The process of natural selection takes place in nature. Theory of evolution H

Natural selection is the driving force behind evolution. Selection mechanism. Forms of selection in populations (I.I. Shmalgauzen).

Natural selection- the process by which the number of individuals with the maximum fitness (the most favorable traits) increases in the population, while the number of individuals with unfavorable traits decreases. In the light of the modern synthetic theory of evolution, natural selection is considered as the main reason for the development of adaptations, speciation, and the origin of supraspecific taxa. Natural selection is the only known cause of adaptation, but not the only cause of evolution. Non-adaptive causes include genetic drift, gene flow, and mutations.

The term "natural selection" was popularized by Charles Darwin, comparing this process with artificial selection, the modern form of which is selection. The idea of comparing artificial and natural selection is that in nature the most “successful”, “best” organisms are also selected, but in the role of an “appraiser” of the usefulness of properties in this case is not a person, but the environment. In addition, the material for both natural and artificial selection are small hereditary changes that accumulate from generation to generation.

Mechanism of natural selection

In the process of natural selection, mutations are fixed that increase the fitness of organisms. Natural selection is often referred to as a "self-evident" mechanism because it follows from simple facts such as:

Organisms produce more offspring than can survive;

In the population of these organisms, there is hereditary variability;

Organisms that have different genetic traits have different survival rates and ability to reproduce.

Such conditions create competition between organisms for survival and reproduction and are the minimum necessary conditions for evolution through natural selection. Thus, organisms with inherited traits that give them a competitive advantage are more likely to pass them on to their offspring than organisms with inherited traits that do not.

The central concept of the concept of natural selection is the fitness of organisms. Fitness is defined as the ability of an organism to survive and reproduce, which determines the size of its genetic contribution to the next generation. However, the main thing in determining fitness is not the total number of offspring, but the number of offspring with a given genotype (relative fitness). For example, if the offspring of a successful and rapidly reproducing organism are weak and do not reproduce well, then the genetic contribution and, accordingly, the fitness of this organism will be low.

If any allele increases the fitness of an organism more than other alleles of this gene, then with each generation the share of this allele in the population will increase. That is, selection occurs in favor of this allele. And vice versa, for less beneficial or harmful alleles, their share in populations will decrease, that is, selection will act against these alleles. It is important to note that the influence of certain alleles on the fitness of an organism is not constant - when environmental conditions change, harmful or neutral alleles can become beneficial, and beneficial ones can become harmful.

Natural selection for traits that can vary over some range of values (such as the size of an organism) can be divided into three types:

Directed Selection- changes in the average value of the trait over time, for example, an increase in body size;

Disruptive selection- selection for the extreme values of the trait and against the average values, for example, large and small body sizes;

Stabilizing selection- selection against the extreme values of the trait, which leads to a decrease in the variance of the trait.

A special case of natural selection is sexual selection, the substrate of which is any trait that increases mating success by increasing the individual's attractiveness to potential partners. Traits that have evolved through sexual selection are particularly evident in the males of certain animal species. Such traits as large horns, bright coloration, on the one hand, can attract predators and reduce the survival rate of males, and on the other hand, this is balanced by the reproductive success of males with similar pronounced traits.

Selection can operate at various levels of organization such as genes, cells, individual organisms, groups of organisms, and species. Moreover, selection can simultaneously act on different levels. Selection at levels above the individual, such as group selection, can lead to cooperation.

Forms of natural selection

There are different classifications of forms of selection. A classification based on the nature of the influence of selection forms on the variability of a trait in a population is widely used.

driving selection- a form of natural selection that operates under directed changing environmental conditions. Described by Darwin and Wallace. In this case, individuals with traits that deviate in a certain direction from the average value receive advantages. At the same time, other variations of the trait (its deviations in the opposite direction from the average value) are subjected to negative selection. As a result, in the population from generation to generation, there is a shift in the average value of the trait in certain direction. At the same time, the pressure of driving selection must correspond to the adaptive capabilities of the population and the rate of mutational changes (otherwise, environmental pressure can lead to extinction).

A classic example of motive selection is the evolution of color in the birch moth. The color of the wings of this butterfly imitates the color of the bark of trees covered with lichens, on which it spends daylight hours. Obviously, such a protective coloration was formed over many generations of previous evolution. However, with the beginning of the industrial revolution in England, this device began to lose its importance. Atmospheric pollution has led to the mass death of lichens and the darkening of tree trunks. Light butterflies on dark background become easily visible to birds. Since the middle of the 19th century, mutant dark (melanistic) forms of butterflies began to appear in populations of the birch moth. Their frequency increased rapidly. By the end of the 19th century, some urban populations of the moth were almost entirely composed of dark forms, while light forms still predominated in rural populations. This phenomenon has been called industrial melanism. Scientists have found that in polluted areas, birds are more likely to eat light forms, and in clean areas - dark ones. The imposition of restrictions on atmospheric pollution in the 1950s caused natural selection to change direction again, and the frequency of dark forms in urban populations began to decline. They are almost as rare today as they were before the Industrial Revolution.

Driving selection is carried out when changing environment or adaptation to new conditions with the expansion of the range. It preserves hereditary changes in a certain direction, shifting the rate of reaction accordingly. For example, during the development of the soil as a habitat for various unrelated groups of animals, the limbs turned into burrowing ones.

Stabilizing selection- a form of natural selection, in which its action is directed against individuals with extreme deviations from the average norm, in favor of individuals with an average severity of the trait. The concept of stabilizing selection was introduced into science and analyzed by I. I. Shmalgauzen.

Many examples of the action of stabilizing selection in nature have been described. For example, at first glance it seems that individuals with maximum fecundity should make the greatest contribution to the gene pool of the next generation. However, observations of natural populations of birds and mammals show that this is not the case. The more chicks or cubs in the nest, the more difficult it is to feed them, the smaller and weaker each of them. As a result, individuals with average fecundity turn out to be the most adapted.

Selection in favor of averages has been found for a variety of traits. In mammals, very low and very high birth weight newborns are more likely to die at birth or in the first weeks of life than middle weight newborns. Accounting for the size of the wings of sparrows that died after a storm in the 50s near Leningrad showed that most of them had too small or too large wings. And in this case, the average individuals turned out to be the most adapted.

The most widely known example of such a polymorphism is sickle cell anemia. This severe blood disease occurs in people homozygous for a mutant hemoglobin allele ( Hb S) and leads to their death at an early age. In most human populations, the frequency of this allele is very low and approximately equal to the frequency of its occurrence due to mutations. However, it is quite common in areas of the world where malaria is common. It turned out that heterozygotes for Hb S have a higher resistance to malaria than homozygotes for the normal allele. Due to this, heterozygosity for this lethal allele in the homozygote is created and stably maintained in populations inhabiting malaria areas.

Stabilizing selection is a mechanism for the accumulation of variability in natural populations. The outstanding scientist I. I. Shmalgauzen was the first to pay attention to this feature of stabilizing selection. He showed that even under stable conditions of existence, neither natural selection nor evolution ceases. Even remaining phenotypically unchanged, the population does not cease to evolve. Its genetic makeup is constantly changing. Stabilizing selection creates such genetic systems that provide the formation of similar optimal phenotypes on the basis of a wide variety of genotypes. Such genetic mechanisms as dominance, epistasis, complementary action of genes, incomplete penetrance and other means of concealing genetic variation owe their existence to stabilizing selection.

Thus, stabilizing selection, sweeping aside deviations from the norm, actively forms genetic mechanisms that ensure the stable development of organisms and the formation of optimal phenotypes based on various genotypes. It ensures the stable functioning of organisms in a wide range of fluctuations in external conditions familiar to the species.

Disruptive (tearing) selection- a form of natural selection, in which conditions favor two or more extreme variants (directions) of variability, but do not favor the intermediate, average state of the trait. As a result, several new forms may appear from one initial one. Darwin described the operation of disruptive selection, believing that it underlies divergence, although he could not provide evidence for its existence in nature. Disruptive selection contributes to the emergence and maintenance of population polymorphism, and in some cases can cause speciation.

One of the possible situations in nature in which disruptive selection comes into play is when a polymorphic population occupies a heterogeneous habitat. At the same time, different forms adapt to different ecological niches or subniches.

The formation of seasonal races in some weeds is explained by the action of disruptive selection. It was shown that the timing of flowering and seed ripening in one of the species of such plants - meadow rattle - stretched almost all summer, and most of the plants bloom and bear fruit in the middle of summer. However, in hay meadows, those plants that have time to bloom and produce seeds before mowing, and those that produce seeds at the end of summer, after mowing, receive advantages. As a result, two races of rattle are formed - early and late flowering.

Disruptive selection was carried out artificially in experiments with Drosophila. The selection was carried out according to the number of setae, leaving only individuals with a small and large number of setae. As a result, from about the 30th generation, the two lines diverged very strongly, despite the fact that the flies continued to interbreed with each other, exchanging genes. In a number of other experiments (with plants), intensive crossing prevented the effective action of disruptive selection.

Two hypotheses about the mechanisms of sexual selection are common.

According to the “good genes” hypothesis, the female “reasons” in the following way: “If this male, despite his bright plumage and long tail, somehow managed not to die in the clutches of a predator and live to puberty, then, therefore, he has good genes that allowed him to do this. So, he should be chosen as a father for his children: he will pass on his good genes to them. By choosing bright males, females choose good genes for their offspring.

According to the “attractive sons” hypothesis, the logic of female selection is somewhat different. If bright males, for whatever reason, are attractive to females, then it is worth choosing a bright father for your future sons, because his sons will inherit the bright color genes and will be attractive to females in the next generation. Thus, there is a positive Feedback, which leads to the fact that from generation to generation the brightness of the plumage of males is more and more enhanced. The process goes on increasing until it reaches the limit of viability.

In choosing males, females are no more and no less logical than in all other behavior. When an animal feels thirsty, it does not reason that it should drink water in order to restore the water-salt balance in the body - it goes to the watering hole because it feels thirsty. In the same way, females, choosing bright males, follow their instincts - they like bright tails. All those who instinctively prompted a different behavior, all of them left no offspring. Thus, we discussed not the logic of females, but the logic of the struggle for existence and natural selection - a blind and automatic process that, acting constantly from generation to generation, formed all that amazing variety of shapes, colors and instincts that we observe in the world of wildlife. .

positive and negative selection

There are two forms of natural selection: Positive and Clipping (negative) selection.

Positive selection increases the number of individuals in the population that have useful traits that increase the viability of the species as a whole.

Cut-off selection culls out from the population the vast majority of individuals that carry traits that sharply reduce viability under given environmental conditions. With the help of cut-off selection, strongly harmful alleles are removed from the population. Also, individuals with chromosomal rearrangements and a set of chromosomes that sharply disrupt the normal operation of the genetic apparatus can be subjected to cutting selection.

The role of natural selection in evolution

Charles Darwin considered natural selection to be the main driving force of evolution; in the modern synthetic theory of evolution, it is also the main regulator of the development and adaptation of populations, the mechanism for the emergence of species and supraspecific taxa, although accumulation in late XIX At the beginning of the 20th century, information on genetics, in particular the discovery of the discrete nature of the inheritance of phenotypic traits, led some researchers to deny the importance of natural selection, and alternatively proposed concepts based on the assessment of the genotype mutation factor as extremely important. The authors of such theories postulated not a gradual, but a very rapid (over several generations) spasmodic nature of evolution (the mutationism of Hugo de Vries, the saltationism of Richard Goldschmitt, and other less well-known concepts). The discovery of well-known correlations among the traits of related species (the law of homological series) by N. I. Vavilov prompted some researchers to formulate the next “anti-Darwinian” hypotheses about evolution, such as nomogenesis, batmogenesis, autogenesis, ontogenesis, and others. In the 1920s and 1940s in evolutionary biology, those who rejected Darwin's idea of evolution by natural selection (sometimes called "selectionist" theories that emphasized natural selection) revived interest in this theory due to the revision of classical Darwinism in the light of relatively young science of genetics. The resulting synthetic theory of evolution, often incorrectly referred to as neo-Darwinism, relies, among other things, on the quantitative analysis of allele frequencies in populations as they change under the influence of natural selection. There are debates where people with a radical approach, as an argument against the synthetic theory of evolution and the role of natural selection, argue that "discoveries of recent decades in various fields scientific knowledge- from molecular biology with her theory of neutral mutationsMotoo Kimura and paleontology with her theory of punctuated equilibrium Stephen Jay Gould and Niles Eldredge (wherein view understood as a relatively static phase of the evolutionary process) until mathematics with her theorybifurcations and phase transitions- testify to the insufficiency of the classical synthetic theory of evolution for an adequate description of all aspects of biological evolution". The discussion about the role of various factors in evolution began more than 30 years ago and continues to this day, and it is sometimes said that "evolutionary biology (meaning the theory of evolution, of course) has come to the need for its next, third synthesis."

Natural selection is the main, leading, guiding factor in evolution, underlying the theory of Ch. Darwin. All other factors of evolution are random, only natural selection has a direction (in the direction of adapting organisms to environmental conditions).

Definition: selective survival and reproduction of the fittest organisms.

creative role: selecting useful traits, natural selection creates new ones.

Efficiency: the more different mutations in the population (the higher the heterozygosity of the population), the greater the efficiency of natural selection, the faster evolution proceeds.

Forms:

Stabilizing - acts under constant conditions, selects the average manifestations of the trait, preserves the traits of the species (coelacanth coelacanth fish)
Driving - acts in changing conditions, selects the extreme manifestations of a trait (deviations), leads to a change in traits (birch moth)
Sexual - competition for a sexual partner.
Breaking - selects two extreme forms.

Consequences of natural selection:

Evolution (change, complication of organisms)
Emergence of new species (increase in the number [diversity] of species)
The adaptation of organisms to environmental conditions. Any fit is relative., i.e. adapts the body to only one specific conditions.

Choose one, the most correct option. The basis of natural selection is
1) mutation process
2) speciation
3) biological progress
4) relative fitness

Answer

Choose one, the most correct option. What are the consequences of stabilizing selection
1) preservation of old species
2) change in reaction rate
3) the emergence of new species
4) preservation of individuals with altered traits

Answer

Choose one, the most correct option. In the process of evolution, a creative role is played by
1) natural selection
2) artificial selection
3) modification variability
4) mutational variability

Answer

Choose three options. What are the characteristics of motive selection?
1) operates under relatively constant living conditions
2) eliminates individuals with an average value of the trait
3) promotes the reproduction of individuals with a modified genotype
4) preserves individuals with deviations from the average values of the trait
5) preserves individuals with the established norm of the reaction of the trait
6) contributes to the appearance of mutations in the population

Answer

Choose three features that characterize the driving form of natural selection
1) provides the appearance of a new species
2) manifests itself in changing environmental conditions
3) the adaptability of individuals to the original environment is improved
4) individuals with a deviation from the norm are culled
5) the number of individuals with the average value of the trait increases
6) individuals with new traits are preserved

Answer

Choose one, the most correct option. The starting material for natural selection is
1) struggle for existence
2) mutational variability
3) changing the habitat of organisms
4) adaptation of organisms to the environment

Answer

Choose one, the most correct option. The starting material for natural selection is
1) modification variability
2) hereditary variability
3) the struggle of individuals for the conditions of survival
4) adaptability of populations to the environment

Answer

Choose three options. The stabilizing form of natural selection is manifested in
1) constant environmental conditions
2) change in the average reaction rate
3) the preservation of adapted individuals in the original habitat
4) culling of individuals with deviations from the norm
5) saving individuals with mutations
6) preservation of individuals with new phenotypes

Answer

Choose one, the most correct option. The effectiveness of natural selection decreases when
1) the occurrence of recessive mutations
2) an increase in homozygous individuals in the population
3) change in the norm of the reaction of a sign
4) increase in the number of species in the ecosystem

Answer

Choose one, the most correct option. In arid conditions, in the process of evolution, plants with pubescent leaves were formed due to the action of
1) relative variability

3) natural selection
4) artificial selection

Answer

Choose one, the most correct option. Insect pests acquire resistance to pesticides over time as a result of
1) high fecundity
2) modification variability
3) preservation of mutations by natural selection
4) artificial selection

Answer

Choose one, the most correct option. The material for artificial selection is
1) genetic code
2) population
3) genetic drift
4) mutation

Answer

Choose one, the most correct option. Are the following statements about the forms of natural selection correct? A) The emergence of resistance to pesticides in insect pests of agricultural plants is an example of a stabilizing form of natural selection. B) Driving selection contributes to an increase in the number of individuals of a species with an average value of a trait
1) only A is true
2) only B is true
3) both statements are correct
4) both judgments are wrong

Answer

Establish a correspondence between the results of the action of natural selection and its forms: 1) stabilizing, 2) moving, 3) disruptive (tearing). Write the numbers 1, 2 and 3 in the correct order.
A) development of resistance to antibiotics in bacteria
B) The existence of fast and slow growing predatory fish in the same lake
C) Similar structure of the organs of vision in chordates
D) The emergence of flippers in waterfowl mammals
E) Selection of newborn mammals with an average weight
E) Preservation of phenotypes with extreme deviations within one population

Answer

1. Establish a correspondence between the characteristic of natural selection and its form: 1) driving, 2) stabilizing. Write the numbers 1 and 2 in the correct order.
A) preserves the mean value of the feature
B) contributes to adaptation to changing environmental conditions
C) retains individuals with a trait that deviates from its average value
D) contributes to an increase in the diversity of organisms
D) contributes to the preservation of species characteristics

Answer

2. Compare the characteristics and forms of natural selection: 1) Driving, 2) Stabilizing. Write the numbers 1 and 2 in the correct order.
A) acts against individuals with extreme values of traits
B) leads to a narrowing of the reaction norm
B) usually operates under constant conditions
D) occurs during the development of new habitats
D) changes the average values of the trait in the population
E) can lead to the emergence of new species

Answer

3. Establish a correspondence between the forms of natural selection and their characteristics: 1) driving, 2) stabilizing. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) operates in changing environmental conditions
B) operates in constant environmental conditions
C) is aimed at maintaining the previously established average value of the trait
D) leads to a shift in the average value of the trait in the population
D) under its action, both an increase in a sign and a weakening can occur

Answer

4. Establish a correspondence between the signs and forms of natural selection: 1) stabilizing, 2) driving. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) forms adaptations to new environmental conditions
B) leads to the formation of new species
B) maintains the average norm of the trait
D) culls individuals with deviations from the average norm of signs
D) increases the heterozygosity of the population

Answer

Establish a correspondence between examples and forms of natural selection, which are illustrated by these examples: 1) driving, 2) stabilizing. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) an increase in the number of dark butterflies in industrial areas compared to light ones
B) the emergence of insect pest resistance to pesticides
C) the preservation of the reptile tuatara living in New Zealand to the present day
D) a decrease in the size of the cephalothorax in crabs that live in muddy water
E) in mammals, the mortality of newborns with an average weight is less than with very low or very high
E) the death of winged ancestors and the preservation of insects with reduced wings on islands with strong winds

Answer

Establish a correspondence between the forms of the struggle for existence and examples illustrating them: 1) intraspecific, 2) interspecific. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) fish eat plankton
B) seagulls kill chicks when there are a large number of them
C) capercaillie lekking
D) nosed monkeys try to shout down each other, puffing out huge noses
D) chaga mushroom settles on a birch
E) the main prey of the marten is squirrel

Answer

Analyze the table "Forms of natural selection". For each letter, select the appropriate concept, characteristic and example from the list provided.
1) sexual
2) driving
3) group
4) preservation of organisms with two extreme deviations from the average value of the trait
5) the emergence of a new sign
6) the formation of bacterial resistance to antibiotics
7) preservation of the relict plant species Gingko biloba 8) increase in the number of heterozygous organisms

Answer

The idea of comparing artificial and natural selection is that in nature the selection of the most “successful”, “best” organisms also takes place, but in this case it is not a person who acts as an “appraiser” of the usefulness of properties, but the environment. In addition, the material for both natural and artificial selection are small hereditary changes that accumulate from generation to generation.

Mechanism of natural selection

In the process of natural selection, mutations are fixed that increase the adaptability of organisms to their environment. Natural selection is often referred to as a "self-evident" mechanism because it follows from simple facts such as:

Organisms produce more offspring than can survive;
In the population of these organisms, there is hereditary variability;
Organisms that have different genetic traits have different survival rates and ability to reproduce.

The central concept of the concept of natural selection is the fitness of organisms. Fitness is defined as the ability of an organism to survive and reproduce in its existing environment. This determines the size of his genetic contribution to the next generation. However, the main thing in determining fitness is not the total number of offspring, but the number of offspring with a given genotype (relative fitness). For example, if the offspring of a successful and rapidly reproducing organism are weak and do not reproduce well, then the genetic contribution and, accordingly, the fitness of this organism will be low.

Natural selection for traits that can vary over some range of values (such as the size of an organism) can be divided into three types:

Directed Selection- changes in the average value of the trait over time, for example, an increase in body size;
Disruptive selection- selection for the extreme values of the trait and against the average values, for example, large and small body sizes;
Stabilizing selection- selection against the extreme values of the trait, which leads to a decrease in the variance of the trait.

A special case of natural selection is sexual selection, whose substrate is any trait that increases the success of mating by increasing the attractiveness of an individual for potential partners. Traits that have evolved through sexual selection are particularly evident in the males of certain animal species. Traits such as large horns, bright colors, on the one hand, can attract predators and reduce the survival rate of males, and on the other hand, this is balanced by the reproductive success of males with similar pronounced traits.

Selection can operate at various levels of organization such as genes, cells, individual organisms, groups of organisms, and species. Moreover, selection can act simultaneously at different levels. Selection at levels above the individual, such as group selection, can lead to cooperation (see Evolution#Cooperation).

Forms of natural selection

There are different classifications of forms of selection. A classification based on the nature of the influence of selection forms on the variability of a trait in a population is widely used.

driving selection

driving selection- a form of natural selection that operates under directed changing environmental conditions. Described by Darwin and Wallace. In this case, individuals with traits that deviate in a certain direction from the average value receive advantages. At the same time, other variations of the trait (its deviations in the opposite direction from the average value) are subjected to negative selection. As a result, in the population from generation to generation, there is a shift in the average value of the trait in a certain direction. At the same time, the pressure of driving selection must correspond to the adaptive capabilities of the population and the rate of mutational changes (otherwise, environmental pressure can lead to extinction).

An example of the action of motive selection is "industrial melanism" in insects. "Industrial melanism" is a sharp increase in the proportion of melanistic (having a dark color) individuals in those populations of insects (for example, butterflies) that live in industrial areas. Due to industrial impact, tree trunks darkened significantly, and light lichens also died, which made light butterflies more visible to birds, and dark ones worse. In the 20th century, in a number of areas, the proportion of dark-colored butterflies in some well-studied populations of the birch moth in England reached 95%, while for the first time the dark-colored butterfly ( Morfa carbonaria) was captured in 1848.

Driving selection is carried out when the environment changes or adapts to new conditions with the expansion of the range. It preserves hereditary changes in a certain direction, moving the norm of the reaction accordingly. For example, during the development of the soil as a habitat for various unrelated groups of animals, the limbs turned into burrowing ones.

Stabilizing selection

Disruptive selection

An example of disruptive selection is the formation of two races in a large rattle in hay meadows. Under normal conditions, the flowering and seed ripening periods of this plant cover the whole summer. But in hay meadows, seeds are produced mainly by those plants that have time to bloom and ripen either before the mowing period, or bloom at the end of summer, after mowing. As a result, two races of the rattle are formed - early and late flowering.

sexual selection

Two hypotheses about the mechanisms of sexual selection are common.

According to the “good genes” hypothesis, the female “reasons” as follows: “If this male, despite the bright plumage and long tail, managed not to die in the clutches of a predator and survive to puberty, then he has good genes that allowed him to do this . Therefore, he should be chosen as the father of his children: he will pass on his good genes to them. By choosing bright males, females choose good genes for their offspring.
According to the “attractive sons” hypothesis, the logic of female selection is somewhat different. If bright males, for whatever reason, are attractive to females, it is worth choosing a bright father for your future sons, because his sons will inherit the bright color genes and will be attractive to females in the next generation. Thus, a positive feedback occurs, which leads to the fact that from generation to generation the brightness of the plumage of males increases more and more. The process goes on increasing until it reaches the limit of viability.

When choosing males, females do not think about the reasons for their behavior. When an animal feels thirsty, it does not reason that it should drink water in order to restore the water-salt balance in the body - it goes to the watering hole because it feels thirsty. In the same way, females, choosing bright males, follow their instincts - they like bright tails. Those who instinctively prompted a different behavior did not leave offspring. The logic of the struggle for existence and natural selection is the logic of a blind and automatic process that, acting constantly from generation to generation, has formed that amazing variety of forms, colors and instincts that we observe in the world of wildlife.

Selection methods: positive and negative selection

There are two forms of artificial selection: Positive and Clipping (negative) selection.

Positive selection increases the number of individuals in the population that have useful traits that increase the viability of the species as a whole.

The role of natural selection in evolution

In the example of the worker ant, we have an insect extremely different from its parents, yet absolutely barren and therefore unable to transmit from generation to generation acquired modifications of structure or instincts. One can ask a good question - to what extent is it possible to reconcile this case with the theory of natural selection?
- Origin of Species (1859)

Darwin assumed that selection could be applied not only to the individual organism, but also to the family. He also said that, perhaps, to one degree or another, this can also explain the behavior of people. He turned out to be right, but it was not until the advent of genetics that it became possible to provide a more extended view of this concept. The first outline of the "kind selection theory" was made by the English biologist William Hamilton in 1963, who was the first to propose considering natural selection not only at the level of an individual or a whole family, but also at the level of a gene.

Notes

, With. 43-47.
, p. 251-252.
Orr H.A. Fitness and its role in evolutionary genetics // Nature Reviews Genetics. - 2009. - Vol. 10, no. 8. - P. 531-539. - DOI:10.1038/nrg2603. - PMID 19546856 .
Haldane J.B.S. The theory of natural selection today // Nature. - 1959. - Vol. 183, no. 4663. - P. 710-713. - PMID 13644170 .
Lande R., Arnold S. J. The measurement of selection on correlated characters // Evolution. - 1983. - Vol. 37, no. 6. - P. 1210-1226. -

Living in natural conditions, there is individual variability that can manifest itself in three types useful, neutral and harmful. Usually, organisms with harmful variability die at various stages of individual development. The neutral variability of organisms does not affect their viability. Individuals with beneficial variability survive by virtue of an advantage in intraspecific, interspecific, or against adverse conditions environment.

driving selection

When environmental conditions change, those individuals of the species survive in which hereditary variability has manifested itself and, in connection with this, signs and properties have developed that correspond to new conditions, and those individuals that did not have such variability die. During his voyage, Darwin discovered that on oceanic islands where strong winds prevail, there are few long-winged insects and many insects with rudimentary wings and wingless insects. As Darwin explains, insects with normal wings could not withstand the strong winds on these islands and died. And insects with rudimentary wings and wingless did not rise at all into the air and hid in the cracks, finding shelter there. This process, which was accompanied by hereditary variability and natural selection and continued for many thousands of years, led to a decrease in the number of long-winged insects on these islands and the appearance of individuals with rudimentary wings and wingless insects. Natural selection, which ensures the emergence and development of new features and properties of organisms, is called motive selection.

Disruptive selection

Disruptive selection- this is a form of natural selection, leading to the formation of a number of polymorphic forms that differ from each other within the same population.

Among organisms of a certain species, individuals with two or more different forms are sometimes found. This is the result of a special form of natural selection, disruptive selection. Yes, at ladybugs there are two forms of rigid wings - with a dark red and reddish color. Beetles with reddish wings rarely die from cold in winter, but give few offspring in summer, and with dark red wings, on the contrary, they die more often in winter, being unable to withstand the cold, but give numerous offspring in summer. Consequently, these two forms of ladybugs, due to their different adaptability to different seasons, managed to keep their offspring for centuries.

Natural selection is a process originally defined by Charles Darwin as leading to the survival and preferential reproduction of individuals who are more adapted to given environmental conditions and have useful hereditary traits. In accordance with Darwin's theory and the modern synthetic theory of evolution, the main material for natural selection is random hereditary changes - recombination of genotypes, mutations and their combinations.

In the absence of a sexual process, natural selection leads to an increase in the proportion of a given genotype in the next generation. However, natural selection is "blind" in the sense that it "evaluates" not genotypes but phenotypes, and the preferential transmission to the next generation of the genes of an individual with useful traits occurs regardless of whether these traits are heritable.

There are different classifications of forms of selection. A classification based on the nature of the influence of selection forms on the variability of a trait in a population is widely used.

driving selection- a form of natural selection, which operates with a directed change in environmental conditions. Described by Darwin and Wallace. In this case, individuals with traits that deviate in a certain direction from the average value receive advantages. At the same time, other variations of the trait (its deviations in the opposite direction from the average value) are subjected to negative selection. As a result, in the population from generation to generation, there is a shift in the average value of the trait in a certain direction. At the same time, the pressure of driving selection must correspond to the adaptive capabilities of the population and the rate of mutational changes (otherwise, environmental pressure can lead to extinction).

An example of the action of motive selection is "industrial melanism" in insects. "Industrial melanism" is a sharp increase in the proportion of melanistic (having a dark color) individuals in those populations of insects (for example, butterflies) that live in industrial areas. Due to industrial impact, tree trunks darkened significantly, and light lichens also died, which made light butterflies more visible to birds, and dark ones worse. In the 20th century, in a number of areas, the proportion of dark-colored butterflies in some well-studied populations of the birch moth in England reached 95%, while the first dark butterfly (morfa carbonaria) was captured in 1848.

Driving selection is carried out when the environment changes or adapts to new conditions with the expansion of the range. It preserves hereditary changes in a certain direction, shifting the rate of reaction accordingly. For example, during the development of the soil as a habitat for various unrelated groups of animals, the limbs turned into burrowing ones.

sexual selection This is natural selection for success in reproduction. The survival of organisms is an important but not the only component of natural selection. Another important component is attractiveness to members of the opposite sex. Darwin called this phenomenon sexual selection. "This form of selection is determined not by the struggle for existence in the relations of organic beings among themselves or with external conditions, but by the rivalry between individuals of the same sex, usually males, for the possession of individuals of the other sex." Traits that reduce the viability of their carriers can emerge and spread if the advantages they provide in breeding success are significantly greater than their disadvantages for survival. Two main hypotheses about the mechanisms of sexual selection have been proposed. According to the “good genes” hypothesis, the female “reasons” as follows: “If this male, despite his bright plumage and long tail, somehow managed not to die in the clutches of a predator and survive to puberty, then, therefore, he has good the genes that let him do it. So, he should be chosen as a father for his children: he will pass on his good genes to them. By choosing bright males, females choose good genes for their offspring. According to the “attractive sons” hypothesis, the logic of female selection is somewhat different. If bright males, for whatever reason, are attractive to females, then it is worth choosing a bright father for your future sons, because his sons will inherit the bright color genes and will be attractive to females in the next generation. Thus, a positive feedback occurs, which leads to the fact that from generation to generation the brightness of the plumage of males is more and more enhanced. The process goes on increasing until it reaches the limit of viability. In choosing males, females are no more and no less logical than in all other behavior. When an animal feels thirsty, it does not reason that it should drink water in order to restore the water-salt balance in the body - it goes to the watering hole because it feels thirsty. In the same way, females, choosing bright males, follow their instincts - they like bright tails. All those who instinctively prompted a different behavior, all of them left no offspring. Thus, we discussed not the logic of females, but the logic of the struggle for existence and natural selection - a blind and automatic process that, acting constantly from generation to generation, formed all that amazing variety of shapes, colors and instincts that we observe in the world of wildlife. .

Women's Portal Flero

The process of natural selection takes place in nature. Theory of evolution H

Mechanism of natural selection

Forms of natural selection

driving selection

Stabilizing selection

Disruptive selection

sexual selection

Selection methods: positive and negative selection

The role of natural selection in evolution

see also

Notes

driving selection

Disruptive selection

Women's Portal Flero

Mechanism of natural selection

Forms of natural selection

driving selection

Stabilizing selection

Disruptive selection

sexual selection

Selection methods: positive and negative selection

The role of natural selection in evolution

see also

Notes

driving selection

Disruptive selection

RELATED ARTICLES