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What did Charles Darwin understand by natural selection? Charles Darwin's theory of evolution (1859). The role of natural selection in evolution

Charles Robert Darwin(1809 - 1882) - English naturalist and traveler, one of the first to realize and clearly demonstrate that all types of living organisms evolve over time from common ancestors. In his theory, the first detailed presentation of which was published in 1859 in the book “The Origin of Species” (full title: “The Origin of Species by Means of Natural Selection, or the Preservation of Favored Races in the Struggle for Life”), Darwin called natural selection the main driving force of evolution and uncertain variability.

The existence of evolution was recognized by most scientists during Darwin's lifetime, while his theory of natural selection as the main explanation of evolution became generally accepted only in the 30s of the 20th century. Darwin's ideas and discoveries, as revised, form the foundation of the modern synthetic theory of evolution and form the basis of biology as providing a logical explanation for biodiversity.

The essence of evolutionary teaching lies in the following basic principles:

1. All types of living beings inhabiting the Earth were never created by anyone.

2. Having arisen naturally, organic forms were slowly and gradually transformed and improved in accordance with environmental conditions.

3. The transformation of species in nature is based on such properties of organisms as heredity and variability, as well as natural selection that constantly occurs in nature. Natural selection occurs through the complex interaction of organisms with each other and with factors of inanimate nature; Darwin called this relationship the struggle for existence.

4. The result of evolution is the adaptability of organisms to their living conditions and the diversity of species in nature.

In 1831, after graduating from university, Darwin set out as a naturalist on a voyage around the world on a Royal Navy expedition ship. The journey lasted almost five years (Fig. 1). He spends most of his time on the shore, studying geology and collecting natural history collections. Having compared the found remains of plants and animals with modern ones, Charles Darwin made an assumption about the historical, evolutionary relationship.

On the Galapagos Islands, he found species of lizards, turtles, and birds that were not found anywhere else. The Galapagos Islands are islands of volcanic origin, so Charles Darwin suggested that these animals came to them from the mainland and gradually changed. In Australia, he became interested in marsupials and oviparous animals, which became extinct in other parts of the globe. So gradually the scientist’s conviction in the variability of species grew stronger. After returning from his trip, Darwin worked hard for 20 years to create the doctrine of evolution and collected additional facts about the development of new breeds of animals and plant varieties in agriculture.

He considered artificial selection as a unique model of natural selection. Based on the material collected during the journey and proving the validity of his theory, as well as on scientific achievements (geology, chemistry, paleontology, comparative anatomy, etc.) and, above all, in the field of selection, Darwin for the first time began to consider evolutionary transformations not in individual organisms, and at the sight.

Rice. 1 Voyage on the Beagle (1831-1836)

Darwin was directly influenced in the process of creating the concept by Lyell and Malthuss with his geometric progression of numbers from the demographic work “An Essay on the Law of Population” (1798). In this work, Malthus hypothesized that humanity is multiplying many times faster compared to increasing food supplies. While the human population increases geometrically, food supplies, according to the author, can only increase arithmetically. Malthus's work prompted Darwin to think about possible paths of evolution.

A huge number of facts speak in favor of the theory of the evolution of organisms. But Darwin understood that it was not enough just to show the existence of evolution. In collecting evidence, he worked primarily empirically. Darwin went further, developing a hypothesis that revealed the mechanism of the evolutionary process. In the very formulation of the hypothesis, Darwin as a scientist showed a truly creative approach.

1 . Darwin's first assumption was that the number of animals of each species tends to increase exponentially from generation to generation.

2. Darwin then proposed that although the number of organisms tends to increase, the number of individuals of a given species actually remains the same.

These two assumptions led Darwin to the conclusion that there must be a struggle for existence among all species of living beings. Why? If each next generation produces more descendants than the previous one, and if the number of individuals of the species remains unchanged, then, apparently, in nature there is a struggle for food, water, light and other environmental factors. Some organisms survive this struggle, while others die .

Darwin identified three forms of struggle for existence: intraspecific, interspecific and combating unfavorable environmental factors. The most acute intraspecific struggle is between individuals of the same species due to the same food needs and living conditions, for example, the struggle between moose feeding on the bark of trees and shrubs.

Interspecific- between individuals of different species: between wolves and deer (predator - prey), between moose and hares (competition for food). The impact on organisms of unfavorable conditions, such as drought, severe frosts, is also an example of the struggle for existence. The survival or death of individuals in the struggle for existence are the results, consequences of its manifestation.

Charles Darwin, in contrast to J. Lamarck, drew attention to the fact that although any living creature changes during life, individuals of the same species are not born the same.

3. Darwin's next assumption was that every species is inherently variable. Variability is the property of all organisms to acquire new characteristics. In other words, individuals of the same species differ from each other, even in the offspring of one pair of parents there are no identical individuals. He rejected, as untenable, the idea of “exercising” or “non-exercising” organs and turned to the facts of the breeding of new breeds of animals and varieties of plants by people - to artificial selection.

Darwin distinguished between definite (group) and indefinite (individual) variability. A certain variability manifests itself in the entire group of living organisms in a similar way - if the entire herd of cows is well fed, then their milk yield and milk fat content will all increase, but no more than the maximum possible for a given breed. Group variability will not be inherited.

4. Heredity is the property of all organisms to preserve and transmit characteristics from parents to offspring. Changes that are inherited from parents are called hereditary variability. Darwin showed that indefinite (individual) variability of organisms is inherited and can become the beginning of a new breed or variety if it is useful to man. Having transferred these data to wild species, Darwin noted that only those changes that are beneficial to the species for successful competition can be preserved in nature. The giraffe acquired a long neck not at all because it constantly stretched it, reaching the branches of tall trees, but simply because species endowed with a very long neck could find food higher than those branches that had already been eaten by their fellows with a shorter neck, and as a result they could survive during famine. .

Under fairly stable conditions, small differences may not matter. However, with sudden changes in living conditions, one or more distinctive features may become decisive for survival. Having compared the facts of the struggle for existence and the general variability of organisms, Darwin makes a generalized conclusion about the existence of natural selection in nature - the selective survival of some individuals and the death of other individuals.

The result of natural selection is the formation of a large number of adaptations to specific living conditions. The material for natural selection is supplied by the hereditary variability of organisms. In 1842, Charles Darwin wrote the first essay on the origin of species. Under the influence of the English geologist and naturalist Charles Lyell, Darwin began preparing an expanded version of the book in 1856. In June 1858, when the work was half completed, he received a letter from the English naturalist A. R. Wallace with the manuscript of the latter's article.

In this article, Darwin discovered an abbreviated statement of his own theory of natural selection. Two naturalists independently and simultaneously developed identical theories. Both were influenced by T. R. Malthus's work on population; both were aware of Lyell's views, both studied the fauna, flora and geological formations of island groups and discovered significant differences between the species inhabiting them. Darwin sent Wallace's manuscript to Lyell along with his own essay, and on July 1, 1858, they together presented their work to the Linnean Society in London.

Darwin's book was published in 1859 " The Origin of Species by Natural Selection, or the Preservation of Favored Breeds in the Struggle for Life,” in which he explained the mechanism of the evolutionary process. Constantly thinking about the driving causes of the evolutionary process, Charles Darwin came to the most important idea for the entire theory. Natural selection is the main driving force of evolution .

The process as a result of which individuals survive and leave offspring with hereditary changes that are useful under given conditions, i.e. survival and successful production of offspring by the fittest organisms. Based on facts, Charles Darwin was able to prove that natural selection is the driving factor in the evolutionary process in nature, and artificial selection plays an equally important role in the creation of animal breeds and plant varieties.

Darwin also formulated the principle of divergence of characters, which is very important for understanding the process of formation of new species. As a result of natural selection, forms arise that differ from the original species and are adapted to specific environmental conditions. Over time, divergence leads to the appearance of large differences in initially slightly different forms. As a result, they develop differences in many ways. Over time, so many differences accumulate that new species arise. This is what ensures the diversity of species on our planet.

Charles Darwin's merit in science lies not in the fact that he proved the existence of evolution, but in the fact that he explained how it could occur, i.e. proposed a natural mechanism that ensures evolution and improvement of living organisms, and proved that this mechanism exists and works.

What statements relate to the theory of Ch. Darwin?

1) Within a species, the diversity of signs leads to a view.

2) The view is not one-but-ro-den and is represented by many po-la-tions.

3) Natural selection is the main factor of evolution.

4) When creating varieties and breeds, the main factor is artificial selection.

5) The internal desire for perfection is a factor of evolution.

6) Po-pu-la-tion is a unit of evolution.

Clarification.

Statements from the theory of Ch. Darwin: within a species, the divergence of signs leads to vi-do-ob-ra-zo-va-nu; natural selection is the right-hand factor of evolution; When creating varieties and breeds, the main factor is artificial selection.

Answer: 134.

Note.

Dar-vi-n's evolutionary theory is a holistic doctrine about the historical development of or- no world.

The basic principles of the evolutionary theory of Ch. Darwin.

1. In the context of each species of living organisms, there is a huge scope of in-di-vi-du-al-noy on-the-next national of men-chi-in-sti according to mor-fo-lo-gi-che-skim, phy-sio-lo-gi-che-skim, ve-den-che-skim and any other Gym sign. This change-ability may have a continuous, quantitative, or continuous qualitative character, but it always exists.

2. All living orga-niz-we multiply in geo-met-ri-che-skoy pro-gres-sion.

3. Life resources for any kind of living organisms are limited, and therefore there must be a struggle -ba for existence either between individuals of the same species, or between individuals of different species, or with natural conditions -I-mi. In the concept of “struggle for existence,” Darwin included not only the individual’s own struggle for life, but also the struggle for success in multiple times.

4. In conditions of struggle for existence, the most capable individuals survive and give birth to -those deviations in which some cases turned out to be adaptive to the given environmental conditions. This is a prin-tsi-pi-al-but important moment in the ar-gu-men-ta-tion of Dar-vi-na. Deviations occur not in the right way - in response to the action of the environment, but by chance. Not many of them turn out to be useful in specific conditions. Because you are alive, the individuals who subsequently suffer from a useful deviation are allowed to survive. ku, they appear to be more suitable for a given environment than other representatives of the population.

5. Survival and predominant multiplication in capable individuals Darwin called natural from -bo-rum.

6. Natural selection of individual iso-li-ro-van-varieties in different conditions of existence according to -gradually leads to diversification (diversity) of the signs of these different species and, ultimately, to vi-do-about-ra-zo-va-nu.

Answer: 134

Source: Unified State Examination in Biology 05/30/2013. Main wave. Siberia. Option 4.

Ilya Safronov (Veliky Novgorod) 02.09.2013 18:14

Well, in theory, the sixth option is also correct. The local population is considered the elementary unit of evolution.

Natalia Evgenievna Bashtannik

The population is the elementary unit of evolution - this is already the position of the Synthetic Theory of Evolution

Olga Ivanova 27.01.2014 17:14

Artificial selection is not the subject of evolutionary theory, but the synthetic theory of evolution develops Darwin's. The historical development of the world does not affect selection issues.

Natalia Evgenievna Bashtannik

Darwin emphasized the particular importance of unconscious selection from a theoretical point of view, since this form of selection sheds light on the process of speciation. It can be seen as a bridge between artificial and natural selection. Artificial selection was a good model on which Darwin deciphered the process of morphogenesis. Darwin's analysis of artificial selection played an important role in substantiating the evolutionary process: firstly, he finally established the position of variability: secondly, he established the basic mechanisms of morphogenesis (variability, heredity, preferential reproduction of individuals with useful traits) and, finally, showed the ways of development expedient adaptations and divergence of varieties and breeds. These important premises paved the way for a successful solution to the problem of natural selection.

It is a holistic doctrine about the historical development of the organic world.

The essence of evolutionary teaching lies in the following basic principles:

1. All types of living beings inhabiting the Earth were never created by anyone.

2. Having arisen naturally, organic forms were slowly and gradually transformed and improved in accordance with environmental conditions.

4. The result of evolution is the adaptability of organisms to their living conditions and the diversity of species in nature.

Natural selection. However, Darwin's main merit in creating the theory of evolution lies in the fact that he developed the doctrine of natural selection as the leading and directing factor of evolution. Natural selection, according to Darwin, is a set of changes occurring in nature that ensure the survival of the most adapted individuals and the predominance of their offspring, as well as the selective destruction of organisms that are unadapted to existing or changed environmental conditions.

In the process of natural selection, organisms adapt, i.e. they develop the necessary adaptations to the conditions of existence. As a result of competition between different species that have similar vital needs, less adapted species become extinct. Improving the mechanism of adaptation of organisms leads to the fact that the level of their organization gradually becomes more complex and thus the evolutionary process is carried out. At the same time, Darwin drew attention to such characteristic features of natural selection as the gradual and slow process of change and the ability to summarize these changes into large, decisive causes leading to the formation of new species.

Based on the fact that natural selection operates among diverse and unequal individuals, it is considered as a combined interaction of hereditary variability, preferential survival and reproduction of individuals and groups of individuals better adapted than others to given conditions of existence. Therefore, the doctrine of natural selection as the driving and directing factor in the historical development of the organic world is central to Darwin’s theory of evolution.

Forms of natural selection:

Driving selection is a form of natural selection that operates under directed changes 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. In this case, other variations of the trait (its deviations in the opposite direction from the average value) are subject to negative selection.

As a result, in a population from generation to generation there is a shift in the average value of the trait in a certain direction. In this case, 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 driving selection is “industrial melanism” in insects. “Industrial melanism” is a sharp increase in the proportion of melanistic (dark-colored) individuals in those populations of insects (for example, butterflies) that live in industrial areas. Due to industrial impact, tree trunks darkened significantly, and light-colored lichens also died, which is why light-colored butterflies became better visible to birds, and dark-colored ones became less visible.

In the 20th century, the proportion of dark-colored butterflies in some well-studied moth populations in England reached 95% in some areas, while the first dark-colored butterfly (morfa carbonaria) was captured in 1848.

Driving selection occurs when the environment changes or adapts to new conditions when the range expands. It preserves hereditary changes in a certain direction, moving the reaction rate accordingly. For example, during the development of soil as a habitat, various unrelated groups of animals developed limbs that turned into burrowing limbs.

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 expression 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 the greatest contribution to the gene pool of the next generation should be made by individuals with maximum fertility. 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 is. As a result, individuals with average fertility are the most fit.

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

Disruptive 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 a trait. As a result, several new forms may appear from one original one. Darwin described the action of disruptive selection, believing that it underlies divergence, although he could not provide evidence of 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 the greater rattle in hay meadows. Under normal conditions, the flowering and seed ripening periods of this plant cover the entire summer. But in hay meadows, seeds are produced mainly by those plants that manage to bloom and ripen either before the mowing period, or bloom at the end of summer, after mowing. 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 bristles; only individuals with a small and large number of bristles were retained. As a result, from about the 30th generation, the two lines diverged very much, 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 is natural selection for reproductive success. 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 competition between individuals of one sex, usually males, for the possession of individuals of the other sex.”

Traits that reduce the viability of their hosts can emerge and spread if the advantages they provide for reproductive success are significantly greater than their disadvantages for survival. 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 a watering hole because it feels thirsty.

In the same way, females, when choosing bright males, follow their instincts - they like bright tails. Those for whom instinct suggested 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, which, acting constantly from generation to generation, has formed the amazing variety of forms, colors and instincts that we observe in the world of living nature.

When analyzing the reasons for the increase in the organization of organisms or their adaptability to living conditions, Darwin drew attention to the fact that selection does not necessarily require the selection of the best, it can only come down to the destruction of the worst. This is exactly what happens during unconscious selection. But the destruction (elimination) of the worst, less adapted organisms in nature can be observed at every step. Consequently, natural selection can be carried out by “blind” forces of nature.

Darwin emphasized that the expression “natural selection” should in no case be understood in the sense that someone is conducting this selection, since this term speaks of the action of spontaneous forces of nature, as a result of which organisms adapted to given conditions survive and die unadapted. The accumulation of beneficial changes leads first to small and then to large changes. This is how new varieties, species, genera and other systematic units of a higher rank appear. This is the leading, creative role of natural selection in evolution.

Elementary evolutionary factors. Mutation process and genetic combinatorics. Population waves, isolation, genetic drift, natural selection. Interaction of elementary evolutionary factors.

Elementary evolutionary factors are stochastic (probabilistic) processes occurring in populations that serve as sources of primary intrapopulation variability.

3. Periodic with high amplitude. Found in a wide variety of organisms. Often they are periodic in nature, for example, in the “predator-prey” system. May be associated with exogenous rhythms. It is this type of population waves that plays the greatest role in evolution.

Historical reference. The expression “wave of life” was probably first used by the explorer of the South American pampas, W.H. Hudson (1872-1873). Hudson noted that under favorable conditions (light, frequent rainfall), vegetation that usually burned out was preserved; the abundance of flowers gave rise to an abundance of bumblebees, then mice, and then birds that fed on mice (including cuckoos, storks, short-eared owls).

S.S. Chetverikov drew attention to the waves of life, noting the appearance in 1903 in the Moscow province of certain species of butterflies that had not been found there for 30...50 years. Before this, in 1897 and somewhat later, there was a massive appearance of the gypsy moth, which denuded vast areas of forests and caused significant damage to orchards. In 1901, the admiral butterfly appeared in significant numbers. He presented the results of his observations in a short essay “Waves of Life” (1905).

If during the period of maximum population size (for example, a million individuals) a mutation appears with a frequency of 10-6, then the probability of its phenotypic manifestation will be 10-12. If, during a period of population decline to 1000 individuals, the carrier of this mutation survives completely by chance, then the frequency of the mutant allele will increase to 10-3. The same frequency will continue during the period of subsequent population growth, then the probability of the phenotypic manifestation of the mutation will be 10-6.

Insulation. Provides manifestation of the Baldwin effect in space.

In a large population (for example, one million diploid individuals), a mutation rate of the order of 10-6 means that approximately one in a million individuals are carriers of the new mutant allele. Accordingly, the probability of phenotypic manifestation of this allele in a diploid recessive homozygote is 10-12 (one trillionth).

If this population is divided into 1000 small isolated populations of 1000 individuals, then in one of the isolated populations there will most likely be one mutant allele, and its frequency will be 0.001. The probability of its phenotypic manifestation in the next subsequent generations will be (10 - 3)2 = 10 - 6 (one millionth). In ultra-small populations (tens of individuals), the probability of a mutant allele manifesting itself in the phenotype increases to (10 - 2)2 = 10 - 4 (one ten-thousandth).

Thus, only by isolating small and ultra-small populations will the chances of a phenotypic manifestation of a mutation in the coming generations increase thousands of times. At the same time, it is difficult to imagine that the same mutant allele would appear in the phenotype completely randomly in different small populations. Most likely, each small population will be characterized by a high frequency of one or a few mutant alleles: either a, or b, or c, etc.

Natural selection is a process originally defined by Charles Darwin as leading to the survival and preferential reproduction of individuals more adapted to given environmental conditions and possessing 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.

The main provisions of the evolutionary theory of Charles Darwin Variability Heredity Artificial selection Struggle for existence Natural selection	The basis of Charles Darwin's evolutionary theory is the idea of a species, its variability in the process of adaptation to the environment and the transmission of characteristics from ancestors to offspring. The evolution of cultural forms occurs under the influence of artificial selection, the factors of which are variability, heredity and human creative activity, and the evolution of natural species is carried out thanks to natural selection, the factors of which are variability, heredity and the struggle for existence.
	Driving forces of evolution
	breeds and varieties	organic world
	hereditary variability and artificial selection	the struggle for existence and natural selection based on hereditary variability

Variability

When comparing many breeds of animals and varieties of plants, Darwin noticed that within any species of animals and plants, and in culture, within any variety and breed there are no identical individuals. Based on the instructions of K. Linnaeus that reindeer herders recognize every deer in their herd, shepherds recognize every sheep, and many gardeners recognize varieties of hyacinths and tulips by bulbs, Darwin concluded that variability is inherent in all animals and plants.

Analyzing the material on the variability of animals, the scientist noticed that any change in living conditions is enough to cause variability. Thus, Darwin understood variability as the ability of organisms to acquire new characteristics under the influence of environmental conditions. He distinguished the following forms of variability:

In his books “On the Origin of Species by Means of Natural Selection, or the Preservation of Favored Breeds in the Struggle for Life” (1859) and “Changes in Domestic Animals and Cultivated Plants” (1868), Darwin described in detail the variety of breeds of domestic animals and analyzed their origin. He noted the diversity of cattle breeds, of which there are about 400. They differ from each other in a number of characteristics: color, body shape, degree of skeletal and muscle development, the presence and shape of horns. The scientist examined in detail the question of the origin of these breeds and came to the conclusion that all European breeds of cattle, despite the great differences between them, originated from two ancestral forms domesticated by humans.

The breeds of domestic sheep are also extremely diverse, there are more than 200 of them, but they come from a limited number of ancestors - mouflon and argali. Various breeds of domestic pigs were also bred from wild forms of wild boar, which, in the process of domestication, changed many features of their structure. The breeds of dogs, rabbits, chickens and other domestic animals are unusually diverse.

Darwin was particularly interested in the question of the origin of pigeons. He proved that all existing breeds of pigeons descended from one wild ancestor - the rock (mountain) pigeon. The breeds of pigeons are so different that any ornithologist, finding them in the wild, would recognize them as independent species. However, Darwin showed their common origin based on the following facts:

none of the species of wild pigeons, except the rocky one, has any characteristics of domestic breeds;
many features of all domestic breeds are similar to those of the wild rock pigeon. Domestic pigeons do not build nests in trees, retaining the instinct of a wild pigeon. All breeds have the same behavior when courting a female;
when crossing pigeons of different breeds, hybrids sometimes appear with characteristics of a wild rock pigeon;
all hybrids between any breeds of pigeons are fertile, which confirms that they belong to the same species. It is quite obvious that all these numerous breeds were the result of a change in one original form. This conclusion is also true for most domestic animals and cultivated plants.

Darwin paid much attention to the study of various varieties of cultivated plants. Thus, comparing various varieties of cabbage, he concluded that they were all bred by man from one wild species: they differ in the shape of the leaves with similar flowers and seeds. Ornamental plants, for example, different varieties of pansies, produce a variety of flowers, and their leaves are almost the same. Gooseberry varieties have a variety of fruits, but the leaves are almost the same.

Reasons for variability. Having shown the variety of forms of variability, Darwin explained the material causes of variability, which are environmental factors, the conditions of existence and development of living beings. But the influence of these factors varies depending on the physiological state of the organism and the stage of its development. Among the specific causes of variability, Darwin identifies:

direct or indirect (through the reproduction system) influence of living conditions (climate, food, care, etc.);
functional tension of organs (exercise or non-exercise);
crossing (the appearance in hybrids of characteristics not characteristic of the original forms);
changes caused by the correlative dependence of parts of the body.

Among the various forms of variability for the evolutionary process, hereditary changes are of paramount importance as the primary material for variety, breed and speciation - those changes that are fixed in subsequent generations.

Heredity

By heredity, Darwin understood the ability of organisms to preserve their species, varietal and individual characteristics in their offspring. This feature was well known and represented hereditary variation. Darwin analyzed in detail the importance of heredity in the evolutionary process. He drew attention to cases of same-suit hybrids of the first generation and splitting of characters in the second generation; he was aware of heredity associated with sex, hybrid atavisms and a number of other phenomena of heredity.

At the same time, Darwin noted that the study of variability and heredity, their immediate causes and patterns is associated with great difficulties. The science of that time could not yet give a satisfactory answer to a number of important questions. The works of G. Mendel were also unknown to Darwin. Only much later did extensive research into variability and heredity begin, and modern genetics made a giant step in the study of the material foundations, causes and mechanisms of heredity and variability, in the causal understanding of these phenomena.

Darwin attached great importance to the presence of variability and heredity in nature, considering them the main factors of evolution, which is adaptive in nature [show] .

Adaptive nature of evolution

Darwin in his work "The Origin of Species..." noted the most important feature of the evolutionary process - the continuous adaptation of species to the conditions of existence and the improvement of the organization of the species as a result of the accumulation of adaptations. However, he noted that the adaptability of a species, developed by selection to the conditions of existence, although it is important for the self-preservation and self-reproduction of species, cannot be absolute; it is always relative and is useful only in those environmental conditions in which species exist for a long time. The body shape, respiratory organs and other features of fish are suitable only for life in water and are not suitable for life on land. The green coloration of locusts camouflages insects on green vegetation, etc.

The process of expedient adaptation can be traced using the example of any group of organisms that has been sufficiently studied in evolutionary terms. A good example is the evolution of the horse.

The study of the horse's ancestors made it possible to show that its evolution was associated with the transition from life in forests on marshy soil to life in open, dry steppes. Changes in the horse's known ancestors occurred in the following directions:

increased growth due to the transition to life in open spaces (high growth is an adaptation to the expansion of the horizon in the steppes);
an increase in running speed was achieved by lightening the leg skeleton and gradually reducing the number of toes (the ability to run quickly has a protective value and allows you to more effectively find water bodies and feeding grounds);
intensification of the grinding function of the dental apparatus as a result of the development of ridges on the molars, which was especially important in connection with the transition to feeding on tough cereal vegetation.

Naturally, along with these changes, correlative ones also occurred, for example, lengthening of the skull, changes in the shape of the jaws, the physiology of digestion, etc.

Along with the development of adaptations, the so-called adaptive diversity appears in the evolution of any group. It lies in the fact that, against the background of unity of organization and the presence of common systematic characteristics, representatives of any natural group of organisms always differ in specific characteristics that determine their adaptability to specific living conditions.

Due to living in similar living conditions, unrelated forms of organisms can acquire similar adaptations. For example, such systematically distant forms as a shark (class Pisces), ichthyosaur (class Reptiles) and dolphin (class Mammals) have a similar appearance, which is an adaptation to the same living conditions in a certain environment, in this case in water. The similarity between systematically distant organisms is called convergence (see below). In sessile protozoa, sponges, coelenterates, annelids, crustaceans, echinoderms, and ascidians, the development of root-like rhizoids is observed, with the help of which they are strengthened in the ground. Many of these organisms are characterized by a stalk-like body shape, which makes it possible, during a sedentary lifestyle, to soften the blows of waves, the impacts of fish fins, etc. All sessile forms are characterized by a tendency to form clusters of individuals and even coloniality, where the individual is subordinate to a new whole - the colony, which reduces the likelihood of death as a result of mechanical damage.

In different living conditions, related forms of organisms acquire different adaptations, i.e. two or more species can arise from one ancestral form. Darwin called this process of divergence of species in different environmental conditions divergence (see below). An example of this is the finches on the Galapagos Islands (west of Ecuador): some feed on seeds, others on cacti, and others on insects. Each of these forms differs from the other in the size and shape of the beak and could have arisen as a result of divergent variability and selection.

The adaptations of placental mammals are even more diverse, among which there are terrestrial forms with fast running (dogs, deer), species leading an arboreal lifestyle (squirrel, monkey), animals living on land and in water (beavers, seals), living in air environment (bats), aquatic animals (whales, dolphins) and species with an underground lifestyle (moles, shrews). All of them descend from a single primitive ancestor - an arboreal insectivorous mammal (Fig. 3).

Adaptation is never absolutely perfect due to the duration of the process of accumulation of adaptations. Changes in relief, climate, composition of fauna and flora, etc. can quickly change the direction of selection, and then adaptations developed in some conditions of existence lose their significance in others, to which new adaptations begin to be developed again. At the same time, the number of some species decreases, while the more adapted ones increase. Newly adapted organisms may retain previous signs of adaptation, which in new conditions of existence are not of decisive importance for self-preservation and self-reproduction. This allowed Darwin to talk about the inexpediency of signs of adaptation, which were found in the organization and behavior of organisms quite often. This is especially clearly seen when the behavior of organisms is not determined by their way of life. Thus, the webbed feet of geese serve as an adaptation for swimming and their presence is advisable. However, mountain geese also have webbed feet, which is clearly impractical given their lifestyle. The frigate bird does not usually land on the surface of the ocean, although, like bar-headed geese, it has webbed feet. It is safe to say that membranes were necessary and useful for the ancestors of these birds, just like modern aquatic birds. Over time, the descendants adapted to new living conditions and lost the habit of swimming, but they retained their swimming organs.

It is known that many plants are sensitive to temperature fluctuations and this is an appropriate response to the seasonal periodicity of vegetation and reproduction. However, such sensitivity to temperature fluctuations can lead to mass plant mortality if temperatures rise in the fall, stimulating the transition to repeated flowering and fruiting. This prevents the normal preparation of perennial plants for winter and they die when cold weather sets in. All these examples indicate relative feasibility.

The relativity of expediency manifests itself when there is a significant change in the conditions of existence of the organism, since in this case the loss of the adaptive nature of one or another characteristic is especially obvious. In particular, the rational construction of burrows with exits at the water level of the muskrat is destructive during winter floods. Erroneous reactions are often observed in migratory birds. Sometimes waterfowl fly to our latitudes before the opening of reservoirs, and the lack of food at this time leads to their mass death.

Purposefulness is a historically arose phenomenon under the constant action of natural selection, and therefore it manifests itself differently at different stages of evolution. In addition, the relativity of fitness provides the possibility of further restructuring and improvement of the adaptations available to a given type, i.e. the infinity of the evolutionary process.

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However, having substantiated the question of variability and heredity as factors of evolution, Darwin showed that by themselves they do not yet explain the emergence of new breeds of animals, plant varieties, species, or their fitness. Darwin's great merit is that he developed the doctrine of selection as the leading and directing factor in the evolution of domestic forms (artificial selection) and wild species (natural selection).

Darwin established that as a result of selection, a change in species occurs, i.e. selection leads to divergence - deviation from the original form, divergence of characteristics in breeds and varieties, the formation of a large variety of them [show] .

Divergent nature of evolution

Darwin developed the principle of divergence, i.e., divergence of characteristics of varieties and breeds, using the example of artificial selection. Subsequently, he used this principle to explain the origin of animal and plant species, their diversity, the emergence of differentiation between species, and substantiation of the doctrine of the monophyletic origin of species from a common root.

The divergence of the evolutionary process is derived from the facts of multidirectional variability, preferential survival and reproduction in a number of generations of extreme variants that compete with each other to a lesser extent. Intermediate forms, whose life requires similar food and habitats, are in less favorable conditions and, therefore, die out faster. This leads to a greater gap between extreme options, the formation of new varieties, which later become independent species.

Divergence under the control of natural selection leads to the differentiation of species and their specialization. For example, the genus of tits unites species that live in different places (biotopes) and feed on different foods (Fig. 2). In butterflies of the white butterfly family, divergence went in the direction of caterpillars adapting to eating different food plants - cabbage, turnips, rutabaga and other wild plants of the cruciferous family. Among buttercups, one species lives in water, others live in swampy places, forests or meadows.

Based on similarity, as well as common origin, taxonomy unites closely related species of plants and animals into genera, genera into families, families into orders, etc. Modern taxonomy is a reflection of the monophyletic nature of evolution.

The principle of divergence developed by Darwin has important biological significance. It explains the origin of the wealth of life forms, the ways of development of numerous and more diverse habitats.

A direct consequence of the divergent development of most groups within similar habitats is convergence - the convergence of characters and the development of outwardly similar traits in forms of different origins. A classic example of convergence is the similarity of body shape and organs of movement in a shark (fish), ichthyosaur (reptile) and dolphin (mammal), i.e., the similarity of adaptations to life in water (Fig. 3). There are similarities between placental and marsupial mammals, between the smallest bird, the hummingbird, and the large butterfly, the hummingbird hawk moth. Convergent similarity of individual organs occurs in unrelated animals and plants, i.e. is built on a different genetic basis.

Progress and regression

Darwin showed that the inevitable consequence of divergent evolution is the progressive development of organic nature from simple to complex. This historical process of increasing organization is well illustrated by paleontological data, and is also reflected in the natural system of plants and animals, combining lower and higher forms.

Thus, evolution can take different paths. The main directions of evolutionary development and morphophysiological patterns of evolution were developed in detail by Academician. A.N. Severtsov (see macroevolution).

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Artificial selection

Analyzing the characteristics of breeds of domestic animals and varieties of cultivated plants, Darwin drew attention to the significant development in them of precisely those characteristics that are valued by humans. This was achieved using the same technique: when breeding animals or plants, breeders left for reproduction those specimens that most fully satisfied their needs and from generation to generation accumulated changes useful for humans, i.e. carried out artificial selection.

By artificial selection, Darwin understood a system of measures to improve existing and create new breeds of animals and plant varieties with useful (economically) hereditary traits and distinguished the following forms of artificial selection:

Purposeful breeding of a breed or variety. When starting work, the breeder sets himself a certain task in relation to the characteristics that he wants to develop in a given breed. First of all, these characteristics must be economically valuable or satisfy the aesthetic needs of humans. The traits with which the breeder works can be both morphological and functional. These may also include the nature of animal behavior, for example, pugnacity in fighting cocks. When solving the task set for himself, the breeder selects from the already available material all the best, in which the characteristics of interest to him are manifested, at least to a small extent. Selected individuals are kept in isolation to avoid unwanted crossbreeding. The breeder then selects pairs to cross. After this, starting from the first generation, he strictly selects the best material and rejects those that do not meet the requirements.

Thus, methodical selection is a creative process leading to the formation of new breeds and varieties. Using this method, the breeder, like a sculptor, sculpts new organic forms according to a pre-thought-out plan. Its success depends on the degree of variability of the original form (the more the characteristics change, the easier it is to find the desired changes) and the size of the original batch (in a large batch there are greater opportunities for choice).

Methodical selection in our time, using the achievements of genetics, has been significantly improved and has become the basis of modern theory and practice of animal and plant breeding.

Unconscious selection carried out by a person without a specific, pre-set task. This is the oldest form of artificial selection, elements of which were already used by primitive people. With unconscious selection, a person does not set a goal to create a new breed, variety, but only leaves it to the tribe and mainly reproduces the best individuals. So, for example, a peasant who has two cows, wanting to use one of them for meat, will slaughter the one that gives less milk; Of the chickens, he uses the worst laying hens for meat. In both cases, the peasant, preserving the most productive animals, carries out directed selection, although he does not set himself the goal of breeding new breeds. It is precisely this primitive form of selection that Darwin calls unconscious selection.

The doctrine of natural selection as a driving and guiding factor in the historical development of the organic world -
central part of Darwin's theory of evolution .

The basis of natural selection is the struggle for existence - the complex relationships between organisms and their connection with the environment.

Struggle for existence

In nature, there is a constant tendency towards unlimited reproduction of all organisms in geometric progression. [show] .

According to Darwin's calculations, one poppy box contains 3 thousand seeds, and a poppy plant grown from one seed produces up to 60 thousand seeds. Many fish annually lay up to 10-100 thousand eggs, cod and sturgeon - up to 6 million.

Russian scientist K. A. Timiryazev gives the following example illustrating this point.

Dandelion, according to rough estimates, produces 100 seeds. Of these, 100 plants can grow next year, each of which will also produce 100 seeds. This means that with unhindered reproduction, the number of descendants of one dandelion could be represented as a geometric progression: the first year - 1 plant; second - 100; third - 10,000; tenth year - 10 18 plants. To resettle the descendants of one dandelion obtained in the tenth year, an area 15 times larger than the area of the globe will be needed.

This conclusion can be reached by analyzing the reproductive ability of a wide variety of plants and animals.

However, if you count, for example, the number of dandelions in a certain area of a meadow over several years, it turns out that the number of dandelions changes little. A similar situation is observed among representatives of the fauna. Those. "geometric progression of reproduction" is never carried out, because between organisms there is a struggle for space, food, shelter, competition when choosing a sexual partner, a struggle for survival with fluctuations in temperature, humidity, lighting, etc. In this struggle, the majority of those born die (eliminate, are removed) without leaving offspring, and therefore in nature the number of individuals of each species on average remains constant. In this case, the surviving individuals turn out to be the most adapted to the conditions of existence.

Darwin laid the discrepancy between the number of individuals born and the number of individuals surviving to adulthood as a result of complex and varied relationships with other living beings and environmental factors as the basis of his doctrine of the struggle for existence or the struggle for life [show] . At the same time, Darwin realized that this term was unsuccessful and warned that he was using it in a broad metaphorical sense, and not literally.

Darwin reduced the various manifestations of the struggle for existence to three types:

interspecific struggle - the relationship of an organism with individuals of other species (interspecific relationships);
intraspecific struggle - relationships between individuals and groups of individuals of the same species (intraspecific relationships)
struggle with the conditions of the inorganic external environment - the relationship of organisms and species with the physical conditions of life, the abiotic environment

Intraspecific relationships are also quite complex (relationships between individuals of different sexes, between parental and daughter generations, between individuals of the same generation in the process of individual development, relationships in a flock, herd, colony, etc.). Most forms of intraspecific relationships are important for the reproduction of the species and maintaining its numbers, ensuring a change of generations. With a significant increase in the number of individuals of a species and restrictions on the conditions for their existence (for example, with dense plantings), acute interaction arises between individual individuals, which leads to the death of some or all individuals or their elimination from reproduction. Extreme forms of such relationships include intraspecific struggle and cannibalism - eating individuals of one's own species.

The fight against inorganic environmental conditions occurs depending on climatic and soil conditions, temperature, humidity, light and other factors affecting the life of organisms. During the process of evolution, animal and plant species develop adaptations to life in a particular environment.

It should be noted that the three named main forms of struggle for existence in nature are not carried out in isolation - they are closely intertwined with each other, due to which the relationships of individuals, groups of individuals and species are multifaceted and quite complex.

Darwin was the first to reveal the content and meaning of such important concepts in biology as “environment”, “external conditions”, “interrelations of organisms” in the process of their life and development. Academician I. I. Shmalgauzen considered the struggle for existence to be one of the main factors of evolution.

Natural selection

Natural selection, in contrast to artificial selection, is carried out in nature itself and consists of the selection within a species of the most adapted individuals to the conditions of a particular environment. Darwin discovered a certain commonality in the mechanisms of artificial and natural selection: in the first form of selection, the conscious or unconscious will of man is embodied in the results, in the second, the laws of nature prevail. In both cases, new forms are created, but with artificial selection, despite the fact that variability affects all organs and properties of animals and plants, the resulting animal breeds and plant varieties retain characteristics that are useful for humans, but not for the organisms themselves. On the contrary, natural selection preserves individuals whose changes are useful for their own existence in given conditions.

In “The Origin of Species,” Darwin gives the following definition of natural selection: “The preservation of beneficial individual differences or changes and the destruction of harmful ones I called natural selection, or the survival of the fittest” (c)-(Darwin Ch. Origin of Species. - M., L.; Selkhozgi, 1937, p. 171). He warns that "selection" should be understood as a metaphor, as a fact of survival, and not as a conscious choice.

So, natural selection is understood as a process that constantly occurs in nature, in which the most adapted individuals of each species survive and leave offspring and the less adapted ones die. [show] . The extinction of the unadapted is called elimination.

Consequently, as a result of natural selection, the species that are most adapted to the specific environmental conditions in which their lives take place survive.

Constant changes in environmental conditions over a long period of time cause a variety of individual hereditary changes, which can be neutral, harmful or beneficial. As a result of life competition in nature, there is a constant selective elimination of some individuals and the preferential survival and reproduction of those that, by changing, have acquired useful characteristics. As a result of crossing, a combination of characteristics of two different forms occurs. Thus, from generation to generation, minor useful hereditary changes and their combinations accumulate, which over time become characteristic features of populations, varieties, and species. Moreover, due to the law of correlation, simultaneously with the intensification of adaptive changes in the body, a restructuring of other characteristics also occurs. Selection constantly influences the entire organism, its external and internal organs, their structure and function. This reveals the creative role of selection (see microevolution).

Darwin wrote: “Metaphorically speaking, we can say that natural selection daily, hourly investigates throughout the world the smallest changes, discarding the bad, preserving and adding the good, working silently, invisibly, wherever and whenever the opportunity presents itself, to improve every organic being in relation to the conditions of its life, organic and inorganic" (c)-(Darwin Ch. Origin of Species. - M., Leningrad; Selkhozgi, 1937, p. 174.).

Natural selection is a historical process. Its effect manifests itself after many generations, when subtle individual changes are summed up, combined and become characteristic adaptive characteristics of groups of organisms (populations, species, etc.).

Sexual selection. As a special type of intraspecific natural selection, Darwin identified sexual selection, under the influence of which secondary sexual characteristics are formed (bright colors and various decorations of males of many birds, sexual differences in the development, appearance, behavior of other animals) in the process of active relationships between the sexes of animals, especially during the breeding season .

Darwin distinguished between two types of sexual selection:

fight between males for a female
active searches, choice of males by females, males only compete with each other in order to excite females, who choose the most attractive males

The results of both types of sexual selection differ. With the first form of selection, strong and healthy offspring appear, well-armed males (the appearance of spurs, horns). During the second, such secondary sexual characteristics of males as the brightness of plumage, characteristics of mating songs, and the smell emitted by the male, which serves to attract a female, are enhanced. Despite the seeming inexpediency of such traits, since they attract predators, such a male has an increased chance of leaving offspring, which turns out to be beneficial for the species as a whole. The most important result of sexual selection is the appearance of secondary sexual characteristics and associated sexual dimorphism.

Under different circumstances, natural selection can proceed at different rates. Darwin notes circumstances favoring natural selection:

the number of individuals and their diversity, increasing the likelihood of beneficial changes;
a fairly high frequency of manifestation of uncertain hereditary changes;
intensity of reproduction and rate of generation change;
unrelated crossing, increasing the range of variability in the offspring. Darwin notes that cross-pollination occurs occasionally even among self-pollinating plants;

isolation of a group of individuals, preventing them from interbreeding with the rest of the organisms of a given population;

Comparative characteristics of artificial and natural selection
Comparison indicator	Evolution of cultural forms (artificial selection)	Evolution of natural species (natural selection)
Material for selection	Individual hereditary variability
Selective factor	Human	Struggle for existence
The nature of the selection action	Accumulation of changes in a successive series of generations
Selection action speed	Acts quickly (methodical selection)	Acts slowly, evolution is gradual
Selection results	Creation of forms useful to humans; formation of breeds and varieties	Education of adaptations to the environment; formation of species and larger taxa

wide distribution of the species, since at the boundaries of the range individuals encounter different conditions and natural selection will go in different directions and increase intraspecific diversity.

In its most general form, the scheme of action of natural selection, according to Darwin, comes down to the following. Due to the inherent indefinite variability of all organisms, individuals with new characteristics appear within a species. They differ from ordinary individuals of a given group (species) in their needs. Due to the difference between old and new forms, the struggle for existence leads some of them to elimination. As a rule, less evaded organisms that became intermediate in the process of divergence are eliminated. Intermediate forms find themselves in conditions of intense competition. This means that monotony, which increases competition, is harmful, and evading forms find themselves in a more advantageous position and their numbers increase. The process of divergence (divergence of characteristics) occurs constantly in nature. As a result, new varieties are formed and such separation of varieties ultimately leads to the emergence of new species.

Thus, the evolution of cultural forms occurs under the influence of artificial selection, the components (factors) of which are variability, heredity and human creative activity. The evolution of natural species is carried out thanks to natural selection, the factors of which are variability, heredity and the struggle for existence. Comparative characteristics of these forms of evolution are given in the table.

Darwin's process of speciation

Darwin saw the emergence of new species as a long process of accumulation of beneficial changes, increasing from generation to generation. The scientist took small individual changes as the first steps of speciation. Their accumulation over many generations leads to the formation of varieties, which he considered as steps towards the formation of a new species. The transition from one to another occurs as a result of the cumulative action of natural selection. A variety, according to Darwin, is an emerging species, and a species is a distinct variety.

In the process of evolution, several new ones can arise from one ancestral species. For example, species A, as a result of divergence, can give rise to two new species B and C, which in turn will be the basis for other species (D, E), etc. Of the changed forms, only the most deviated varieties survive and give birth to offspring, each of which again produces a fan of changed forms, and again the most deviated and better adapted survive. Thus, step by step, greater and greater differences arise between extreme forms, finally developing into differences between species, families, etc. The reason for divergence, according to Darwin, is the presence of uncertain variability, intraspecific competition and the multidirectional nature of the action of selection. A new species can also arise as a result of hybridization between two species (A x B).

Thus, C. Darwin in his teaching combines the positive aspects of the doctrine of the species of C. Linnaeus (recognition of the reality of species in nature) and J.-B. Lamarck (recognition of the limitless variability of species) and proves the natural path of their formation on the basis of hereditary variability and selection. They were offered four species criteria - morphological, geographical, ecological and physiological. However, as Darwin pointed out, these characteristics were not sufficient to clearly classify species.

The species is a historical phenomenon; it arises, develops, reaches full development, and then, under changing environmental conditions, disappears, giving way to other species, or itself changes, giving rise to other forms.

Species extinction

Darwin's doctrine of the struggle for existence, natural selection and divergence satisfactorily explains the question of the extinction of species. He showed that in constantly changing environmental conditions, some species, decreasing in number, must inevitably die and give way to others, better adapted to these conditions. Thus, in the process of evolution, the destruction and creation of organic forms are constantly carried out as a necessary condition for development.

The reason for the extinction of species may be various environmental conditions unfavorable for the species, a decrease in the evolutionary plasticity of the species, a lag in the rate of variation of the species or the rate of change in conditions, and narrow specialization. More competitive species displace others, as the fossil record clearly demonstrates.

Assessing Charles Darwin's evolutionary theory, it should be noted that he proved the historical development of living nature, explained the paths of speciation as a natural process, and actually substantiated the formation of adaptations of living systems as a result of natural selection, revealing for the first time their relative nature. Charles Darwin explained the main causes and driving forces of the evolution of plants and animals in culture and the wild. Darwin's teaching was the first materialist theory of the evolution of living things. His theory played a major role in strengthening the historical view of organic nature and largely determined the further development of biology and all natural science.

The brilliant scientist Charles Darwin wrote what every person needs to know in order not to fall into utopia, namely: “Natural selection daily and hourly investigates throughout the world beneficial changes, discarding the bad ones, preserving and creating the best ones.” It is obvious that natural selection implements the principle of improvement. The famous founder of the theory, Ean Baptiste Lamarck, argued that the main force driving the entire evolutionary process is the internal desire for perfection inherent in organisms. However, the desire for perfection, as balance shows, is possessed by the entire Universe. The desire for perfection is inherent in the structure and operating principle of balance and is expressed by gravity. Therefore, we can rightfully say that the main type of gravitation is evolutionary gravitation, which is a gravitation towards improvement, towards harmonization, towards order, towards perfection - this is the main feature of spirituality.

This means that the entire Universe is spiritual to the highest degree. The cosmic mind is tirelessly working on the spirituality of the Universe with the help of its equilibrium mechanism of creation, the work of which requires truthful information in the universe, and its quality at the moment and about improving its quality for the next period. Constantly improving the quality of information stage by stage creates a harmonious process that improves the forms being created. Man belongs to highly organized forms. His brain is capable of working like a cosmic mind, harmonizing the world, himself and society. The law of improvement is a condition of life for both man and society.

Natural selection according to Darwin is a harmonic process regulated by an equilibrium mechanism. Moreover, this is a continuous process of nature; it specifically shows how the formation of the upper limit of a measure and the movement of the measure upward along the evolutionary axis towards progress occurs in life. Natural selection should be considered as a structural element of evolution. He is always aimed at progress.

It is unacceptable to identify the process of evolution with the process of natural selection, because the laws of evolution are laws of equilibrium, which are more complex than the laws of natural selection according to Darwin. Identifying the process of evolution with the process of natural selection strikes at the very teachings of Darwin, contributing to the emergence of anti-Darwinian trends. One cannot identify the broad with the narrow, the more complex with the simpler. Moreover, the complexity of evolution in society is due to the action of the information component, which is an extremely contradictory process.

The driving form of natural selection according to Darwin

The most valuable thing in Darwin's teaching is the disclosure of an element of the equilibrium mechanism of the general evolutionary process of the Universe with the help of the driving form of selection. This element shows how the evolutionary equilibrium mechanism, using information about changing traits, controls population harmonization. The implementation of the tendency towards improvement at all stages of harmonious development is the harmonization of a complex developing system, forming the orderliness of the world. It was Darwin who studied information about the development of a population using the arithmetic mean. He said that population development follows the growth of the average. It is from the arithmetic mean that the cosmic mind originates. Hegel called it absolute reason. Both Darwin and Hegel suffered from those who used their brilliant works for their own selfish interests. But many people suffered even more, tormented by acute conflicts and poverty in the 19th and 20th centuries.

The teachings of Charles Darwin are the basis of the modern theory of evolution

The basis of Charles Darwin's evolutionary theory is the idea of a species, its variability in the process of adaptation to the environment and the transmission of characteristics from ancestors to offspring. The evolution of cultural forms occurs under the influence of artificial selection, the factors of which are variability, heredity and human creative activity, and the evolution of natural species is carried out thanks to natural selection, the factors of which are variability, heredity and the struggle for existence.

Variability

In his books On the Origin of Species by Means of Natural Selection, or the Preservation of Favored Breeds in the Struggle for Life (1859) and Variations in Domestic Animals and Cultivated Plants (1868), Darwin described in detail the variety of breeds of domestic animals and analyzed their origins. He noted the diversity of cattle breeds, of which there are about 400. They differ from each other in a number of characteristics: color, body shape, degree of skeletal and muscle development, the presence and shape of horns. The scientist examined in detail the question of the origin of these breeds and came to the conclusion that all European breeds of cattle, despite the great differences between them, originated from two ancestral forms domesticated by humans.

none of the species of wild pigeons, except the rocky one, has any characteristics of domestic breeds;
many features of all domestic breeds are similar to those of the wild rock pigeon. Domestic pigeons do not build nests in trees, retaining the instinct of a wild pigeon. All breeds have the same behavior when courting a female;
when crossing pigeons of different breeds, hybrids sometimes appear with characteristics of a wild rock pigeon;
all hybrids between any breeds of pigeons are fertile, which confirms that they belong to the same species. It is quite obvious that all these numerous breeds were the result of a change in one original form. This conclusion is also true for most domestic animals and cultivated plants.

direct or indirect (through the reproduction system) influence of living conditions (climate, food, care, etc.);
functional tension of organs (exercise or non-exercise);
crossing (the appearance in hybrids of characteristics not characteristic of the original forms);
changes caused by the correlative dependence of parts of the body.

Among the various forms of variability for the evolutionary process, hereditary changes are of paramount importance as the primary material for variety, breed and speciation formation - those changes that are fixed in subsequent generations.

Heredity

Darwin attached great importance to the presence of variability and heredity in nature, considering them the main factors of evolution, which is adaptive in nature [show] .

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Natural selection- the main evolutionary process, as a result of which in a population the number of individuals with maximum fitness (the most favorable traits) increases, 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 is not the only cause of evolution. Maladaptive causes include genetic drift, gene flow, and mutations.

The term "Natural selection" was popularized by Charles Darwin, comparing the process to artificial selection, the modern form of which is selective breeding. The idea of comparing artificial and natural selection is that in nature the selection of the most “successful”, “best” organisms also occurs, but in this case the role of “evaluator” of the usefulness of properties is not a person, but the environment. In addition, the material for both natural and artificial selection is 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 called a "self-evident" mechanism because it follows from such simple facts as:

Organisms produce more offspring than can survive;
There is heritable variation in the population of these organisms;
Organisms with different genetic traits have different survival rates and ability to reproduce.

Disruptive selection

Disruptive 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 a trait. As a result, several new forms may appear from one original one. Darwin described the action 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.

Sexual selection

Sexual selection- This is natural selection for reproductive success. 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 competition between individuals of one sex, usually males, for the possession of individuals of the other sex.” Traits that reduce the viability of their hosts can emerge and spread if the advantages they provide for reproductive 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 a given male, despite his bright plumage and long tail, managed not to die in the clutches of a predator and survive to sexual maturity, 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 colorful males, females are choosing good genes for their offspring.
According to the “attractive sons” hypothesis, the logic of female choice is somewhat different. If brightly colored males, for whatever reason, are attractive to females, it is worth choosing a brightly colored father for his future sons, because his sons will inherit the brightly colored 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 increasingly increasing. The process continues to grow 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 a watering hole because it feels thirsty. In the same way, females, when choosing bright males, follow their instincts - they like bright tails. Those for whom instinct suggested 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, which, acting constantly from generation to generation, has formed the amazing variety of forms, colors and instincts that we observe in the world of living nature.

Selection methods: positive and negative selection

There are two forms of artificial selection: Positive And Cut-off (negative) selection.

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

Eliminating selection eliminates from a population the vast majority of individuals that carry traits that sharply reduce viability under given environmental conditions. Using selection selection, highly deleterious alleles are removed from the population. Also, individuals with chromosomal rearrangements and a set of chromosomes that sharply disrupt the normal functioning of the genetic apparatus can be subjected to cutting selection.

The role of natural selection in evolution

Charles Darwin believed 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 of the emergence of species and supraspecific taxa, although the accumulation of information on genetics in the late 19th - early 20th centuries, in particular the discovery of a discrete nature inheritance of phenotypic traits has led some researchers to deny the importance of natural selection and, as an alternative, to propose concepts based on assessing the genotype mutation factor as extremely important. The authors of such theories postulated not a gradual, but a very fast (over several generations) spasmodic nature of evolution (hypotheses, the synthetic theory of evolution and - indicate 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 today, and sometimes it is said that “evolutionary biology has come to the need for its next, third synthesis.”

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. A good question to ask is how reconcilable is this case with the theory of natural selection?

- Origin of Species (1859)

Darwin assumed that selection could apply not only to an individual organism, but also to a family. He also said that perhaps, to one degree or another, this could explain people's behavior. He was right, but it was only with the advent of genetics that it became possible to provide a more expanded view of the concept. The first sketch of the “theory of kin selection” 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 an entire family, but also at the level of the gene.