Surprisingly, Charles Darwin arrived at his theory of evolution by natural selection almost by accident. After all, he initially planned to become a doctor, then studied religion, and then generally took up shooting and horse riding.
And the “culprit” of Darwin’s idea was his trip around the world on the Beagle. During this journey (which lasted five years), Darwin saw the world and made notes about what he saw.
So Darwin came to biology. After the return of the Beagle, Darwin became seriously interested in biology and even published many books. At some point, he came up with the idea that life on the planet is evolving due to the struggle for survival - so to speak, nature selects the fittest creatures - natural selection.
This idea was not new - Jean Lamarck and others had already spoken about it (in particular, the grandfather of Charles Darwin himself and Alfred Wallace, who wrote a book on this topic at the same time as Darwin).
However, when Darwin's book On the Origin of Species by Means of Natural Selection was published, the event was like a bomb exploding. Thousands of people - both eminent scientists and ordinary people - fiercely debated whether Darwin's theory was true or not.
Why did people pay attention to the theory of evolution by natural selection only after the book was published? But because Darwin not only put forward a theory, but also provided a lot of evidence in its favor. That is why he managed to attract attention to his idea.
A little later, Darwin once again stunned the world community by publishing the book “The Descent of Man and Sexual Selection,” where he argued that man descended from the ape. At this point the world shook even more.
However, Charles Darwin did not become a great person because he proved to the world the correctness of the theory of evolution through natural selection (by the way, the debate about whether Darwin was right or not has not subsided to this day). But because he changed his view of the world, of science, politics, sociology and, of course, religion. After all, before Darwin, the world was perceived as an unchangeable given (from a religious point of view, created by God). And if we accept the truth of Darwin’s theory of evolution, then the entire history of the world and man in it looks completely different.
Darwin made humanity doubt the immutability of existence itself, and this is precisely where his greatest merit lies, and not at all in the discovery/popularization of the theory of evolution through natural selection, and this is why we recognize his right to be considered a great man.
§ 3- SCIENTIFIC AND SOCIO-ECONOMIC PREREQUISITES FOR THE ARISE OF THE THEORY OF CHARLES DARWIN
1) List the main scientific prerequisites for the emergence evolutionary theory. Fill the table.
-
Scientific area
Basic Premise
Geology
The works of Charles Lyell, showing that the surface of the Earth is continuously changing under the influence of everyday factors - temperature fluctuations, wind, rain, the life of organisms and others.
Cytology
T. Schwann's cell theory, showing that the structure of all living beings is based on a cell.
Embryology
Research by K. Baer showing similarities in the structure of vertebrate embryos and that the development of all organisms begins with the egg.
Comparative anatomy
Accumulated materials indicating the variability of species, rudiments, atavisms, homologous and similar organs.
2) Describe the observations made by Charles Darwin during the expedition on the Beagle ship, which made him doubt the divine creation of species.
- Answer:
- 1- Skeletons of extinct giant mammals similar to modern armadillos and sloths.
- 2- Close species of Galapagos finches, differing in their feeding patterns and beak shape.
- 3- Significant differences in the structure of animals living on the Cape Verde Islands from closely related species living on the continent.
§ 4 THE TEACHING OF CHARLES DARWIN ABOUT ARTIFICIAL SELECTION
1) Answer the questions.
1-What achievements of English agriculture in the 19th century did Charles Darwin pay special attention to?
- Answer: By that time, English farmers had developed many breeds of dogs, pigeons, cattle and chickens, and intensive selection of new varieties of cultivated plants was carried out.
2- What were his scientific interests that caused this?
- Answer: Proponents of the constancy of species argued that every variety and breed has its own wild ancestor, but Darwin believed that this was not the case.
2) Fill in the blanks in the table.
3) Answer what explains the variety of breeds of domestic animals and varieties of cultivated plants. Give two examples each of plant varieties and animal breeds that are the result of the efforts of breeders.
- Answer: Breeders developed animals or plants, leaving those organisms in which the trait had the most pronounced degree. Domestic apple tree, black currant - plants, rabbit, domestic duck - animals.
4) Complete the proposal.
- Answer: The traditional method of breeding new varieties of plants and animal breeds comes down to artificial systematic selection and reproduction of individuals with the most valuable traits and properties for humans.
§ 5 THE TEACHING OF CHARLES DARWIN ABOUT NATURAL SELECTION
1) Select and underline the correct answer.
What pattern does the process of reproduction of living organisms follow in the complete absence of limiting factors?
- Answer: arithmetic progression, geometric progression, logarithmic progression.
2) Complete the definition.
- Answer: The struggle for existence - it is a set of diverse and complex relationships that exist between organisms and conditions external environment.
3) Name three forms of the struggle for existence that Charles Darwin identified.
- Answer:
- 1- Interspecific.
- 2- Intraspecific.
- 3- Combating unfavorable environmental conditions.
4) Explain why intraspecific struggle is the most intense.
- Answer: Individuals of the same species have the same needs for food, territory and other living conditions. Males of some species compete for females.
5) Describe the organisms that win the struggle for existence.
- Answer: In the struggle for existence, individuals who have a hereditary complex of characteristics and properties survive and leave offspring.
6) Explain what Charles Darwin understood by natural selection.
- Answer: He understood the processes occurring in nature of the selective destruction of some individuals and the preferential reproduction of others.
7) Complete the statement.
- Answer: The material for natural selection is hereditary variability.
8) Explain why variation due to direct environmental influences is not important for evolution.
- Answer: Variation due to the direct influence of the external environment is not important for evolution, since it is not inherited.
9) Give comparative characteristics natural and artificial selection. Fill the table.
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Characteristic
Natural selection
Artificial selection
Source of genetic diversity
Hereditary variability, natural mutations
Hereditary variability, Artificial mutations, crossing, etc.
Selective factor
Environmental conditions
The significance of acquired characteristics for the organisms themselves
New species
New varieties of plants, breeds of animals, strains of microorganisms lead to the emergence of species impossible in nature
Dependence of the result on the will of a person
Increase the adaptability of organisms to environmental conditions
May be harmful to the organisms themselves
§6- FORMS OF NATURAL SELECTION
1) List the main forms of natural selection.
- Answer:
- 1- Driving.
- 2- Stabilizing.
2) Name the form of natural selection that maintains similar shape and size between flowers of insect-pollinated plants and pollinating insects.
- Answer: Stabilizing selection.
3) Complete the sentence.
- Answer:
- Living fossils (relict forms of plants and animals) have survived to this day thanks to the action of stabilizing forms of natural selection.
- Give an example of a relict animal and a relict plant: lobe-finned fish coelacanth, gymnosperm plant Ginkgo biloba.
4) Select and fill in the correct options for the missing words.
- Answer:
- Stabilizing selection acts in permanent environmental conditions throughout large periods of time.
5) Name the form of natural selection that operates under changing environmental conditions and indicate its evolutionary results.
- Answer:
- Form of natural selection - driving selection.
- Results:
- A) The appearance of new characters within a species.
- B) Weakening or loss of an irrelevant sign.
- C) Elimination of less successful gene combinations.
6) It is known that some time after the start of using a particular pesticide, forms of animals resistant to it appear. Explain this phenomenon from the perspective of natural selection.
- Answer: Driving selection is at work. Species develop new characteristics that provide resistance to environmental changes.
7) Complete the statements.
- Answer:
- 1- The form of natural selection that transforms species is called driving selection.
- 2- The form of natural selection that fixes the resulting forms is called stabilizing selection.
8) Expand the meaning of the thesis: “Natural selection plays a creative role in the evolution of organisms.”
- Answer: It eliminates less successful individuals, that is, less successful combinations of genes, from reproducing. The creative role of selection is that the result of its action is the emergence of new species of organisms and new forms of life.
9) Define the concepts.
- Answer:
- Sexual selection - This is competition between males for the opportunity to reproduce.
- Sexual dimorphism - external differences in the structure of the sexes.
Charles Robert Darwin(1809 - 1882) - English naturalist and traveler, one of the first to realize and clearly demonstrate that all types of living organisms evolve over time from common ancestors. In his theory, the first detailed presentation of which was published in 1859 in the book “The Origin of Species” (full title: “The Origin of Species by Means of Natural Selection, or the Preservation of Favored Breeds in the Struggle for Life”), the main driving force Darwin called evolution natural selection and uncertain variability.
The existence of evolution was recognized by most scientists during Darwin's lifetime, while his theory of natural selection as the main explanation of evolution became generally accepted only in the 30s of the 20th century. Darwin's ideas and discoveries, as revised, form the foundation of the modern synthetic theory of evolution and form the basis of biology as providing a logical explanation for biodiversity.
The essence of evolutionary teaching lies in the following basic principles:
1. All types of living beings inhabiting the Earth were never created by anyone.
2. Having arisen naturally, organic forms were slowly and gradually transformed and improved in accordance with environmental conditions.
3. The transformation of species in nature is based on such properties of organisms as heredity and variability, as well as natural selection that constantly occurs in nature. Natural selection occurs through complex interactions of organisms with each other and with factors inanimate nature; Darwin called this relationship the struggle for existence.
4. The result of evolution is the adaptability of organisms to their living conditions and the diversity of species in nature.
In 1831, after graduating from university, Darwin set out as a naturalist on a voyage around the world on a Royal Navy expedition ship. The journey lasted almost five years (Fig. 1). He spends most of his time on the shore, studying geology and collecting natural history collections. Having compared the found remains of plants and animals with modern ones, Charles Darwin made an assumption about the historical, evolutionary relationship.
On the Galapagos Islands, he found species of lizards, turtles, and birds that were not found anywhere else. The Galapagos Islands are islands of volcanic origin, so Charles Darwin suggested that these animals came to them from the mainland and gradually changed. In Australia, he became interested in marsupials and oviparous animals, which became extinct in other parts of the globe. So gradually the scientist’s conviction in the variability of species grew stronger. After returning from his journey, Darwin worked hard for 20 years to create the doctrine of evolution, collected additional facts on the development of new breeds of animals and plant varieties in agriculture.
He considered artificial selection as a unique model of natural selection. Based on the material collected during the trip and proving the validity of his theory, as well as on scientific achievements(geology, chemistry, paleontology, comparative anatomy, etc.) and, above all, in the field of selection, Darwin for the first time began to consider evolutionary transformations not in individual organisms, but in species.
Rice. 1 Voyage on the Beagle (1831-1836)
Darwin was directly influenced in the process of creating the concept by Lyell and Malthuss with his geometric progression of numbers from the demographic work “An Essay on the Law of Population” (1798). In this work, Malthus hypothesized that humanity is multiplying many times faster compared to increasing food supplies. While the human population increases geometrically, food supplies, according to the author, can only increase arithmetically. Malthus's work prompted Darwin to think about possible paths of evolution.
A huge number of facts speak in favor of the theory of the evolution of organisms. But Darwin understood that it was not enough just to show the existence of evolution. In collecting evidence, he worked primarily empirically. Darwin went further by developing a hypothesis that revealed the mechanism of the evolutionary process. In the very formulation of the hypothesis, Darwin as a scientist showed a truly creative approach.
1 . Darwin's first assumption was that the number of animals of each species tends to increase exponentially from generation to generation.
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2. Darwin then proposed that although the number of organisms tends to increase, the number of individuals of a given species actually remains the same.
These two assumptions led Darwin to the conclusion that there must be a struggle for existence among all species of living beings. Why? If each next generation produces more descendants than the previous one, and if the number of individuals of the species remains unchanged, then, apparently, in nature there is a struggle for food, water, light and other environmental factors. Some organisms survive this struggle, while others die .
Darwin identified three forms of struggle for existence: intraspecific, interspecific and combating unfavorable environmental factors. The most acute intraspecific struggle is between individuals of the same species due to the same food needs and living conditions, for example, the struggle between moose feeding on the bark of trees and shrubs.
Interspecific- between individuals of different species: between wolves and deer (predator - prey), between moose and hares (competition for food). The impact on organisms of unfavorable conditions, such as drought, severe frosts, is also an example of the struggle for existence. The survival or death of individuals in the struggle for existence are the results, consequences of its manifestation.
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Charles Darwin, in contrast to J. Lamarck, drew attention to the fact that although any living creature changes during life, individuals of the same species are not born the same.
3. Darwin's next assumption was that every species is inherently variable. Variability is the property of all organisms to acquire new characteristics. In other words, individuals of the same species differ from each other, even in the offspring of one pair of parents there are no identical individuals. He rejected, as untenable, the idea of “exercising” or “non-exercising” organs and turned to the facts of the breeding of new breeds of animals and varieties of plants by people - to artificial selection.
Darwin distinguished between definite (group) and indefinite (individual) variability. A certain variability manifests itself in the entire group of living organisms in a similar way - if the entire herd of cows is well fed, then their milk yield and milk fat content will all increase, but no more than the maximum possible for a given breed. Group variability will not be inherited.
 4. Heredity is the property of all organisms to preserve and transmit characteristics from parents to offspring. Changes that are inherited from parents are called hereditary variability. Darwin showed that indefinite (individual) variability of organisms is inherited and can become the beginning of a new breed or variety if it is useful to man. Having transferred these data to wild species, Darwin noted that only those changes that are beneficial to the species for successful competition can be preserved in nature. The giraffe acquired a long neck not at all because it constantly stretched it, reaching the branches of tall trees, but simply because species endowed with a very long neck could find food higher than those branches that had already been eaten by their fellows with a shorter neck, and as a result they could survive during famine. . |
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The result of natural selection is the formation of a large number of adaptations to specific living conditions. The material for natural selection is supplied by the hereditary variability of organisms. In 1842, Charles Darwin wrote the first essay on the origin of species. Under the influence of the English geologist and naturalist Charles Lyell, Darwin began preparing an expanded version of the book in 1856. In June 1858, when the work was half completed, he received a letter from the English naturalist A. R. Wallace with the manuscript of the latter's article. In this article, Darwin discovered an abbreviated statement of his own theory of natural selection. Two naturalists independently and simultaneously developed identical theories. Both were influenced by T. R. Malthus's work on population; both were aware of Lyell's views, both studied the fauna, flora and geological formations of island groups and discovered significant differences between the species inhabiting them. Darwin sent Wallace's manuscript to Lyell along with his own essay, and on July 1, 1858, they together presented their work to the Linnean Society in London. |
Under fairly stable conditions, small differences may not matter. However, when Darwin's book was published in 1859 " The Origin of Species by Natural Selection, or the Preservation of Favored Breeds in the Struggle for Life,” in which he explained the mechanism of the evolutionary process. Constantly thinking about the driving causes of the evolutionary process, Charles Darwin came to the most important idea for the entire theory. Natural selection is the main driving force of evolution .
The process as a result of which individuals survive and leave offspring with hereditary changes that are useful under given conditions, i.e. survival and successful production of offspring by the fittest organisms. Based on facts, Charles Darwin was able to prove that natural selection is the driving factor in the evolutionary process in nature, and artificial selection plays the same role important role when creating animal breeds and plant varieties.
Darwin also formulated the principle of divergence of characters, which is very important for understanding the process of formation of new species. As a result of natural selection, forms arise that differ from the original species and are adapted to specific environmental conditions. Over time, divergence leads to the appearance of large differences in initially slightly different forms. As a result, they develop differences in many ways. Over a long period of time, this accumulates a large number of differences that new species arise. This is what ensures the diversity of species on our planet.
Charles Darwin's merit in science lies not in the fact that he proved the existence of evolution, but in the fact that he explained how it could occur, i.e. proposed a natural mechanism that ensures evolution and improvement of living organisms, and proved that this mechanism exists and works.
What statements relate to the theory of Ch. Darwin?
1) Within a species, the diversity of signs leads to a view.
2) The view is not one-but-ro-den and is represented by many po-la-tions.
3) Natural selection is the main factor of evolution.
4) When creating varieties and breeds, the main factor is artificial selection.
5) The internal desire for perfection is a factor of evolution.
6) Po-pu-la-tion is a unit of evolution.
Clarification.
Statements from the theory of Ch. Darwin: within a species, the divergence of signs leads to vi-do-ob-ra-zo-va-nu; natural selection is the right-hand factor of evolution; When creating varieties and breeds, the main factor is artificial selection.
Answer: 134.
Note.
Dar-vi-n's evolutionary theory is a holistic doctrine about the historical development of or- no world.
The basic principles of the evolutionary theory of Ch. Darwin.
1. In the context of each species of living organisms, there is a huge scope of in-di-vi-du-al-noy on-the-next national of men-chi-in-sti according to mor-fo-lo-gi-che-skim, phy-sio-lo-gi-che-skim, ve-den-che-skim and any other Gym sign. This change-ability may have a continuous, quantitative, or continuous qualitative character, but it always exists.
2. All living orga-niz-we multiply in geo-met-ri-che-skoy pro-gres-sion.
3. Life resources for any kind of living organisms are limited, and therefore there must be a struggle -ba for existence either between individuals of the same species, or between individuals of different species, or with natural conditions -I-mi. In the concept of “struggle for existence,” Darwin included not only the individual’s own struggle for life, but also the struggle for success in multiple times.
4. In conditions of struggle for existence, the most capable individuals survive and give birth to -those deviations in which some cases turned out to be adaptive to the given environmental conditions. This is a prin-tsi-pi-al-but important moment in the ar-gu-men-ta-tion of Dar-vi-na. Deviations occur not in the right way - in response to the action of the environment, but by chance. Not many of them turn out to be useful in specific conditions. Because you are alive, the individuals who subsequently suffer from a useful deviation are allowed to survive. ku, they appear to be more suitable for a given environment than other representatives of the population.
5. Survival and predominant multiplication in capable individuals Darwin called natural from -bo-rum.
6. Natural selection of individual iso-li-ro-van-varieties in different conditions of existence according to -gradually leads to diversification (diversity) of the signs of these different species and, ultimately, to vi-do-about-ra-zo-va-nu.
Answer: 134
Source: Unified State Examination in Biology 05/30/2013. Main wave. Siberia. Option 4.
Ilya Safronov (Veliky Novgorod) 02.09.2013 18:14
Well, in theory, the sixth option is also correct. The local population is considered the elementary unit of evolution.
Natalia Evgenievna Bashtannik
The population is the elementary unit of evolution - this is already the position of the Synthetic Theory of Evolution
Olga Ivanova 27.01.2014 17:14
Artificial selection is not the subject of evolutionary theory, but the synthetic theory of evolution develops Darwin's. Historical development the world does not address issues of selection.
Natalia Evgenievna Bashtannik
Darwin emphasized the particular importance of unconscious selection from a theoretical point of view, since this form of selection sheds light on the process of speciation. It can be seen as a bridge between artificial and natural selection. Artificial selection was a good model on which Darwin deciphered the process of morphogenesis. Darwin's analysis of artificial selection played an important role in substantiating the evolutionary process: firstly, he finally established the position of variability: secondly, he established the basic mechanisms of morphogenesis (variability, heredity, preferential reproduction of individuals with useful traits) and, finally, showed the ways of development expedient adaptations and divergence of varieties and breeds. These important premises paved the way for a successful solution to the problem of natural selection.
According to Darwin, the evolution of species in nature is determined by factors similar to those that determine the evolution of cultural forms. A prerequisite for the evolution of species is hereditary variability. Here too, Darwin distinguishes between the types of variability that he identified in relation to cultural forms, noting the special significance of indefinite (individual) variability. He believed that minor individual changes in organisms lead to the formation of their varieties. That is why he begins his proof of the variability of species with an analysis of the individual variability that exists in nature. Then Darwin proves the presence in nature of other factors that determine the possibility of evolution: in addition to hereditary variability, the presence of a selection factor is necessary. The role of the selecting factor is played by natural selection, which is based on the struggle for existence that arises as a result of the enormous intensity of reproduction of organisms, leading to overpopulation.
A special case of natural selection is sexual selection, which is not associated with the survival of a given individual, but only with its reproductive function, that is, with reproduction. Sexual selection acts on characters associated with various aspects of this essential function.
Sexual selection manifests itself most clearly during intense competition between individuals of the same sex, which arises as a result of specific forms of organization of the life of the species (polygamy or polyandry). The consequence of sexual selection is the development of external characteristics that distinguish males and females.
The intensity of reproduction of organisms.
The ability to reproduce is one of the basic properties of all living things. In nature, there is a tendency for organisms to reproduce unlimitedly. K. A. Timiryazev gives the following example illustrating this point. Dandelion, according to rough estimates, produces one hundred seeds. Of these, one hundred plants can grow next year, each of which also produces one hundred seeds. This means that with unhindered reproduction, the number of descendants of one dandelion could be represented as a geometric progression: the first year - one plant; second year - one hundred; the third - ten thousand; ...; the tenth year - ten to the eighteenth power of plants. To resettle the descendants of one dandelion, obtained in the tenth year, an area fifteen times larger than the area of the globe will be needed. this doesn't actually happen. Consequently, not all plants leave offspring; some of them die. If you count the number of dandelions per certain area in a meadow for several years, it turns out that it will change little.
This conclusion can be reached by analyzing the reproductive ability of a wide variety of plants and animals. According to Darwin's calculations, one poppy box contains three thousand seeds, and a poppy bush grown from one seed produces up to 60,000 seeds. Many fish annually lay up to ten to one hundred thousand eggs, cod and sturgeon - up to six million. Along with this, there are examples of relatively low fertility. Thus, a female elephant gives birth to offspring between the ages of thirty and ninety years. During these sixty years, she gives birth to about six cubs. However, even with such low fertility, the offspring of one pair of elephants in 750 years can amount to 19 million individuals.
From the above it follows that in nature there is a strong elimination (removal, exclusion) of organisms. In other words, not all offspring reach puberty and produce offspring - some of them die. Darwin laid the discrepancy between the number of individuals born and the number of individuals surviving to adulthood as the basis for his doctrine of the struggle for existence.
Hereditary (indeterminate) variability provides natural selection with material for the accumulation of new characteristics, just as humans accumulate in domestic animals and cultivated plants individual differences and creates new forms.
Charles Darwin provides evidence of the existence of variability in nature, and among them are the so-called “dubious species.” These include forms that are close in systematic position, for which it is difficult to say whether they are species or just subspecies of a more difficult species. The ambiguity of the boundaries between dubious species is due to the existence of transitional forms between them and neighboring species. Because of this, different descriptions of the flora and fauna of the same area may contain different numbers of species.
Darwin considered another proof of the variability of species to be the fact that species that have large distribution areas with diverse living conditions, as a rule, form a number of geographical subspecies.
Struggle for existence.
The most important place in the theory of natural selection is occupied by the concept of the struggle for existence. According to Darwin, the struggle for existence is the result of the tendency of organisms of any species to multiply without limits. What forces carry out the elimination of part of the offspring in nature? Darwin draws attention to the broad interrelationship between organisms and their connection with environment. A predator, in order to live, must eat, and herbivores serve as food for it. A herbivore eats many thousands of meadow plants to live. Plants are destroyed by insects. Insects are food for insectivorous birds, which in turn are exterminated by birds of prey. Darwin called these complex relationships the struggle for existence.
The term “struggle for existence” does not quite accurately correspond to the meaning that Darwin himself put into it, proposing to understand this term “in a broad and metaphorical sense.” Firstly, Darwin included in the concept of “existence” not only the life of a given individual, but also its success in leaving offspring. Secondly, the word “struggle” meant not so much struggle as such, but competition, often occurring in a passive form. Darwin understood the struggle for existence as the totality of all the complex relationships between an organism and the external environment that determine the success or failure of a given individual in its survival and leaving offspring.
The struggle for existence takes many different forms. This is, firstly, the direct destruction of one individual by another, and secondly, widespread competition in the struggle for light, moisture, food and place on earth. A plant that is stunted in growth is crowded out by other plants, the lack of light depresses it even more, and finally it dies. Darwin reduced the various manifestations of the struggle for existence to three types: interspecific, intraspecific, and struggle with the conditions of the inorganic external environment.
Examples of interspecies struggle are numerous. These are the relationships between predator and prey, herbivores and plants, insects and insectivorous birds; This is a competitive struggle between cultivated plants and weeds, between trees of different species in the forest and between grasses in the meadow. This also includes the phenomenon of antagonism between different types microorganisms.
Since by the struggle for existence Darwin understood the dependence of the organism on the physical factors of the external environment and other living beings, as well as the success of the individual “in providing itself with offspring,” then in his book “The Origin of Species” he also considers intraspecific relations as one of the main types of struggle for existence.
Emphasizing the role of overpopulation as a factor determining the struggle for existence, Darwin concluded that the most fierce should be intraspecific struggle, as competition between individuals of the same species that have similar vital needs. In addition, he analyzed the relationships between individuals of close and distant species. Individuals of distant species tend to have different needs. Sometimes their needs overlap, and then competition arises between them for certain living conditions. On the contrary, in individuals of closely related species, and especially in the same species, almost all the needs coincide, so the competitive struggle between them becomes especially intense.
The conditions of the inorganic external environment play a huge role in the process of elimination of individuals in the plant and animal world. Darwin gives an example when, during a severe winter in the area where he lived, 80% of the birds died. Many plants are destroyed almost every year by late frosts, drought, and sharp climatic fluctuations. With a lack of oxygen dissolved in water, fish die in water bodies. A significant mass of seeds is lost, blown by the wind in unfavorable conditions.
The struggle for existence leads to the death of organisms or a decrease in fertility, which in evolutionary terms is the same thing. Which individuals survive the struggle for existence, and which die? Is survival pure chance?
To resolve this issue, let us again turn to agricultural practice. In artificial selection, the breeder leaves for reproduction individuals that have at least small useful changes. The presence of beneficial changes should play a certain role in natural selection, only in the first case we're talking about about changes useful for humans, and in the second - about changes useful for the organisms themselves. Any change, even a small one, that is beneficial to the body will increase the likelihood of its survival. In other words, the individuals most adapted to environmental conditions survive.
Consequently, natural selection is a process occurring in nature in which, as a result of the influence of environmental conditions on developing organisms, individuals with useful traits are preserved that increase survival in given environmental conditions and determine their higher fertility.
Under different circumstances, natural selection can proceed at different rates. Darwin notes circumstances favoring natural selection:
Quite a high frequency of manifestation of uncertain hereditary changes.
The large number of individuals of a species increases the likelihood of beneficial changes occurring.
Unrelated crossing, increasing the range of variability in the offspring. Darwin notes that cross-pollination occurs occasionally even among self-pollinating plants.
Isolation of a group of individuals, preventing them from interbreeding with the rest of the organisms of a given population.
Wide distribution of the species, since at the borders of the range individuals meet with different conditions, and natural selection will go in different directions and increase intraspecific diversity.
Along with these circumstances, the main condition for the success of natural selection is its accumulating action, which is the basis of its creative species-forming activity.
