteria. Since none of the criteria is absolute, to correctly determine the type it is necessary to use a set of criteria.
The main criteria of a species are morphological, physiological, biochemical, ecological, geographical, ethological (behavioural) and genetic.
- Morphological- a set of external and internal characteristics of organisms of the same species. Although some species have unique characters, it is often very difficult to distinguish closely related species using morphological traits alone. Thus, recently a number of twin species living in the same territory have been discovered, for example, the house mouse and the Kurganchik mouse, so it is unacceptable to use exclusively morphological criteria to determine the species.
- Physiological- the similarity of life processes in organisms, primarily reproduction. It is also not universal, since some species interbreed in nature and produce fertile offspring.
- Biochemical- similarity of chemical composition and metabolic processes. Despite the fact that these indicators can vary significantly among different individuals of the same species, they are currently receiving much attention, since the structural features and composition of biopolymers help to identify species even at the molecular level and establish the degree of their relationship.
- Ecological- distinction of species according to their belonging to certain ecosystems and ecological niches that they occupy. However, many unrelated species occupy similar ecological niches, so this criterion can be used to distinguish a species only in combination with other characteristics.
- Geographical- the existence of a population of each species in a certain part of the biosphere - an area that differs from the areas of all other species. Due to the fact that for many species the boundaries of their ranges coincide, and there are also a number of cosmopolitan species whose range covers vast spaces, the geographical criterion also cannot serve as a marker “species” feature.
- Genetic- constancy of the characteristics of the chromosome set - karyotype - and the nucleotide composition of DNA in individuals of the same species. Due to the fact that non-homologous chromosomes cannot conjugate during meiosis, offspring from crossing individuals of different species with an unequal set of chromosomes either do not appear at all or are not fertile. This creates reproductive isolation of the species, maintains its integrity and ensures the reality of existence in nature. This rule may be violated in the case of crossing species of similar origin with the same karyotype or the occurrence of various mutations, but the exception only confirms the general rule, and species should be considered as stable genetic systems. The genetic criterion is the main one in the system of species criteria, but also not exhaustive.
Despite the complexity of the system of criteria, a species cannot be represented as a group of organisms that are absolutely identical in all respects, that is, clones. On the contrary, many species are characterized by a significant diversity even in external characteristics, as, for example, some populations of ladybirds are characterized by a predominance of red in color, while others are characterized by a predominance of black.
Population is a structural unit of a species and an elementary unit of evolution
It is difficult to imagine that in reality, individuals of one species would be evenly distributed over the earth's surface within the range, since, for example, the lake frog lives mainly in rather rare standing fresh water bodies, and it is unlikely to be found in fields and forests. Species in nature most often fall into separate groups, depending on the combination of conditions suitable for their habitats - populations.
Population- a group of individuals of the same species, occupying part of its range, freely interbreeding with each other and relatively isolated from other groups of individuals of the same species for a more or less long time.
Populations can be separated not only spatially; they can even live in the same territory, but have differences in food preferences, timing of reproduction, etc.
Thus, a species is a collection of populations of individuals that have a number of common morphological, physiological, biochemical characteristics and types of relationships with the environment, inhabiting a certain area, and also capable of interbreeding with each other to form fertile offspring, but almost or not at all interbreeding with other groups individuals of the same species.
Within species with large ranges covering territories with different living conditions, they are sometimes distinguished subspecies- large populations or groups of neighboring populations that have persistent morphological differences from other populations.
Populations are not scattered across the earth's surface randomly; they are tied to specific areas. The totality of all factors of inanimate nature necessary for the residence of individuals of a given species is called habitat. However, these factors alone may not be enough for a population to occupy this area, since it must still be involved in close interaction with populations of other species, that is, occupy a certain place in the community of living organisms - ecological niche. Thus, the Australian koala marsupial bear, all other things being equal, cannot exist without its main source of food - eucalyptus.
Populations of various species that form an inextricable unity in the same habitats usually provide a more or less closed cycle of substances and are elementary ecological systems (ecosystems) - biogeocenoses.
For all their demands on environmental conditions, populations of the same species are heterogeneous in area, number, density and spatial distribution of individuals, often forming smaller groups (families, flocks, herds, etc.), sex, age, gene pool, etc. , therefore, their size, age, gender, spatial, genetic, ethological and other structures, as well as dynamics, are distinguished.
Important characteristics of a population are gene pool- a set of genes characteristic of individuals of a given population or species, as well as the frequency of certain alleles and genotypes. Different populations of the same species initially have different gene pools, since new territories are colonized by individuals with random rather than specially selected genes. Under the influence of internal and external factors, the gene pool undergoes even more significant changes: it is enriched due to the occurrence of mutations and a new combination of traits and depleted as a result of the loss of individual alleles during the death or migration of a certain number of individuals.
New traits and their combinations can be beneficial, neutral or harmful, therefore, only individuals adapted to given environmental conditions survive and reproduce successfully in the population. However, at two different points on the earth's surface, environmental conditions are never completely identical, therefore the direction of changes even in two neighboring populations can be completely opposite or they will occur at different rates. The result of changes in the gene pool is the divergence of populations according to morphological, physiological, biochemical and other characteristics. If populations are also isolated from each other, then they can give rise to new species.
Thus, the emergence of any obstacles in the crossing of individuals of different populations of the same species, for example, due to the formation of mountain ranges, changes in river beds, differences in the timing of reproduction, etc., leads to the fact that populations gradually acquire more and more differences and, in eventually become different species. For some time, at the borders of these populations, crossing of individuals occurs and hybrids arise, but over time, these contacts disappear, i.e., populations from open genetic systems become closed.
Despite the fact that individuals are primarily exposed to environmental factors, changes in the genetic composition of a single organism are insignificant and will, at best, only appear in its descendants. Subspecies, species and larger taxa are also not suitable for the role of elementary units of evolution, since they do not differ in morphological, physiological, biochemical, ecological, geographical and genetic unity, while populations are the smallest structural units of a species, accumulating a variety of random changes, the worst of which will be eliminated, correspond to this condition and are elementary units of evolution.
Microevolution
Changing the genetic structure of populations does not always lead to the formation of a new species, but can only improve the population’s adaptation to specific environmental conditions; however, species are not eternal and unchanging - they are capable of developing. This process of irreversible historical change in living things is called evolution. Primary evolutionary transformations occur within a species at the population level. They are based, first of all, on the mutation process and natural selection, leading to changes in the gene pool of populations and the species as a whole, or even to the formation of new species. The set of these elementary evolutionary events is called microevolution.
Populations are characterized by enormous genetic diversity, which is often not expressed phenotypically. Genetic diversity arises due to spontaneous mutagenesis, which occurs continuously. Most mutations are unfavorable for the organism and reduce the viability of the population as a whole, but if they are recessive, they can persist in heterozygotes for a long time. Some mutations that do not have adaptive value under given conditions of existence are capable of acquiring such value in the future or when new ecological niches are developed, thus creating a reserve of hereditary variability.
Microevolutionary processes are significantly influenced by fluctuations in the number of individuals in populations, migration and disasters, as well as isolation of populations and species.
A new species is an intermediate result of evolution, but in no way its result, since microevolution does not stop there - it continues further. Emerging new species, in the case of a successful combination of characteristics, populate new habitats, and, in turn, give rise to new species. Such groups of closely related species are united into genera, families, etc. Evolutionary processes occurring in supraspecific groups are already called macroevolution. Unlike macroevolution, microevolution takes place in a much shorter period of time, while the first requires tens and hundreds of thousands and millions of years, such as human evolution.
As a result of microevolution, the entire diversity of species of living organisms that have ever existed and are now living on Earth is formed.
At the same time, evolution is irreversible, and species that have already disappeared never arise again. Emerging species consolidate everything achieved in the process of evolution, but this does not guarantee that in the future new species will not appear that will have more advanced adaptations to environmental conditions.
Formation of new species
In a broad sense, the formation of new species is understood not only as the splitting off of a new species from the main trunk or the disintegration of the parent species into several daughter species, but also the general development of the species as an integral system, leading to significant changes in its morphostructural organization. However, more often than not speciation considered as a process of formation of new species through the branching of the “family tree” of the species.
A fundamental solution to the problem of speciation was proposed by Charles Darwin. According to his theory, the spread of individuals of the same species leads to the formation of populations that, due to differences in environmental conditions, are forced to adapt to them. This, in turn, entails an intensification of the intraspecific struggle for existence, directed by natural selection. Currently, it is believed that the struggle for existence is not at all an obligatory factor in speciation; on the contrary, selection pressure in a number of populations may decrease. Differences in living conditions contribute to the emergence of unequal adaptive changes in populations of a species, the consequence of which is a divergence of characteristics and properties of populations - divergence.
However, the accumulation of differences, even at the genetic level, is by no means sufficient for the emergence of a new species. As long as populations differing in some characteristics are not only in contact, but are also capable of interbreeding with the formation of fertile offspring, they belong to the same species. Only the impossibility of the flow of genes from one group of individuals to another, even in the event of the destruction of the barriers separating them, i.e., crossing, means the completion of the most complex evolutionary process of the formation of a new species.
Speciation is a continuation of microevolutionary processes. There is a point of view that speciation cannot be reduced to microevolution; it represents a qualitative stage of evolution and is carried out thanks to other mechanisms.
Methods of speciation
There are two main methods of speciation: allopatric and sympatric.
Allopatric, or geographic speciation is a consequence of the spatial separation of populations by physical barriers (mountain ranges, seas and rivers) due to their emergence or dispersal into new habitats (geographical isolation). Since in this case the gene pool of the separated population differs significantly from the maternal one, and the conditions in its habitat will not coincide with the original ones, over time this will lead to divergence and the formation of a new species. A striking example of geographic speciation is the diversity of finch species discovered by Charles Darwin during his voyage on the Beagle ship on the Galapagos Islands off the coast of Ecuador. Apparently, individual individuals of the only finch inhabiting the South American continent somehow ended up on the islands, and, due to differences in conditions (primarily food availability) and geographic isolation, they gradually evolved, forming a group of related species.
At the core sympatric, or biological speciation lies some form of reproductive isolation, with new species arising within the range of the original species. A prerequisite for sympatric speciation is the rapid isolation of the resulting forms. This is a faster process than allopatric speciation, and new forms are similar to the original ancestors.
Sympatric speciation can be caused by rapid changes in chromosome composition (polyploidization) or chromosomal rearrangements. Sometimes new species arise as a result of hybridization of two original species, as, for example, in the domestic plum, which is a hybrid of sloe and cherry plum. In some cases, sympatric speciation is associated with the division of ecological niches in populations of the same species within a single range or seasonal isolation - divergence in the timing of reproduction in plants (different types of pine in California produce dust in February and April) and in the timing of reproduction in animals.
Of the entire variety of newly emerging species, only a few, the most adapted, can exist for a long time and give rise to new species. The reasons for the death of most species are still unknown; most likely this is due to sudden climate changes, geological processes and their displacement by more adapted organisms. Currently, one of the reasons for the death of a significant number of species is man, who exterminates the largest animals and the most beautiful plants, and if in the 17th century this process only began with the extermination of the last round, then in the 21st century more than 10 species are disappearing every hour.
Preservation of species diversity as the basis for the sustainability of the biosphere
Despite the fact that, according to various estimates, the planet is home to 5–10 million species of organisms that have not yet been described, we will never know about the existence of most of them, since about 50 species disappear from the face of the Earth every hour. The disappearance of living organisms at the present time is not necessarily associated with their physical extermination; more often it is due to the destruction of their natural habitats as a result of human activity. The death of an individual species is unlikely to lead to fatal consequences for the biosphere, but it has long been established that the extinction of one plant species entails the death of 10–12 animal species, and this already poses a threat both to the existence of individual biogeocenoses and to the global ecosystem in in general.
The sad facts accumulated over the previous decades forced the International Union for Conservation of Nature and Natural Resources (IUCN) to begin collecting information on rare and endangered species of plants and animals in 1949. In 1966, the IUCN published the first Red Book of Facts.
Red Book is an official document containing regularly updated data on the status and distribution of rare and endangered species of plants, animals and fungi.
This document adopted a five-level scale of status of a protected species, with the first level of protection including species whose salvation is impossible without special measures, and the fifth - restored species, the condition of which, thanks to the measures taken, does not cause concern, but they are not yet subject to industrial use. The development of such a scale makes it possible to direct priority conservation efforts specifically to the rarest species, such as Amur tigers.
In addition to the international version of the Red Book, there are also national and regional versions. In the USSR, the Red Book was established in 1974, and in the Russian Federation, the procedure for its maintenance is regulated by the Federal Laws “On Environmental Protection”, “On Wildlife” and the Decree of the Government of the Russian Federation “On the Red Book of the Russian Federation”. Today, 610 species of plants, 247 species of animals, 42 species of lichens and 24 species of fungi are listed in the Red Book of the Russian Federation. The populations of some of them, once endangered (European beaver, bison), have already been quite successfully restored.
The following animal species are protected in Russia: Russian muskrat, tarbagan (Mongolian marmot), polar bear, Caucasian European mink, sea otter, manul, Amur tiger, leopard, snow leopard, sea lion, walrus, seals, dolphins, whales, Przewalski's horse, wild ass, pink pelican, common flamingo, black stork, small swan, steppe eagle, golden eagle, black crane, Siberian crane, bustard, eagle owl, white gull, Mediterranean turtle, Japanese snake, viper, jungle toad, Caspian lamprey, all types of sturgeon fish, lake salmon, stag beetle, extraordinary bumblebee, common Apollo, mantis crab, common pearl mussel, etc.
The plants of the Red Data Book of the Russian Federation include 7 species of snowdrops, some types of wormwood, true ginseng, 7 types of bluebells, serrated oak, scilla, 11 species of iris, Russian hazel grouse, Schrenk's tulip, nut-bearing lotus, lady's slipper, thin-leaved peony, feather grass, Julia's primrose, meadow lumbago (sleep-grass), belladonna belladonna, Pitsunda pine, yew, Chinese shieldweed, lake grass, soft sphagnum, curly phylllophora, filamentous chara, etc.
Rare mushrooms are represented by summer truffle, or Russian black truffle, lacquered tinder fungus, etc.
The protection of rare species in most cases is associated with a ban on their destruction, preservation of them in artificially created habitats (zoos), protection of their habitats and the creation of low-temperature genetic banks.
The most effective measure for the protection of rare species is the conservation of their habitats, which is achieved by organizing a network of specially protected protected areas that, in accordance with the Federal Law “On Specially Protected Natural Areas” (1995), have international, federal, regional or local significance. These include state nature reserves, national parks, natural parks, state nature reserves, natural monuments, dendrological parks, botanical gardens, etc.
State Nature Reserve- this is a specially protected natural complex (land, water bodies, subsoil, flora and fauna) completely withdrawn from economic use, which has environmental, scientific, environmental and educational significance as an example of the natural environment, typical or rare landscapes, places where the genetic fund of plants is preserved and the animal world.
Reserves that are part of the international system of biosphere reserves that carry out global environmental monitoring have the status state natural biosphere reserves. The reserve is an environmental, research and environmental educational institution aimed at preserving and studying the natural course of natural processes and phenomena, the genetic fund of flora and fauna, individual species and communities of plants and animals, typical and unique ecological systems.
Currently in Russia there are about 100 state nature reserves, 19 of which have biosphere status, including Baikalsky, Barguzinsky, Caucasian, Kedrovaya Pad, Kronotsky, Prioksko-Terrasny, etc.
Unlike nature reserves, territories (water areas) national parks include natural complexes and objects that have special environmental, historical and aesthetic values, and are intended for use for environmental, educational, scientific and cultural purposes and for regulated tourism. 39 specially protected natural areas have this status, including the Trans-Baikal and Sochi national parks, as well as the national parks “Curonian Spit”, “Russian North”, “Shushensky Bor”, etc.
Natural parks are environmental recreational institutions under the jurisdiction of the constituent entities of the Russian Federation, the territories (water areas) of which include natural complexes and objects that have significant environmental and aesthetic values, and are intended for use for environmental, educational and recreational purposes.
State nature reserves are territories (water areas) that are of particular importance for the preservation or restoration of natural complexes or their components and maintaining the ecological balance.
Development of evolutionary ideas. The meaning of Charles Darwin's evolutionary theory. Interrelation of the driving forces of evolution. Forms of natural selection, types of struggle for existence. Synthetic theory of evolution. Elementary factors of evolution. Research by S. S. Chetverikov. The role of evolutionary theory in the formation of the modern natural science picture of the world
Development of evolutionary ideas
All theories of the origin and development of the organic world can be reduced to three main directions: creationism, transformism and evolutionism. Creationism is the concept of permanence of species, considering the diversity of the organic world as a result of its creation by God. This direction was formed as a result of the establishment of the dominance of the Christian church in Europe, based on biblical texts. Prominent representatives of creationism were C. Linnaeus and J. Cuvier.
“The Prince of Botanists” C. Linnaeus, who discovered and described hundreds of new plant species and created their first harmonious system, nevertheless argued that the total number of species of organisms has remained unchanged since the creation of the Earth, that is, they not only do not appear again, but and don't disappear. Only towards the end of his life did he come to the conclusion that genera are the work of God, while species can develop due to adaptation to local conditions.
The contribution of the outstanding French zoologist J. Cuvier (1769–1832) to biology was based on numerous data from paleontology, comparative anatomy and physiology doctrine of correlations- relationships between parts of the body. Thanks to this, it became possible to reconstruct the external appearance of the animal in individual parts. However, in the process of paleontological research, J. Cuvier could not help but pay attention to both the obvious abundance of fossil forms and the sharp changes in animal groups during geological history. These data served as the starting point for formulating catastrophe theories, according to which all or almost all organisms on Earth were repeatedly killed as a result of periodic natural disasters, and then the planet was repopulated by species that survived the disaster. The followers of J. Cuvier counted up to 27 such catastrophes in the history of the Earth. Considerations about evolution seemed to J. Cuvier to be divorced from reality.
The contradictions in the initial premises of creationism, which became more and more obvious as scientific facts accumulated, served as the starting point for the formation of another system of views - transformism, recognizing the real existence of species and their historical development. Representatives of this trend - J. Buffon, I. Goethe, E. Darwin and E. Geoffroy Saint-Hilaire, being unable to reveal the true causes of evolution, reduced them to adaptation to environmental conditions and the inheritance of acquired characteristics. The roots of transformism can be found in the works of ancient Greek and medieval philosophers who recognized historical changes in the organic world. Thus, Aristotle expressed the idea of the unity of nature and the gradual transition from bodies of inanimate nature to plants, and from them to animals - the “ladder of nature.” He considered the main reason for changes in living organisms to be their internal desire for perfection.
The French naturalist J. Buffon (1707–1788), whose main life work was the 36-volume Natural History, contrary to the views of creationists, expanded the scope of the history of the Earth to 80–90 thousand years. At the same time, he noted the unity of the flora and fauna, as well as the possibility of changes in related organisms under the influence of environmental factors as a result of domestication and hybridization.
The English physician, philosopher and poet E. Darwin (1731–1802), Charles Darwin’s grandfather, believed that the history of the organic world goes back millions of years, and the diversity of the animal world is the result of a mixture of several “natural” groups, the influence of the external environment, exercise and lack of exercise organs, and other factors.
E. Geoffroy Saint-Hilaire (1772–1844) considered the unity of the structural plan of groups of animals to be one of the main proofs of the development of the living world. However, unlike his predecessors, he was inclined to believe that changes in species are caused by the influence of environmental factors not on adult individuals, but on embryos.
Despite the fact that in the discussion that flared up in 1831 between J. Cuvier and E. Geoffroy Saint-Hilaire in the form of a series of reports at the Academy of Sciences, a clear advantage remained on the side of the former, it was transformism that became the forerunner of evolutionism. Evolutionism(theory of evolution, evolutionary doctrine) is a system of views that recognizes the development of nature according to certain laws. It is the theoretical pinnacle of biology, which allows us to explain the diversity and complexity of living systems that we observe. However, due to the fact that evolutionary teaching describes phenomena that are difficult to observe, it faces significant difficulties. Sometimes the theory of evolution is called “Darwinism” and is identified with the teachings of Charles Darwin, which is fundamentally incorrect, because, although Charles Darwin’s theory made an invaluable contribution to the development of not only the doctrine of evolution, but also biology in general (as well as many other sciences ), the foundations of evolutionary theory were laid by other scientists, it continues to develop to this day, and “Darwinism” in many aspects has only historical significance.
The creator of the first evolutionary theory - Lamarckism - was the French naturalist J. B. Lamarck (1744–1829). He considered the driving force of evolution to be the internal desire of organisms for perfection ( law of gradation), however, adaptation to environmental conditions forces them to deviate from this main line. At the same time, organs that are intensively used by the animal in the process of life develop, and those that are unnecessary to it, on the contrary, are weakened and may even disappear ( law of exercise and non-exercise of organs). Characteristics acquired during life are fixed and passed on to descendants. Thus, he explained the presence of membranes between the toes of waterfowl by the attempts of their ancestors to move in the aquatic environment, and the long neck of giraffes, according to Lamarck, is a consequence of the fact that their ancestors tried to get leaves from the tops of trees.
The disadvantages of Lamarckism were the theoretical nature of many constructions, as well as the assumption of the intervention of the Creator in evolution. In the process of the development of biology, it became clear that individual changes acquired by organisms during life, for the most part, fall within the limits of phenotypic variability, and their transmission is practically impossible. For example, the German zoologist and evolutionary theorist A. Weismann (1834–1914) cut off the tails of mice for many generations and always received only tailed rodents in their offspring. The theory of J. B. Lamarck was not accepted by his contemporaries, but at the turn of the century it formed the basis of the so-called neo-Lamarckism.
The meaning of Charles Darwin's evolutionary theory
The prerequisites for the creation of the most famous evolutionary theory of Charles Darwin, or Darwinism, were the publication in 1778 of the work of the English economist T. Malthus “Treatise on Population”, the work of the geologist Charles Lyell, the formulation of the cell theory, the success of selection in England and Charles’s own observations. Darwin (1809–1882), taken during his studies at Cambridge, during the expedition as a naturalist on the Beagle and at its completion.
Thus, T. Malthus argued that the Earth's population is increasing exponentially, which significantly exceeds the planet's ability to provide it with food and leads to the death of some of the offspring. Parallels drawn by Charles Darwin and his co-author A. Wallace (1823–1913) indicated that in nature, individuals reproduce at a very high speed, but population sizes remain relatively constant. The research of the English geologist C. Lyell made it possible to establish that the surface of the Earth was not always the same as it is now, and its changes were caused by the influence of water, wind, volcanic eruptions and the activity of living organisms. Even in his student years, Charles Darwin himself was struck by the extreme degree of variability of beetles, and during his travels by the similarity of the flora and fauna of continental South America and the nearby Galapagos Islands, and at the same time by the significant diversity of species, such as finches and turtles. In addition, on the expedition he was able to observe the skeletons of giant extinct mammals, similar to modern armadillos and sloths, which significantly shook his belief in the creation of species.
The basic principles of the theory of evolution were expressed by Charles Darwin in 1859 at a meeting of the Royal Society of London, and subsequently developed in the books “The Origin of Species by Natural Selection, or the Preservation of Favored Breeds in the Struggle for Life” (1859), “Changes in Domestic Animals and Cultivated Plants "(1868), "The Origin of Man and Sexual Selection" (1871), "The Expression of Emotions in Man and Animals" (1872), etc.
The essence developed by Charles Darwin evolution concepts can be reduced to a series of provisions arising from each other, having corresponding proof:
- The individuals that make up any population produce many more offspring than is necessary to maintain the population size.
- Due to the fact that life resources for any type of living organisms are limited, there inevitably arises between them struggle for existence. Charles Darwin distinguished between intraspecific and interspecific struggle, as well as struggle with environmental factors. At the same time, he also pointed out that we are talking not only about the struggle of a particular individual for existence, but also for leaving offspring.
- The consequence of the struggle for existence is natural selection- the predominant survival and reproduction of organisms that accidentally turned out to be the most adapted to the given conditions of existence. Natural selection is in many ways similar to artificial selection, which humans have used since ancient times to breed new varieties of plants and breeds of domestic animals. By selecting individuals that have some desirable trait, man preserves these traits through artificial breeding through selective breeding or pollination. A special form of natural selection is sexual selection for traits that usually do not have direct adaptive significance (long feathers, huge horns, etc.), but contribute to reproductive success because they make the individual more attractive to the opposite sex or more formidable to rivals of the same gender.
- The material for evolution is the differences between organisms that arise as a result of their variability. Charles Darwin distinguished between indefinite and definite variability. Certain(group) variability manifests itself in all individuals of a species equally under the influence of a certain factor and disappears in descendants when the effect of this factor ceases. Uncertain(individual) variability are changes that occur in each individual, regardless of fluctuations in the values of environmental factors, and are transmitted to descendants. Such variability does not have an adaptive nature. Subsequently, it turned out that certain variability is non-hereditary, and indeterminate variability is hereditary.
- Natural selection ultimately leads to divergence in the characteristics of individual isolated varieties - divergence, and, ultimately, to the formation of new species.
Charles Darwin's theory of evolution not only postulated the process of the emergence and development of species, but also revealed the mechanism of evolution itself, which is based on the principle of natural selection. Darwinism also denied the programmed nature of evolution and postulated its continuous nature.
At the same time, Charles Darwin's evolutionary theory could not answer a number of questions, for example, about the nature of genetic material and its properties, the essence of hereditary and non-hereditary variability, and their evolutionary role. This led to a crisis of Darwinism and the emergence of new theories: neo-Lamarckism, saltationism, the concept of nomogenesis, etc. Neo-Lamarckism is based on the position of J. B. Lamarck’s theory of the inheritance of acquired characteristics. Saltationism is a system of views on the process of evolution as abrupt changes leading to the rapid emergence of new species, genera and larger systematic groups. Concept nomogenesis postulates the programmed direction of evolution and the development of various characteristics based on internal laws. Only the synthesis of Darwinism and genetics in the 20-30s of the twentieth century was able to overcome the contradictions that inevitably arose when explaining a number of facts.
Interrelation of the driving forces of evolution
Evolution cannot be associated with the action of any one factor, since mutations themselves are random and undirected changes, and cannot ensure the adaptation of individuals to environmental factors, while natural selection already sorts these changes. Likewise, selection itself cannot be the only factor in evolution, since selection requires appropriate material supplied by mutations.
However, it can be noted that the mutation process and gene flow create variation, while natural selection and genetic drift sort out this variation. This means that factors that create variability initiate the process of microevolution, and those that sort variability continue it, leading to the establishment of new frequencies of variants. Thus, evolutionary change within a population can be viewed as the result of opposing forces creating and sorting genotypic variation.
An example of the interaction between the mutation process and selection is hemophilia in humans. Hemophilia is a disease caused by decreased blood clotting. It has previously led to death in the pre-reproductive period, as any damage to the soft tissue could potentially lead to significant blood loss. This disease is caused by a recessive mutation of the sex-linked gene H (Xh). Women suffer from hemophilia extremely rarely; they are more often heterozygous carriers, but their sons can inherit the disease. Theoretically, over the course of several generations, such men die before puberty and gradually this allele should disappear from the population, but the frequency of occurrence of this disease does not decrease due to repeated mutations in this locus, as happened in Queen Victoria, who transmitted the disease to three generations of the royal houses of Europe. The constant frequency of this disease indicates a balance between the mutation process and selection pressure.
Forms of natural selection, types of struggle for existence
Natural selection They call the selective survival and leaving of offspring by the most fit individuals and the death of the least fit.
The essence of natural selection in the theory of evolution lies in the differentiated (non-random) preservation of certain genotypes in a population and their selective participation in the transmission of genes to the next generation. Moreover, it affects not a single trait (or gene), but the entire phenotype, which is formed as a result of the interaction of the genotype with environmental factors. Natural selection will be of a different nature in different environmental conditions. Currently, there are several forms of natural selection: stabilizing, driving and tearing.
Stabilizing selection is aimed at consolidating a narrow norm of reaction, which turned out to be the most favorable under the given conditions of existence. It is typical for those cases when phenotypic characteristics are optimal for unchanging environmental conditions. A striking example of the action of stabilizing selection is the preservation of a relatively constant body temperature of warm-blooded animals. This form of selection was studied in detail by the outstanding Russian zoologist I. I. Shmalgauzen.
Driving selection arises in response to changes in environmental conditions, as a result of which mutations deviating from the average value of the trait are preserved, while the previously dominant form is destroyed because it does not sufficiently meet the new conditions of existence. For example, in England, as a result of air pollution from industrial emissions, birch moth butterflies, previously unseen in many places, with dark colored wings, which were less visible to birds against the backdrop of sooty birch trunks, became widespread. Driving selection does not contribute to the complete destruction of the form against which it acts, since, as a result of measures taken by the government and environmental organizations, the situation with air pollution has sharply improved, and the color of butterfly wings has returned to its original version.
Tearing, or disruptive selection favors the preservation of extreme variants of a trait and removes intermediate ones, as, for example, as a result of the use of pesticides, groups of insect individuals resistant to it appear. In its mechanism, disruptive selection is the opposite of stabilizing selection. Through this form of selection, several sharply demarcated phenotypes arise in a population. This phenomenon is called polymorphism. The occurrence of reproductive isolation between distinct forms can lead to speciation.
Sometimes they are also considered separately destabilizing selection, which preserves mutations that lead to a wide variety of any characteristic, for example, the color and structure of the shells of some mollusks living in the heterogeneous microconditions of the rocky surf of the sea. This form of selection was discovered by D.K. Belyaev while studying the domestication of animals.
In nature, none of the forms of natural selection exists in a pure form, but on the contrary, there are various combinations of them, and as environmental conditions change, first one or the other of them comes to the fore. Thus, upon completion of changes in the environment, driving selection is replaced by stabilizing selection, which optimizes a group of individuals in new conditions of existence.
Natural selection occurs at various levels, and therefore individual, group and sexual selection are also distinguished. Individual selection eliminates less adapted individuals from participating in reproduction, while group selection is aimed at preserving a trait that is useful not to an individual, but to the group as a whole. Under pressure group selection can completely wipe out entire populations, species and larger groups of organisms without leaving offspring. Unlike individual selection, group selection reduces the diversity of forms in nature.
Sexual selection carried out within one gender. It promotes the development of traits that ensure success in leaving the largest offspring. Thanks to this form of natural selection, sexual dimorphism has developed, expressed in the size and color of the peacock’s tail, the antlers of deer, etc.
Natural selection is the result struggle for existence based on hereditary variability. The struggle for existence is understood as the entire set of relationships between individuals of one’s own and other species, as well as with abiotic environmental factors. These relationships determine the success or failure of a particular individual in surviving and producing offspring. The reason for the struggle for existence is the appearance of an excess number of individuals in relation to the available resources. In addition to competition, these relationships should also include mutual assistance, which increases the chances of survival of individuals.
Interaction with environmental factors can also lead to the death of the vast majority of individuals, for example, in insects, only a small part of which survive the winter.
Synthetic theory of evolution
The successes of genetics at the beginning of the twentieth century, for example, the discovery of mutations, suggested that hereditary changes in the phenotype of organisms occur suddenly, and do not form over a long period of time, as postulated by the evolutionary theory of Charles Darwin. However, further research in the field of population genetics led to the formulation in the 20–50s of the twentieth century of a new system of evolutionary views - synthetic theory of evolution. Significant contributions to its creation were made by scientists from different countries: Soviet scientists S. S. Chetverikov, I. I. Shmalgauzen and A. N. Severtsov, English biochemist and geneticist D. Haldane, American geneticists S. Wright and F. Dobzhansky, evolutionist D. Huxley, paleontologist D. Simpson and zoologist E. Mayr.
Basic provisions of the synthetic theory of evolution:
- The elementary material of evolution is hereditary variability (mutational and combinative) in individuals of a population.
- The elementary unit of evolution is the population in which all evolutionary changes occur.
- An elementary evolutionary phenomenon is a change in the genetic structure of a population.
- Elementary factors of evolution - genetic drift, waves of life, gene flow - are undirected, random in nature.
- The only directional factor in evolution is natural selection, which is creative in nature. Natural selection can be stabilizing, driving and disruptive.
- Evolution is divergent in nature, that is, one taxon can give rise to several new taxa, while each species has only one ancestor (species, population).
- Evolution is gradual and continuous. Speciation as a stage of the evolutionary process is the sequential replacement of one population by a series of other temporary populations.
- There are two types of evolutionary process: microevolution and macroevolution. Macroevolution does not have its own special mechanisms and is carried out only thanks to microevolutionary mechanisms.
- Any systematic group can either flourish (biological progress) or die out (biological regression). Biological progress is achieved through changes in the structure of organisms: aromorphoses, idioadaptations or general degeneration.
- The main laws of evolution are its irreversible nature, the progressive complication of life forms and the development of the adaptability of species to their environment. At the same time, evolution does not have an ultimate goal, that is, the process is undirected.
Despite the fact that evolutionary theory over the past decades has been enriched with data from related sciences - genetics, selection, etc., it still does not take into account a number of aspects, for example, directed changes in hereditary material, therefore in the future it is possible to create a new concept of evolution that will replace the synthetic theory .
Elementary factors of evolution
According to the synthetic theory of evolution, an elementary evolutionary phenomenon consists of a change in the genetic composition of a population, and events and processes that lead to changes in gene pools are called elementary factors of evolution. These include the mutation process, population waves, genetic drift, isolation and natural selection. Due to the exceptional significance of natural selection in evolution, it will be considered separately.
Mutation process which is as continuous as evolution itself, maintains the genetic heterogeneity of the population due to the emergence of more and more new gene variants. Mutations that arise under the influence of external and internal factors are classified as gene, chromosomal and genomic.
Gene mutations occur with a frequency of 10 –4 –10 –7 per gamete, however, due to the fact that in humans and most higher organisms the total number of genes can reach several tens of thousands, it is impossible to imagine that two organisms are absolutely identical. Most mutations that arise are recessive, especially since dominant mutations are immediately subject to natural selection. Recessive mutations create that very reserve of hereditary variability, but before they manifest themselves in the phenotype, they must become established in many individuals in a heterozygous state due to free crossing in the population.
Chromosomal mutations associated with the loss or transfer of a part of a chromosome (a whole chromosome) to another, are also quite common in various organisms, for example, the difference between some species of rats lies in a single pair of chromosomes, which makes it difficult to cross them.
Genomic mutations, associated with polyploidization, also lead to reproductive isolation of the newly emerged population due to disturbances in mitosis of the first division of the zygote. Nevertheless, they are quite widespread in plants and such plants can grow in the Arctic and alpine meadows due to their greater resistance to environmental factors.
Combinative variability, which ensures the emergence of new variants of combining genes in the genotype, and, accordingly, increases the likelihood of the emergence of new phenotypes, also contributes to evolutionary processes, since in humans alone the number of variants of chromosome combinations is 2 23, that is, the appearance of an organism similar to that already existing, is almost impossible.
Population waves. The opposite result (depletion of gene composition) is often caused by fluctuations in the number of organisms in natural populations, which in some species (insects, fish, etc.) can change tens or hundreds of times - population waves, or "waves of life". An increase or decrease in the number of individuals in populations can be either periodic, so non-periodic. The first are seasonal or perennial, such as migrations in migratory birds, or reproduction in daphnia, which have only female individuals in spring and summer, and by autumn males appear, necessary for sexual reproduction. Non-periodic fluctuations in numbers are often caused by a sharp increase in the amount of food in a favorable year, disruption of habitat conditions, and the proliferation of pests or predators.
Since population restoration occurs due to a small number of individuals that do not have the entire set of alleles, the new and original populations will have different genetic structures. A change in the frequency of genes in a population under the influence of random factors is called genetic drift, or genetic-automatic processes. It also occurs during the development of new territories, because they receive an extremely limited number of individuals of a given species, which can give rise to a new population. Therefore, the genotypes of these individuals ( founder effect). As a result of genetic drift, new homozygous forms (for mutant alleles) often emerge, which may turn out to be adaptively valuable and will be subsequently picked up by natural selection.
Thus, among the Indian population of the American continent and the Laplanders, the proportion of people with blood group I (0) is very high, while groups III and IV are extremely rare. Probably, in the first case, the founders of the population were individuals who did not have the IB allele, or it was lost during the selection process.
Up to a certain point, an exchange of alleles occurs between neighboring populations as a result of crossing between individuals of different populations - gene flow, which reduces the divergence between individual populations, but with the emergence of isolation it stops. In essence, gene flow is a delayed mutation process.
Insulation. Any changes in the genetic structure of the population must be fixed, which is what happens thanks to isolation- the emergence of any barriers (geographical, environmental, behavioral, reproductive, etc.) that complicate and make impossible the crossing of individuals of different populations. Although isolation itself does not create new forms, it nevertheless preserves genetic differences between populations subject to the action of natural selection. There are two forms of isolation: geographical and biological.
Geographical isolation arises as a result of the division of the area by physical barriers (water obstacles for terrestrial organisms, land areas for aquatic species, alternation of elevated areas and plains); This is facilitated by a sedentary or attached (in plants) lifestyle. Sometimes geographic isolation can be caused by the expansion of the range of a species with the subsequent extinction of its populations in intermediate territories.
Biological isolation is a consequence of certain divergences of organisms within the same species that somehow prevent free interbreeding. There are several types of biological isolation: environmental, seasonal, ethological, morphological and genetic. Environmental insulation achieved through the division of ecological niches (for example, preference for certain habitats or food types, as in the spruce crossbill and pine crossbill). Seasonal(temporary) isolation is observed in the case of reproduction of individuals of the same species at different times (different herring stocks). Ethological isolation depends on the characteristics of behavior (features of the courtship ritual, coloring, “singing” of females and males from different populations). At morphological isolation An obstacle to crossing is the discrepancy in the structure of the reproductive organs or even body size (Pekingese and Great Dane). Genetic isolation has the greatest impact and manifests itself in the incompatibility of germ cells (death of the zygote after fertilization), sterility or reduced viability of hybrids. The reasons for this are the peculiarities of the number and shape of chromosomes, as a result of which full cell division (mitosis and meiosis) becomes impossible.
By disrupting free crossing between populations, isolation thereby reinforces in them those differences that arose at the genotypic level due to mutations and fluctuations in numbers. In this case, each population is subject to the action of natural selection separately from the other, and this ultimately leads to divergence.
The creative role of natural selection in evolution
Natural selection functions as a kind of “sieve” that sorts genotypes according to their degree of fitness. However, Charles Darwin emphasized that selection is not only and not so much aimed at preserving exclusively the best, but at removing the worst, that is, it allows you to preserve multivariance. The function of natural selection is not limited to this, since it ensures the reproduction of adapted genotypes, and, thus, determines the direction of evolution, consistently adding up random and numerous deviations. Natural selection does not have a specific goal: based on the same material (hereditary variability) under different conditions, different results can be obtained.
In this regard, the factor of evolution under consideration cannot be compared with the work of a sculptor hewing a block of marble; rather, it acts like a distant ancestor of man, making a tool from a stone fragment, without imagining the final result, which depends not only on the nature of the stone and its shape, but and on the strength, direction of the blow, etc. However, in case of failure, selection, like a humanoid creature, rejects the “wrong” form.
The price for selection is the occurrence genetic load, that is, the accumulation of mutations in a population, which over time may become predominant due to the sudden death of most individuals or the migration of a small number of them.
Under the pressure of natural selection, not only the diversity of species is formed, but their level of organization also increases, including their complication or specialization. However, in contrast to artificial selection, carried out by humans only for economically valuable traits, often to the detriment of adaptive properties, natural selection cannot contribute to this, since no adaptation in nature can compensate for the harm from a decrease in the viability of the population.
Research by S. S. Chetverikov
One of the important steps towards the reconciliation of Darwinism and genetics was made by the Moscow zoologist S. S. Chetverikov (1880–1959). Based on the results of a study of the genetic composition of natural populations of the fruit fly Drosophila, he proved that they carry many recessive mutations in a heterozygous form that do not violate phenotypic uniformity. Most of these mutations are unfavorable for the body and create the so-called genetic load, reducing the adaptability of the population as a whole to its environment. Some mutations that do not have adaptive significance at a given moment in the development of the species may acquire a certain value later, and thus are reserve of hereditary variability. The spread of such mutations among individuals of a population as a result of successive free crossings can ultimately lead to their transition to a homozygous state and manifestation in the phenotype. If this state of the sign is hair dryer- is adaptive, then after a few generations it will completely displace the dominant phene, along with its carriers, from the population that is less appropriate to the given conditions. Thus, due to such evolutionary changes, only the recessive mutant allele is retained, and its dominant allele disappears.
Let's try to prove this with a specific example. When studying any particular population, you can find that not only its phenotypic, but also its genotypic structure can remain unchanged for a long time, due to free crossing, or panmixia diploid organisms.
This phenomenon is described by the law Hardy–Weinberg, according to which in an ideal population of unlimited size in the absence of mutations, migrations, population waves, genetic drift, natural selection and subject to free crossing, the frequencies of alleles and genotypes of diploid organisms will not change over a number of generations.
For example, in a population a certain trait is encoded by two alleles of the same gene - dominant ( A) and recessive ( A). The frequency of the dominant allele is designated as R, and recessive - q. The sum of the frequencies of these alleles is 1: p + q= 1. Therefore, if we know the frequency of the dominant allele, then we can determine the frequency of the recessive allele: q = 1 – p. In fact, the frequencies of the alleles are equal to the probabilities of the formation of the corresponding gametes. Then, after the formation of zygotes, the genotype frequencies in the first generation will be:
(pA + qa) 2 = p 2 A.A. + 2pqAa + q 2 aa = 1,
Where p 2 A.A.- frequency of dominant homozygotes;
2pqAa- frequency of heterozygotes;
q 2 aa- frequency of recessive homozygotes.
It is easy to calculate that in subsequent generations the frequencies of genotypes will remain the same, maintaining the genetic diversity of the population. But in nature there are no ideal populations, and therefore, in them, mutant alleles can not only persist, but also spread, and even replace previously more common alleles.
S. S. Chetverikov clearly realized that natural selection does not simply eliminate individual less successful traits, and, accordingly, the alleles encoding them, but also acts on the entire complex of genes that influence the manifestation of a particular gene in the phenotype, or genotypic environment. As a genotypic environment, the entire genotype is currently considered as a set of genes that can enhance or weaken the manifestation of specific alleles.
No less important in the development of evolutionary teaching are the studies of S. S. Chetverikov in the field of population dynamics, in particular “waves of life”, or population waves. While still a student, in 1905 he published an article about the possibility of outbreaks of mass reproduction of insects and an equally rapid decline in their numbers.
The role of evolutionary theory in the formation of the modern natural science picture of the world
The importance of evolutionary theory in the development of biology and other natural sciences can hardly be overestimated, since it was the first to explain the conditions, causes, mechanisms and results of the historical development of life on our planet, that is, it gave a materialistic explanation of the development of the organic world. In addition, the theory of natural selection was the first truly scientific theory of biological evolution, since when it was created, Charles Darwin did not rely on speculative constructions, but proceeded from his own observations and relied on the real properties of living organisms. At the same time, she enriched the biological tools with the historical method.
The formulation of evolutionary theory not only caused a heated scientific debate, but also gave impetus to the development of such sciences as general biology, genetics, selection, anthropology and a number of others. In this regard, one cannot but agree with the statement that the theory of evolution crowned the next stage in the development of biology and became the starting point for its progress in the twentieth century.
Evidence of the evolution of living nature. Results of evolution: adaptability of organisms to their environment, diversity of species
Evidence of the evolution of wildlife
In various fields of biology, even before Charles Darwin and after the publication of his theory of evolution, a whole series of evidence was obtained to support it. This evidence is called evidence of evolution. The most often cited are paleontological, biogeographical, comparative embryological, comparative anatomical and comparative biochemical evidence of evolution, although taxonomy data, as well as the selection of plants and animals, cannot be discounted.
Paleontological evidence based on the study of fossil remains of organisms. These include not only well-preserved organisms frozen in ice or encased in amber, but also “mummies” discovered in acidic peat bogs, as well as remains of organisms and fossils preserved in sedimentary rocks. The presence in ancient rocks of simpler organisms than in later layers, and the fact that species found at one level disappear at another, is considered one of the most significant evidence of evolution and is explained by the emergence and extinction of species in corresponding eras due to changes in environmental conditions.
Despite the fact that few fossil remains have been discovered so far and many fragments are missing from the fossil record due to the low probability of preservation of organic remains, forms of organisms have still been found that have signs of both evolutionarily more ancient and younger groups of organisms. Such forms of organisms are called transitional forms. Prominent representatives of transitional forms, illustrating the transition from fish to terrestrial vertebrates, are lobe-finned fish and stegocephals, and Archeopteryx occupies a certain place between reptiles and birds.
Rows of fossil forms that are consistently connected with each other in the process of evolution not only by general but also by particular structural features are called phylogenetic series. They may be represented by fossil remains from different continents, and claim to be more or less complete, but their study is impossible without comparison with living forms in order to demonstrate the progression of the evolutionary process. A classic example of a phylogenetic series is the evolution of the ancestors of the horse, studied by the founder of evolutionary paleontology V. O. Kovalevsky.
Biogeographic evidence. Biogeography how science studies the patterns of distribution and distribution of species, genera and other groups of living organisms, as well as their communities, on the surface of our planet.
The absence in any part of the earth's surface of species of organisms that are adapted to such a habitat and take root well when artificially imported, like rabbits in Australia, as well as the presence of similar forms of organisms in parts of the land located at considerable distances from each other indicate, first of all, that the appearance of the Earth was not always this way, and geological transformations, in particular, continental drift, the formation of mountains, the rise and fall of the level of the World Ocean affect the evolution of organisms. For example, four similar species of lungfish live in the tropical regions of South America, South Africa and Australia, while the habitats of camels and llamas belonging to the same order are located in North Africa, most of Asia and South America. Paleontological studies have shown that camels and llamas descend from a common ancestor that once lived in North America, and then spread to Asia through the pre-existing isthmus at the site of the Bering Strait, and also through the Isthmus of Panama to South America. Subsequently, all representatives of this family in the intermediate regions became extinct, and in the regional regions, new species were formed in the process of evolution. The earlier separation of Australia from other land masses allowed the formation of a completely special flora and fauna there, in which such forms of mammals as monotremes - the platypus and echidna - were preserved.
From the point of view of biogeography, the diversity of Darwin's finches on the Galapagos Islands, which are 1200 km from the coast of South America and are of volcanic origin, can also be explained. Apparently, representatives of the only species of finches in Ecuador once flew or were introduced to them, and then, as they multiplied, some of the individuals settled across the remaining islands. On the central large islands, the struggle for existence (food, nesting sites, etc.) was most acute, which is why species slightly different from each other in external characteristics were formed, consuming different foods (seeds, fruits, nectar, insects, etc.) .).
They influenced the distribution of various groups of organisms and changes in climatic conditions on Earth, which contributed to the prosperity of some groups and the extinction of others. Individual species or groups of organisms that have survived from previously widespread floras and faunas are called relics. These include ginkgo, sequoia, tulip tree, lobe-finned fish coelacanth, etc. In a broader sense, species of plants and animals that live in limited areas of territory or water area are called endemic, or endemic. For example, all representatives of the indigenous flora and fauna of Australia are endemic, and in the flora and fauna of Lake Baikal up to 75% of them are endemic.
Comparative anatomical evidence. The study of the anatomy of related groups of animals and plants provides convincing evidence of the similarity in the structure of their organs. Despite the fact that environmental factors certainly leave their mark on the structure of organs, in angiosperms, with all their amazing diversity, flowers have sepals, petals, stamens and pistils, and in terrestrial vertebrates, the limb is built according to a five-fingered plan. Organs that have a similar structure, occupy the same position in the body and develop from the same rudiments in related organisms, but perform different functions, are called homologous. Thus, the auditory ossicles (hammer, incus and stirrup) are homologous to the gill arches of fish, the poisonous glands of snakes are the salivary glands of other vertebrates, the mammary glands of mammals are the sweat glands, the flippers of seals and cetaceans are the wings of birds, the limbs of horses and moles.
Organs that have not functioned for a long time most likely turn into vestigial (rudiments)- structures that are underdeveloped in comparison with ancestral forms and have lost their basic meaning. These include the fibula in birds, eyes in moles and mole rats, hair, coccyx and appendix in humans, etc.
Individual individuals, however, may exhibit characteristics that are absent in a given species, but were present in distant ancestors - atavisms, for example, three-toedness in modern horses, the development of additional pairs of mammary glands, a tail and hair on the entire human body.
If homologous organs are evidence in favor of the relatedness of organisms and divergence in the process of evolution, then similar bodies- similar structures in organisms of different groups that perform the same functions, on the contrary, are examples convergence(convergence is the generally independent development of similar characteristics in different groups of organisms existing in the same conditions) and confirm the fact that the environment leaves a significant imprint on the organism. Analogues are the wings of insects and birds, the eyes of vertebrates and cephalopods (squid, octopuses), and the jointed limbs of arthropods and terrestrial vertebrates.
Comparative embryological evidence. Studying embryonic development in representatives of different groups of vertebrates, K. Baer discovered their striking structural unity, especially in the early stages of development ( law of germinal resemblance). Later E. Haeckel formulated biogenetic law, according to which ontogenesis is a brief repetition of phylogeny, i.e., the stages that an organism goes through in the process of its individual development repeat the historical development of the group to which it belongs.
Thus, in the first stages of development, a vertebrate embryo acquires structural features characteristic of fish, and then of amphibians and, ultimately, of the group to which it belongs. This transformation is explained by the fact that each of the above classes has common ancestors with modern reptiles, birds and mammals.
However, the biogenetic law has a number of limitations, and therefore the Russian scientist A. N. Severtsov significantly limited the scope of its application by repeating in ontogenesis exclusively the features of the embryonic stages of development of ancestral forms.
Comparative biochemical evidence. The development of more accurate methods of biochemical analysis has provided evolutionary scientists with a new group of data in favor of the historical development of the organic world, since the presence of the same substances in all organisms indicates possible biochemical homology, similar to that at the level of organs and tissues. Comparative biochemical studies of the primary structure of such widespread proteins as cytochrome With and hemoglobin, as well as nucleic acids, especially rRNA, have shown that many of them have almost the same structure and perform the same functions in representatives of different species, and the closer the relationship, the greater the similarity is found in the structure of the substances under study.
Thus, the theory of evolution is confirmed by a significant amount of data from various sources, which once again indicates its reliability, but it will still change and be refined, since many aspects of the life of organisms remain outside the field of view of researchers.
Results of evolution: adaptability of organisms to their environment, diversity of species
In addition to the general characteristics characteristic of representatives of a particular kingdom, species of living organisms are characterized by an amazing variety of features of external and internal structure, life activity and even behavior that appeared and were selected in the process of evolution and ensure adaptation to living conditions. However, one should not assume that since birds and insects have wings, this is due to the direct action of the air, because there are plenty of wingless insects and birds. The above-mentioned adaptations were selected through a process of natural selection from the entire spectrum of available mutations.
Epiphytic plants, which live not on the soil, but on trees, have adapted to absorbing atmospheric moisture with the help of roots without root hairs, but with a special hygroscopic tissue - velamen. Some bromeliads can absorb water vapor in the humid atmosphere of the tropics using the hairs on their leaves.
Insectivorous plants (sundews, Venus flytraps) that live on soils where nitrogen is unavailable for one reason or another have developed a mechanism for attracting and absorbing small animals, most often insects, which are a source of the required element for them.
To protect against being eaten by herbivores, many plants leading an attached way of life have developed passive means of protection, such as thorns (hawthorn), thorns (rose), stinging hairs (nettle), accumulation of crystals of calcium oxalate (sorrel), biologically active substances in tissues (coffee, hawthorn), etc. In some of them, even the seeds in unripe fruits are surrounded by stony cells that prevent pests from reaching them, and only in the fall does the process of dewooding occur, which allows the seeds to enter the soil and germinate (pear).
The environment also has a formative influence on animals. Thus, many fish and aquatic mammals have a streamlined body shape, which makes it easier for them to move through its thickness. However, one should not assume that water directly affects the shape of the body; it is simply that in the process of evolution those animals that possessed this trait turned out to be the most adapted to it.
The body of whales and dolphins is not covered with hair, while the related group of pinnipeds has a more or less reduced coat of hair, since, unlike the former, they spend part of their time on land, where without wool their skin would immediately become icy .
The body of most fish is covered with scales, which on the underside are lighter colored than on the top, as a result of which these animals are hardly noticeable from above to natural enemies against the background of the bottom, and from below - against the background of the sky. Coloring that makes animals invisible to their enemies or prey is called patronizing. It is widespread in nature. A striking example of such coloring is the coloring of the underside of the wings of the callima butterfly, which, having sat on a branch and folded its wings together, turns out to look like a dry leaf. Other insects, such as stick insects, camouflage themselves as plant twigs.
Spotted or striped coloration also has adaptive significance, since against the background of the soil, birds such as quails or eiders are not visible even at close range. The spotted eggs of birds nesting on the ground are also invisible.
The coloring of animals is not always as constant as that of a zebra; for example, flounder and chameleon are able to change it depending on the nature of the place where they are. Cuckoos, by laying their eggs in the nests of various birds, can vary the color of their shells in such a way that the “owners” of the nest do not notice the differences between it and their own eggs.
The coloring of animals does not always make them invisible - many of them simply catch the eye, which should warn of danger. Most of these insects and reptiles are poisonous to one degree or another, such as a ladybug or a wasp, so a predator, having experienced unpleasant sensations several times after eating such an object, avoids it. Nevertheless, warning coloring is not universal, since some birds have adapted to feed on them (buzzard).
The increased chances of survival in individuals with warning coloration contributed to its appearance in representatives of other species without proper reasons. This phenomenon is called mimicry. Thus, non-poisonous caterpillars of some species of butterflies imitate poisonous ones, and ladybugs imitate one of the types of cockroaches. However, birds can quickly learn to distinguish poisonous organisms from non-poisonous ones and consume the latter, avoiding the individuals that served as role models.
In some cases, the opposite phenomenon can also be observed - predatory animals imitate harmless animals in color, which allows them to approach the victim at a close distance and then attack (saber-toothed blenny).
Protection for many species is also provided by adaptive behavior, which is associated with storing food for the winter, caring for offspring, freezing in place or, conversely, adopting a threatening pose. Thus, river beavers prepare several cubic meters of branches, parts of trunks and other plant food for the winter, flooding it in water near the “huts”.
Caring for offspring is characteristic mainly of mammals and birds, however, it is also found in representatives of other classes of chordates. For example, the aggressive behavior of male sticklebacks is known, driving away all enemies from the nest in which the eggs are located. Male clawed frogs wrap the eggs around their legs and carry them until the tadpoles hatch.
Even some insects are able to provide their offspring with a more favorable habitat. For example, bees feed their larvae, and young bees at first “work” only in the hive. Ants move their pupae up and down in the anthill, depending on temperature and humidity, and when there is a threat of flooding, they generally take them with them. Carab beetles prepare special balls from animal waste for their larvae.
Many insects, when threatened with attack, freeze in place and take the form of dry sticks, twigs and leaves. Vipers, on the contrary, rise and inflate their hood, while the rattlesnake makes a special sound with a rattle located at the end of its tail.
Behavioral adaptations are complemented by physiological ones related to the characteristics of the habitat. Thus, a person is able to stay under water without scuba gear for only a few minutes, after which he can lose consciousness and die due to lack of oxygen, and whales do not surface for quite a long time. Their lung volume is not too large, but there are other physiological adaptations, for example, in the muscles there is a high concentration of the respiratory pigment - myoglobin, which, as it were, stores oxygen and releases it during immersion. In addition, whales have a special formation - a “wonderful network”, which allows the use of oxygen even from venous blood.
Animals in hot habitats, such as deserts, are constantly at risk of overheating and losing excess moisture. Therefore, the fennec fox has extremely large ears that allow it to radiate heat. Amphibians of desert regions, in order to avoid loss of moisture through the skin, are forced to switch to a nocturnal lifestyle, when humidity rises and dew appears.
Birds that have mastered the air habitat, in addition to anatomical and morphological adaptations for flight, also have important physiological characteristics. For example, due to the fact that movement in the air requires extremely high energy expenditure, this group of vertebrates is characterized by a high metabolic rate, and the excreted metabolic products are eliminated immediately, which helps to reduce the specific density of the body.
Adaptations to the environment, despite all their perfection, are relative. Thus, some species of milkweed produce alkaloids that are poisonous to most animals, but the caterpillars of one species of butterfly - danaids - not only feed on milkweed tissues, but also accumulate these alkaloids, becoming inedible for birds.
In addition, adaptations are only useful in a particular environment and are useless in another environment. For example, a rare and large predator, the Ussuri tiger, like all cats, has soft pads on its paws and retractable sharp claws, sharp teeth, excellent vision even in the dark, keen hearing and strong muscles, which allows it to detect its prey, sneak up on it unnoticed and ambush. However, its striped color camouflages it only in spring, summer and autumn, while in the snow it becomes clearly visible and the tiger can only count on a lightning-fast attack.
Fig inflorescences, which produce valuable fruit, have such a specific structure that they are pollinated only by blastophagous wasps, and therefore, when introduced into culture, they did not bear fruit for a long time. Only the development of parthenocarpic varieties of figs (forming fruits without fertilization) could save the situation.
Despite the fact that examples of speciation over very short periods of time have been described, as in the case of the rattle in the Caucasian meadows, which, due to regular mowing, first divided into two populations - early flowering and fruiting and late flowering, in fact microevolution is most likely requires much longer periods - many centuries, because humanity, whose different groups were separated from each other for millennia, nevertheless, never divided into different species. However, since evolution has practically unlimited time, over hundreds of millions and billions of years, several billion species have already lived on Earth, most of which have become extinct, and those that have come down to us are qualitative stages of this ongoing process.
According to modern data, there are over 2 million species of living organisms on Earth, most of which (approximately 1.5 million species) belong to the animal kingdom, about 400 thousand to the plant kingdom, over 100 thousand to the mushroom kingdom, and the rest - to bacteria. Such amazing diversity is the result of divergence (divergence) of species according to various morphological, physiological-biochemical, ecological, genetic and reproductive characteristics. For example, one of the largest genera of plants belonging to the Orchidaceae family, dendrobium, includes over 1,400 species, and the genus of beetles includes over 1,600 species.
Classification of organisms is a task of taxonomy, which for 2 thousand years has been trying to build not just a harmonious hierarchy, but a “natural” system reflecting the degree of relatedness of organisms. However, all attempts to do this have not yet been crowned with success, since in a number of cases, in the process of evolution, not only divergence of characters was observed, but also convergence (convergence), as a result of which in very distant groups the organs acquired similarities, such as the eyes of cephalopods and the eyes of mammals.
Macroevolution. Directions and paths of evolution (A. N. Severtsov, I. I. Shmalgauzen). Biological progress and regression, aromorphosis, idioadaptation, degeneration. Causes of biological progress and regression. Hypotheses of the origin of life on Earth. Basic aromorphoses in the evolution of plants and animals. Complication of living organisms in the process of evolution
Macroevolution
The formation of a species marks a new round of the evolutionary process, since individuals of this species, being more adapted to environmental conditions than individuals of the parent species, gradually settle into new territories, and mutagenesis, population waves, isolation and natural selection play their creative role in its populations . Over time, these populations give rise to new species, which, due to genetic isolation, have much more similarities with each other than with the species of the genus from which the parent species branched off, and thus a new genus arises, then a new family, order (order) , class, etc. The set of evolutionary processes that lead to the emergence of supraspecific taxa (genera, families, orders, classes, etc.) is called macroevolution. Macroevolutionary processes, as it were, generalize microevolutionary changes that occur over a long period of time, while identifying the main trends, directions and patterns of evolution of the organic world, which are not observable at a lower level. So far, no specific mechanisms of macroevolution have been identified, therefore it is believed that it is carried out only through microevolutionary processes, however, this position is constantly subject to well-founded criticism.
The emergence of a complex hierarchical system of the organic world is largely the result of the unequal rate of evolution of various groups of organisms. Thus, the already mentioned ginkgo biloba was, as it were, “preserved” for thousands of years, while the pines that are quite close to it have changed significantly during this time.
Directions and paths of evolution (A. N. Severtsov, I. I. Shmalgauzen). Biological progress and regression, aromorphosis, idioadaptation, degeneration
Analyzing the history of the organic world, one can notice that at certain periods of time certain groups of organisms dominated, which then declined or disappeared altogether. Thus, three main lines can be distinguished directions of evolution: biological progress, biological regression and biological stabilization. A significant contribution to the development of the doctrine of the directions and paths of evolution was made by the Russian evolutionists A. N. Severtsov and I. I. Shmalgauzen.
Biological progress associated with the biological prosperity of the group as a whole and characterizes its evolutionary success. It reflects the natural development of living nature from simple to complex, from a lower degree of organization to a higher one. According to A.N. Severtsov, the criteria for biological progress are an increase in the number of individuals of a given group, an expansion of its range, as well as the emergence and development of lower-ranking groups within its composition (transformation of a species into a genus, a genus into a family, etc.). Currently, biological progress is observed in angiosperms, insects, bony fish and mammals.
According to A. N. Severtsov, biological progress can be achieved as a result of certain morphophysiological transformations of organisms, and he identified three main ways of achievement: arogenesis, allogenesis and catagenesis.
Arogenesis, or morphophysiological progress, is associated with a significant expansion of the range of this group of organisms due to the acquisition of large structural changes - aromorphoses.
Aromorphosis called an evolutionary transformation of the structure and functions of an organism, which increases its level of organization and opens up new opportunities for adaptation to various conditions of existence.
Examples of aromorphoses are the emergence of a eukaryotic cell, multicellularity, the appearance of a heart in fish and its division by a complete septum in birds and mammals, the formation of a flower in angiosperms, etc.
Allogenesis, unlike arogenesis, is not accompanied by an expansion of the range, however, within the old one, a significant diversity of forms arises that have particular adaptations to the environment - idioadaptations.
Idiomatic adaptation- this is a minor morphophysiological adaptation to special environmental conditions, useful in the struggle for existence, but does not change the level of organization. These changes are illustrated by the protective coloration in animals, the variety of mouthparts in insects, the spines of plants, etc. An equally successful example is Darwin's finches, specializing in various types of food, in which transformations first affected the beak, and then other parts of the body - plumage, tail and so on.
Paradoxical as it may seem, simplification of organization can lead to biological progress. This path is called catagenesis.
Degeneration- this is the simplification of organisms in the process of evolution, which is accompanied by the loss of certain functions or organs.
The phase of biological progress is replaced by a phase biological stabilization, the essence of which is to preserve the characteristics of a given species as the most favorable in a given microenvironment. According to I. I. Shmalhausen, it “does not mean the cessation of evolution; on the contrary, it means the maximum consistency of the organism with changes in the environment.” The “living fossils” of coelacanth, gingko, etc. are in the phase of biological stabilization.
The antipode of biological progress is biological regression- evolutionary decline of a given group due to the inability to adapt to environmental changes. It manifests itself in a decrease in population numbers, narrowing of ranges, and a decrease in the number of lower-ranking groups within a higher taxon. A group of organisms that is in a state of biological regression is threatened with extinction. In the history of the organic world one can see many examples of this phenomenon, and at present regression is characteristic of some ferns, amphibians and reptiles. With the advent of man, biological regression is often due to his economic activities.
The directions and paths of evolution of the organic world are not mutually exclusive, that is, the appearance of aromorphosis does not mean that idioadaptation or degeneration can no longer occur. On the contrary, according to what was developed by A. N. Severtsov and I. I. Shmalgauzen phase change rule, various directions of the evolutionary process and ways to achieve biological progress naturally replace each other. In the course of evolution, these paths are combined: fairly rare aromorphoses transfer a group of organisms to a qualitatively new level of organization, and further historical development follows the path of idioadaptation or degeneration, ensuring adaptation to specific environmental conditions.
Causes of biological progress and regression
In the process of evolution, the bar of natural selection is overcome and, accordingly, only those groups of organisms progress in which hereditary variability creates a sufficient number of combinations that can ensure the survival of the group as a whole.
Those groups that for some reason do not have such a reserve are, in most cases, doomed to extinction. This is often due to low selection pressure at previous stages of the evolutionary process, which led to narrow specialization of the group or even degenerative phenomena. The consequence of this is the inability to adapt to new environmental conditions when there are sudden changes. A striking example of this is the sudden death of dinosaurs due to the fall of a giant celestial body to Earth 65 million years ago, which resulted in an earthquake, the rise of millions of tons of dust into the air, a sharp cold snap, and the death of most plants and herbivorous animals. At the same time, the ancestors of modern mammals, not having narrow preferences for food sources and being warm-blooded, were able to survive these conditions and occupy a dominant position on the planet.
Hypotheses for the origin of life on Earth
Of the entire range of hypotheses for the formation of the Earth, the largest number of facts testify in favor of the “Big Bang” theory. Due to the fact that this scientific assumption is based mainly on theoretical calculations, the Large Hadron Collider, built at the European Nuclear Research Center near Geneva (Switzerland), is called upon to confirm it experimentally. According to the Big Bang theory, the Earth was formed over 4.5 billion years ago along with the Sun and other planets of the solar system as a result of the condensation of a gas and dust cloud. The decrease in the temperature of the planet and the migration of chemical elements on it contributed to its stratification into the core, mantle and crust, and the subsequent geological processes (movement of tectonic plates, volcanic activity, etc.) caused the formation of the atmosphere and hydrosphere.
Life has also existed on Earth for a very long time, as evidenced by the fossil remains of various organisms in rocks, but physical theories cannot answer the question of the time and reasons for its emergence. There are two opposing points of view on the origin of life on Earth: the theories of abiogenesis and biogenesis. Theories of abiogenesis affirm the possibility of the origin of living things from non-living things. These include creationism, the hypothesis of spontaneous generation and the theory of biochemical evolution by A.I. Oparin.
Fundamental position creationism the creation of the world was a certain supernatural being (Creator), which is reflected in the myths of the peoples of the world and religious cults, but the age of the planet and life on it far exceeds the dates indicated in these sources, and there are plenty of inconsistencies in them.
Founder theories of spontaneous generation life is considered to be the ancient Greek scientist Aristotle, who argued that it is possible for new creatures to appear multiple times, for example, earthworms from puddles, and worms and flies from rotten meat. However, these views were refuted in the 17th–19th centuries by the bold experiments of F. Redi and L. Pasteur.
The Italian physician Francesco Redi in 1688 placed pieces of meat in pots and sealed them tightly, but no worms appeared in them, whereas they appeared in open pots. In order to refute the prevailing belief that the life principle was contained in the air, he repeated his experiments, but did not seal the pots, but covered them with several layers of muslin, and again life did not appear. Despite the convincing data obtained by F. Redi, the research of A. van Leeuwenhoek provided new food for discussions about the “vital principle”, which continued throughout the next century.
Another Italian researcher, Lazzaro Spallanzani, modified the experiments of F. Redi in 1765 by boiling meat and vegetable decoctions for several hours and sealing them. After several days, he also did not find any signs of life there and concluded that living things can only arise from living things.
The final blow to the theory of spontaneous generation came from the great French microbiologist Louis Pasteur in 1860, when he placed boiled broth in an S-neck flask and failed to obtain any germs. It would seem that this testified in favor of the theories of biogenesis, but the question remained open about how the very, very first organism arose.
The Soviet biochemist A.I. Oparin tried to answer it, coming to the conclusion that the composition of the Earth’s atmosphere in the first stages of its existence was completely different from what it is in our time. Most likely, it consisted of ammonia, methane, carbon dioxide and water vapor, but did not contain free oxygen. Under the influence of high-power electrical discharges and at high temperatures, the simplest organic compounds could be synthesized in it, which was confirmed by the experiments of S. Miller and G. Urey in 1953, who obtained from the above-mentioned compounds several amino acids, simple carbohydrates, adenine, urea, as well as simple fatty acids, formic and acetic acids.
Nevertheless, the synthesis of organic substances does not yet mean the emergence of life, therefore A.I. Oparin put forward biochemical evolution hypothesis, according to which various organic substances arose and combined into larger molecules in the shallow waters of seas and oceans, where conditions for chemical synthesis and polymerization are most favorable. RNA molecules are currently considered to be the first carriers of life.
Some of these substances gradually formed stable complexes in water - coacervates, or coacervate drops, resembling drops of fat in broth. These coacervates received various substances from the surrounding solution, which underwent chemical transformations occurring in the drops. Like organic substances, coacervates themselves were not living beings, but were the next step in their emergence.
Those coacervates that had a favorable ratio of substances in their composition, especially proteins and nucleic acids, thanks to the catalytic properties of enzyme proteins, over time acquired the ability to reproduce their own kind and carry out metabolic reactions, while the structure of proteins was encoded by nucleic acids.
However, in addition to reproduction, living systems are characterized by dependence on the supply of energy from the outside. This problem was initially solved through the oxygen-free breakdown of organic substances from the environment (there was no oxygen in the atmosphere at that time), i.e.
heterotrophic nutrition. Some of the absorbed organic substances turned out to be able to accumulate the energy of sunlight, such as chlorophyll, which made it possible for a number of organisms to switch to autotrophic nutrition. The release of oxygen into the atmosphere during photosynthesis led to the emergence of more efficient oxygen respiration, the formation of the ozone layer and, ultimately, the emergence of organisms on land.
Thus, the result of chemical evolution was the appearance protobionts- primary living organisms, from which, as a result of biological evolution, all currently existing species originated.
The theory of biochemical evolution in our time is the most confirmed, but the idea of the specific mechanisms of the origin of life has changed. For example, it turned out that the formation of organic substances begins in space, and organic substances play an important role even in the very formation of planets, ensuring the adhesion of small parts. The formation of organic substances also occurs in the bowels of the planet: during one eruption, a volcano releases up to 15 tons of organic matter. There are other hypotheses regarding the mechanisms of concentration of organic substances: freezing of the solution, absorption (binding) on the surface of certain mineral compounds, the action of natural catalysts, etc. The emergence of life on Earth is currently impossible, since any organic substances spontaneously formed at any point planets would immediately be oxidized by the free oxygen of the atmosphere or used by heterotrophic organisms. This was understood back in 1871 by Charles Darwin.
Theories of biogenesis deny the spontaneous origin of life. The main ones are the steady state hypothesis and the panspermia hypothesis. The first of them is based on the fact that life exists forever, however, on our planet there are very ancient rocks in which there are no traces of the activity of the organic world.
Panspermia hypothesis claims that the embryos of life were brought to Earth from space by some aliens or by divine providence. This hypothesis is supported by two facts: the need for all living things, which is quite rare on the planet, but often found in meteorites, of molybdenum, as well as the discovery of organisms similar to bacteria on meteorites from Mars. However, how life arose on other planets remains unclear.
Basic aromorphoses in the evolution of plants and animals
Plant and animal organisms, representing various branches of the evolution of the organic world, in the process of historical development independently acquired certain structural features, which will be described further.
In plants, the most important of them are the transition from haploid to diploid, independence from water during the process of fertilization, the transition from external to internal fertilization and the occurrence of double fertilization, the division of the body into organs, the development of the conducting system, the complication and improvement of tissues, as well as the specialization of pollination with the help of insects and distribution of seeds and fruits.
The transition from haploidy to diploidy made plants more resistant to environmental factors due to a reduced risk of recessive mutations. Apparently, this transformation affected the ancestors of vascular plants, which do not include bryophytes, which are characterized by a predominance of the gametophyte in the life cycle.
The main aromorphoses in the evolution of animals are associated with the emergence of multicellularity and the increasing dismemberment of all organ systems, the emergence of a strong skeleton, the development of the central nervous system, as well as social behavior in various groups of highly organized animals, which gave impetus to human progress.
Complication of living organisms in the process of evolution
The history of the organic world on Earth is studied from the preserved remains, prints and other traces of the vital activity of living organisms. She is a subject of science paleontology. Based on the fact that the remains of different organisms are located in different rock layers, a geochronological scale was created, according to which the history of the Earth was divided into certain periods of time: eons, eras, periods and centuries.
Eon called a large period of time in geological history, combining several eras. Currently, only two eons are distinguished: cryptozoic (hidden life) and phanerozoic (manifest life). Era- this is a period of time in geological history, which is a division of an eon, which, in turn, unites periods. In the Cryptozoic there are two eras (Archean and Proterozoic), while in the Phanerozoic there are three (Paleozoic, Mesozoic and Cenozoic).
An important role in the creation of the geochronological scale was played by guiding fossils- the remains of organisms that were numerous at certain periods of time and are well preserved.
Development of life in the cryptozoic. The Archean and Proterozoic make up most of the history of life (period 4.6 billion years ago - 0.6 billion years ago), but there is little information about life during that period. The first remains of organic substances of biogenic origin are about 3.8 billion years old, and prokaryotic organisms existed already 3.5 billion years ago. The first prokaryotes were part of specific ecosystems - cyanobacterial mats, thanks to the activity of which specific sedimentary rocks stromatolites (“stone carpets”) were formed.
Understanding the life of ancient prokaryotic ecosystems was helped by the discovery of their modern analogues - stromatolites in Shark Bay in Australia and specific films on the soil surface in Syvash Bay in Ukraine. On the surface of cyanobacterial mats there are photosynthetic cyanobacteria, and under their layer there are extremely diverse bacteria of other groups and archaea. Mineral substances that settle on the surface of the mat and are formed due to its vital activity are deposited in layers (approximately 0.3 mm per year). Such primitive ecosystems can only exist in places uninhabitable for other organisms, and indeed, both of the above-mentioned habitats are characterized by extremely high salinity.
Numerous data indicate that at first the Earth had a renewable atmosphere, which included: carbon dioxide, water vapor, sulfur oxide, as well as carbon monoxide, hydrogen, hydrogen sulfide, ammonia, methane, etc. The first organisms of the Earth were anaerobes , however, thanks to the photosynthesis of cyanobacteria, free oxygen was released into the environment, which at first quickly associated with reducing agents in the environment, and only after the binding of all reducing agents did the environment begin to acquire oxidizing properties. This transition is evidenced by the deposition of oxidized forms of iron - hematite and magnetite.
About 2 billion years ago, as a result of geophysical processes, almost all the iron unbound in sedimentary rocks moved to the core of the planet, and oxygen began to accumulate in the atmosphere due to the absence of this element - the “oxygen revolution” occurred. It was a turning point in the history of the Earth, which entailed not only a change in the composition of the atmosphere and the formation of an ozone screen in the atmosphere - the main prerequisite for the settlement of land, but also the composition of the rocks formed on the surface of the Earth.
Another important event occurred in the Proterozoic - the emergence of eukaryotes. In recent years, it has been possible to collect convincing evidence for the theory of the endosymbiogenetic origin of the eukaryotic cell - through the symbiosis of several prokaryotic cells. Probably, the “main” ancestor of eukaryotes were archaea, which switched to the absorption of food particles by phagocytosis. The hereditary apparatus moved deep into the cell, nevertheless maintaining its connection with the membrane due to the transition of the outer membrane of the emerging nuclear membrane into the membranes of the endoplasmic reticulum.
Geochronological history of the Earth Eon Era Period Beginning, million years ago Duration, million years Development of life Phanerozoic Cenozoic Anthropogen 1.5 1.5 Four ice ages, followed by floods, led to the formation of cold-resistant flora and fauna (mammoths, musk oxen, reindeer, lemmings). Exchange of animals and plants between continents due to the emergence of land bridges. Dominance of placental mammals. Extinction of many large mammals. The formation of man as a biological species and its settlement. Domestication of animals and cultivation of plants. Disappearance of many species of living organisms due to human economic activity Neogene 25 23.5 Distribution of cereals. Formation of all modern orders of mammals. The emergence of apes Paleogene 65 40 Dominance of flowering plants, mammals and birds. The emergence of ungulates, carnivores, pinnipeds, primates, etc. Mesozoic Cretaceous 135 70 The emergence of angiosperms, mammals and birds become numerous Jura 195 60 The era of reptiles and cephalopods. The emergence of marsupials and placental mammals. The dominance of gymnosperms Triassic 225 30 The first mammals and birds. Reptiles are numerous. Distribution of herbaceous spores Paleozoic Perm 280 55 The emergence of modern insects. Development of reptiles. Extinction of a number of invertebrate groups. Distribution of conifers Carbon 345 65 First reptiles. The emergence of winged insects. Ferns and horsetails predominate Devon 395 50 Fish are numerous. The first amphibians. The emergence of the main groups of spores, the first gymnosperms and fungi Silurian 430 35 Algae are abundant. The first land plants and animals (spiders). Ghostome fishes and crustacean scorpions are common Ordovician 500 70 Corals and trilobites are abundant. Blooming of green, brown and red algae. The emergence of the first chordates Cambrian 570 70 Numerous fish fossils. Sea urchins and trilobites are common. The emergence of multicellular algae Cryptose Proterozoic 2600 2000 The emergence of eukaryotes. Mostly unicellular green algae are common. The emergence of multicellularity. Outbreak of multicellular animal diversity (emergence of all types of invertebrates) Archaea 3500 1500 The first traces of life on Earth are bacteria and cyanobacteria. The emergence of photosynthesis
Bacteria absorbed by the cell could not be digested, but remained alive and continued to function. It is believed that mitochondria originate from purple bacteria that lost the ability to photosynthesize and switched to the oxidation of organic substances. Symbiosis with other photosynthetic cells led to the emergence of plastids in plant cells. Probably, the flagella of eukaryotic cells arose as a result of symbiosis with bacteria, which, like modern spirochetes, were capable of writhing movements. At first, the hereditary apparatus of eukaryotic cells was structured approximately in the same way as that of prokaryotes, and only later, due to the need to control a large and complex cell, chromosomes were formed. The genomes of intracellular symbionts (mitochondria, plastids and flagella) generally retained the prokaryotic organization, but most of their functions were transferred to the nuclear genome.
Eukaryotic cells arose repeatedly and independently of each other. For example, red algae arose as a result of symbiogenesis with cyanobacteria, and green algae with prochlorophyte bacteria.
The remaining single-membrane organelles and the nucleus of the eukaryotic cell, according to the endomembrane theory, arose from invaginations of the membrane of the prokaryotic cell.
The exact time of the appearance of eukaryotes is unknown, since already in sediments about 3 billion years old there are imprints of cells with similar sizes. Eukaryotes are definitely recorded in rocks about 1.5–2 billion years old, but only after the oxygen revolution (about 1 billion years ago) did conditions favorable for them develop.
At the end of the Proterozoic era (at least 1.5 billion years ago), multicellular eukaryotic organisms already existed. Multicellularity, like the eukaryotic cell, has arisen repeatedly in different groups of organisms.
There are different views on the origin of multicellular animals. According to some data, their ancestors were multinucleate, ciliate-like cells, which then broke up into separate mononuclear cells.
Other hypotheses link the origin of multicellular animals with the differentiation of colonial unicellular cells. The differences between them concern the origin of cell layers in the original multicellular animal. According to E. Haeckel's gastrea hypothesis, this occurs by invagination of one of the walls of a single-layer multicellular organism, as in coelenterates. In contrast, I. I. Mechnikov formulated the phagocytella hypothesis, considering the ancestors of multicellular organisms to be single-layered spherical colonies like Volvox, which absorbed food particles by phagocytosis. The cell that captured the particle lost its flagellum and moved deeper into the body, where it carried out digestion, and at the end of the process returned to the surface. Over time, the cells were divided into two layers with specific functions - the outer one provided movement, and the inner one provided phagocytosis. I. I. Mechnikov called such an organism a phagocytella.
For a long time, multicellular eukaryotes lost in competition to prokaryotic organisms, but at the end of the Proterozoic (800–600 million years ago) due to a sharp change in conditions on Earth - a decrease in sea levels, an increase in oxygen concentration, a decrease in the concentration of carbonates in sea water, regular cycles cooling - multicellular eukaryotes gained advantages over prokaryotes. If until this time only individual multicellular plants and, possibly, fungi were found, then from this point in the history of the Earth animals were also known. Of the faunas that arose at the end of the Proterozoic, the Ediacaran and Vendian are the best studied. Animals of the Vendian period are usually included in a special group of organisms or classified as such types as coelenterates, flatworms, arthropods, etc. However, none of these groups have skeletons, which may indicate the absence of predators.
Development of life in the Paleozoic era. The Paleozoic era, which lasted more than 300 million years, is divided into six periods: Cambrian, Ordovician, Silurian, Devonian, Carboniferous (Carboniferous) and Permian.
IN Cambrian period The land consisted of several continents, located mainly in the Southern Hemisphere. The most abundant photosynthetic organisms during this period were cyanobacteria and red algae. Foraminifera and radiolarians lived in the water column. In the Cambrian, a huge number of skeletal animal organisms appear, as evidenced by numerous fossil remains. These organisms belonged to approximately 100 types of multicellular animals, both modern (sponges, coelenterates, worms, arthropods, mollusks) and extinct, for example: the huge predator Anomalocaris and colonial graptolites that floated in the water column or were attached to the bottom. The land remained almost uninhabited throughout the Cambrian, but the process of soil formation had already begun by bacteria, fungi and, possibly, lichens, and at the end of the period, oligochaete worms and millipedes appeared on land.
IN Ordovician period The water level of the World Ocean rose, which led to the flooding of continental lowlands. The main producers during this period were green, brown and red algae. Unlike the Cambrian, in which reefs were built by sponges, in the Ordovician they were replaced by coral polyps. Gastropods and cephalopods flourished, as did trilobites (now extinct relatives of arachnids). In this period, chordates, in particular jawless ones, were also recorded for the first time. At the end of the Ordovician, a great extinction event occurred, which destroyed about 35% of the families and more than 50% of the genera of marine animals.
Silurian characterized by increased mountain building, which led to the drying of continental platforms. The leading role in the invertebrate fauna of the Silurian was played by cephalopods, echinoderms and giant crustacean scorpions, while among the vertebrates a large variety of jawless animals remained and fish appeared. At the end of the period, the first vascular plants came to land - rhinophytes and lycophytes, which began to colonize shallow waters and the tidal zone of the coasts. The first representatives of the arachnid class also came to land.
IN Devonian period As a result of the rise of the land, large shallow waters formed, which dried out and even froze, as the climate became even more continental than in the Silurian. The seas are dominated by corals and echinoderms, while cephalopods are represented by spirally twisted ammonites. Among the vertebrates of the Devonian, fish flourished, and cartilaginous and bony fishes, as well as lungfishes and lobe-fins, replaced the armored ones. At the end of the period, the first amphibians appear, which first lived in water.
In the Middle Devonian, the first forests of ferns, mosses and horsetails appeared on land, which were inhabited by worms and numerous arthropods (centipedes, spiders, scorpions, wingless insects). At the end of the Devonian, the first gymnosperms appeared. The development of land by plants led to a decrease in weathering and increased soil formation. Consolidation of soils led to the formation of river channels.
IN Carboniferous period the land was represented by two continents separated by an ocean, and the climate became noticeably warmer and wetter. By the end of the period, there was a slight uplift of the land, and the climate changed to a more continental one. The seas were dominated by foraminifera, corals, echinoderms, cartilaginous and bony fish, and fresh water bodies were inhabited by bivalve mollusks, crustaceans and various amphibians. In the middle of the Carboniferous, small insectivorous reptiles arose, and winged ones (cockroaches, dragonflies) appeared among insects.
The tropics were characterized by swampy forests dominated by giant horsetails, club mosses and ferns, the dead remains of which subsequently formed coal deposits. In the middle of the period in the temperate zone, thanks to their independence from water during the fertilization process and the presence of seeds, the spread of gymnosperms began.
Permian period was distinguished by the merging of all continents into a single supercontinent Pangea, the retreat of the seas and the strengthening of the continental climate to such an extent that deserts formed in the interior of Pangea. By the end of the period, tree ferns, horsetails and mosses almost disappeared on land, and drought-resistant gymnosperms took a dominant position. Despite the fact that large amphibians still continued to exist, different groups of reptiles arose, including large herbivores and predators. At the end of the Permian, the largest extinction event in the history of life occurred, as many groups of corals, trilobites, most cephalopods, fish (primarily cartilaginous and lobe-finned fish), and amphibians disappeared. Marine fauna lost 40–50% of families and about 70% of genera.
Development of life in the Mesozoic. The Mesozoic era lasted about 165 million years and was characterized by rising land, intense mountain building and a decrease in climate humidity. It is divided into three periods: Triassic, Jurassic and Cretaceous.
At first Triassic period The climate was arid, but later, due to rising sea levels, it became wetter. Among the plants, gymnosperms, ferns and horsetails predominated, but the woody forms of spores almost completely died out. Some corals, ammonites, new groups of foraminifera, bivalves and echinoderms reached high development, while the diversity of cartilaginous fish decreased, and groups of bony fish also changed. The reptiles that dominated the land began to master the aquatic environment, like ichthyosaurs and plesiosaurs. Of the reptiles of the Triassic, crocodiles, tuataria and turtles have survived to this day. At the end of the Triassic, dinosaurs, mammals and birds appeared.
IN Jurassic period The supercontinent Pangea split into several smaller ones. Much of the Jurassic was very wet, and towards the end the climate became drier. The dominant group of plants were gymnosperms, of which the redwoods survived from that time. Molluscs (ammonites and belemnites, bivalves and gastropods), sponges, sea urchins, cartilaginous and bony fish flourished in the seas. Large amphibians almost completely died out in the Jurassic period, but modern groups of amphibians (tailed and tailless) and squamates (lizards and snakes) appeared, and the diversity of mammals increased. By the end of the period, possible ancestors of the first birds also appeared - Archeopteryx. However, all ecosystems were dominated by reptiles - ichthyosaurs and plesiosaurs, dinosaurs and flying lizards - pterosaurs.
Cretaceous period received its name due to the formation of chalk in sedimentary rocks of that time. Throughout the Earth, except for the polar regions, there was a persistent warm and humid climate. During this period, angiosperms arose and became widespread, displacing gymnosperms, which led to a sharp increase in the diversity of insects. In the seas, in addition to mollusks, bony fish, and plesiosaurs, a huge number of foraminifera reappeared, the shells of which formed the chalk deposits, and dinosaurs predominated on land. Birds better adapted to the air began to gradually displace flying dinosaurs.
At the end of the period, a global extinction event occurred, which resulted in the disappearance of ammonites, belemnites, dinosaurs, pterosaurs and sea lizards, ancient groups of birds, as well as some gymnosperms. In general, about 16% of families and 50% of animal genera disappeared from the face of the Earth. The Late Cretaceous crisis has been attributed to the impact of a large meteorite in the Gulf of Mexico, but it most likely was not the only cause of global change. During the subsequent cooling, only small reptiles and warm-blooded mammals survived.
Development of life in the Cenozoic. The Cenozoic era began about 66 million years ago and continues to the present day. It is characterized by the dominance of insects, birds, mammals and angiosperms. The Cenozoic is divided into three periods - Paleogene, Neogene and Anthropocene - the latter of which is the shortest in the history of the Earth.
In the early and middle Paleogene, the climate remained warm and humid; towards the end of the period it became cooler and drier. Angiosperms became the dominant group of plants, however, if evergreen forests predominated at the beginning of the period, then at the end many deciduous forests appeared, and steppes formed in arid zones.
Among fish, bony fish occupied a dominant position, and the number of cartilaginous species, despite their noticeable role in salt water bodies, is insignificant. On land, only scaly reptiles, crocodiles and turtles have survived, while mammals have occupied most of their ecological niches. In the middle of the period, the main orders of mammals appeared, including insectivores, carnivores, pinnipeds, cetaceans, ungulates and primates. The isolation of the continents made the fauna and flora more geographically diverse: South America and Australia became centers for the development of marsupials, and other continents - for placental mammals.
Neogene period. In the Neogene, the earth's surface acquired its modern appearance. The climate became cooler and drier. In the Neogene, all orders of modern mammals had already formed, and in the African shrouds the Hominid family and the Human genus arose. By the end of the period, coniferous forests spread in the polar regions of the continents, tundras appeared, and cereals occupied the temperate steppes.
Quaternary period(anthropocene) is characterized by periodic changes of glaciations and warmings. During glaciations, high latitudes were covered with glaciers, ocean levels dropped sharply, and tropical and subtropical zones narrowed. In the areas close to the glaciers, a cold and dry climate was established, which contributed to the formation of cold-resistant groups of animals - mammoths, giant deer, cave lions, etc. The decrease in the level of the World Ocean that accompanied the glaciation process led to the formation of land bridges between Asia and North America, Europe and the British Isles etc. Animal migrations, on the one hand, led to the mutual enrichment of floras and faunas, and on the other, to the displacement of relicts by aliens, for example, marsupials and ungulates in South America. These processes, however, did not affect Australia, which remained isolated.
In general, periodic climate changes have led to the formation of extremely abundant species diversity, characteristic of the current stage of biosphere evolution, and also influenced human evolution. During the Anthropocene, several species of the Human genus spread from Africa to Eurasia. About 200 thousand years ago in Africa, the species Homo sapiens arose, which, after a long period of existence in Africa, about 70 thousand years ago entered Eurasia and about 35–40 thousand years ago - to America. After a period of coexistence with closely related species, it displaced them and spread throughout the globe. About 10 thousand years ago, human economic activity in moderately warm regions of the globe began to influence both the appearance of the planet (plowing of lands, burning of forests, overgrazing of pastures, desertification, etc.) and the animal and plant world due to the reduction of habitats their habitat and extermination, and the anthropogenic factor came into play.
Human Origins. Man as a species, his place in the system of the organic world. Hypotheses of human origin. Driving forces and stages of human evolution. Human races, their genetic relatedness. Biosocial nature of man. Social and natural environment, human adaptation to it
Human Origins
Just 100 years ago, the overwhelming majority of people on the planet did not even think that humans could descend from such “low-respectable” animals as monkeys. In a discussion with one of the defenders of Darwin's theory of evolution, Professor Thomas Huxley, his ardent opponent, Bishop of Oxford Samuel Wilberforce, who relied on religious dogma, even asked him whether he considered himself related to ape ancestors through his grandfather or grandmother.
However, thoughts about evolutionary origin were expressed by ancient philosophers, and the great Swedish taxonomist C. Linnaeus in the 18th century, based on a set of characteristics, gave a species name to man Homo sapiens L.(Homo sapiens) and classified him, along with the monkeys, into the same order - Primates. J. B. Lamarck supported C. Linnaeus and believed that man even had common ancestors with modern monkeys, but at some point in his history he descended from the tree, which was one of the reasons for the emergence of man as a species.
Charles Darwin also did not ignore this issue and in the 70s of the 19th century he published the works “The Origin of Man and Sexual Selection” and “On the Expression of Emotions in Animals and Man,” in which he provided equally convincing evidence of the common origin of humans and monkeys, than the German researcher E. Haeckel (“Natural History of Creation,” 1868; “Anthropogenesis, or the History of the Origin of Man,” 1874), who even compiled a genealogy of the animal kingdom. However, these studies concerned only the biological side of the formation of man as a species, while the social aspects were revealed by the classic of historical materialism - the German philosopher F. Engels.
Currently, the origin and development of humans as a biological species, as well as the diversity of modern human populations and the patterns of their interaction, are being studied by science anthropology.
Man as a species, his place in the system of the organic world
Homo sapiens ( Homo sapiens) as a biological species belongs to the animal kingdom, the subkingdom of multicellular organisms. The presence of a notochord, gill slits in the pharynx, a neural tube and bilateral symmetry during embryonic development allows it to be classified as a chordate, while the development of the spine, the presence of two pairs of limbs and the location of the heart on the ventral side of the body indicate its relationship with other representatives of the vertebrate subtype.
Feeding the young with milk secreted by the mammary glands, warm-bloodedness, a four-chambered heart, the presence of hair on the surface of the body, seven vertebrae in the cervical spine, the vestibule of the mouth, alveolar teeth and the replacement of milk teeth with permanent ones are signs of the class of mammals, and the intrauterine development of the embryo and its connection with the mother’s body through the placenta - a subclass of placentals.
More specific features, such as grasping limbs with an opposable thumb and fingernails, development of the clavicles, eyes directed forward, an increase in the size of the skull and brain, as well as the presence of all groups of teeth (incisors, canines and molars) leave no doubt about the that his place is in the order of primates.
The significant development of the brain and facial muscles, as well as the structural features of the teeth, make it possible to classify humans as members of the suborder of higher primates, or monkeys.
The absence of a tail, the presence of curvatures of the spine, the development of the cerebral hemispheres of the forebrain, covered with a cortex with numerous grooves and convolutions, the presence of an upper lip and sparse hairline give grounds to place it among the representatives of the family of the great apes, or great apes.
However, even from the most highly organized monkeys, humans are distinguished by a sharp increase in brain volume, upright posture, wide pelvis, protruding chin, articulate speech and the presence of 46 chromosomes in the karyotype and determine its belonging to the genus Human.
The use of the upper limbs for work, the manufacture of tools, abstract thinking, collective activity and development based on more social than biological laws are the specific characteristics of Homo sapiens.
All modern people belong to one species - Homo sapiens ( Homo sapiens), and subspecies H. sapiens sapiens. This species is a collection of populations that produce fertile offspring when crossed. Despite the fairly significant diversity of morphophysiological characteristics, they are not evidence of a higher or lower degree of organization of certain groups of people - they are all at the same level of development.
In our time, a sufficient number of scientific facts have already been collected in the interests of the formation of man as a species in the process of evolution - anthropogenesis. The specific course of anthropogenesis is not yet fully understood, but thanks to new paleontological finds and modern research methods, we can hope that a clear picture will appear soon enough.
Hypotheses of human origins
If we do not take into account the hypotheses of the divine creation of man and his penetration from other planets that are not related to the field of biology, then all more or less consistent hypotheses of the origin of man trace him back to common ancestors with modern primates.
So, hypothesis of human origin from the ancient tropical primate tarsier, or tarsial hypothesis, formulated by the English biologist F. Wood Jones in 1929, is based on the similarity of the body proportions of humans and the tarsier, the features of the hairline, the shortening of the facial part of the skull of the latter, etc. However, the differences in the structure and vital activity of these organisms are so great that it has not gained universal recognition.
Humans even have too many similarities with apes. Thus, in addition to the anatomical and morphological features already mentioned above, attention should be paid to their postembryonic development. For example, small chimpanzees have much sparser hair, the ratio of brain volume to body volume is much larger, and the ability to move on the hind limbs is somewhat wider than in adults. Even puberty in higher primates occurs much later than in representatives of other orders of mammals with similar body sizes.
Cytogenetic studies revealed that one of the human chromosomes was formed as a result of the fusion of chromosomes of two different pairs present in the karyotype of great apes, and this explains the difference in the number of their chromosomes (in humans 2n = 46, and in great apes 2n = 48 ), and is also another evidence of the relationship of these organisms.
The similarity between humans and apes is also very high according to molecular biochemical data, since humans and chimpanzees have the same proteins of the AB0 and Rh blood groups, many enzymes, and the amino acid sequences of hemoglobin chains have only 1.6% differences, whereas with other monkeys this is a discrepancy somewhat more. And at the genetic level, the differences in the nucleotide sequences in DNA between these two organisms are less than 1%. If we take into account the average rate of evolution of such proteins in related groups of organisms, we can determine that human ancestors separated from other groups of primates about 6–8 million years ago.
The behavior of monkeys is in many ways reminiscent of human behavior, since they live in groups in which social roles are clearly distributed. Joint defense, mutual assistance and hunting are not the only goals of creating a group, since within it the monkeys experience affection for each other, express it in every possible way, and react emotionally to various stimuli. In addition, in groups there is an exchange of experience between individuals.
Thus, the similarities between humans and other primates, especially great apes, are found at different levels of biological organization, and the differences between humans as a species are largely determined by the characteristics of this group of mammals.
The group of hypotheses that do not question the origin of humans from common ancestors with modern apes includes the hypotheses of polycentrism and monocentrism.
Starting position polycentrism hypotheses is the emergence and parallel evolution of the modern human species in several regions of the globe from different forms of ancient or even ancient man, but this contradicts the basic provisions of the synthetic theory of evolution.
Hypotheses of the single origin of modern man, on the contrary, postulate the emergence of man in one place, but diverge on where this occurred. So, hypothesis of extratropical origin of humans is based on the fact that only the harsh climatic conditions of the high latitudes of Eurasia could contribute to the “humanization” of monkeys. It was supported by the discovery on the territory of Yakutia of sites dating back to the ancient Paleolithic - the Diring culture, but it was subsequently established that the age of these finds is not 1.8–3.2 million years, but 260–370 thousand years. Thus, this hypothesis is also not sufficiently confirmed.
The greatest amount of evidence has currently been collected in favor of hypotheses of African origins of humans, but it is not without its shortcomings, which a comprehensive broad monocentrism hypothesis, combining the arguments of the hypotheses of polycentrism and monocentrism.
Driving forces and stages in human evolution
Unlike other representatives of the animal world, man in the process of his evolution was exposed not only to biological factors of evolution, but also to social ones, which contributed to the emergence of a species of qualitatively new creatures with biosocial properties. Social factors determined a breakthrough into a fundamentally new adaptive environment, which provided enormous advantages for the survival of human populations and sharply accelerated the pace of its evolution.
Biological factors of evolution that play a certain role in anthropogenesis to this day are hereditary variability, as well as the flow of genes that supply the primary material for natural selection. At the same time, isolation, population waves and genetic drift have almost completely lost their meaning as a result of scientific and technological progress. This gives grounds for some scientists to believe that in the future even minimal differences between representatives of different races will disappear due to their mixing.
As changing environmental conditions forced human ancestors to descend from the trees into open space and move on two limbs, the freed upper limbs were used by them to carry food and children, as well as to make and use tools. However, such a tool can be made only if there is a clear idea of the final result - the image of the object, which is why abstract thinking also developed. It is well known that complex movements and the process of thinking are necessary for the development of certain areas of the cerebral cortex, which happened in the process of evolution. However, it is impossible to inherit such knowledge and skills; they can only be transferred from one individual to another during the life of the latter, which resulted in the creation of a special form of communication - articulate speech.
Thus, the social factors of evolution include human labor activity, abstract thinking and articulate speech. One should not discard the manifestations of altruism of primitive man, who cared for children, women and the elderly.
Man’s labor activity not only influenced his appearance, but also made it possible, at first, to partially ease the conditions of existence through the use of fire, the manufacture of clothing, the construction of housing, and later actively change them through clearing forests, plowing lands, etc. In our time time, uncontrolled economic activity has put humanity under the threat of a global catastrophe as a result of soil erosion, drying out of freshwater bodies, and destruction of the ozone screen, which, in turn, can increase the pressure of biological factors of evolution.
Dryopithecus, who lived about 24 million years ago, was most likely the common ancestor of humans and apes. Despite the fact that he climbed trees and ran on all four limbs, he could move on two legs and carry food in his hands. The complete separation of the great apes and the line leading to humans occurred about 5–8 million years ago.
Australopithecus. The genus apparently originated from Dryopithecus Ardipithecus, which formed over 4 million years ago in the savannas of Africa as a result of cooling and retreat of forests, which forced these monkeys to switch to walking on their hind limbs. This small animal apparently gave rise to a fairly large genus Australopithecus(“southern monkey”).
Australopithecus appeared about 4 million years ago and lived in African savannas and dry forests, where the advantages of bipedal movement were fully felt. From Australopithecus came two branches - large herbivores with powerful jaws Paranthropus and smaller and less specialized People. Over a period of time, these two genera developed in parallel, which, in particular, manifested itself in an increase in the volume of the brain and the complication of the tools used. Features of our genus are the manufacture of stone tools (Paranthropus used only bone) and a relatively large brain.
The first representatives of the human genus appeared about 2.4 million years ago. They belonged to the species of skilled man (Homo habilis) and were short creatures (about 1.5 m) with a brain volume of approximately 670 cm 3. They used crude pebble tools. Apparently, representatives of this species had well-developed facial expressions and rudimentary speech. Homo habilis left the historical scene about 1.5 million years ago, giving rise to the next species - a straight man.
Man upright (H. erectus) as a biological species formed in Africa about 1.6 million years ago and existed for 1.5 million years, quickly settling over vast territories in Asia and Europe. A representative of this species from the island of Java was once described as Pithecanthropus(“ape-man”), discovered in China, was named Sinanthropa, while their European “colleague” is Heidelberg man.
All these forms are also called archanthropes(by ancient people). The erect man was distinguished by a low forehead, large brow ridges and a chin sloping back; his brain volume was 900–1200 cm 3. The torso and limbs of a straightened man resembled those of modern man. Without a doubt, representatives of this genus used fire and made double-edged axes. As recent discoveries have shown, this species even mastered navigation, for its descendants were found on remote islands.
Paleoanthropist. About 200 thousand years ago, Heidelberg man originated Neanderthal man (H. neandertalensis), which is referred to paleoanthropists(ancient people) who lived in Europe and Western Asia between 200 and 28 thousand years ago, including during the glaciation periods. They were strong, physically quite strong and resilient people with a large brain capacity (even larger than that of modern humans). They had articulate speech, made complex tools and clothing, buried their dead, and perhaps even had some rudiments of art. Neanderthals were not the ancestors of Homo sapiens; this group developed in parallel. Their extinction is associated with the disappearance of the mammoth fauna after the last glaciation, and perhaps is also the result of competitive displacement by our species.
The most ancient find of a representative homo sapiens (Homo sapiens) It is 195 thousand years old and comes from Africa. Most likely, the ancestors of modern humans are not Neanderthals, but some form of archanthropes, such as Heidelberg man.
Neoanthrop. About 60 thousand years ago, as a result of unknown events, our species almost went extinct, so all the following people are descendants of a small group that numbered only a few dozen individuals. Having overcome this crisis, our species began to spread throughout Africa and Eurasia. It differs from other species in its slimmer physique, higher reproduction rate, aggressiveness and, of course, the most complex and most flexible behavior. Modern people who inhabited Europe 40 thousand years ago are called Cro-Magnons and refer to neoanthropes(to modern people). They were biologically no different from modern people: height 170–180 cm, brain volume about 1600 cm 3. The Cro-Magnons developed art and religion, they domesticated many species of wild animals and cultivated many species of plants. Modern humans descended from the Cro-Magnons.
Human races, their genetic relatedness
As humanity settled around the planet, certain differences arose between different groups of people regarding skin color, facial features, hair type, as well as the frequency of occurrence of certain biochemical features. The set of such hereditary characteristics characterizes a group of individuals of the same species, the differences between which are less significant than the subspecies - race.
The study and classification of races is complicated by the lack of clear boundaries between them. All modern humanity belongs to one species, within which three large races are distinguished: Australo-Negroid (black), Caucasoid (white) and Mongoloid (yellow). Each of them is divided into small races. Differences between races come down to features of skin color, hair, shape of nose, lips, etc.
Aussie-Negroid, or equatorial race characterized by dark skin color, wavy or curly hair, a wide and slightly protruding nose, transverse nostrils, thick lips and a number of cranial features. Caucasian, or Eurasian race characterized by light or dark skin, straight or wavy soft hair, good development of male facial hair (beard and mustache), narrow protruding nose, thin lips and a number of cranial features. Mongoloid(Asian-American) race characterized by dark or light skin, often coarse hair, average width of the nose and lips, flattened face, strong protrusion of the cheekbones, relatively large face size, noticeable development of the “third eyelid”.
These three races also differ in their settlement. Before the era of European colonization, the Australo-Negroid race was widespread in the Old World south of the Tropic of Cancer; Caucasian race - in Europe, North Africa, Western Asia and Northern India; Mongoloid race - in Southeast, Northern, Central and Eastern Asia, Indonesia, North and South America.
However, the differences between races concern only minor characteristics that have adaptive significance. Thus, the skin of Negroids is burned by a tenfold higher dose of ultraviolet radiation than the skin of Caucasians, but Caucasians suffer less from rickets in high latitudes, where there may be a lack of ultraviolet radiation necessary for the formation of vitamin D.
Previously, some people sought to prove the superiority of one of the races in order to gain moral superiority over others. It is now clear that racial characteristics reflect only the different historical paths of groups of people, but are in no way connected with the advantage or biological backwardness of one or another group. Human races are less clearly defined than the subspecies and races of other animals, and cannot in any way be compared, for example, with breeds of domestic animals (which are the result of purposeful selection). As biomedical research shows, the consequences of interracial marriage depend on the individual characteristics of the man and woman, and not on their race. Therefore, any prohibitions on interracial marriages or certain superstitions are unscientific and inhumane.
More specific than races, groups of people are nationalities- historically formed linguistic, territorial, economic and cultural communities of people. The population of a certain country constitutes its people. With the interaction of many nationalities, a nation can emerge within a nation. Now there are no “pure” races on Earth, and every sufficiently large nation is represented by people who belong to different races.
Biosocial nature of man
Undoubtedly, humans as a biological species must experience pressure from evolutionary factors such as mutagenesis, population waves and isolation. However, as human society develops, some of them weaken, while others, on the contrary, strengthen, since on the planet, captured by the processes of globalization, there are almost no isolated human populations left in which inbreeding takes place, and the numbers of the populations themselves are not subject to sharp fluctuations. Accordingly, the driving factor of evolution - natural selection - thanks to the successes of medicine, no longer plays the same role in human populations as it does in populations of other organisms.
Unfortunately, weakening selection pressure leads to an increase in the frequency of hereditary diseases in populations. For example, in industrialized countries, up to 5% of the population suffers from color blindness, while in less developed countries this figure is up to 2%. The negative consequences of this phenomenon can be overcome thanks to preventive measures and progress in such areas of science as gene therapy.
However, this does not mean that human evolution has ended, since natural selection continues to act, eliminating, for example, gametes and individuals with unfavorable combinations of genes even in the proembryonic and embryonic periods of ontogenesis, as well as resistance to pathogens of various diseases. In addition, the material for natural selection is supplied not only by the mutation process, but also by the accumulation of knowledge, the ability to learn, the perception of culture and other characteristics that can be transmitted from person to person. Unlike genetic information, experience accumulated during the process of individual development is transmitted both from parents to offspring and in the opposite direction. And competition already arises between communities that differ culturally. This form of evolution, unique to humans, is called cultural, or social evolution.
However, cultural evolution does not exclude biological evolution, since it became possible only due to the formation of the human brain, and human biology itself is currently determined by cultural evolution, since in the absence of society and diversity of movements, certain zones do not form in the brain.
Thus, a person has a biosocial nature, which leaves an imprint on the manifestation of biological, including genetic, laws that govern his individual and evolutionary development.
Social and natural environment, human adaptation to it
Under social environment understand, first of all, the social, material and spiritual conditions of his existence and activity surrounding a person. In addition to the economic system, social relations, social consciousness and culture, it also includes the immediate environment of a person - family, work and student groups, as well as other groups. The environment, on the one hand, has a decisive influence on the formation and development of personality, and on the other, it itself changes under the influence of a person, which entails new changes in people, etc.
Adaptation of individuals or their groups to the social environment to realize their own needs, interests, life goals and includes adaptation to the conditions and nature of study, work, interpersonal relationships, ecological and cultural environment, conditions of leisure and everyday life, as well as their active change for satisfy your needs. Changing oneself, one’s motives, values, needs, behavior, etc. also plays a big role in this.
Information loads and emotional experiences in modern society are often the main cause of stress, which can be overcome with the help of clear self-organization, physical training and auto-training. In some particularly severe cases, a visit to a psychotherapist is required. An attempt to find oblivion of these problems through overeating, smoking, drinking alcohol and other bad habits does not lead to the desired result, but only aggravates the condition of the body.
The natural environment has no less influence on humans, despite the fact that humans have been trying to create a comfortable artificial environment for themselves for about 10 thousand years. Thus, rising to a significant altitude due to a decrease in oxygen concentration in the air leads to an increase in the number of red blood cells in the blood, increased breathing and heart rate, and prolonged exposure to the open sun contributes to increased skin pigmentation - tanning. However, the listed changes fit into the norm of the reaction and are not inherited. However, peoples who have lived in such conditions for a long time may have some adaptations. Thus, among northern peoples, the nasal sinuses have a much larger volume for warming the air, and the size of the protruding parts of the body decreases to reduce heat loss. Africans have darker skin color and curly hair because the pigment melanin protects the body organs from the penetration of harmful ultraviolet rays, and the hair cap has thermal insulating properties. The light eyes of Europeans are an adaptation to a more acute perception of visual information at dusk and in fog, and the Mongoloid shape of the eyes is the result of natural selection for the action of winds and dust storms.
These changes require centuries and millennia, but life in a civilized society entails some changes. Thus, a decrease in physical activity leads to a lighter skeleton, a decrease in its strength, and a decrease in muscle mass. Low mobility, excess high-calorie food, stress lead to an increase in the number of overweight people, and adequate protein nutrition and continued daylight hours with the help of artificial lighting contribute to acceleration - accelerated growth and puberty, and an increase in body size.
1. Heredity is the property of organisms to transmit structural features and
life activity from generation to generation.
2. The material basis of heredity is chromosomes and genes, which store information about the characteristics of the organism. Transfer of genes and chromosomes from generation to generation
thanks to reproduction. Development of a daughter organism from one cell - zygote
or a group of cells of the mother's body in the process of reproduction. Localization in
nuclei of cells involved in reproduction, genes and chromosomes that determine
similarity of the daughter organism with the mother.
3. Heredity is a factor in evolution, the basis for the similarity of parents and offspring, individuals of the same species.
4. Variability is a common property of all organisms to acquire new characteristics in the process of individual development.
5. Types of variability: non-hereditary (modification) and hereditary (combinative, mutational).
6. Non-hereditary changes are not associated with changes
genes and chromosomes, are not inherited, arise under the influence of factors
external environment, disappear over time. Manifestation of similar modifications
changes in all individuals of the species (for example, in the cold, horses' fur becomes
thicker). Disappearance of modification changes upon termination of the factor,
causing this change (tanning disappears in winter, as conditions worsen
modification variability: tanning in summer, weight gain
animals with good feeding and maintenance, development of certain muscle groups
when playing sports.
7. Hereditary changes are caused by changes
genes and chromosomes, are inherited, vary among individuals within
of one species are maintained throughout the life of the individual.
8. Combinative variability. Manifestation
combinative variability during crossing, its dependence on the emergence of new
combinations (combinations) of genes in offspring. Sources of combinative
variability: exchange of sections between homologous chromosomes, random
combination of germ cells during fertilization and formation of a zygote. Varied
combinations of genes - the cause of recombination (new combination) of parental
signs in the offspring.
9. Mutations are sudden, persistent changes.
genes or chromosomes. The result of mutations is the appearance of new characteristics in the child
organisms that were absent in its parents, for example, short legs
sheep, lack of plumage in chickens, albinism (lack of pigment). Useful,
harmful and neutral mutations. Most mutations are harmful to the body
due to the manifestation of new signs that do not correspond to its habitat.
10. Hereditary variability is a factor in evolution.
The appearance of new characters in organisms and their diversity is material for
the actions of natural selection, the preservation of individuals with changes,
corresponding to the habitat, the formation of the adaptability of organisms to
changing environmental conditions.
2. Natural and artificial ecosystems, their features.
1. Ecosystem - a collection of living organisms of different species interconnected
and with components of inanimate nature, metabolism and energy conversion
a certain area of the biosphere.
2. Ecosystem structure:
Species - the number of species living in an ecosystem and
the ratio of their numbers. Example: about 30 species growing in a coniferous forest
plants, in an oak forest - 40-50 species, in a meadow - 30-50 species, in humid
tropical forest - over 100 species;
Spatial - placement of organisms in
vertical (tiered) and horizontal (mosaic) directions. Examples:
the presence of 5-6 tiers in a broad-leaved forest; differences in plant composition
edge and in the thicket of the forest, in dry and moist areas.
3. Community components: abiotic and biotic.
Abiotic components of inanimate nature - light, pressure, humidity, wind,
relief, soil composition, etc. Biotic components: organisms - producers,
consumers and destroyers.
4. Producers - plants and some bacteria,
creating organic substances from inorganic ones using energy
sunlight.
5. Consumers - animals, some plants and
bacteria that feed on prepared organic substances and use
6. Destroyers are fungi and some bacteria,
destroying organic matter to inorganic matter, feeding on corpses,
plant remains.
7. The circulation of substances and energy transformations -
a necessary condition for the existence of any ecosystem. Transfer of substances and energy into
food chains in the ecosystem.
8. Ecosystem sustainability. Stability dependency
ecosystems on the number of species living in them and the length of food chains: the more
species, food chains, the more stable the ecosystem is from the cycle of substances.
9. Artificial ecosystem - created as a result
human activity. Examples of artificial ecosystems: park, field, garden,
10. Differences between an artificial ecosystem and a natural one:
A small number of species (for example, wheat and some
types of weeds in a wheat field and associated animals)
Predominance of organisms of one or more species
(wheat in the field);
Short food chains due to the small number of species;
Unclosed circulation of substances due to
significant removal of organic substances and their removal from the cycle in the form
Low stability and inability to
independent existence without human support.
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