Natural selection in nature and in the laboratory The action of selection is studied not only in laboratory experiments, but also in the course of many years of observations in nature. The first approach allows you to control environmental conditions, distinguishing from the countless number of real life

Natural selection I do not see the limit of the activity of this force, slowly and perfectly adapting each form to the most complex life relationships. C. Darwin Wasps, Butterflies, and Darwinism In previous chapters, we talked about natural selection. This and

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Natural selection - to be stronger than its animal nature It is especially important for us that it is the commandant who makes the body follow instincts by his strength. (Don't miss this moment!) That is, it is the commandant (his power) that determines the animal nature in the body. And in terms of physics

From Wikipedia, the free encyclopedia

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

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

Natural selection mechanism

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

1. Organisms produce more offspring than they can survive;
2. In the population of these organisms, there is hereditary variability;
3. Organisms with different genetic traits have different survival and reproductive capacity.

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

Natural selection for traits that can vary over a range of values ​​(for example, body size) 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 extreme values ​​of the trait and against average values, for example, large and small body sizes;
3. Stabilizing selection- selection against the extreme values ​​of the feature, which leads to a decrease in the variance of the feature.

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 mates. Traits that have evolved through sexual selection are especially noticeable in males of some animal species. Traits such 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 act simultaneously at different levels. Selection at levels higher than individual selection, 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 forms of selection on the variability of a trait in a population is widely used.

Driving selection

Driving selection- a form of natural selection that acts when 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 benefits. At the same time, other variations of the trait (its deviations in the opposite direction from the mean value) are subject to negative selection. As a result, in the population, from generation to generation, the average value of the trait shifts 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, the pressure of the environment can lead to extinction).

An example of the action of motive selection is "industrial melanism" in insects. "Industrial melanism" is a dramatic increase in the proportion of melanistic (dark colored) individuals in insect populations (such as butterflies) that inhabit industrial areas. Due to industrial impact, tree trunks darkened significantly, and light lichens also died, due to which light butterflies became better 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 butterfly ( morfa carbonaria) was captured in 1848.

Driving selection is carried out when the environment changes or adapts to new conditions when the area expands. It preserves hereditary changes in a certain direction, moving the reaction rate accordingly. For example, during the development of soil as a habitat in 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 effect 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 the maximum fecundity. 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 fertility are the most adapted.

Selection in favor of mean values ​​was found for a variety of features. In mammals, very low and very high birth weights are more likely to die at birth or in the first weeks of life than medium-weight newborns. Taking into account the size of the wings of the 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 (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 the trait. As a result, several new forms may appear from one initial 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 sub-niches.

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

Disruptive selection was carried out artificially in experiments with fruit flies. The selection was carried out according to the number of bristles; only individuals with a small or large number of bristles were left. 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, carrying out the exchange of genes. In a number of other experiments (with plants), intensive crossing interfered with the effective action of disruptive selection.

Sexual selection

Sexual selection is natural selection for breeding success. The survival of organisms is an important, but not the only, component of natural selection. Another important component is attraction 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 relations between organic beings among themselves or with external conditions, but by the rivalry between individuals of the same sex, usually males, for the possession of individuals of the other sex." Traits that reduce the viability of their carriers can arise and spread if the benefits they provide in breeding success are significantly greater than their disadvantages for survival.

There are two popular hypotheses about the mechanisms of sexual selection.

• According to the “good genes” hypothesis, the female “reasoned” as follows: “If a given male, despite his bright plumage and long tail, managed not to die in the paws 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 brightly colored genes and will be attractive to females in the next generation. Thus, a positive feedback arises, which leads to the fact that from generation to generation, the brightness of the plumage of males is increasing 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. Likewise, females, choosing bright males, follow their instincts - they like bright tails. Those who were prompted by instinct to behave differently 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 the amazing variety of forms, colors and instincts that we observe in the world of living nature.

Breeding 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 the population that have useful traits that increase the viability of the species as a whole.

Cut-off selection rejects from the population the vast majority of individuals carrying traits that sharply reduce their viability under given environmental conditions. Cut-off selection removes highly deleterious alleles from the population. Individuals with chromosomal rearrangements and a set of chromosomes that sharply disrupt the normal functioning of the genetic apparatus can also undergo cutoff selection.

The role of natural selection in evolution

Taking the worker ant as an example, we have an insect that is extremely different from its parents, nevertheless, it is absolutely sterile and, therefore, cannot transmit from generation to generation the acquired modifications of structure or instincts. A good question may be asked - how much is it possible to reconcile this case with the theory of natural selection?

- Origin of Species (1859)

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

see also

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Notes (edit)

1. , With. 43-47.
2. , p. 251-252.
3. Orr HA// Nat Rev Genet. - 2009. - Vol. 10 (8). - P. 531-539.
4. Haldane j// Nature. - 1959. - Vol. 183. - P. 710-713.
5. Lande R, Arnold SJ The measurement of selection on correlated characters // Evolution. - 1983. - Vol. 37. - P. 1210–26. - DOI: 10.2307 / 2408842.
6. .
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8. Andersson M, Simmons L// Trends Ecol Evol. - 2001. - Vol. 21 (6). - P. 296-302.
9. Kokko H, Brooks R, McNamara J, Houston A// Proc Biol Sci. - 2002. - Vol. 269. - P. 1331-1340.
10. Hunt J, Brooks R, Jennions MD, Smith MJ, Bentsen CL, Bussière LF// Nature. - 2004. - Vol. 432. - P. 1024-1027.
11. Okasha, S. Evolution and the Levels of Selection. - Oxford University Press, 2007 .-- 263 p. - ISBN 0-19-926797-9.
12. Mayr e// Philos. Trans. R. Soc. Lond., B, Biol. Sci. - 1998 .-- T. 353. - S. 307-14.
13. Maynard smith j// Novartis Found. Symp. - 1998 .-- T. 213. - S. 211–217.
14. Gould SJ, Lloyd EA// Proc. Natl. Acad. Sci. U.S.A. - 1999. - T. 96, No. 21. - S. 11904-11909.

Literature

• Lua error: attempt to index local "entity" (a nil value).

Links

• - article with well-known examples: butterfly color, human resistance to malaria, etc.
• - Chapter 4, Natural Selection
• - Modeling for Understanding in Science Education, University of Wisconsin
• from University of Berkeley education website
• Evolution: Education and Outreach

Excerpt from Natural Selection

At four o'clock in the afternoon, Murat's troops entered Moscow. A detachment of Virtemberg hussars rode in front, behind on horseback, with a large retinue, rode the Neapolitan king himself.
Near the middle of the Arbat, near Nikola the Yavlenniy, Murat stopped, awaiting news from the advance detachment about the situation in the city fortress "le Kremlin".
A small group of people from the residents who remained in Moscow gathered around Murat. Everyone looked with timid bewilderment at the strange, long-haired boss, adorned with feathers and gold.
- Well, is it himself, or what, the king of theirs? Nothing! - quiet voices were heard.
The translator drove up to a handful of people.
“Take off your hat ... then take off your hat,” they started talking in the crowd, addressing each other. The translator turned to an old janitor and asked how far it was to the Kremlin? The janitor, listening with bewilderment to the Polish accent alien to him and not recognizing the sounds of the translator's dialect as Russian, did not understand what was being said to him and hid behind others.
Murat moved up to the translator and told him to ask where the Russian troops were. One of the Russian people understood what was being asked of him, and several voices suddenly began to answer the translator. A French officer from the forward detachment drove up to Murat and reported that the gates to the fortress were sealed up and that there was probably an ambush there.
“All right,” said Murat, and, turning to one of the gentlemen of his retinue, ordered to put forward four light guns and fire at the gate.
The artillery trotted out from behind the column following Murat and drove along the Arbat. Having gone down to the end of Vzdvizhenka, the artillery stopped and lined up on the square. Several French officers were in charge of the cannons, positioning them, and looking into the Kremlin through the telescope.
The bells rang in the Kremlin for Vespers, and this ringing confused the French. They assumed it was a call to arms. Several infantry soldiers ran to the Kutafyevsky gate. At the gate lay logs and boards. Two rifle shots rang out from under the gate as soon as the officer and his team began to run up to them. The general, who was standing at the cannons, shouted command words to the officer, and the officer with the soldiers ran back.
Three more shots were heard from the gate.
One shot struck a French soldier in the leg, and the strange cry of a few voices was heard from behind the shields. On the faces of the French general, officers and soldiers at the same time, as if on command, the former expression of gaiety and calm was replaced by a stubborn, concentrated expression of readiness for struggle and suffering. For all of them, from the marshal to the last soldier, this place was not Vzdvizhenka, Mokhovaya, Kutafya and Trinity Gates, but this was a new area of ​​a new field, probably a bloody battle. And everyone prepared for this battle. The screams from the gate died away. The guns were extended. The artillerymen blew off the burnt-out blazers. The officer commanded "feu!" [fell!], and the two whistling sounds of the cans rang out one after the other. Card bullets crackled against the stone of the gate, logs and shields; and two clouds of smoke wavered in the square.
A few moments after the rolling of shots at the stone Kremlin died down, a strange sound was heard over the heads of the French. A huge flock of jackdaws rose above the walls and, croaking and rustling with thousands of wings, whirled in the air. Together with this sound, a lonely human scream was heard at the gate, and from behind the smoke a figure of a man without a hat, in a caftan, appeared. Holding the gun, he aimed at the French. Feu! - repeated the artillery officer, and at the same time one rifle and two cannon shots rang out. The smoke closed the gate again.
Nothing more moved behind the shields, and the French infantry soldiers and officers went to the gate. At the gate lay three wounded and four killed people. Two men in caftans ran down the bottom, along the walls, towards Znamenka.
- Enlevez moi ca, [Take it away,] - said the officer, pointing to the logs and corpses; and the French, finishing off the wounded, threw the corpses down the fence. Who these people were, no one knew. “Enlevez moi ca” is only said about them, and they were thrown out and cleaned up later so that they would not stink. Thiers alone dedicated several eloquent lines to their memory: "Ces miserables avaient envahi la citadelle sacree, s" etaient empares des fusils de l "arsenal, et tiraient (ces miserables) sur les Francais. On en sabra quelques "uns et on purgea le Kremlin de leur presence. [These unfortunates filled the sacred fortress, took possession of the arsenal's guns and fired at the French. Some of them were chopped down with sabers and cleared the Kremlin of their presence.]
Murat was informed that the path was clear. The French entered the gate and began to camp on Senate Square. The soldiers threw chairs from the windows of the Senate onto the square and laid out the lights.
Other detachments passed through the Kremlin and were stationed along Maroseyka, Lubyanka, Pokrovka. Still others were located at Vzdvizhenka, Znamenka, Nikolskaya, Tverskaya. Everywhere, not finding owners, the French were accommodated not as in the city in apartments, but as in the camp, which is located in the city.
Although ragged, hungry, exhausted and reduced to 1/3 of their former number, the French soldiers entered Moscow in orderly order. It was an exhausted, exhausted, but still fighting and formidable army. But this was an army only until the moment when the soldiers of this army dispersed to their apartments. As soon as the people of the regiments began to disperse to empty and rich houses, the army was destroyed forever and not residents or soldiers were formed, but something in between, called marauders. When, five weeks later, the same people left Moscow, they no longer constituted an army. It was a crowd of marauders, each of whom was carrying or carrying with him a bunch of things that he thought were valuable and needed. The goal of each of these people when leaving Moscow was not, as before, to conquer, but only to retain what they had acquired. Like that monkey who, having thrust his hand into the narrow throat of a jug and grabbing a handful of nuts, does not unclench his fist so as not to lose the grabbed one, and this ruins himself, the French, when leaving Moscow, obviously had to die due to the fact that they were dragging with the loot, but it was just as impossible for a monkey to unclench a handful of nuts to throw this loot away. Ten minutes after the entry of each French regiment into some quarter of Moscow, not a single soldier or officer remained. In the windows of the houses people could be seen in greatcoats and boots, laughing, walking about the rooms; in the cellars, in the basements, the same people took care of the provisions; in the courtyards the same people opened or beat off the gates of sheds and stables; fires were laid out in the kitchens, baked with rolled-up hands, kneaded and boiled, frightened, amused and caressed women and children. And there were many of these people everywhere, in the shops and in their homes; but the troops were gone.
On the same day, order after order was given by the French commanders to prohibit the troops from leaving the city, to strictly prohibit the violence of the inhabitants and looting, and to make a general roll call that evening; but in spite of any measures. the people who had previously constituted the army were spreading across the empty city, abundant in amenities and supplies. As a hungry herd goes in a heap across a bare field, but immediately scatters irresistibly as soon as it attacks rich pastures, so the army scattered irresistibly throughout the rich city.
There were no inhabitants in Moscow, and the soldiers, like water in sand, were sucked into it and spread like an irresistible star in all directions from the Kremlin, into which they entered first. The cavalry soldiers, entering the merchant's house that had been left with all their good, and finding stalls not only for their horses, but also extra ones, nevertheless went alongside to occupy another house, which seemed to them better. Many occupied several houses, inscribing in chalk who he was doing, and argued and even fought with other teams. Not having time to fit yet, the soldiers fled into the street to inspect the city and, according to the rumor that everything had been abandoned, rushed to where it was possible to take valuable things for free. The chiefs went to stop the soldiers and themselves were involuntarily involved in the same actions. In Karetny Row there were still shops with carriages, and the generals crowded there, choosing carriages and carriages for themselves. The remaining residents invited the chiefs to their place, hoping to secure themselves from robbery. The riches were an abyss, and there was no end in sight; everywhere, around the place occupied by the French, there were still unexplored, unoccupied places, in which, as it seemed to the French, there was even more wealth. And Moscow sucked them further and further into itself. Just as water and dry land disappear due to the pouring of water on dry land; in the same way, due to the fact that the hungry army entered the plentiful, empty city, the army was destroyed, and the plentiful city was destroyed; and there was dirt, there were fires and looting.

The French attributed the Moscow fire to au patriotisme feroce de Rastopchine [to the wild patriotism of Rostopchin]; Russians - to the fanaticism of the French. In essence, the reasons for the fire in Moscow in the sense of attributing this fire to the responsibility of one or several persons, there were no such reasons and could not have been. Moscow burned down due to the fact that it was placed in such conditions under which every wooden city must burn down, regardless of whether or not there are one hundred and thirty bad fire pipes in the city. Moscow should have burnt down due to the fact that residents left it, and just as inevitably as a heap of shavings should catch fire, on which sparks of fire would fall for several days. The wooden city, in which fires occur almost every day in the summer with the residents of the house owners and the police, cannot help but burn when there are no residents in it, and troops live, smoking pipes, making fires on Senate Square from Senate chairs and making themselves two once a day. In peacetime, the troops should settle in apartments in villages in a certain area, and the number of fires in this area immediately increases. To what extent should the likelihood of fires increase in an empty wooden city in which a foreign army will be located? Le patriotisme feroce de Rastopchine and the fanaticism of the French are in no way to blame. Moscow caught fire from pipes, from kitchens, from bonfires, from the slovenliness of enemy soldiers, residents - not the owners of houses. If there were arson (which is highly doubtful, because there was no reason for anyone to set fire, and, in any case, it was troublesome and dangerous), then the arson cannot be taken for the reason, since without arson it would have been the same.
No matter how flattering it was for the French to accuse the atrocities of Rostopchin and the Russians to accuse the villain of Bonaparte or then to put a heroic torch in the hands of their people, one cannot help but see that such an immediate cause of the fire could not have been, because Moscow had to burn down, as every village and factory must burn down. , every house from which the owners come out and into which they will be allowed to manage and cook their own porridge of strangers. Moscow was burnt by residents, it's true; but not by those inhabitants who remained in it, but by those who left it. Moscow, occupied by the enemy, did not remain intact, like Berlin, Vienna and other cities, only due to the fact that its inhabitants did not bring bread, salt and keys to the French, but left it.

The sucking in of the French, which spread like a star across Moscow, on the day of September 2, reached the quarter in which Pierre now lived, only in the evening.
Pierre was after the last two solitary and unusually spent days in a state close to madness. One persistent thought took possession of his whole being. He himself did not know how and when, but this thought took possession of him now so that he did not remember anything from the past, did not understand anything from the present; and everything that he saw and heard happened in front of him as in a dream.
Pierre left his home only to get rid of the complex confusion of the requirements of life that gripped him, and which he, in the then state, but was able to unravel. He went to Iosif Alekseevich's apartment under the pretext of sorting out the books and papers of the deceased only because he was looking for reassurance from life's anxiety - and the memory of Joseph Alekseevich connected in his soul the world of eternal, calm and solemn thoughts, completely opposite to the alarming confusion in which he felt sucked in. He sought a quiet refuge and actually found it in the office of Joseph Alekseevich. When he, in the dead silence of the office, sat, leaning on his hands, over the dusty writing-table of the deceased, in his imagination calmly and significantly, one after another, the memories of the last days, especially the Battle of Borodino and that indefinable for him feeling of his insignificance, began to appear. falsity in comparison with the truth, simplicity and strength of the category of people who are imprinted in his soul under the name they. When Gerasim woke him up from his reverie, Pierre got the idea that he would take part in the supposed - as he knew - the people's defense of Moscow. And for this purpose, he immediately asked Gerasim to get him a caftan and a pistol and announced to him his intention, hiding his name, to stay in the house of Joseph Alekseevich. Then, during the first solitary and idle day spent (Pierre several times tried and could not stop his attention on the Masonic manuscripts), several times he vaguely imagined the idea of ​​the cabalistic meaning of his name in connection with the name of Bonaparte; but this thought that he, l "Russe Besuhof, was destined to put an end to the power of the beast, came to him only as one of the dreams that run through the imagination without reason and without a trace.
When, having bought a caftan (with the aim of only participating in the people's defense of Moscow), Pierre met the Rostovs and Natasha said to him: “Are you staying? Oh, how good it is! " - the thought flashed through his head that it would be really good, even if they took Moscow, he would stay in it and fulfill what was predetermined for him.
The next day, with the only thought not to feel sorry for himself and not to lag behind them in anything, he went with the people to the Trekhgornaya Zastava. But when he returned home, convinced that Moscow would not be defended, he suddenly felt that what had previously seemed to him only a possibility had now become a necessity and an inevitability. He had to, hiding his name, stay in Moscow, meet Napoleon and kill him in order to either perish or end the misfortune of all of Europe, which, in Pierre's opinion, stemmed from Napoleon alone.
Pierre knew all the details of the attempt on the life of a German student on Bonaparte's life in Vienna in 1809 and knew that this student had been shot. And the danger to which he exposed his life in the fulfillment of his intention, even more aroused him.
Two equally strong feelings attracted Pierre irresistibly to his intention. The first was the feeling of the need for sacrifice and suffering with the consciousness of general misfortune, that feeling, as a result of which he went to Mozhaisk on the 25th and drove into the heat of the battle, now ran away from his home and, instead of the usual luxury and comforts of life, slept without undressing on a hard sofa and ate the same meal with Gerasim; the other was that vague, exclusively Russian feeling of contempt for everything conventional, artificial, human, for everything that is considered by most people to be the highest blessing of the world. For the first time Pierre experienced this strange and charming feeling in the Sloboda Palace, when he suddenly felt that wealth, power, and life, everything that people arrange and cherish with such diligence - all this, if it is worth anything, then only by the pleasure with which all this can be thrown.
It was that feeling, as a result of which a hunter-recruit was drinking the last penny, a drunken man smashing mirrors and glass for no apparent reason and knowing that it would cost him his last money; that feeling, as a result of which a person, committing (in a vulgar sense) crazy deeds, as it were, tries his personal power and strength, declaring the presence of a higher, standing outside human conditions, judgment over life.
From the very day when Pierre first experienced this feeling in the Sloboda Palace, he was incessantly under his influence, but now he only found him complete satisfaction. In addition, at the present moment Pierre was supported in his intention and made it impossible to renounce him by what he had already done along the way. And his escape from home, and his caftan, and his pistol, and his statement by Rostov that he remains in Moscow - everything would lose not only meaning, but all this would be contemptible and ridiculous (to which Pierre was sensitive), if After all this, he, like the others, left Moscow.

NATURAL SELECTION, the process of selective survival and differential reproduction of organisms, the main driving factor of their evolution. The ideas about the existence of natural selection have been expressed since the beginning of the 19th century by various English naturalists (including A. Wallace). But only Charles Darwin (1842, 1859) estimated it as the main factor of evolution. For Darwin, natural selection is the result of the struggle for existence; even insignificant inherited differences between individuals of the same species can give advantages in this struggle, which is due to the tendency of organisms to a high intensity of reproduction (in geometric progression) and the impossibility of preserving all offspring due to limited natural resources. The death of the overwhelming number of individuals in each generation inevitably leads to natural selection - the "survival of the fittest" to the given conditions. As a result of the summation of beneficial changes over many generations, new adaptations are formed and, ultimately, new species arise. Darwin based his reasoning about the action of natural selection mainly on the generalization of the experience of domestication of animals and plants by analogy with artificial selection, emphasizing, however, that, unlike human selection, natural selection is determined by the interaction of organisms with environmental conditions and has no specific purpose.

A systematic study of natural selection, expansion and improvement of methods of its study began in the late 19th century. The use of biometric methods made it possible to establish statistically significant differences between surviving and dead organisms under changing environmental conditions. Thanks to the developments of R. Fisher, J. Haldane, S. Wright and S. S. Chetverikov, who synthesized classical Darwinism and genetics, it became possible to begin an experimental study of the genetic foundations of natural selection. The examined natural populations were literally saturated with mutations, many of which became useful when the conditions of existence changed or when combined with other mutations. It was found that the mutational process and free crossing (panmixia) provide the genetic diversity of populations and the uniqueness of individuals with different chances of survival; this determines the high intensity and efficiency of natural selection. In addition, it became obvious that natural selection deals not with single traits, but with whole organisms, and that the genetic essence of natural selection consists in the non-random (differentiated) preservation of certain genotypes in the population, which are selectively transmitted to future generations. Natural selection is probabilistic in nature, acts on the basis of the mutational process and the existing gene pool, affects the frequency of propagation of genes and their combinations, helps to reduce the negative effect of mutations and the formation of defense mechanisms against their harmful effects, thereby determining the pace and direction of evolution. Under the control of natural selection are not only various characteristics, but also the factors of evolution, for example, the intensity and nature of mutability, the apparatus of heredity (hence the concept of "evolution of evolution"). In the absence of natural selection, there is a decrease or loss of the fitness of organisms due to the accumulation of unwanted mutations, which manifests itself in an increase in genetic burden, including in populations of modern humans.

There are more than 30 forms of natural selection; none of them exists in a pure form, but rather characterizes the tendency of selection in a particular ecological situation. Thus, motive selection contributes to the preservation of a certain deviation from the previous norm and leads to the development of new adaptations through the directed restructuring of the entire gene pool of populations, as well as the genotypes and phenotypes of individuals. It can lead to the dominance of one (or several) pre-existing forms over others. A classic example of its action was the predominance in industrial areas of dark-colored forms of the birch moth, invisible to birds on tree trunks contaminated with soot (until the middle of the 19th century, only a light form was found, imitating lichen spots on light birch trunks). Rapid addiction to the poisons of various species of insects and rodents, the emergence of resistance of microorganisms to antibiotics indicate that the pressure of driving selection in natural populations is sufficient to provide a quick adaptive response to abrupt changes in the environment. As a rule, selection for one trait entails a number of transformations. For example, a long-term selection for protein or oil content in corn kernels is accompanied by changes in the shape of the kernels, the size of the ears, their location above the soil level, etc.

The result of the action of driving selection in the phylogenesis of large taxa is orthoselection, an example of which is the directed evolution of the limb of the horse's ancestors (from five-toed to one-fingered) established by V.O.

Disruptive, or disruptive, selection favors the persistence of extreme deviations and leads to an increase in polymorphism. It manifests itself in those cases when none of the intraspecific forms with different genotypes receives an absolute advantage in the struggle for existence due to the variety of conditions simultaneously encountered in the same territory; in this case, first of all, individuals with an average or intermediate character of traits are eliminated. At the beginning of the 20th century, the Russian botanist N.V. Tsinger showed that the large rattle (Alectoroleophus major), flowering and bearing fruit on unmown meadows throughout the summer, forms two races on mown meadows: early spring, which has time to bring seeds before the mowing begins, and late autumn - low plants that are not damaged by mowing, and then bloom quickly and have time to give seeds before the frost begins. Another example of polymorphism is the difference in the color of shells in the earthen snail (Capacea nemoralis), which is food for birds: in dense beech forests, where a litter of red-brown litter is preserved throughout the year, individuals with brown and pink coloration are common; in meadows with yellow litter, snails with a yellow color predominate. In mixed deciduous forests, where the nature of the background changes with the onset of a new season, snails with brown and pink colors dominate in early spring, and yellow in summer. Darwin's finches (Geospizinae) on the Galapagos Islands (a classic example of adaptive radiation) are the end result of long-term disruptive selection, which led to the formation of dozens of closely related species.

If these forms of natural selection lead to a change in both the phenotypic and genetic structure of populations, then stabilizing selection, first described by I.I.Shmal'gauzen (1938), preserves the average value of traits (norm) in the population and does not let the genomes of individuals most deviating from this norm. It is aimed at maintaining and increasing resistance in the population of an average, previously developed phenotype. It is known, for example, that during snowstorms birds survive, which in many ways (wing length, beak, body weight, etc.) approach the average norm, and individuals deviating from this norm die. The size and shape of flowers in plants pollinated by insects are more stable than in plants pollinated by the wind, which is due to the coupled evolution of plants and their pollinators, "culling" of deviated forms (for example, a bumblebee cannot penetrate into a too narrow corolla of a flower, and the proboscis of a butterfly does not touch too short stamens in plants with a long corolla). Due to stabilizing selection, with an external unchanged phenotype, significant genetic changes can occur, ensuring the independence of the development of adaptations from fluctuating environmental conditions. One of the results of the action of stabilizing selection can be considered the "biochemical universality" of life on Earth.

Destabilizing selection (the name was proposed by D.K.Belyaev, 1970) leads to a sharp disruption of the systems of regulation of ontogenesis, the opening of the mobilization reserve and an increase in phenotypic variability with intensive selection in any particular direction. For example, selection to reduce the aggressiveness of predatory animals in captivity through restructuring of the neurohumoral system leads to destabilization of the breeding cycle, shifts in molting times, changes in the position of the tail, ears, color, etc.

Genes have been found that can be lethal or reduce the viability of organisms in a homozygous state, and in a heterozygous state, on the contrary, increase ecological plasticity and other indicators. In this case, we can talk about the so-called balanced selection, which ensures the maintenance of genetic diversity with a certain ratio of allele frequencies. An example of its action can serve as an increase in resistance in patients with sickle cell anemia (heterozygous for the hemoglobin S gene) to infection with various strains of malaria plasmodium (see Hemoglobins).

An important step in overcoming the tendency to explain all the characteristics of organisms by the action of natural selection was the concept of neutral evolution, according to which part of the changes at the level of proteins and nucleic acids occurs by fixing adaptively neutral or almost neutral mutations. It is possible to select species that arise in peripheral populations "suddenly" from a geochronological point of view. Even earlier, it was proved that catastrophic selection, in which a small number of individuals and even a single organism survive during a period of abrupt changes in the environment, can become the basis for the formation of a new species due to chromosomal rearrangement and a change in the ecological niche. For example, the formation of the xerophytic, endemic species Clarkia lingulata in the Sierra Nevada mountains in California is explained by a severe drought that caused massive plant death, which became catastrophic in peripheral populations.

Natural selection affecting the secondary sexual characteristics of individuals is called sexual (for example, the bright mating coloration of males in many species of fish and birds, inviting calls, specific smells, highly developed instruments for tournament combat in mammals). These traits are useful because they increase the ability of their carriers to participate in the reproduction of offspring. In sexual selection, males are most active, which is beneficial for the species as a whole, because females remain safer during the breeding season.

Group selection is also distinguished, which contributes to the preservation of traits useful to the family, flock, colony. Its special case in colonial insects is the selection of congeners, in which sterile castes (workers, soldiers, etc.) ensure (often at the cost of their own lives) the survival of fertile individuals (queens) and larvae, and thus the preservation of the entire colony. The altruistic behavior of parents pretending to be injured in order to take the predator away from their children threatens the death of the imitator, but in general increases the chances of survival of his offspring.

Although the concept of the leading role of natural selection in evolution has been confirmed in many experiments, they are still criticized based on the idea that organisms cannot be formed as a result of a random combination of mutations. At the same time, the fact is ignored that each act of natural selection is performed on the basis of the previous results of its own actions, which, in turn, predetermine the forms, intensity and directions of natural selection, and therefore the paths and laws of evolution.

Lit .: Shmalgauzen I.I.Factors of evolution. 2nd ed. M., 1968; Mayr E. Zoological species and evolution. M., 1968; Sheppard F.M. Natural selection and heredity. M., 1970; Levontin R. Genetic foundations of evolution. M., 1978; Wilson D. S. The natural selection of populations and communities. Menlo Park, 1980; Gall Ya.M. Research on natural selection // Development of evolutionary theory in the USSR. L., 1983; Gauze GF Ecology and some problems of the origin of species // Ecology and evolutionary theory. L., 1984; Ratner V.A.A short outline of the theory of molecular evolution. Novosib., 1992; Dawkins R. Selfish General M., 1993; Sober E. The nature of selection: evolutionary theory in philosophical focus. Chi., 1993; Darwin Ch. The Origin of Species ... 2nd ed. SPb., 2001; Coyne J., Orr H. A. Speciation. Sunderland, 2004; Gavrilets S. Fitness landscapes and the origin of species. Princeton, 2004; Yablokov A.V., Yusufov A.G. Evolutionary doctrine. 5th ed. M., 2004; Severtsov A.S.The theory of evolution. M., 2005; Kolchinsky E. I. E. Mayr and modern evolutionary synthesis. M., 2006.

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

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

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

Natural selection mechanism

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

Organisms produce more offspring than they can survive;

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

Organisms with different genetic traits have different survival and reproductive capacity.

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

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

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

Natural selection for traits that can vary over a range of values ​​(for example, body size) can be divided into three types:

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

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

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

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 mates. Traits that have evolved through sexual selection are especially noticeable in males of some animal species. Traits such 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 act simultaneously at different levels. Selection at levels above the individual, such as group selection, can lead to cooperation.

Forms of natural selection

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

Driving selection- a form of natural selection that acts when 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 benefits. At the same time, other variations of the trait (its deviations in the opposite direction from the mean value) are subject to negative selection. As a result, in the population, from generation to generation, the average value of the trait shifts 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, the pressure of the environment can lead to extinction).

A classic example of driving selection is the color evolution of the birch moth. The color of the wings of this butterfly mimics the color of the lichen-covered bark of the trees on which it spends the day. Obviously, such a patronizing coloration was formed over many generations of previous evolution. However, with the beginning of the Industrial Revolution in England, this adaptation began to lose its significance. Air pollution has led to the mass death of lichens and darkening of tree trunks. Light-colored butterflies against a dark background became easily visible to birds. Beginning in the middle of the 19th century, mutant dark (melanistic) forms of butterflies began to appear in the populations of the birch moth. Their frequency increased rapidly. By the end of the 19th century, some urban populations of the birch moth consisted almost entirely of dark forms, while in rural populations, light forms predominated. This phenomenon was named industrial melanism. Scientists have found that in polluted areas, birds are more likely to eat light forms, and in clean ones - dark ones. The introduction of restrictions on air pollution in the 1950s caused natural selection to reverse direction again, and the frequency of dark forms in urban populations began to decline. They are almost as rare today as they were before the industrial revolution.

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

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

Many examples of the effect 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 the maximum fecundity. 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 fertility are the most adapted.

Selection in favor of mean values ​​was found for a variety of features. In mammals, very low and very high birth weights are more likely to die at birth or in the first weeks of life than medium-weight newborns. Taking into account the size of the wings of the 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 most adapted were the average individuals.

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

Stabilizing selection is a mechanism for the accumulation of variability in natural populations. The eminent scientist I.I.Shmalgauzen was the first to draw attention to this feature of stabilizing selection. He showed that even in stable conditions of existence, neither natural selection nor evolution stops. Even remaining phenotypically unchanged, the population does not stop evolving. Its genetic makeup is constantly changing. Stabilizing selection creates genetic systems that ensure the formation of similar optimal phenotypes based on a wide variety of genotypes. Genetic mechanisms such as dominance, epistasis, complementary gene action, incomplete penetrance and other means of concealing genetic variation owe their existence to stabilizing selection.

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

Disruptive (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 the trait. As a result, several new forms may appear from one initial 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 sub-niches.

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

Disruptive selection was carried out artificially in experiments with fruit flies. The selection was carried out according to the number of bristles; only individuals with a small or large number of bristles were left. 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, carrying out the exchange of genes. In a number of other experiments (with plants), intensive crossing interfered with the effective action of disruptive selection.

Sexual selection is natural selection for breeding success. The survival of organisms is an important, but not the only, component of natural selection. Another critical component is attraction 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 relations between organic beings among themselves or with external conditions, but by the rivalry between individuals of the same sex, usually males, for the possession of individuals of the other sex." Traits that reduce the viability of their carriers can arise and spread if the benefits they provide in breeding success are significantly greater than their disadvantages for survival.

There are two common hypotheses about the mechanisms of sexual selection.

According to the hypothesis of "good genes", the female "reasons" as follows: genes that allowed him to 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 brightly colored genes and will be attractive to females in the next generation. Thus, a positive feedback arises, 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.

In the choice of males, females are no more and no less logical than in all the rest of 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. Likewise, females, choosing bright males, follow their instincts - they like bright tails. All those who were prompted by instinct to behave differently, they all left no offspring. Thus, we discussed not the logic of females, but the logic of the struggle for existence and natural selection - a blind and automatic process that, acting constantly from generation to generation, formed all the amazing variety of forms, colors and instincts that we observe in the world of wildlife. ...

Positive and negative selection

There are two forms of natural selection: Positive and Cut-off (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 rejects from the population the vast majority of individuals carrying traits that sharply reduce their viability under given environmental conditions. Cut-off selection removes highly deleterious alleles from the population. Individuals with chromosomal rearrangements and a set of chromosomes that sharply disrupt the normal functioning of the genetic apparatus can also undergo cutoff 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 for the emergence of species and superspecific 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, led some researchers to deny the importance of natural selection, and, as an alternative, proposed concepts based on the assessment of the factor of genotype mutation as extremely important. The authors of such theories postulated not a gradual, but a very rapid (over several generations) spasmodic nature of evolution (Hugo de Vries' mutationism, Richard Goldschmitt's saltationism, and other less well-known concepts). The discovery of the known correlations among the characters of related species (the law of homologous series) by NI Vavilov prompted some researchers to formulate the next "anti-Darwinian" hypotheses about evolution, such as nomogenesis, batmogenesis, autogenesis, ontogenesis and others. In the 1920s and 1940s, in evolutionary biology, those who rejected Darwin's idea of ​​evolution by natural selection (sometimes called “selectionist” theories that emphasized natural selection) revived interest in this theory due to the revision of classical Darwinism in the light of relatively young science of genetics. The resulting synthetic theory of evolution, often incorrectly called neo-Darwinism, also relies on quantitative analysis of allele frequencies in populations that change under the influence of natural selection. There is controversy, where people with a radical approach, as an argument against the synthetic theory of evolution and the role of natural selection, argue that “Discoveries of recent decades in various fields of scientific knowledge - from molecular biology with her theory of neutral mutationsMotoo Kimura and paleontology with her theory of intermittent equilibrium Stephen Jay Gould and Niles Eldridge (wherein view is understood as a relatively static phase of the evolutionary process) to mathematics with her theorybifurcations and phase transitions- testify to the inadequacy of the classical synthetic theory of evolution for an adequate description of all aspects of biological evolution "... The discussion about the role of various factors in evolution began more than 30 years ago and continues to this day, and sometimes it is said that "evolutionary biology (meaning by this the theory of evolution, of course) has come to the need for its next, third synthesis."

Natural selection is a natural process in which, of all living organisms, only those that have qualities that contribute to the successful reproduction of their own kind are preserved in time. According to the synthetic theory of evolution, natural selection is one of the most important factors in evolution.

The idea that a mechanism similar to artificial selection operates in living nature was first expressed by English scientists Charles Darwin and Alfred Wallace. The essence of their idea is that for the appearance of successful creatures, nature does not at all need to understand and analyze the situation, but it is possible to act at random. It is enough to create a wide range of diverse individuals - and, ultimately, the fittest will survive.

1. First, an individual appears with new, completely random, properties

2. Then she turns out or is not able to leave offspring, depending on these properties

3. Finally, if the outcome of the previous stage is positive, then she leaves offspring and her descendants inherit the newly acquired properties

At present, the partly naive views of Darwin himself have been partially revised. So, Darwin imagined that changes should occur very smoothly, and the spectrum of variability is continuous. Today, however, the mechanisms of natural selection are explained with the help of genetics, which brings some originality to this picture. Mutations in genes that work in the first step of the process described above are essentially discrete. It is clear, however, that the basic essence of Darwin's idea has remained unchanged.

Forms of natural selection

Driving selection- a form of natural selection, when environmental conditions contribute to a certain direction of change of any trait or group of traits. In this case, other possibilities of changing the trait are subject to negative selection. As a result, in the population, from generation to generation, the average value of the trait shifts 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, the pressure of the environment can lead to extinction).

A modern case of motive selection is the "industrial melanism of English butterflies." "Industrial melanism" is a sharp increase in the proportion of melanistic (dark-colored) individuals in those populations of butterflies that live in industrial areas. Due to industrial impact, tree trunks darkened significantly, and light lichens also died, due to which light butterflies became better visible to birds, and dark ones - worse. In the 20th century, in a number of areas, the share of dark-colored butterflies reached 95%, while the first dark butterfly (Morfa carbonaria) was caught in 1848.

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

Stabilizing selection- a form of natural selection, in which the action is directed against individuals with extreme deviations from the average norm, in favor of individuals with an average severity of the trait.

Many examples of the effect 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 the maximum fecundity. 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 fertility are the most adapted.

Selection in favor of mean values ​​was found for a variety of features. In mammals, very low and very high birth weights are more likely to die at birth or in the first weeks of life than medium-weight newborns. Consideration of the size of the wings of birds that died after the storm showed that most of them had too small or too large wings. And in this case, the most adapted were the average individuals.

Disruptive (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 the trait. As a result, several new forms may appear from one initial one. 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 sub-niches.

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

Disruptive selection was carried out artificially in experiments with fruit flies. The selection was carried out according to the number of bristles; only individuals with a small or large number of bristles were left. 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, carrying out the exchange of genes. In a number of other experiments (with plants), intensive crossing interfered with the effective action of disruptive selection.

Shut-off selection- a form of natural selection. Its action is the opposite of positive selection. Cut-off selection rejects from the population the vast majority of individuals carrying traits that sharply reduce their viability under given environmental conditions. Cut-off selection removes highly deleterious alleles from the population. Individuals with chromosomal rearrangements and a set of chromosomes that sharply disrupt the normal functioning of the genetic apparatus can also undergo cutoff selection.

Positive selection- a form of natural selection. Its action is opposite to cutoff 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. With the help of positive selection and cut-off selection, a change in species occurs (and not only through the destruction of unnecessary individuals, then any development should stop, but this does not happen). Examples of positive selection include: a stuffed Archeopteryx can be used as a glider, but a stuffed swallow or gull cannot. But the first birds flew better than Archeopteryx.

Another example of positive selection is the emergence of predators superior in their "mental abilities" to many other warm-blooded animals. Or the emergence of such reptiles as crocodiles, which have a four-chambered heart and are able to live both on land and in water.

Paleontologist Ivan Efremov argued that a person passed not only selection for the best adaptation to environmental conditions, but also “selection for sociality” - those communities survived whose members supported each other better. This is another example of positive selection.

Private areas of natural selection

· Survival of the most adapted species and populations, for example, species with gills in the water, since fitness can win the struggle for survival.

· Survival of physically healthy organisms.

· Survival of the physically strongest organisms, since the physical struggle for resources is an integral part of life. It is important in intraspecific struggle.

· Survival of the most sexually successful organisms, as sexual reproduction is the dominant mode of reproduction. In this case, sexual selection comes into play.

However, all these cases are private, and the main thing is the successful preservation in time. Therefore, sometimes these directions are violated in order to follow the main goal.

C. Darwin believed natural selection to be a fundamental factor in the evolution of living things (selectionism in biology). The accumulation of information on genetics in the late 19th - early 20th centuries, in particular the discovery of the discrete nature of inheritance of phenotypic traits, prompted many researchers to revise this Darwin's thesis: mutations of the genotype began to be considered as extremely important factors of evolution (H. de Vries mutationism, R. Goldschmitt and others). On the other hand, the discovery of known correlations among the traits of related species (the law of homologous series) by N.I. etc.). In the 1920s and 1940s, in evolutionary biology, interest in breeding theories was revived through the synthesis of classical genetics and the theory of natural selection.

The resulting synthetic theory of evolution (STE), often referred to as neo-Darwinism, relies on a quantitative analysis of allele frequencies in populations that change under the influence of natural selection. Nevertheless, the discoveries of recent decades in various fields of scientific knowledge - from molecular biology with her theory of neutral mutations by M. Kimura and paleontology with her theory of discontinuous equilibrium by S. J. Gould and N. Eldridge (in which the species is understood as a relatively static phase of the evolutionary process) to mathematics with its theory of bifurcations and phase transitions - indicate the insufficiency of the classical STE for an adequate description of all aspects of biological evolution. The discussion about the role of various factors in evolution continues today, and evolutionary biology has come to the need for its next, third synthesis.

The emergence of adaptations as a result of natural selection

Adaptations are the properties and characteristics of organisms that provide adaptation to the environment in which these organisms live. Adaptation is also called the process of the emergence of adaptations. Above, we looked at how some adaptations arise as a result of natural selection. The populations of the birch moth have adapted to the changed external conditions due to the accumulation of dark color mutations. In human populations inhabiting malarial regions, adaptation has arisen due to the spread of the sickle cell mutation. In both cases, adaptation is achieved through the action of natural selection.

In this case, the material for selection is the hereditary variability accumulated in the populations. Since different populations differ from each other in the set of accumulated mutations, they adapt to the same environmental factors in different ways. Thus, African populations have adapted to life in malarial regions due to the accumulation of Hb S sickle cell anemia mutations, and in the populations inhabiting Southeast Asia, resistance to malaria has formed on the basis of the accumulation of a number of other mutations that, in a homozygous state, also cause blood diseases. and in the heterozygous, they provide protection against malaria.

These examples illustrate the role of natural selection in shaping adaptations. However, it should be clearly understood that these are special cases of relatively simple adaptations arising from the selective multiplication of carriers of single "useful" mutations. It is unlikely that most adaptations arose this way.

Protective, cautionary and imitative coloration. Consider, for example, such widespread adaptations as patronizing, warning, and imitative coloration (mimicry). The protective coloration allows the animals to become invisible, merging with the substrate. Some insects are strikingly similar to the leaves of the trees on which they live, others resemble dried twigs or thorns on tree trunks. These morphological adaptations are complemented by behavioral adaptations. Insects choose places for shelter where they are less visible.

Inedible insects and poisonous animals - snakes and frogs - have a bright warning color. A predator, once faced with such an animal, associates this type of color with danger for a long time. This is used by some non-poisonous animals. They acquire a striking resemblance to poisonous, and thereby reduce the danger from predators. Already imitates the color of a viper, a fly imitates a bee. This phenomenon is called mimicry.

How did all these amazing devices come about? It is unlikely that a single mutation could provide such an exact match between an insect's wing and a living leaf, between a fly and a bee. It is incredible that a single mutation would cause a patronizingly colored insect to hide on exactly the leaves that it looks like. It is obvious that such adaptations as protective and warning colors and mimicry arose through the gradual selection of all those small deviations in body shape, in the distribution of certain pigments, in innate behavior that existed in the populations of the ancestors of these animals. One of the most important characteristics of natural selection is its cumulativeness - its ability to accumulate and enhance these deviations in a series of generations, adding up changes in individual genes and the systems of organisms controlled by them.

The most interesting and difficult problem is the initial stages of the emergence of adaptations. It is clear what advantages the almost perfect resemblance of a praying mantis to a dry knot gives. But what advantages could his distant ancestor, who only vaguely resembled a twig, have? Are predators so stupid that they can be fooled so easily? No, predators are by no means stupid, and natural selection from generation to generation "teaches" them better and better to recognize the tricks of their prey. Even the perfect resemblance of a modern praying mantis to a knot does not give it a 100% guarantee that no bird will ever notice it. However, its chances of eluding a predator are higher than that of an insect with a less perfect protective coloration. Likewise, his distant ancestor, only a little bit like a bitch, had a slightly higher chance of life than his relative did not look like a bitch at all. Of course, the bird that sits next to him will easily notice him on a clear day. But if the day is foggy, if the bird does not sit nearby, but flies by and decides not to waste time on what may be a praying mantis, or maybe a knot, then a minimal similarity keeps the bearer of this barely noticeable similarity alive. His descendants who will inherit this minimal similarity will be more numerous. Their share in the population will increase. This will make life difficult for the birds. Among them, those who will more accurately recognize camouflaged prey will become more successful. The same principle of the Red Queen comes into play, which we discussed in the paragraph on the struggle for existence. In order to maintain the advantage in the struggle for life, achieved through minimal similarity, the victim species has to change.

Natural selection picks up all those minute changes that enhance the similarity in color and shape with the substrate, the similarity between the edible species and the inedible species that it imitates. It should be borne in mind that different types of predators use different methods of finding prey. Some pay attention to shape, others to color, some have color vision, others do not. Therefore, natural selection automatically enhances, as much as possible, the similarity between the simulator and the model and leads to those amazing adaptations that we observe in nature.

The emergence of complex adaptations

Many adaptations come across as carefully thought out and targeted devices. How could such a complex structure as the human eye have arisen by natural selection of randomly occurring mutations?

Scientists suggest that the evolution of the eye began with small groups of light-sensitive cells on the surface of the body of our very distant ancestors, who lived about 550 million years ago. The ability to distinguish between light and darkness was, of course, useful for them, increased their chances of life in comparison with their completely blind relatives. The accidental curvature of the "visual" surface improved vision, this made it possible to determine the direction to the light source. An eye cup appeared. Newly emerging mutations could lead to narrowing and widening of the optic cup opening. The narrowing gradually improved vision - the light began to pass through a narrow aperture. As you can see, each step increased the fitness of those individuals that changed in the "right" direction. The light-sensitive cells formed the retina. Over time, a lens has formed in the front of the eyeball, which acts as a lens. It appeared, apparently, as a transparent two-layer structure filled with liquid.

Scientists have tried to simulate this process on a computer. They showed that an eye, like the compound eye of a mollusk, could emerge from a layer of photosensitive cells with relatively gentle selection in just 364,000 generations. In other words, animals that change generations every year could have formed a fully developed and optically perfect eye in less than half a million years. This is a very short time for evolution, considering that the average age of a species in molluscs is several million years.

We can find all the supposed stages of evolution of the human eye among living animals. The evolution of the eye followed different paths in different types of animals. Through natural selection, many different forms of the eye have independently emerged, and the human eye is only one of them, and not the most perfect.

If you look closely at the structure of the eye in humans and other vertebrates, you will find a number of strange incongruities. When light enters a person's eye, it passes through the lens and hits the light-sensitive cells of the retina. Light is forced to break through a dense network of capillaries and neurons to reach the photoreceptor layer. Surprisingly, but the nerve endings approach the light-sensitive cells not from behind, but from the front! Moreover, the nerve endings are collected in the optic nerve, which departs from the center of the retina, and thus creates a blind spot. To compensate for the shading of photoreceptors by neurons and capillaries and get rid of the blind spot, our eye constantly moves, sending a series of different projections of the same image to the brain. Our brain performs the most complex operations, adding these images, subtracting shadows, and calculating the real picture. All these difficulties could be avoided if the nerve endings approached the neurons not from the front, but from the back, as, for example, in an octopus.

The very imperfection of the vertebrate eye sheds light on the mechanisms of evolution through natural selection. We have already said more than once that selection always operates "here and now." He sorts out the various options for existing structures, choosing and putting together the best of them: the best here and now, regardless of what these structures may turn into in the distant future. Therefore, the key to explaining both the perfections and imperfections of modern structures must be sought in the past. Scientists believe that all modern vertebrates descended from animals like the lancelet. In the lancelet, light-sensitive neurons are located at the anterior end of the neural tube. In front of them are nerve and pigment cells that cover the photoreceptors from light coming from the front. The lancelet receives light signals coming from the sides of its transparent body. One might think that the common ancestor of the vertebrates had a similar structure to the eye. Then this flat structure began to transform into an optic cup. The front of the neural tube bulged inward, and the neurons in front of the receptor cells were on top of them. The development of the eye in modern vertebrate embryos, in a sense, reproduces the sequence of events that took place in the distant past.

Evolution does not create new structures from scratch; it changes (often unrecognizably changes) old structures so that each stage of these changes is adaptive. Any change should increase the fitness of its carriers, or at least not reduce it. This feature of evolution leads to the steady improvement of various structures. It is also the reason for the imperfection of many adaptations, strange incongruities in the structure of living organisms.

It should be remembered, however, that all adaptations, however perfect they may be, are of a relative nature. It is clear that the development of the ability to fly does not go well with the ability to run fast. Therefore, the birds with the best flying ability are poor runners. On the contrary, ostriches, which are unable to fly, run beautifully. Adjusting to certain conditions can be useless or even harmful when new conditions arise. However, living conditions change constantly and sometimes very dramatically. In these cases, previously accumulated adaptations can hinder the formation of new ones, which can lead to the extinction of large groups of organisms, as happened more than 60-70 million years ago with the once very numerous and diverse dinosaurs.