Natural selection, its mechanisms and forms. c) Group selection

Natural selection increases the chances of survival and continuation of the whole genus, it is on the same level as mutations, migrations and transformations in genes. The main mechanism of evolution works flawlessly, but on the condition that no one interferes with its work.

What is natural selection?

The meaning of this term was given by English scientist Charles Darwin. He established that natural selection is a process that determines the survival and reproduction of only those adapted to the conditions. environment individuals. According to Darwin's theory, the most important role in evolution is played by random hereditary changes.

• recombination of genotypes;
• mutations and their combinations.

Natural selection in humans

In times of underdeveloped medicine and other sciences, only a person with strong immunity and a stable healthy body survived. They did not know how to care for premature newborns, they did not use antibiotics in the treatment, they did not perform operations, and they had to cope with their illnesses on their own. Natural selection in humans has selected the strongest representatives of humanity for further reproduction.

In the civilized world, it is not customary to acquire numerous offspring and in most families there are no more than two children, who, thanks to modern conditions life and medicine, may well live to a ripe old age. Previously, families had 12 children or more, and survived under favorable conditions no more than four. Natural selection in man has led to the fact that most of the hardened, exceptionally healthy and strong people. Thanks to their gene pool, humanity still lives on earth.

Reasons for natural selection

All life on earth developed gradually, from the simplest organisms to the most complex ones. Representatives of certain forms of life that failed to adapt to the environment did not survive and did not reproduce, their genes were not passed on to subsequent generations. The role of natural selection in evolution has led to the emergence of the ability at the cellular level to adapt to the environment and quickly respond to its changes. The causes of natural selection are influenced by a number of simple factors:

1. Natural selection works when more offspring are produced than can survive.
2. In the genes of the body there is hereditary variability.
3. Genetic differences dictate survival and reproductive ability in different conditions.

Signs of natural selection

The evolution of any living organism is the creativity of nature itself and this is not a whim, but a necessity. Acting in various conditions environment, it is not difficult to guess what features natural selection preserves, all of them are aimed at the evolution of the species, increasing its resistance to external influences:

1. The selection factor plays an important role. If in artificial selection a person chooses which features of the species to preserve and which not (for example, when breeding a new breed of dogs), then in natural selection the strongest wins in the struggle for his existence.
2. The material for selection is hereditary changes, the signs of which can help in adapting to new living conditions or for specific purposes.
3. The result is another stage of natural selection, as a result of which new species were formed with traits that are beneficial in certain environmental conditions.
4. The speed of action - mother nature is not in a hurry, she thinks over her every step, and therefore natural selection is characterized by low speed changes, for artificial - fast.

What is the result of natural selection?

All organisms have their own degree of adaptability and it is impossible to say with certainty how one or another species will behave in unfamiliar environmental conditions. The struggle for survival and hereditary variability is the essence of natural selection. There are many examples of plants and animals that have been introduced from other continents and have adapted better to new living conditions. The result of natural selection is a whole set of acquired changes.

• adaptation - adaptation to new conditions;
• variety of forms of organisms - arise from a common ancestor;
• evolutionary progress - the complication of species.

How is natural selection different from artificial selection?

It can be said with certainty that almost everything that is eaten by humans sooner or later was subjected to artificial selection. The fundamental difference is that by conducting "his" selection, a person pursues his own benefit. Thanks to selection, he received selected products, brought out new breeds of animals. Natural, natural selection is not focused on the benefit for humanity, it pursues only the interests of this particular organism.

Natural and artificial selection equally affect the lives of all people. They fight for the life of a premature baby, as well as for the life of a healthy one, but at the same time, natural selection kills drunkards frozen on the streets, deadly diseases take the lives of ordinary people, mentally unbalanced people commit suicide, natural disasters crash to the ground.

Types of natural selection

Why are only certain representatives of species able to survive in different environmental conditions? The forms of natural selection are not written rules of nature:

1. Driving selection occurs when environmental conditions change and species have to adapt, it keeps the genetic heritage in certain directions.
2. Stabilizing selection is aimed at individuals with deviations from the average statistical norm in favor of average individuals of the same species.
3. Disruptive selection is when individuals with extreme indicators survive, and not with average ones. As a result of such selection, two new species can be formed at once. More common in plants.
4. Sexual selection - based on reproduction, when the key role is played not by the ability to survive, but by attractiveness. Females, without thinking about the reasons for their behavior, choose beautiful, bright males.

Why is a person able to weaken the impact of natural selection?

Medical progress has come a long way. People who were supposed to die - survive, develop, have their own children. By passing on their genetics to them, they give rise to a weak race. Natural selection and the struggle for existence clash hourly. Nature comes up with more and more sophisticated ways to control people, and man tries to keep up with her, thereby preventing natural selection. Human humanism leads to the weak appearance of people.

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 genes of an individual with useful traits occurs regardless of whether these traits are heritable.

Exist different classifications selection forms. 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 a directed change in conditions external environment. 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 opposite side from the mean) 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-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, 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. Schmalhausen.

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.

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. Wherein different forms adapt to different ecological niches or subnishes.

An example of disruptive selection is the formation of two races in a large rattle in hay meadows. AT normal conditions the timing of flowering and seed ripening in 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.

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 small and large quantity bristles. 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.

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 rivalry between individuals of one 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, has formed all that amazing variety of shapes, colors and instincts that we observe in the world of wildlife. .

One of the main mechanisms of evolution along with mutations, migration processes and gene transformations is natural selection. Types of natural selection involve such changes in the genotype that increase the chances of an organism to survive and procreate. Evolution is often seen as a consequence of this process, which may result from differences in species survival, fertility, development rates, mating success, or any other aspect of life.

natural balance

Gene frequencies remain constant from generation to generation, provided that there are no perturbing factors that disturb the natural balance. These include mutations, migrations (or gene flow), random genetic drift, and natural selection. A mutation is a spontaneous change in the frequency of genes in a population that is characterized by a low rate of development. In this case, the individual moves from one population to another and then changes. Random is a change that is passed from one generation to another in a completely random way.

All these factors change the frequencies of genes without taking into account the increase or decrease in the likelihood of an organism surviving and reproducing in its own natural environment. All of them are random processes. And natural selection, types of natural selection, are mildly disruptive effects of these processes because they multiply the frequency of beneficial mutations over many generations and eliminate harmful constituents.

What is natural selection?

Natural selection contributes to the conservation of those groups of organisms that are better adapted to the physical and biological conditions of their habitat. He
can act on any heritable phenotypic trait and, through selective pressure, can influence any aspect of the environment, including sexual selection and competition with members of the same or other species.

However, this does not mean that this process is always directed and effective in adaptive evolution. Natural selection, types of natural selection in general, often results in the elimination of less fit variants.

Variations exist within the entire population of organisms. This is partly because random mutations occur in the genome of one organism, and its offspring can inherit such mutations. Throughout life, genomes interact with the environment. Therefore, the population is evolving.

The concept of natural selection

Natural selection is one of the cornerstones of modern biology. It acts on the phenotype, the genetic basis of which gives a reproductive advantage for greater prevalence in the population. Over time, this process can lead to the emergence of new species. In other words, this is an important (though not the only) evolutionary process within a population.
The concept itself was formulated and published in 1858 by Charles Darwin and Alfredo Russell Wallace in a joint paper presentation regarding

The term has been described as analogue, i.e. it is the process by which animals and plants with certain traits are deemed desirable for breeding and reproduction. The concept of "natural selection" was originally developed in the absence of the theory of heredity. At the time of Darwin's writings, science had yet to develop The unification of traditional Darwinian evolution with subsequent discoveries in classical and molecular genetics is called the modern evolutionary synthesis. The 3 kinds of natural selection remain the main explanation for adaptive evolution.

How does natural selection work?

Natural selection is the mechanism by which an animal organism adapts and evolves. At their core, the individual organisms that are best adapted to their environment survive and reproduce most successfully, producing fertile offspring. After numerous breeding cycles, such species are dominant. In this way, nature filters out ill-adapted individuals for the benefit of the entire population.

This is a relatively simple mechanism that causes members of a particular population to change over time. In fact, it can be broken down into five main stages: variability, inheritance, selection, timing, and adaptation.

Darwin on natural selection

According to Darwin, natural selection has four components:

1. Variations. Organisms within a population exhibit individual differences in appearance and behavior. These changes may include body size, hair color, muzzle patches, voice quality, or the number of offspring produced. On the other hand, some character traits are not associated with differences between individuals, such as the number of eyes in vertebrates.
2. Inheritance. Some traits are passed down sequentially from parent to offspring. Such traits are inherited, while others are strongly influenced by environmental conditions and are weakly inherited.
3. high populations. The bulk of animals annually produces offspring in much larger numbers than is necessary for an equal distribution of resources between them. This leads to interspecific competition and premature mortality.
4. Differential survival and reproduction. All types of natural selection in populations leave behind those animals that can fight for local resources.

Natural selection: types of natural selection

Darwin's theory of evolution radically changed the direction of future scientific thought. At its center is natural selection, a process that occurs over successive generations and is defined as the differential reproduction of genotypes. Any change in the environment (such as changing the color of a tree trunk) can lead to local adaptation. There are the following types of natural selection (Table No. 1):

Stabilizing selection

Often, the frequency of mutations in DNA in some species is statistically higher than in others. This type of natural selection tends to eliminate any extremes in the phenotypes of the fittest individuals in a population. This reduces diversity within the same species. However, this does not mean that all individuals are exactly the same.

Stabilizing natural selection and its types can be briefly described as averaging or stabilization in which a population becomes more homogeneous. First of all, polygenic traits are affected. This means that the phenotype is controlled by several genes and there is a wide range of possible outcomes. Over time, some of the genes are turned off or masked by others, depending on the favorable adaptation.

Many human characteristics are the result of such selection. Human birth weight is not only a polygenic trait, it is also controlled by environmental factors. Newborns with an average birth weight are more likely to survive than those who are too small or too large.

Directed natural selection

This phenomenon is usually observed under conditions that have changed over time, for example weather, climate or food supply may lead to directional breeding. Human involvement can also speed up this process. Hunters most often kill large individuals for meat or other large ornamental or useful parts. Consequently, the population will tend to skew towards smaller individuals.

The more predators kill and eat slow individuals in the population, the more the bias will be towards the luckier and faster members of the population. The types of natural selection (example table no. 1) can be more clearly demonstrated using examples from wildlife.

Charles Darwin studied directional selection when he was in the Galapagos Islands. The beak length of native finches has varied over time due to available food sources. In the absence of insects, finches survived with large and long beaks, which helped them eat the seeds. Over time, insects became more numerous, and with the help of directional selection, bird beaks gradually became smaller.

Features of diversification (disruptive) selection

Disruptive selection is a type of natural selection that opposes the averaging of species characteristics within a population. This process is the rarest, if we describe the types of natural selection briefly. Diversification selection can result in the speciation of two or more various forms in places of sharp changes in the environment. Like directional selection, this process can also be slowed down due to the destructive influence of the human factor and environmental pollution.

One of the best studied examples of subversive selection is the case of butterflies in London. In rural areas, almost all individuals were light in color. However, these same butterflies were very dark in color in industrial areas. There were also specimens with an average color intensity. This is because dark butterflies have learned to survive and escape predators in industrial areas in urban environments. Light moths in industrial areas were easily found and eaten by predators. The reverse picture was observed in countryside. Butterflies of medium color intensity were easily visible in both places and therefore very few remained.

Thus, the meaning of subversive selection is the movement of the phenotype to the extreme that is necessary for the survival of the species.

Natural selection and evolution

The main idea of ​​the theory of evolution is that all species diversity gradually developed from simple forms life that appeared more than three billion years ago (for comparison, the age of the Earth is about 4.5 billion years). Types of natural selection with examples from the first bacteria to the first modern people played in this evolutionary development significant role.

Organisms that have been poorly adapted to their environment are less likely to survive and reproduce. This means that their genes are less likely to be passed on to the next generation. Way to genetic diversity should not be lost, as well as the ability at the cellular level to respond to changing environmental conditions.

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 it is not the person who acts, 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:

1. Organisms produce more offspring than can survive;
2. In the population of these organisms, there is hereditary variability;
3. 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 total number descendants, and the number of descendants 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:

1. Directed Selection- changes in the average value of the trait over time, for example, an increase in body size;
2. Disruptive selection- selection for the extreme values ​​of the trait and against the average values, for example, large and small body sizes;
3. 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 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. 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 (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 regions, 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

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.

Disruptive selection

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.

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.

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.

sexual selection

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. Other 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 one 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 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.

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

In the example of the worker ant, we have an insect extremely different from its parents, yet absolutely sterile, 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 expanded 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.

see also

Notes

1. , With. 43-47.
2. , p. 251-252.
3. 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 .
4. Haldane J.B.S. The theory of natural selection today // Nature. - 1959. - Vol. 183, no. 4663. - P. 710-713. - PMID 13644170 .
5. Lande R., Arnold S. J. The measurement of selection on correlated characters // Evolution. - 1983. - Vol. 37, no. 6. - P. 1210-1226. -

main historical factor. organic development. peace; consists in the fact that of the nascent individuals, only those survive and, most importantly, produce offspring, to-rye have at least a subtle, but still significant advantage over other individuals - a more perfect adaptability to the conditions of life. E.'s opening about. like ch. patterns of biology. development is the most important merit of Darwin and is the core of Darwinism. The most important prerequisites for E. o. are variability and the struggle for existence between individuals both within a given species and between individuals belonging to different types. As a result of the action of these factors, not all individuals survive to adulthood and, therefore, give offspring. The winners in the struggle for existence are individuals that are better adapted to given conditions than others and therefore with great success oppose enemies and competitors and adverse conditions nature. They reproduce more intensively, leave more offspring than less adapted ones. Finally, necessary condition success E. o. is the inheritance of new useful features of the organization of living beings (see. Heredity). The gradual accumulation and strengthening of these traits in subsequent generations and the disappearance of intermediate forms (since the struggle for existence is the sharper, the closer the organisms are to each other, since they have similar needs for the means of subsistence) lead to an ever greater increase in differences between organisms, to a divergence signs - the so-called. divergence. As a result, new forms of organisms arise: first ecotypes, varieties, subspecies, and then species. Thus, species and speciation occur due to E. o. the fittest and E. o. as a whole leads to the improvement of forms, to the strengthening of their vital activity. The appearance of new forms, better adapted to the given conditions of existence and especially more perfectly organized, conceals in itself the germ of the death of forms living in the same conditions, but inferior to new forms in terms of adaptability to given environmental conditions or in terms of the level of organization. E. o., as the main. the law of evolution of species, characterized, therefore, by qualities, a peculiar dependence of the individual, variability and general evolution. development. Individual. differences, in themselves causally determined by the processes of vital activity of individual organisms, in relation to evolution. processes appear as random. E. o. discovers their necessity by checking whether they will be adapted. meaning. Thus, E. o. there is a regularity in which the dialectic of necessity and chance manifests itself as specific. biological content. evolution. Engels specifically emphasizes this dialectic. the basis of Darwin's theory of E. o .: "Darwin in his epoch-making work proceeds from the broadest, based on chance, factual basis. It is the endless random differences of individuals within separate species ... that make him question ... the concept of a species in its former metaphysical ossification and immutability ... Chance overturns the understanding of necessity that has existed until now" ("Dialectics of Nature", 1955, pp. 174–75). E. o. averages a variety of random variations, ultimately creating forms that are most adapted to given conditions. Non-mechanical biological character. causality is clearly visible from such cases of adaptation, in to-rykh developed in the course of E. o. traits are beneficial to the species, although they are harmful to the individual. For example, the sting of a bee is designed so that when it is used, the insect dies. However, the ability to sting is useful for the preservation of the species. Specific biological character. causality determines the objective content of the concept of biological. expediency, which is a natural result of E. o. Thus, the theory of E. o. completely refutes teleology. This theory is essentially built on the recognition of the role of the contradiction between random individual variability and general biological. species adaptation as the driving principle of speciation. These contradictions are resolved by victory and b. or m. the rapid spread of new forms and the displacement of old ones. This process sometimes proceeds so rapidly and violently that one can speak of upheavals in the history of this group. The resolution of contradictions leads to the creation of new, more advanced devices, and, thus, as a result of the action of E. o. the organization of living beings acquires features related. expediency, it turns out to be harmonious in structure and functions, adapted to the changing conditions of life. Occurrence by E. about. devices that are useful not only in that biotope, which is occupied by populations of the species in the crust. time, but also beyond it, i.e. fixtures wide meaning, opening up the possibility of capture by the descendants of this species of a new ecological. zone, leads to evolution. progress. Acquisition of such adaptations, to-rye are valuable and useful hl. arr. within the framework of certain specific conditions of existence, does not open prospects for going beyond this ecological. areas. Such adaptations, especially if they are associated with strictly defined conditions of existence, lead to the specialization of living beings. However, it must be sharply contrasted with specialization and progress. Facts from the history of organic of the world testify to the presence of a certain kind of "interpenetration" of progress and specialization. These facts also show that progress in the sense of a general rise in organization is not harmonious. development of all systems of functions and organs. It is associated with the loss of certain features that are necessary and useful in certain conditions of existence, and, consequently, with a certain regression. Thus, the theory of E. o. considers regress dialectically as a moment, a form of biological. progress. Creative, creating new forms, the role of E. o. is especially clearly visible from observations, for example, over a rattle plant. On nature. rattle has a self-opening box and wind-blown winged seeds. In rye crops, a form of rattle grows with a non-opening box and wingless seeds, which prevents the elimination of the rattle from crops (the box is threshed together with rye, but the seeds are not carried away by the wind when winnowing). It turned out that the degree of wing development in the seed pods varies greatly (from normal wings to complete winglessness). E. o. acted in the direction of eliminating winged forms (they were carried away by the wind during winnowing), which, in the end, led to the formation of a wingless form of rattle in cultivated crops. The value of E. o. like a creative the force of speciation decisively refutes the interpretation of it as a factor, the action of which is limited only to the elimination of forms that are not sufficiently adapted to the ecological data. conditions. Lit.: Engels F., Dialectics of Nature, Moscow, 1955; Darwin Ch., The origin of species by means of natural selection, Soch., v. 3, M.–L., 1939; its the same, Pet changes and cultivated plants, ibid., vol. 4, M.–L., 1951; Lysenko T. D., Natural selection and intraspecific competition, Minsk, 1951; ?Miryazev K. ?., Fav. soch., vol. 2, M., 1957; Gabunia L.K., On the issue of progressive development in the phylogenesis of mammals, in: Tr. department of paleobiology of the Academy of Sciences of Georgia. SSR, [vol.] 2, Tb., 1954; Golinevich P. N., Overpopulation and the struggle for existence, "Problems of Philosophy", 1956, No 4; Davitashvili L. Sh., Essays on the history of the doctrine of evolution. progress, M., 1956; Gilyarov M.S., Problems of modern. ecology and theory of natures. selection, "Successful modern biol.", 1959, v. 48, no. 3(6) (named after bibliography); Wallace A. R., Natural selection, St. Petersburg, 1878; Schmidt G. ?., Natural. selection as general and non-specific. factor of evolutionary progress, "Izv. AN SSSR. Ser. biol.", 1959, No 6 (named after bibliogr.); Frolov I. T., About causality and expediency in living nature, M., 1961; Plate L., Selectionsprinzip und Probleme der Artbildung. Ein Handbuch des Darwinismus, 3 Aufl., Lpz., 1908; L'H?ritier Ph., G?n?tique et ?volution, P., 1934; D'Ancona U., The struggle for existence, Leiden, 1954; Fisher R.?., The genetic theory of natural selection, N. Y., . L. Gabunia. Tbilisi.