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Having explained the origin of species on the basis of natural selection as a grandiose and all-encompassing process of successive change of adaptations, Darwin's theory also explained the phenomenon of the purposeful structure of organic forms. The forms of adaptations, as a reflection of expediency, are infinitely diverse: the swim bladder in the body of a fish is filled with air and lightens the mass of its body; it is more convenient to overcome swamps on long legs with widely spaced fingers, like a heron, or with wide hooves, like an elk; jumping animals have more developed hind limbs (kangaroo, grasshopper, frog). In animals that lead an underground lifestyle, the limbs are spade-shaped and adapted for digging the earth. There are expedient adaptations in plants and animals to daily and annual fluctuations in temperature and humidity.

Adherents of idealistic views and ministers of the church in the phenomena of the adaptability of organisms and their purposeful structure saw an expression of the general harmony of nature, allegedly emanating from its creator. Ch. Darwin's theory rejects any participation in the emergence of devices of supernatural forces, she convincingly proved that the whole animal and vegetable world from the time of its appearance, it has been improving along the path of expedient adaptations to living conditions: to water, air, sunlight, gravity. The amazing harmony of living nature, its perfection are created by nature itself: the struggle for survival. This struggle is the force that gives strength to roots, sophisticated beauty to flowers, causes a bizarre mosaic of leaf arrangement and sharpens teeth, gives powerful strength to muscles, sharpness of vision, hearing and instinct for many animals.

Adaptability as an expression of expediency is manifested in everything. For example, predators have claws, fangs, beaks, poisonous teeth, from which it can be very difficult for the victim to escape. But in the struggle for life, means of protection were also developed: some respond to force with force, others save their legs, others have a shell, shell, needles, etc. Many weak and defenseless insects, being harmless or edible, for long years the actions of natural selection adopted the color and shape of hornets, wasps, became similar to poisonous or inedible forms. Their imitative color or shape is at the same time protective, as it matches the background. environment: it makes predators invisible and helps them sneak up on prey, it makes it possible for pursued species to hide from enemies. If the insects pursued by birds were not colored like green grass or tree bark, they would be exterminated by birds. The plumage of the tundra partridge merges with the tone of the rocks and peaks covered with lichens, the woodcock is invisible among the dried and fallen oak leaves, etc. eye-like spots; at the moment of danger, it raises the front of the body, thus scaring away the birds.

A variety of adaptations prevent most plants from self-pollinating, allowing them to spread fruits and seeds, or, thanks to their spines, to resist being eaten by herbivores. The fragrance and bright colors of the flowers originated as adaptations to attract insects that visit the flowers to cross-pollinate these plants, or as an adaptation to more effectively absorb sunlight of a certain length.

Protective coloration. Protective coloration is developed in species that live openly and can be accessible to enemies. This coloration makes organisms less visible against the background of the surrounding area. Some have a bright pattern (the color of a zebra, tiger, giraffe) - alternating light and dark stripes and spots. This dismembering coloring imitates the alternation of spots of light and shadow.

Disguise. Camouflage - a device in which the shape of the body and color of the animal merges with the surrounding objects. For example, the caterpillars of some butterflies resemble knots in body shape and color.

Mimicry. Mimicry is the imitation of a less protected organism of one species by a more protected organism of another species. This imitation can manifest itself in body shape, coloration, and so on. So, some types of non-venomous snakes and insects are similar to poisonous ones. Mimicry is the result of selection for similar mutations in various kinds. It helps unprotected animals to survive, contributes to the preservation of the organism in the struggle for existence.

Warning (threatening) coloring Species often have a bright, memorable coloration. Once trying to taste an inedible ladybug that stings a wasp, the bird will remember their bright color for life.

(According to the personal page of Andrey Ivanov)

In the doctrine of natural selection, Darwin not only materialistically substantiated the fitness of organisms (their expedient structure), but also showed its relative nature. So, warning and protective coloration, various other protective devices do not act on all pursuers, but, having devices, individuals are less likely to be attacked. The owners of the sting - wasps, bees, hornets - are easily eaten by flycatchers, bee-eaters. Flying fish, jumping out of the water into the air, deftly escape from predatory fish, but this is used by the albatross, which overtakes its prey in the air. The tortoise shell is a good defense, but the eagle picks it up in the air and throws it on the rocks; the shell breaks and the eagle eats the turtle.

Each animal and plant cannot be fully adapted to all the conditions that have developed throughout life on Earth. Any adaptation lasts as long as it is supported by natural selection, but disappears as soon as it ceases to be useful. As an example of a change in adaptations, one can cite the development of protective coloration in the birch moth butterfly.

Thus, the basis of Darwin's theory is the doctrine of natural selection, the main and guiding factor in evolution. In the struggle for existence on the basis of hereditary variability, there is a successive change of adaptations and the survival of the fittest, the diversity of forms of living nature increases, the process of speciation takes place, and the general progressive development of the plant and animal world takes place. In this theory, two problems were resolved: the mechanism of speciation and the origin of the expediency of the organic world.

Adaptability of organisms as a result of evolution (T.A. Kozlova, V.S. Kuchmenko. Biology in tables. M., 2000)

Organisms that are best adapted to their environment survive through selection, but adaptations are always relative. Enough minor changes in the environment, as what was useful in the previous conditions, loses its adaptive value.

Examples of Relative Fittings

The Ussuri tiger has a protective coloration that hides it well in the thickets in summer, but in winter, after the snow falls, the coloring unmasks the predator. With the onset of autumn, the hare molts, but if the snowfall is delayed, then the whitened hare becomes clearly visible against the dark background of bare fields.

The characteristics of an organism, even under the conditions in which they have been preserved by selection, never achieve absolute perfection. So, the roundworm egg is well protected from the effects of poisons, but quickly dies from a lack of moisture and from high temperature.

Poisonous glands are a reliable defense of many animals, but the poison of the karakurt, which is deadly for camels and cattle, is safe for sheep and pigs. The viper does not pose a danger to the hedgehog.

Euphorbia stalks are not eaten by herbivorous mammals, but remain defenseless against caterpillars of Euphorbia hawk, etc. Selection always has a wide field of activity for the further improvement of adaptations.

If conditions change, then arrangements that were previously expedient cease to be so. Then new adaptations appear, and forms that were previously "expedient" die out.

The adaptability of organisms is the result of natural selection. Prepared by Chiritso Elizaveta, a student of the 11th "M" class.

it is a combination of those features of the structure, physiology and behavior that provide for a given species the possibility of a specific lifestyle in certain environmental conditions. Adaptation -

How are adaptations formed? C. Linnaeus: Species are created by God and are already adapted to their environment. J. B. Lamarck: the formation of fitness by the desire of organisms for self-improvement. Charles Darwin: explained the origin of fitness in the organic world with the help of natural selection.

Adaptations to the environment are manifested in the external and internal structure, life processes, behavior. The shape of the body of various animals is an example of the adaptability of organisms to the environment. The protective coloration and body shape of some animals make them invisible against the background of the environment, masking them. Some animals have bright colors that make them stand out from their surroundings. This coloring is called warning. Some defenseless and edible animals imitate species that are well protected from predation. This phenomenon is called mimicry. Protection against eating is characteristic of many animals and plants. They protect themselves. Behavioral adaptations are changes in the behavior of animals in certain conditions: care for offspring, the formation of separate pairs during the mating season, and in winter they unite in flocks, which facilitates food and protection, frightening behavior, freezing, imitation of injury or death, hibernation, food storage . The adaptability of life processes to living conditions are called physiological adaptations: the accumulation of fat by desert animals, glands that get rid of excess salts, thermal location, echolocation. Biochemical adaptations are associated with the formation in the body of certain substances that facilitate defense against enemies or attacks on other animals.

Forms of adaptations Examples Description of adaptations Body shape Protective coloration (camouflage) Warning coloration Mimicry Behavioral adaptations Classification of adaptations

Body shape The streamlined shape of the body allows the dolphin to reach a speed of 40 km / h in the water. The peregrine falcon, in pursuit of prey, develops a speed of 290 km / h. The speed of the penguin in the water column is 35 km / h.

Protective coloration (camouflage) In openly nesting birds, the female sitting on the nest is almost indistinguishable from the surrounding background. Corresponds to the background and pigmented egg shells. Interestingly, in birds nesting in hollows, on trees, females often have a bright color, and the shell is light. Quail and its eggs Redstart, cuckoo egg in redstart nest

Protective coloration (camouflage) A surprising resemblance to twigs is observed in stick insects. The caterpillars of some butterflies resemble knots, and the body of some butterflies is like a leaf. The effect of protective coloration is enhanced when it is combined with the appropriate behavior: at the moment of danger, many animals freeze, taking a resting pose.

Warning coloration Very bright coloration (usually white, yellow, red, black) is characteristic of well-protected poisonous, stinging forms. Having tried several times to taste the “soldier” bug, ladybug, wasp, the birds eventually refuse to attack the victim with a bright color. Sand efa Bed bug - soldier Ladybug

Mimicry The viceroy butterfly repeats the shape and color of the wings of the poisonous monarch butterfly. The fly mimics the appearance and behavior of the bee This is the similarity of a defenseless or edible species with a well-protected and warning color

Mimicry The milk snake successfully imitates the coloration of the coral snake. As a rule, the number of copied individuals is many times higher than the copying ones.

Behavioral adaptations Characteristic Possum behavior - the ability to pretend to be dead in danger, in this "game" the possum is simply inimitable. changes in behavior in certain conditions Frog paws. The desert amphibian, which lives most of its life in burrows, goes hunting at night when the heat subsides.

Behavioral Adaptations River beaver stores up to 20 cubic meters. fodder Male stickleback builds a nest with 2 exits - care for the safety of offspring

The relative nature of fitness Poisonous snakes, dangerous to many animals, are eaten by mongooses. The hedgehog defends itself from the fox with needles and curls up into a ball, but if there is a stream nearby, the fox rolls it into the water, where the muscles of the hedgehog open up and it becomes easy prey.

Natural selection is the driving force behind evolution

Natural selection is a process that favors the survival of the fittest and the destruction of the less fit. More adapted individuals have the opportunity to leave offspring. The material for selection is individual hereditary changes. Harmful changes reduce the fecundity and survival of individuals, while beneficial ones accumulate in the population. Selection always has a directional character: it preserves those changes that are most consistent with environmental conditions, increase the fertility of individuals.

Selection can be individual, aimed at preserving single individuals with traits that ensure success in the struggle for existence within the population. It can also be group, fixing signs favorable for the group.

I. I. Shmalgauzen determined the forms of natural selection.

1. Stabilizing - aimed at maintaining the average rate of reaction of the trait against individuals with extreme, deviant traits. Selection operates under constant environmental conditions, is conservative, and is aimed at preserving the main features of the species unchanged.

2. Driving - leads to the consolidation of evading signs. Selection acts in changing environmental conditions, leads to a change in the average reaction rate, the evolution of the species.

3. Disruptive, tearing - aimed at maintaining individuals with extreme signs and the destruction of individuals with average signs. It acts in changing conditions, leads to a split in a single population and the formation of two new populations with opposite characteristics. Selection can lead to the emergence of new populations and species. For example, populations of wingless and winged forms of insects.

Any form of selection does not occur by chance, it acts through the preservation and accumulation of useful features. The selection is the more successful for the species, the greater the range of variability and the greater the diversity of genotypes.

Fitness - the relative expediency of the structure and functions of the body, which is the result of natural selection, eliminating unfit individuals. Traits result from mutations. If they increase the viability of the organism, its fecundity, allow to expand the area, then such characters are "caught up" by selection, are fixed in the offspring and become adaptations.

Types of fixtures.

The shape of the body of animals allows them to easily move in the appropriate environment, making organisms inconspicuous among objects. For example, the streamlined shape of the body of fish, the presence of long limbs in a grasshopper.

Camouflage - the acquisition of the resemblance of an organism to some object of the environment, for example, resemblance to a dry leaf or tree bark of a butterfly's wings. The body shape of the stick insect makes it invisible among the branches of plants. Needlefish are not visible among the algae. In plants, the shape of the flower: the position on the shoot promotes pollination.

Protective coloring hides the organism in the environment, making it invisible. For example, a hare has a white color, a grasshopper has a green one. Dissecting coloration - the alternation of light and dark stripes on the body creates the illusion of chiaroscuro, blurs the contours of the animal (zebras, tigers).

Warning coloration indicates the presence of toxic substances or special protective organs, the danger of the body to a predator (wasps, snakes, ladybugs).

Mimicry is the imitation of a less protected organism of one species to a more protected organism of another species (or environmental objects), which protects it from extermination (wasp flies, non-poisonous snakes).

Adaptive behavior in animals is a threatening posture that warns and scares off the enemy, freezing, caring for offspring, storing food, building a nest, burrows. The behavior of animals is aimed at protection and preservation from enemies and the harmful effects of environmental factors.

Plants have also developed adaptations: spines protect against eating; the bright color of the flowers attracts pollinating insects; different time maturation of pollen and ovules prevents self-pollination; variety of fruits promotes seed dispersal.

All adaptations are relative in nature, as they operate under certain conditions to which the body is adapted. When conditions change, adaptations may not protect the organism from death, and, consequently, the signs cease to be adaptive. Narrow specialization can cause death in changing conditions.

The reason for the emergence of adaptations is that organisms that do not meet these conditions die and do not leave offspring. Organisms that survive in the struggle for existence have the opportunity to pass on their genotype and fix it in generations.

In the 19th century studies brought more and more new data revealing the adaptability of animals and plants to environmental conditions; the question of the reasons for this perfection of the organic world remained open. Darwin explained the origin of fitness in the organic world with the help of natural selection.

Let us first get acquainted with some facts testifying to the adaptability of animals and plants.

Examples of adaptability in the animal world. In the animal kingdom, various forms of protective coloration are widespread. They can be reduced to three types: patronizing, warning, camouflage.

Protective coloration helps the body become less visible against the background of the surrounding area. Among the green vegetation, bugs, flies, grasshoppers and other insects are often colored in green color. The fauna of the Far North (polar bear, polar hare, white partridge) is characterized by white color. In the deserts, yellow tones of animals (snakes, lizards, antelopes, lions) predominate.

Warning coloration clearly distinguishes the organism in the environment with bright, colorful stripes, spots (endpaper 2). It is found in poisonous, burning or stinging insects: bumblebees, wasps, bees, blister beetles. Bright, warning coloration usually accompanies other means of protection: hairs, spikes, stingers, caustic or pungent-smelling liquids. The same type of coloration includes menacing.

Disguise can be achieved by similarity in body shape and color with any object: a leaf, branch, knot, stone, etc. In case of danger, the moth caterpillar stretches out and freezes on a branch like a knot. Butterfly rotten scoops in a motionless state can easily be mistaken for a piece of rotten wood. Masking is also achieved mimicry. Mimicry refers to the similarities in color, body shape, and even behavior and habits between two or more species of organisms. For example, bumblebees are prominent and wasp-like flies, devoid of sting, very similar to bumblebees and wasps - stinging insects.

It should not be thought that protective coloration necessarily and always saves animals from extermination by enemies. But organisms or groups of them that are more adapted in color die much less frequently than those that are less adapted.

Along with the protective coloration, animals have developed many other adaptations to the conditions of life, expressed in their habits, instincts, and behavior. For example, quails, in case of danger, quickly fall onto the field and freeze in a motionless pose. In the deserts, snakes, lizards, beetles hide from the heat in the sand. At the moment of danger, many animals take 16 threatening postures.

Examples of adaptability in plants. Tall trees, the crowns of which are freely blown by the wind, as a rule, have fruits and seeds with flying. The undergrowth and shrubs where the birds live are characterized by bright fruits with edible pulp. In many meadow herbs, the fruits and seeds have hooks with which they cling to the fur of mammals.

A variety of adaptations prevent self-pollination and ensure cross-pollination of plants.

In monoecious plants, male and female flowers do not ripen at the same time (cucumbers). Plants with bisexual flowers are protected from self-pollination by maturation of stamens and pistils at different times or by the peculiarities of their structure and relative position(at the primrose).

Let us point out more examples: tender sprouts of spring plants - anemone, chistyak, blue copse, goose onion, etc. - tolerate temperatures below zero due to the presence of a concentrated sugar solution in cell sap. Very slow growth, short stature, small leaves, shallow roots of trees and shrubs in the tundra (willow, birch, juniper), extremely rapid development of the polar flora in spring and summer - all these are adaptations to life in permafrost conditions.

Many weeds produce immeasurably large quantity seeds than cultivated - this is an adaptive trait.

Manifold fixtures. Species of plants and animals differ in adaptability not only to the conditions of the inorganic environment, but also to each other. For example, in a broad-leaved forest, grass cover in spring is formed by light-loving plants (corydalis, anemone, lungwort, chistyak), and in summer - shade-tolerant (budra, lily of the valley, zelenchuk). Pollinators of early flowering plants are mainly bees, bumblebees and butterflies; summer flowering plants are usually pollinated by flies. Numerous insectivorous birds (oriole, nuthatch), nesting in a broad-leaved forest, destroy its pests.

In the same environment, organisms have different adaptations. The dipper bird does not have swimming membranes, although it obtains its food by water, diving, using its wings and clinging to stones with its feet. The mole and mole rat belong to burrowing animals, but the former digs with its limbs, while the latter makes underground passages with its head and strong incisors. The seal swims with flippers, while the dolphin uses its tail fin.

Origin of adaptations in organisms. Darwin's explanation of the appearance of complex diverse adaptations to specific environmental conditions was fundamentally different from Lamarck's understanding of this issue. These scientists also differed sharply in determining the main driving forces of evolution.

Darwin's theory gives a completely logical materialistic explanation of the origin, for example, of a protective color. Consider the appearance of a green body color in caterpillars living on green leaves. Their ancestors could be painted in some other color and not eat leaves. Suppose that due to some circumstances they were forced to switch to eating green leaves. It is easy to imagine that the birds have pecked at many of these insects, clearly visible against the green background. Among the various hereditary changes that are always observed in the offspring, there could be changes in the color of the body of caterpillars, which made them less noticeable on green leaves. Of the caterpillars with a greenish tinge, some individuals survived and gave fertile offspring. In subsequent generations, the process of predominant survival of caterpillars, less noticeable in color on green leaves, continued. Over time, due to natural selection, the green color of the body of the caterpillars more and more corresponded to the main background.

The emergence of mimicry can also be explained only by natural selection. Organisms with the slightest deviations in body shape, coloration, behavior, enhancing the resemblance to protected animals, were more likely to survive and leave numerous offspring. The percentage of death of such organisms was lower than those that did not have beneficial changes. From generation to generation, beneficial change has been strengthened and improved through the accumulation of signs of similarity with protected animals.

Driving Force of Evolution-- natural selection.

Lamarck's theory turned out to be completely helpless in explaining the organic expediency, for example, the origin of various types of protective coloration. It cannot be supposed that the animals "exercised" in color or firmness of the body and through the exercise acquired fitness. It is also impossible to explain the mutual adaptation of organisms to each other. For example, it is completely inexplicable that the proboscis of worker bees corresponds to the structure of the flower of certain types of plants pollinated by them. Worker bees do not reproduce, and queen bees, although they produce offspring, cannot "exercise" the proboscis, since they do not collect pollen.

Let us recall the driving forces of evolution according to Lamarck: 1) "the desire of nature to progress", as a result of which the organic world develops from simple forms to complex ones, and 2) the changing effect of the external environment (directly on plants and lower animals and indirectly with the participation of nervous system on higher animals).

Lamarck's understanding of gradation as a gradual increase in the organization of living beings according to "immutable" laws, in essence, leads to the recognition of faith in God. The theory of direct adaptation of organisms to environmental conditions through the appearance of only adequate changes in them and the obligatory inheritance of traits acquired in this way logically follows from the idea of ​​initial expediency. The inheritance of acquired traits has not been experimentally confirmed.

In order to show more clearly the main difference between Lamarck and Darwin in understanding the mechanism of evolution, we will give an explanation in their own words of one and the same example.

The formation of long legs and a long neck in a giraffe

According to Lamarck

“It is known that this highest of mammals lives in the interior of Africa and is found in places where the soil is always dry and devoid of vegetation. This causes the giraffe to eat the leaves of the trees and make a constant effort to reach them. As a result of this habit, which has existed for a long time in all individuals of this breed, the front legs of the giraffe have become longer than the hind legs, and its neck has lengthened so much that this animal, without even rising on its hind legs, raising only its head, reaches six meters (about twenty feet) in height ... Any change acquired by an organ through habitual use sufficient to produce this change is subsequently preserved by reproduction, provided that it is inherent in both individuals jointly participating in fertilization in the reproduction of their species. This change is passed on and thus passes on to all individuals of succeeding generations exposed to the same conditions, although posterity no longer has to acquire it in the way in which it was actually created.

According to Darwin

“The giraffe, by its high stature, very long neck, forelegs, head and tongue, is perfectly adapted to stripping leaves from the upper branches of trees ... the tallest individuals, which were an inch or two taller than others, could often survive during periods of drought, wandering in searching for food all over the country. This slight difference in size, due to the laws of growth and variability, does not matter for most species. But it was different with the nascent 10 giraffe, if we take into account its likely lifestyle, because those individuals in which any or several different parts of the body were longer than usual, generally had to worry. When crossed, they should have left offspring either with the same structural features, or with a tendency to change in the same direction, while individuals less favorably organized in this respect should have been the most prone to death. ... natural selection both protects and thereby separates all higher individuals, giving them the full opportunity to interbreed, and contributes to the destruction of all lower individuals.

The theory of direct adaptation of organisms to environmental conditions through the appearance of adequate changes and their inheritance finds supporters at the present time. It is possible to reveal its idealistic character only on the basis of a deep assimilation of Darwin's doctrine of natural selection - driving force evolution.

Relativity of adaptations of organisms. Darwin's doctrine of natural selection not only explained how fitness could arise in the organic world, but also proved that it always has relative character. In animals and plants, along with useful features, there are useless and even harmful ones.

Here are a few examples of organs that are useless for organisms, inappropriate organs: the slate bones in a horse, the remains of the hind limbs of a whale, the remains of the third eyelid in monkeys and humans, the appendix of the caecum in humans.

Any adaptation helps organisms to survive only in those conditions in which it was developed by natural selection. But even under these conditions it is relative. On a bright, sunny day in winter, the ptarmigan gives itself out as a shadow on the snow. The white hare, imperceptible on the snow in the forest, becomes visible against the background of the trunks, running out to the edge of the forest.

Observations of the manifestation of instincts in animals in a number of cases show their inappropriate nature. Night butterflies fly to the fire, although they die in the process. They are attracted to fire by instinct: they collect nectar mainly from light flowers, clearly visible at night. The best defense of organisms is by no means reliable in all cases. Sheep eat the Central Asian karakurt spider without harm to themselves, whose bite is poisonous to many animals.

The narrow specialization of the body can cause the death of the body. The swift cannot take off from a flat surface, as it has long wings, but very short legs. It takes off only by pushing off from some edge, like from a springboard.

Plant adaptations that prevent animals from eating are relative. Hungry cattle also eat plants protected by thorns. The mutual benefit of organisms connected by symbiotic relationships is also relative. Sometimes fungal threads of a lichen destroy the algae cohabiting with them. All these and many other facts show that expediency is not absolute, but relative.

Experimental evidence of natural selection. In the post-Darwinian time, a number of experiments were carried out that confirmed the presence of natural selection in nature. For example, fish (gambusia) were placed in pools with differently colored bottoms. Birds destroyed 70% of the fish in the pool where they were more visible, and 43% where they matched the bottom background better in color.

In another experiment, the behavior of the wren (a group of passerines) was observed, which did not peck at the caterpillars of the patronizing moth until they moved.

Experiments have confirmed the importance of warning coloration in the process of natural selection. At the edge of the forest, insects belonging to 200 species were laid out on boards. Birds flew about 2000 times and pecked only those insects that did not have a warning color.

It has also been experimentally found that most birds avoid hymenoptera insects with an unpleasant taste. Having pecked at a wasp, the bird does not touch wasp flies for three to six months. Then he begins to peck at them until he gets on a wasp, after which he again does not touch the flies for a long time.

Experiments were carried out on "artificial mimicry". Birds willingly ate beetle larvae - flour beetle, painted with tasteless paint carmine. Some of the larvae were covered with a mixture of paint with quinine or another unpleasant substance. Birds, having come across such larvae, stopped pecking at all colored larvae. The experience was changed: various drawings were made on the body of the larvae, and the birds took only those whose drawing was not accompanied by an unpleasant taste. Thus, birds have conditioned reflex to warning bright signals or patterns.

An experimental study of natural selection was also carried out by botanists. It turned out that weeds have a number of biological features, the emergence and development of which can only be explained as adaptations to the conditions created by human culture. For example, camelina (cruciferous family) and toritsa (clove family) plants have seeds very similar in size and weight to flax seeds, whose crops they infest. The same can be said about the seeds of the wingless rattle (of the Norichnikov family), which litters rye crops. Weeds usually mature at the same time as cultivated plants. The seeds of both are difficult to separate from each other when winnowing. The man mowed, threshed the weeds along with the harvest, and then sown on the field. Unwittingly and unconsciously, he contributed to the natural selection of seeds of various weeds along the line of similarity with the seeds of cultivated plants.