Ministry of Education of the Saratov Region
Municipal educational establishment no
"Average comprehensive school № 21
them. P.A. Stolypin"
Public lesson
Biology teacher Tatyana Vasilievna Glubokaya .
Saratov 2014
Topic: “Basic provisions of the theory of Charles Darwin
about the evolution of the organic world"
Lesson objectives.
Educational :
To consolidate students' knowledge of the contribution of European scientists to the development of evolutionary ideas,
To update students’ knowledge about the life activity of Charles Darwin,
To introduce students to the basic principles of the evolutionary theory of Ch, Darwin,
To develop their knowledge about the driving forces of evolution, about the evolutionary significance of heredity and variability of organisms, the forms and significance of natural selection,
Show the essence of the struggle for existence and the role of artificial selection as the driving force in the evolution of cultivated plants.
text, create presentations based on this material,
Developmental :
- the ability to highlight the main thing,
Establish cause and effect relationships,
Develop skills independent work with a textbook,
To develop cognitive interest in the subject and broaden the horizons of students.
Educational:
Instill respect for nature
Methods: conversation, story, testing (work in pairs), experiment
Means of education : tables on “General Biology”, educational cards, houseplants, multimedia projects.
Literature:
1. Ponomareva I.N.: Biology: 9th grade: textbook for students of general education institutions / I.N. Ponomareva, O.A. Kornilova, N.M. Chernova; edited by Prof. I.N. Ponomareva. - 4th ed., revised - M.: Ventana-graf, 2010.
2. Ponomareva I.N. Biology: 9th grade: methodological manual / I.N. Ponomareva. - 2nd ed., revised - M.: Ventana-Graf, 2011.
3. Lerner G.I. General biology (grades 10-11): Preparation for the Unified State Exam. Tests and independent works / G.I. Lerner.-M.: Eksmo, 2009.
4. Pimenov A.V., Pimenova I.N. Biology: Didactic materials to the section “General Biology” 9th grade; 10-11 grades –M.: Publishing House NC ENAS, 2004. (Teacher's portfolio).
During the classes
I . Organization of the beginning of the lesson .(mark those absent, repeat the home paragraph)
II . Testing students' knowledge:
A) conversation for guiding questions (7 min)
What is evolution? Which scientist first proposed this term?
What does evolutionary science study?
What have you learned about the ancient Greek scientist Heraclitus?
Which scientist, recognizing the material basis of the world, introduced the concept of the ladder of nature? What is its meaning?
What do you know about C. Linnaeus, where did we get acquainted with his works?
What is the merit of the French scientist J-L Buffon and the Russian scientist Peter Pallas?
b) Testing (work in pairs)(7 min) tests for §36(1)
V) summarizing knowledge tests: working with tables (4)
The emergence of organismal fitness
and variety of species
(according to C. Linnaeus, J.B. Lamarck, C. Darwin)
scientist
Reasons for the adaptability of organisms, the emergence of diversity of species (to be filled in by students)
Carl Linnaeus
The diversity of species was created by the Creator, organisms were created initially adapted (the theory of creationism)
Jean Baptiste Lamarck
The diversity of species appeared as a result of evolution, fitness appeared under the influence of the internal desire for progress, abilities will expediently change when the environment changes. The organs are exercised and changed; the acquired characteristics are inherited.
Charles Darwin.
Both the fitness of organisms and the diversity of species are the result of evolution. Hereditary variability supplies material; as a result of the struggle for existence, natural selection of the most adapted occurs and new species are formed
III . Learning new material:
Lesson topic: “Basic provisions of Charles Darwin’s theory of the evolution of the organic world”
1. Introduction
Updating students' knowledge about the life activity of Charles Darwin.
a) Oral answers to questions:
What did you learn about this scientist from the home paragraph?
Who was he, where did he live, what did he do?
What century did Charles Darwin live in?
What was his hobby?
What was the result of his many years of research?)
b) View the student's multimedia project.
2. Driving forces of evolution.( explanation using a multimedia project)
Charles Darwin's idea of the driving forces of evolution as four interrelated factors: variability, heredity, the struggle for existence and natural selection. The significance of variability and heredity of organisms in the evolutionary process.
The result of 20 years of research by Charles Darwin was the work “The Origin of Species by Natural Selection or the Preservation of Favored Breeds in the Struggle for Life”
To explain the process of evolution in the organic world, Darwin explores 4 main interrelated factors: a). Variability, b) heredity, c) struggle for existence, d) natural selection.
a) Variability . Comparing several individuals of the same species, he observed differences in them: size, color, habits and concluded that each species is characterized by variability. For example: - coleus, a flower on the window sill, has different leaf colors. What type of variability is this? What does it depend on?
This modification variability. The color of the leaves depends on their illumination
b) Heredity. Their parents also had some signs of living organisms: color, size, exterior, i.e. "children" received them from their parents. Changes that can be inherited are found in every species, especially if reproduction is sexual.
c) Intraspecific and interspecific struggle for existence between organisms as a provision of Charles Darwin’s evolutionary theory.The struggle of organisms with inanimate nature as one of the manifestations of the struggle for existence.
Struggle for existence. Some changes that appear in descendants help individuals survive in certain conditions environment. But not all individuals of the offspring reach sexual maturity: diseases, food, living conditions, i.e. There is a constant struggle for survival between individuals.
Types of wrestling: 1) intraspecific struggle (between individuals of the same species) (Fig. 47, p. 137, No. 3)(1)
An example of intraspecific struggle can be seen among plants. For example, among adolescents of flowering Kalanchoe plants or bryophyllum. (demonstration of a living window sill flower) there is a struggle for light, water, for land, i.e. struggle for equal living conditions.
2) fight between individuals different types –(interspecific struggle) (see Fig. 47, on p. 137, No. 1)(1)
An example of intraspecific struggle among adolescent flowering plants Kalanchoe or bryophyllum and a flowering plant Gasteria living in the same pot. (demonstration of an experimental plant) We see that Gasteria, being a larger and older plant, kills young Kalanchoe plants.
3 ) the struggle between an individual and environmental conditions - with inanimate nature. (see Fig. 47, on p. 137, No. 2)(1)
d) Survival and preferential reproduction of the fittest individuals as a result of the struggle for existence. The role of natural selection in the formation of new species from existing ones.
As a result of these types of struggle, the strongest survive. They produce more resistant offspring, possibly with new characteristics that were formed during the struggle for survival, as a result of selection.
The appearance of new characteristics and properties can change the original form of a species so much that we are talking about the appearance of individuals of a new subspecies, and then a species.
Darwin argued that natural selection is the path to the formation of new species. He considered the main point in evolution to be the divergence of characters in individuals, the emergence of new forms from one form or divergence (Latin - I am moving away, deviating). These characteristics helped the individual to survive and adapt to various living conditions.
As a result:
1-there was a gradual complication, an increase in the level of organization of the body,
2- increased adaptability to environmental conditions,
3- a variety of species appeared.
Conclusion. With the help of natural selection, according to Darwin, new species are formed in nature from already existing species. (See Fig. 48, p. 139.)
It follows from this that man, thanks to the variability of species, obtains new varieties of plants, breeds of animals through artificial selection, i.e., man, when breeding animals and plants, looked for specimens among them that had the characteristic he needed in the most vivid expression and left only it for reproduction. And then, through methodical conscious selection, he received a large number of individuals he needed.Darwin called this purposeful creation of new species artificial selection.
Darwin's theory of the evolution of the organic world explains the fitness of organisms (adaptation) to the environment. Considers the diversity of species as an inevitable result of natural selection due to the divergence of heritable characteristics.
3. Adaptation and its relative nature.
The adaptive nature of an individual is called adaptation. Adaptation is a set of morphological-physiological behavioral, population and other adaptive characteristics of a species that provide it with the opportunity to exist in certain conditions external environment.
Any adaptation is relative in nature, since it is useful to the organism only in its specific, familiar habitat. (See the table on “General Biology” on the board.)
The hazel grouse on the nest is not visible under the bush, but the fox finds it by smell. The white hare is not visible in the winter forest, but on the hairdryer of gray bushes it is clearly visible.
4. Generalization. The significance of Charles Darwin's work:
The significance of Charles Darwin's work (conclusions)
Discovered the moving forces of evolution,
Proved that modern species evolved from previously existing species,
Created a scientific theory of the evolution of the organic world.
III Homework: §37, questions after §, p.140, repeat §36
IV . Fastening:
a) Based on the material studiedfinish the table “The emergence of the fitness of organisms and the diversity of species” (third section of the second column)
b)Test: "The Driving Forces of Evolution" (oral)
1. The reason for the formation of new species, according to Darwin, is:
a) the struggle for existence,
b) gradual divergence in characters of individuals of the same species,
c) unlimited reproduction.
2. Natural selection is called:
a) the struggle for existence,
b) survival and reproduction of the strongest individuals,
c) survival and reproduction of the fittest individuals.
3. In what case will the struggle for existence be less fierce?
a) if several different species live in the territory,
b) if one species lives in the territory,
c) if two closely related species live in the territory.
4. The following are inherited from parents to offspring:
a) only useful signs,
b) useful and harmful signs,
c) only characteristics acquired by parents during their lives.
5) The significance of Charles Darwin’s theory lies in the fact that he:
a) proved the existence of an evolutionary process,
b) proved that species change during historical development,
c) identified the factors that determine the causes of diversity and fitness of species.
TOPIC: “DEVELOPMENT OF LIFE ON EARTH” (9th grade)
1.The longest conventional period of life on Earth is:
A) era
B) period,
B) era.
2. The era during which life arose is called:
A) early Proterozoic,
B) archaea,
B) Paleozoic.
3. The most important event of the Archean should be considered:
A) accumulation of oxygen in the atmosphere,
B) the appearance of coacervates,
C) formation of the first organic compounds.
4. One of the advantages of C. Linnaeus’ work was:
A) compliance of his system with modern ideas in taxonomy:
B) establishing relationships between species,
C) introduction of binary nomenclature.
5. A necessary condition for plant life on land was:
A) the presence of oxygen in the atmosphere,
B) presence of soil,
B) the presence of chlorophyll.
6. Which animals are considered to be the ancestors of trilobites and annelids:
A) arthropods,
B) shellfish,
B) ciliates.
7. In what era did lungfish and lobe-finned fish appear, from which land vertebrates originated:
A) in the Proterozoic,
B) in the Paleozoic,
B) in the Mesozoic,
D) in the Cenozoic.
After his trip, Darwin worked hard for 20 years to create the theory of evolution and published it in his work “The Origin of Species by Means of Natural Selection, or the Preservation of Favored Races in the Struggle for Life” (1859).
In further works Darwin developed and deepened different sides The main problem is the origin of species.
In the book “Changes in Domestic Animals and Cultivated Plants”, using a wealth of factual material, he showed the patterns of evolution of breeds of domestic animals and varieties of cultivated plants.
In The Descent of Man and Sexual Selection, Darwin applied evolutionary theory to explain the origin of man from animals.
Darwin wrote major works on botany, zoology and geology, in which individual issues of evolutionary theory were examined in detail.
Darwin's main merit is that he revealed the driving forces of evolution. He materialistically explained the emergence and relative nature of fitness through the action of only natural laws, without the intervention of supernatural forces.
Darwin's teaching fundamentally undermined the metaphysical ideas about the constancy of species and their creation by God.
What are the driving forces behind the evolution of domestic animal breeds, cultivated plant varieties, and species in the wild?
The driving forces of evolution of breeds and varieties are hereditary variability and human selection, namely:
The struggle for existence is a set of diverse and complex relationships that exist between organisms and environmental conditions. There are intraspecific struggles (between individuals of the same species), interspecific struggles (between individuals of different species) and struggles against unfavorable conditions. Intraspecific struggle is the most acute, since individuals of the same species have similar needs for survival.
Natural selection is a process of selective reproduction of organisms that occurs in nature, as a result of which the proportion of individuals with traits and properties useful for the species in specific environmental conditions increases in the population. The creative role of selection lies in the fact that in the process of evolution it preserves and accumulates from multidirectional mutations those that are most appropriate to environmental conditions and useful for the species.
Hereditary variability (mutational or genotypic) is associated with a change in the genotype of an individual, so the resulting changes are inherited. It is the material for natural selection. Darwin called this heredity indeterminate. The source of hereditary variability is mutations.
Darwin established that various breeds of animals and varieties of cultivated plants were created by man through the process of artificial selection. From generation to generation, a person selected and left individuals with some interesting change for him, necessarily hereditary, and eliminated other individuals from reproduction. As a result, new breeds and varieties were obtained, the characteristics and properties of which corresponded to human interests.
Is there a similar process in nature?
Organisms reproduce exponentially, but relatively few survive to adulthood. A significant proportion of individuals die, leaving no offspring at all or leaving few. Between individuals of both the same species and different species, a struggle for existence arises, by which Darwin understood the complex and diverse relationships of organisms with each other and with environmental conditions. He meant “not only the life of one individual, but also its success in providing itself with offspring.”
The formation of new species begins in populations saturated with constantly occurring mutations, which, when freely crossed, lead to changes in genotypes and phenotypes. Changes in living conditions lead to divergence of characteristics among individuals of a given population, to divergence. The initial population forms a group of forms with varying degrees of characteristic deviations. Individual organisms with altered characteristics are able to colonize new habitats and increase their numbers.
At driving selection Individuals with extreme, contrasting deviations have the greatest opportunity to survive and leave fertile offspring. Intermediate forms have more contact and die out faster. Thus, “new individuals” arise in the original population, from which new populations are first formed, and then, with subsequent divergence, new subspecies and species. The principle of divergence explains the origin of the diversity of life forms. According to the generally accepted classification, the systematic unit of living organisms is the species.
A species is a group of individuals similar in structure, origin and nature of physiological processes; freely interbreeding and producing fertile offspring. Individuals of the same species have the same adaptations to life in certain conditions. Any species consisting of one or more populations is a single entity. Integrity is achieved by connections between individuals of a species: caring for offspring, communication through various signals, joint protection from enemies, crossing. Integrity is also achieved through biological isolation - isolation from other species (individuals of different species, as a rule, do not interbreed). All this characterizes the species as a supraorganismal system. Type criteria:
The consequence of the struggle for existence is natural selection. Darwin used this term to describe “the preservation of favorable individual differences and changes and the elimination of harmful ones.”
Living things have variability; Even children of the same parents are not completely alike. There are always some differences between animals of the same species: each individual has certain characteristics that distinguish it from other individuals.
For example, among wolves of the same litter, each one differs in some way from its brothers and sisters: one may have darker fur, another may have a slightly sharper sense of smell, a third may have weaker hearing, and so on. Some of these features may not be important for the life of wolves, for example, more dark color wool; other features can be favorable for life, for example, a sharper sense of smell: a wolf endowed with it will sense prey earlier than others and will be more likely than others to discover the presence of an enemy - a dog or a hunter. This keen hearing will serve him well and help him survive in difficult conditions. A wolf endowed with this feature can live longer than others and leave behind more numerous offspring.
Finally, features of the third kind are those that are harmful to the life of the animal; such is the weak hearing in our example: a deaf wolf will be more likely than others to be in a difficult situation and will probably die before them; his offspring will not be so numerous. The characteristics by which some individuals differ from others can be either hereditary or non-hereditary. If they are not transmitted to offspring (non-hereditary traits), they have only indirect significance for the development of a given animal species. Darwin therefore relies only on hereditary characteristics.
If the traits of our wolves are hereditary, then in the next generation we can see a slightly different picture: the first wolf will produce wolves with darker fur (a trait neither harmful nor beneficial); from the second wolf more numerous offspring will be born, endowed with a subtle sense of smell, and from the third there will either be no offspring left at all or they will be few in number. If a difficult time comes in the life of these wolves, for example, a very harsh winter, then those wolves that are endowed with the best sense will most likely survive. Fewer wolves with dark fur will survive, and those wolves that have a harmful trait will not survive this time at all.
Thus, after several generations, there will be a selection of wolves best adapted to living conditions. This selection will lead to the extinction of those less adapted and to an increase in the number of those that have traits useful for life.
Thus, due to the differences between animals (or plants) of the same species, due to their variability, the better adapted are selected. Such selection in some cases intensifies and leads to changes in some breeds and the extinction of others. Thus, over an extremely long period of time, the living world gradually changes: some breeds are reborn into new ones, others disappear.
The doctrine of natural selection, variability and heredity is the essence of Darwinism.
The struggle for existence and natural selection based on hereditary variability are, according to Darwin, the main driving forces (factors) in the evolution of the organic world.
Individual hereditary deviations, the struggle for existence and natural selection over a long series of generations will lead to changes in species in the direction of increasing adaptability to specific conditions of existence.
The fitness of organisms is always relative.
Another result of natural selection is the diversity of species inhabiting the Earth.
Answers:
1. The term chromosome was proposed in 1888. German morphologist W. Waldeir. The work of D Morgan and his colleagues established the linearity of the arrangement of genes along the length of the chromosome.
According to the chromosomal theory of heredity, the totality of genes that make up one chromosome forms clutch group.
Chromosomes consist mainly of DNA and proteins, which form a nucleoprotein complex. Proteins make up a significant part of the substance of chromosomes. They account for about 65% of the mass of these structures. All chromosomal proteins are divided into two groups: histones and non-histone proteins. Chromosome RNA is represented mainly by transcription products that have not yet left the site of synthesis.
The regulatory role of chromosome components is to “prohibit” or “permit” the reading of information from the DNA molecule.
In the first half of mitosis, chromosomes consist of two chromatids. interconnected in the area of the primary constriction ( centromeres) a specially organized region of the chromosome common to both sister chromatids. In the second half of mitosis, the chromatids separate from each other. They form single-filamentous daughter chromosomes distributed between daughter cells.
Karyotype– a diploid set of chromosomes, characteristic of somatic cells of organisms of a given species, which is a species-specific feature and is characterized by a certain number and structure of chromosomes. If the number of chromosomes in a haploid set of germ cells is denoted P, then the general karyotype formula will look like 2 P, where the number P different for different species.
2. Morgan's Law. Linked genes localized on the same chromosome are inherited together.
Linked inheritance can be disrupted during the process of crossing over, which leads to the emergence of individuals with a new combination of characteristics. The number of recombinant individuals depends on the distance between genes. This law applies when allelic genes that control different traits are located on the same pair of chromosomes and form a linkage group.
Chromosomal theory of heredity. Key points:
1. Genes are located on chromosomes. Each chromosome represents a gene linkage group. The number of linkage groups is equal to the haploid set of chromosomes.
2. Each gene on a chromosome occupies a specific place - a locus. Genes on chromosomes are arranged linearly.
3. The distance between genes on a chromosome is directly proportional to the percentage of crossing over between them.
Sex-linked inheritance. An analysis of the inheritance of the eye color trait in Drosophila in T. Morgan's laboratory revealed some features that forced us to distinguish it as a separate type of inheritance of traits. interlocked with the floor inheritance. The dependence of the experimental results on which parent was the carrier of the dominant variant of the trait allowed us to propose that the gene that determines eye color in Drosophila is located on the X chromosome and does not have a homologue on the Y chromosome. All features of sex-linked inheritance are explained by the dose of the corresponding genes in a representative of different sexes - homo- and heterogametic.
The homogametic sex carries a double dose of genes located on the X chromosome. The development of corresponding characteristics in heterozygotes (X A X a) depends on the nature of the interaction between allelic genes. The heterogametic sex has one X chromosome (X0 or XY). In some species, the Y chromosome is genetically inert; in others, it contains a number of structural genes, some of which are homologous to the genes of the X chromosome. The genes of non-homologous regions of the X and Y chromosomes (or the only X chromosome) in the heterogametic sex are in a hemizygous state. They are represented by a single dose: X A Y, X a Y, XY B. The formation of such characteristics in the heterogametic sex is determined by which allele of a given gene is present in the genotype of the organism.
The nature of inheritance of sex-linked traits over a number of generations depends on which chromosome the corresponding gene is located on. In this regard, a distinction is made between X-linked and Y-linked (holandric) inheritance.
3. Darwin's theory is a holistic doctrine of the historical development of the organic world. It covers a wide range of problems, the most important of which is the proof of evolution, identifying the driving forces of evolution, determining the paths and patterns of the evolutionary process. 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 variability and heredity, 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.
The main provisions of the evolutionary theory of Charles Darwin
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The basis of Charles Darwin's evolutionary theory is the idea of a species, its variability in the process of adaptation to the environment and the transmission of characteristics from ancestors to offspring. The evolution of cultural forms occurs under the influence of artificial selection, the factors of which are variability, heredity and creative activity human, and evolution natural species is carried out thanks to natural selection, the factors of which are variability, heredity and the struggle for existence. |
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Driving forces of evolution |
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breeds and varieties |
organic world |
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hereditary variability and artificial selection |
the struggle for existence and natural selection based on hereditary variability |
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Variability
When comparing many breeds of animals and varieties of plants, Darwin noticed that within any species of animals and plants, and in culture, within any variety and breed there are no identical individuals. Based on the instructions of K. Linnaeus that reindeer herders recognize every deer in their herd, shepherds recognize every sheep, and many gardeners recognize varieties of hyacinths and tulips by bulbs, Darwin concluded that variability is inherent in all animals and plants.
Analyzing the material on the variability of animals, the scientist noticed that any change in living conditions is enough to cause variability. Thus, Darwin understood variability as the ability of organisms to acquire new characteristics under the influence of environmental conditions. He distinguished the following forms of variability:
In his books “On the Origin of Species by Means of Natural Selection, or the Preservation of Favored Breeds in the Struggle for Life” (1859) and “Changes in Domestic Animals and Cultivated Plants” (1868), Darwin described in detail the variety of breeds of domestic animals and analyzed their origin. He noted the diversity of cattle breeds, of which there are about 400. They differ from each other in a number of characteristics: color, body shape, degree of skeletal and muscle development, the presence and shape of horns. The scientist examined in detail the question of the origin of these breeds and came to the conclusion that all European breeds of cattle, despite the great differences between them, originated from two ancestral forms domesticated by humans.
The breeds of domestic sheep are also extremely diverse, there are more than 200 of them, but they come from a limited number of ancestors - mouflon and argali. Various breeds of domestic pigs were also bred from wild forms of wild boar, which, in the process of domestication, changed many features of their structure. The breeds of dogs, rabbits, chickens and other domestic animals are unusually diverse.
Darwin was particularly interested in the question of the origin of pigeons. He proved that all existing breeds of pigeons descended from one wild ancestor - the rock (mountain) pigeon. The breeds of pigeons are so different that any ornithologist, finding them in the wild, would recognize them as independent species. However, Darwin showed their common origin based on the following facts:
Darwin paid much attention to the study of various varieties of cultivated plants. Thus, comparing various varieties of cabbage, he concluded that they were all bred by man from one wild species: they differ in the shape of the leaves at similar flowers and seeds. U ornamental plants, for example, different varieties of pansies produce a variety of flowers, and their leaves are almost the same. Gooseberry varieties have a variety of fruits, but the leaves are almost the same.
Reasons for variability. Having shown the variety of forms of variability, Darwin explained the material causes of variability, which are environmental factors, the conditions of existence and development of living beings. But the influence of these factors varies depending on the physiological state of the organism and the stage of its development. Among the specific causes of variability, Darwin identifies:
Among the various forms of variability for the evolutionary process, hereditary changes are of paramount importance as the primary material for variety, breed and speciation - those changes that are fixed in subsequent generations.
Heredity
By heredity, Darwin understood the ability of organisms to preserve their species, varietal and individual characteristics in their offspring. This feature was well known and represented hereditary variation. Darwin analyzed in detail the importance of heredity in the evolutionary process. He drew attention to cases of same-suit hybrids of the first generation and splitting of characters in the second generation; he was aware of heredity associated with sex, hybrid atavisms and a number of other phenomena of heredity.
At the same time, Darwin noted that the study of variability and heredity, their immediate causes and patterns is associated with great difficulties. The science of that time could not yet give a satisfactory answer to a number of important questions. The works of G. Mendel were also unknown to Darwin. Only much later did extensive research into variability and heredity begin, and modern genetics made a giant step in the study of the material foundations, causes and mechanisms of heredity and variability, in the causal understanding of these phenomena.
Darwin attached great importance to the presence of variability and heredity in nature, considering them the main factors of evolution, which is adaptive in nature [show] .
Adaptive nature of evolution
Darwin in his work "The Origin of Species..." noted the most important feature of the evolutionary process - the continuous adaptation of species to the conditions of existence and the improvement of the organization of the species as a result of the accumulation of adaptations. However, he noted that the adaptability of a species, developed by selection to the conditions of existence, although it is important for the self-preservation and self-reproduction of species, cannot be absolute; it is always relative and is useful only in those environmental conditions in which species exist for a long time. The body shape, respiratory organs and other features of fish are suitable only for living in water and are not suitable for terrestrial life. The green coloration of locusts camouflages insects on green vegetation, etc.
The process of expedient adaptation can be traced using the example of any group of organisms that has been sufficiently studied in evolutionary terms. A good example is the evolution of the horse.
The study of the horse's ancestors made it possible to show that its evolution was associated with the transition from life in forests on marshy soil to life in open, dry steppes. Changes in the horse's known ancestors occurred in the following directions:
Naturally, along with these changes, correlative ones also occurred, for example, lengthening of the skull, changes in the shape of the jaws, the physiology of digestion, etc.
Along with the development of adaptations, the so-called adaptive diversity appears in the evolution of any group. It lies in the fact that, against the background of unity of organization and the presence of common systematic characteristics, representatives of any natural group of organisms always differ in specific characteristics that determine their adaptability to specific living conditions.
Due to living in similar living conditions, unrelated forms of organisms can acquire similar adaptations. For example, such systematically distant forms as a shark ( Pisces class), ichthyosaur (class Reptiles) and dolphin (class Mammals), have a similar appearance, which is an adaptation to the same living conditions in a certain environment, in this case in water. The similarity between systematically distant organisms is called convergence (see below). In sessile protozoa, sponges, coelenterates, annelids, crustaceans, echinoderms, and ascidians, the development of root-like rhizoids is observed, with the help of which they become stronger in the ground. Many of these organisms are characterized by a stalk-like body shape, which makes it possible, during a sedentary lifestyle, to soften the blows of waves, the impacts of fish fins, etc. All sessile forms are characterized by a tendency to form clusters of individuals and even coloniality, where the individual is subordinate to a new whole - the colony, which reduces the likelihood of death as a result of mechanical damage.
In different living conditions, related forms of organisms acquire different adaptations, i.e. two or more species can arise from one ancestral form. Darwin called this process of divergence of species in different environmental conditions divergence (see below). An example of this is the finches on the Galapagos Islands (west of Ecuador): some feed on seeds, others on cacti, and others on insects. Each of these forms differs from the other in the size and shape of the beak and could have arisen as a result of divergent variability and selection.
The adaptations of placental mammals are even more diverse, among which there are terrestrial forms with fast running (dogs, deer), species leading an arboreal lifestyle (squirrel, monkey), animals living on land and in water (beavers, seals), living in air environment (bats), aquatic animals (whales, dolphins) and species with an underground lifestyle (moles, shrews). All of them descend from a single primitive ancestor - an arboreal insectivorous mammal (Fig. 3).
Adaptation is never absolutely perfect due to the duration of the process of accumulation of adaptations. Changes in relief, climate, composition of fauna and flora, etc. can quickly change the direction of selection, and then adaptations developed in some conditions of existence lose their significance in others, to which new adaptations begin to be developed again. At the same time, the number of some species decreases, while the more adapted ones increase. Newly adapted organisms may retain previous signs of adaptation, which in new conditions of existence are not of decisive importance for self-preservation and self-reproduction. This allowed Darwin to talk about the inexpediency of signs of adaptation, which were found in the organization and behavior of organisms quite often. This is especially clearly seen when the behavior of organisms is not determined by their way of life. Thus, the webbed feet of geese serve as an adaptation for swimming and their presence is advisable. However, mountain geese also have webbed feet, which is clearly impractical given their lifestyle. The frigate bird does not usually land on the surface of the ocean, although, like bar-headed geese, it has webbed feet. It is safe to say that membranes were necessary and useful for the ancestors of these birds, just like modern aquatic birds. Over time, the descendants adapted to new living conditions and lost the habit of swimming, but they retained their swimming organs.
It is known that many plants are sensitive to temperature fluctuations and this is an appropriate response to the seasonal periodicity of vegetation and reproduction. However, such sensitivity to temperature fluctuations can lead to mass plant mortality if temperatures rise in the fall, stimulating the transition to repeated flowering and fruiting. This excludes normal preparation perennial plants towards winter and they die when cold weather sets in. All these examples indicate relative feasibility.
The relativity of expediency manifests itself when there is a significant change in the conditions of existence of the organism, since in this case the loss of the adaptive nature of one or another characteristic is especially obvious. In particular, the rational design of burrows with exits at the water level of the muskrat is destructive during winter floods. Erroneous reactions are often observed in migratory birds. Sometimes waterfowl fly to our latitudes before the opening of reservoirs, and the lack of food at this time leads to their mass death.
Purpose is a historically arose phenomenon under the constant action of natural selection, and therefore it manifests itself differently at different stages of evolution. In addition, the relativity of fitness provides the possibility of further restructuring and improvement of the adaptations available to a given type, i.e. the infinity of the evolutionary process.
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However, having substantiated the question of variability and heredity as factors of evolution, Darwin showed that by themselves they do not yet explain the emergence of new breeds of animals, plant varieties, species, or their fitness. Darwin's great merit is that he developed the doctrine of selection as the leading and directing factor in the evolution of domestic forms (artificial selection) and wild species (natural selection).
Darwin established that as a result of selection, a change in species occurs, i.e. selection leads to divergence - deviation from the original form, divergence of characteristics in breeds and varieties, the formation of a large variety of them [show] .
Divergent nature of evolution
Darwin developed the principle of divergence, i.e., divergence of characteristics of varieties and breeds, using the example of artificial selection. Subsequently, he used this principle to explain the origin of animal and plant species, their diversity, the emergence of differentiation between species, and substantiation of the doctrine of the monophyletic origin of species from a common root.
The divergence of the evolutionary process is derived from the facts of multidirectional variability, preferential survival and reproduction in a number of generations of extreme variants that compete with each other to a lesser extent. Intermediate forms, for which life requires similar food and habitats, are located in less favorable conditions and therefore die out faster. This leads to a greater gap between extreme options, the formation of new varieties, which later become independent species.
Divergence under the control of natural selection leads to the differentiation of species and their specialization. For example, the genus of tits unites species that live in different places(biotopes) and feed on different foods (Fig. 2). In butterflies of the white butterfly family, divergence went in the direction of caterpillars adapting to eating different food plants - cabbage, turnips, rutabaga and other wild plants of the cruciferous family. Among buttercups, one species lives in water, others live in swampy places, forests or meadows.
Based on similarity, as well as common origin, taxonomy unites closely related species of plants and animals into genera, genera into families, families into orders, etc. Modern taxonomy is a reflection of the monophyletic nature of evolution.
The principle of divergence developed by Darwin has important biological significance. It explains the origin of the wealth of life forms, the ways of development of numerous and more diverse habitats.
A direct consequence of the divergent development of most groups within similar habitats is convergence - the convergence of characters and the development of outwardly similar traits in forms of different origins. A classic example of convergence is the similarity of body shape and organs of movement in a shark (fish), ichthyosaur (reptile) and dolphin (mammal), i.e., the similarity of adaptations to life in water (Fig. 3). There are similarities between placental and marsupial mammals, between the smallest bird, the hummingbird, and the large butterfly, the hummingbird hawk moth. Convergent similarity of individual organs occurs in unrelated animals and plants, i.e. is built on a different genetic basis.
Progress and regression
Darwin showed that the inevitable consequence of divergent evolution is the progressive development of organic nature from simple to complex. This historical process of increasing organization is well illustrated by paleontological data and is also depicted in natural system plants and animals, uniting lower and higher forms.
Thus, evolution can take different paths. The main directions of evolutionary development and morphophysiological patterns of evolution were developed in detail by Academician. A.N. Severtsov (see macroevolution).
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Artificial selection
Analyzing the characteristics of breeds of domestic animals and varieties of cultivated plants, Darwin drew attention to the significant development in them of precisely those characteristics that are valued by humans. This was achieved using the same technique: when breeding animals or plants, breeders left for reproduction those specimens that most fully satisfied their needs and from generation to generation accumulated changes useful for humans, i.e. carried out artificial selection.
By artificial selection, Darwin understood a system of measures to improve existing and create new breeds of animals and plant varieties with useful (economically) hereditary traits and distinguished the following forms of artificial selection:
Purposeful breeding of a breed or variety. When starting work, the breeder sets himself a certain task in relation to the characteristics that he wants to develop in a given breed. First of all, these characteristics must be economically valuable or satisfy the aesthetic needs of humans. The traits with which the breeder works can be both morphological and functional. These may also include the nature of animal behavior, for example, pugnacity in fighting cocks. When solving the task set for himself, the breeder selects from the already available material all the best, in which the characteristics of interest to him are manifested, at least to a small extent. Selected individuals are kept in isolation to avoid unwanted crossbreeding. The breeder then selects pairs to cross. After this, starting from the first generation, he strictly selects the best material and rejects those that do not meet the requirements.
Thus, methodical selection is a creative process leading to the formation of new breeds and varieties. Using this method, the breeder, like a sculptor, sculpts new organic forms according to a pre-thought-out plan. Its success depends on the degree of variability of the original form (the more the characteristics change, the easier it is to find the desired changes) and the size of the original batch (in a large batch there are greater opportunities for choice).
Methodical selection in our time, using the achievements of genetics, has been significantly improved and has become the basis of modern theory and practice of animal and plant breeding.
Unconscious selection carried out by a person without a specific, pre-set task. This is the oldest form of artificial selection, elements of which were already used by primitive people. With unconscious selection, a person does not set a goal to create a new breed, variety, but only leaves it to the tribe and mainly reproduces the best individuals. So, for example, a peasant who has two cows, wanting to use one of them for meat, will slaughter the one that gives less milk; Of the chickens, he uses the worst laying hens for meat. In both cases, the peasant, preserving the most productive animals, carries out directed selection, although he does not set himself the goal of breeding new breeds. It is precisely this primitive form of selection that Darwin calls unconscious selection.
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.
The doctrine of natural selection as a driving and guiding factor in the historical development of the organic world -
central part of Darwin's theory of evolution
.
The basis of natural selection is the struggle for existence - the complex relationships between organisms and their connection with the environment.
Struggle for existence
In nature, there is a constant tendency towards unlimited reproduction of all organisms in geometric progression. [show] .
According to Darwin's calculations, one poppy box contains 3 thousand seeds, and a poppy plant grown from one seed produces up to 60 thousand seeds. Many fish annually lay up to 10-100 thousand eggs, cod and sturgeon - up to 6 million.
Russian scientist K. A. Timiryazev gives the following example illustrating this point.
Dandelion, according to rough estimates, produces 100 seeds. Of these, 100 plants can grow next year, each of which will also produce 100 seeds. This means that with unhindered reproduction, the number of descendants of one dandelion could be represented as a geometric progression: the first year - 1 plant; second - 100; third - 10,000; tenth year - 10 18 plants. To resettle the descendants of one dandelion obtained in the tenth year, an area 15 times larger than the area of the globe will be needed.
This conclusion can be reached by analyzing the reproductive ability of a wide variety of plants and animals.
However, if you count, for example, the number of dandelions per certain area meadows for several years, it turns out that the number of dandelions changes little. A similar situation is observed among representatives of the fauna. Those. "geometric progression of reproduction" is never carried out, because between organisms there is a struggle for space, food, shelter, competition when choosing a sexual partner, a struggle for survival with fluctuations in temperature, humidity, lighting, etc. In this struggle, the majority of those born die (are eliminated, removed) without leaving offspring, and therefore in nature the number of individuals of each species on average remains constant. In this case, the surviving individuals turn out to be the most adapted to the conditions of existence.
Darwin laid the discrepancy between the number of individuals born and the number of individuals surviving to adulthood as a result of complex and varied relationships with other living beings and environmental factors as the basis of his doctrine of the struggle for existence or the struggle for life [show] . At the same time, Darwin realized that this term was unsuccessful and warned that he was using it in a broad metaphorical sense, and not literally.
Darwin reduced the various manifestations of the struggle for existence to three types:
Intraspecific relationships are also quite complex (relationships between individuals of different sexes, between parental and daughter generations, between individuals of the same generation in the process of individual development, relationships in a flock, herd, colony, etc.). Most forms of intraspecific relationships are important for the reproduction of the species and maintaining its numbers, ensuring a change of generations. With a significant increase in the number of individuals of a species and restrictions on the conditions for their existence (for example, with dense plantings), acute interaction arises between individual individuals, which leads to the death of some or all individuals or their elimination from reproduction. Extreme forms of such relationships include intraspecific struggle and cannibalism - eating individuals of one's own species.
The fight against inorganic environmental conditions occurs depending on climatic and soil conditions, temperature, humidity, light and other factors affecting the life of organisms. During the process of evolution, animal and plant species develop adaptations to life in a particular environment.
It should be noted that the three named main forms of struggle for existence in nature are not carried out in isolation - they are closely intertwined with each other, due to which the relationships of individuals, groups of individuals and species are multifaceted and quite complex.
Darwin was the first to reveal the content and meaning of such important concepts in biology as “environment”, “ external conditions", "the relationships of organisms" in the process of their life and development. Academician I. I. Shmalgauzen considered the struggle for existence to be one of the main factors of evolution.
Natural selection
Natural selection, in contrast to artificial selection, is carried out in nature itself and consists of the selection within a species of the most adapted individuals to the conditions of a particular environment. Darwin discovered a certain commonality in the mechanisms of artificial and natural selection: in the first form of selection, the conscious or unconscious will of man is embodied in the results, in the second, the laws of nature prevail. In both cases, new forms are created, but with artificial selection, despite the fact that variability affects all organs and properties of animals and plants, the resulting animal breeds and plant varieties retain characteristics that are useful for humans, but not for the organisms themselves. On the contrary, natural selection preserves individuals whose changes are useful for their own existence in given conditions.
In “The Origin of Species,” Darwin gives the following definition of natural selection: “The preservation of beneficial individual differences or changes and the destruction of harmful ones I called natural selection, or the survival of the fittest” (c)-(Darwin Ch. Origin of Species. - M., L.; Selkhozgi, 1937, p. 171). He warns that "selection" should be understood as a metaphor, as a fact of survival, and not as a conscious choice.
So, natural selection is understood as a process that constantly occurs in nature, in which the most adapted individuals of each species survive and leave offspring and the less adapted ones die [show] . The extinction of the unadapted is called elimination.
Consequently, as a result of natural selection, the species that are most adapted to the specific environmental conditions in which their lives take place survive.
Constant changes in environmental conditions over a long period of time cause a variety of individual hereditary changes, which can be neutral, harmful or beneficial. As a result of life competition in nature, there is a constant selective elimination of some individuals and the preferential survival and reproduction of those that, by changing, have acquired useful characteristics. As a result of crossing, a combination of characteristics of two different forms occurs. Thus, from generation to generation, minor useful hereditary changes and their combinations accumulate, which over time become characteristic features of populations, varieties, and species. Moreover, due to the law of correlation, simultaneously with the intensification of adaptive changes in the body, a restructuring of other characteristics also occurs. Selection constantly influences the entire organism, its external and internal organs, on their structure and function. This reveals the creative role of selection (see microevolution).
Darwin wrote: “Metaphorically speaking, we can say that natural selection daily, hourly investigates the smallest changes throughout the world, discarding the bad, preserving and adding the good, working silently, invisibly, wherever and whenever the opportunity presents itself, to improve every organic being in relation to the conditions of its life, organic and inorganic" (c)-(Darwin Ch. Origin of Species. - M., Leningrad; Selkhozgi, 1937, p. 174.).
Natural selection is a historical process. Its effect manifests itself after many generations, when subtle individual changes are summed up, combined and become characteristic adaptive characteristics of groups of organisms (populations, species, etc.).
Sexual selection. As a special type of intraspecific natural selection, Darwin identified sexual selection, under the influence of which secondary sexual characteristics are formed (bright colors and various decorations of males of many birds, sexual differences in the development, appearance, behavior of other animals) in the process of active relationships between the sexes of animals, especially during the breeding season .
Darwin distinguished between two types of sexual selection:
The results of both types of sexual selection differ. With the first form of selection, strong and healthy offspring appear, well-armed males (the appearance of spurs, horns). During the second, such secondary sexual characteristics of males as the brightness of plumage, characteristics of mating songs, and the smell emitted by the male, which serves to attract a female, are enhanced. Despite the seeming inappropriateness of such traits, since they attract predators, such a male has an increased chance of leaving offspring, which turns out to be beneficial for the species as a whole. The most important result of sexual selection is the appearance of secondary sexual characteristics and associated sexual dimorphism.
Under different circumstances, natural selection can proceed at different rates. Darwin notes circumstances favoring natural selection:
| Comparative characteristics artificial and natural selection | ||
| Comparison indicator | Evolution of cultural forms (artificial selection) | Evolution of natural species (natural selection) |
| Material for selection | Individual hereditary variability | |
| Selective factor | Human | Struggle for existence |
| The nature of the selection action | Accumulation of changes in a successive series of generations | |
| Selection action speed | Acts quickly (methodical selection) | Acts slowly, evolution is gradual |
| Selection results | Creation of forms useful to humans; formation of breeds and varieties | Education of adaptations to the environment; formation of species and larger taxa |
In its most general form, the scheme of action of natural selection, according to Darwin, comes down to the following. Due to the inherent indefinite variability of all organisms, individuals with new characteristics appear within a species. They differ from ordinary individuals of a given group (species) in their needs. Due to the difference between old and new forms, the struggle for existence leads some of them to elimination. As a rule, less evaded organisms that became intermediate in the process of divergence are eliminated. Intermediate forms find themselves in conditions of intense competition. This means that monotony, which increases competition, is harmful, and evading forms are more advantageous position and their numbers are increasing. The process of divergence (divergence of characteristics) occurs constantly in nature. As a result, new varieties are formed and such separation of varieties ultimately leads to the emergence of new species.
Thus, the evolution of cultural forms occurs under the influence of artificial selection, the components (factors) of which are variability, heredity and human creative activity. The evolution of natural species is carried out thanks to natural selection, the factors of which are variability, heredity and the struggle for existence. Comparative characteristics of these forms of evolution are given in the table.
Darwin's process of speciation
Darwin saw the emergence of new species as a long process of accumulation of beneficial changes, increasing from generation to generation. The scientist took small individual changes as the first steps of speciation. Their accumulation over many generations leads to the formation of varieties, which he considered as steps towards the formation of a new species. The transition from one to another occurs as a result of the cumulative action of natural selection. A variety, according to Darwin, is an emerging species, and a species is a distinct variety.
In the process of evolution, several new ones can arise from one ancestral species. For example, species A, as a result of divergence, can give rise to two new species B and C, which in turn will be the basis for other species (D, E), etc. Of the changed forms, only the most deviated varieties survive and give birth to offspring, each of which again produces a fan of changed forms, and again the most deviated and better adapted survive. Thus, step by step, greater and greater differences arise between extreme forms, finally developing into differences between species, families, etc. The reason for divergence, according to Darwin, is the presence of uncertain variability, intraspecific competition and the multidirectional nature of the action of selection. A new species can also arise as a result of hybridization between two species (A x B).
Thus, C. Darwin in his teaching combines the positive aspects of the doctrine of the species of C. Linnaeus (recognition of the reality of species in nature) and J.-B. Lamarck (recognition of the limitless variability of species) and proves the natural path of their formation on the basis of hereditary variability and selection. They were offered four species criteria - morphological, geographical, ecological and physiological. However, as Darwin pointed out, these characteristics were not sufficient to clearly classify species.
The species is a historical phenomenon; it arises, develops, reaches full development, and then, under changed environmental conditions, disappears, giving way to other species, or itself changes, giving rise to other forms.
Species extinction
Darwin's doctrine of the struggle for existence, natural selection and divergence satisfactorily explains the question of the extinction of species. He showed that in constantly changing environmental conditions, some species, decreasing in number, must inevitably die and give way to others, better adapted to these conditions. Thus, in the process of evolution, the destruction and creation of organic forms are constantly carried out as a necessary condition for development.
The reason for the extinction of species may be various unfavorable environmental conditions for the species, a decrease in the evolutionary plasticity of the species, a lag in the rate of variability of the species or the rate of change in conditions, narrow specialization. More competitive species displace others, as the fossil record clearly demonstrates.
Assessing the evolutionary theory of Charles Darwin, it should be noted that he proved the historical development of living nature, explained the ways of speciation as natural process and actually substantiated the formation of adaptations of living systems as a result of natural selection, revealing for the first time their relative nature. Charles Darwin explained the main causes and driving forces of the evolution of plants and animals in culture and the wild. Darwin's teaching was the first materialist theory of the evolution of living things. His theory played a major role in strengthening the historical view of organic nature and largely determined the further development of biology and all natural science.
MOSCOW HUMANITIES AND ECONOMICS INSTITUTE NIZHNEKAMSK BRANCH
On the topic “Evolutionary theory of Charles Darwin: basic principles and ideological significance”
Discipline "Concept of modern natural science"
Completed by: student Ez-931 group
Faculty of Economics
Prokazova Tatyana Aleksandrovna
Scientific adviser:
Yakovleva Elena Vladimirovna
Nizhnekamsk 2010
Introduction……………………………………………………………………………….3
1. The concept of “evolution”……………………………………………………5
2. Prerequisites for the emergence of the theory of natural selection…………5
3. Basic provisions of evolutionary theory………………………….7
4. Results of natural selection……………………………8
5. Examples of natural selection…………………………………….10
6. Scientists’ opinions on Charles Darwin’s theory………………… ………………11
7. Confirmation of the evolutionary theory of C. R. Darwin…………….13
8. The meaning of evolutionary theory. Conclusions……………………………17
List of references……………………………………………………….19
Introduction
On our planet there are at least 2 million species of animals, up to 0.5 million species of plants, hundreds of thousands of species of microorganisms and fungi. The origins of such a diversity of species and their adaptability to the environment are of concern to scientists and researchers around the world.
For thousands of years, it seemed obvious to people that living nature was created as we know it now, and has always remained unchanged. However, in ancient times, guesses were made about the gradual change, development (evolution) of living nature. One of the harbingers of evolutionary ideas can be called ancient Greek philosopher Heraclitus, who formulated the position about changes constantly occurring in nature (“everything flows, everything changes”).
Scientific theory The evolution of living nature, the foundations of which were laid by the great English scientist Charles Darwin in the 19th century, finally provided answers to the questions of researchers and scientists.
Charles Darwin's theory, known as the theory of natural selection, is one of the pinnacles of scientific thought in the 19th century.
Most biologists (before Darwin) adhered to the idea of constancy and immutability of living organisms-species. Organisms and organs fully correspond to the goal supposedly set by the creator. The essence of the worldview of this period lies in the ideas of constancy, immutability and the original purposefulness of nature. This worldview is called metaphysical. Metaphysical ideas were supported by the church and ruling circles.
In the 17th-18th centuries. many descriptions of species of animals, plants, and minerals have accumulated. The enormous task of systematizing these materials was carried out by Carl Linnaeus (1707-1778), a Swedish naturalist and physician. Based on similarities in one or two of the most noticeable characteristics, he classified organisms into species, genera, and classes. He correctly placed man and apes in the same order. The significance of Linnaeus's works is enormous: he proposed a system of animals and plants, the best of all previous ones; introduced double species names; improved botanical language.
Charles Darwin, in his main work “The Origin of Species by Means of Natural Selection” (1859), managed, by summarizing the empirical material of contemporary biology and breeding practice, using the results of his own observations during his travels, circumnavigation on the Beagle ship, to reveal the main factors in the evolution of the organic world.
He explored the geological structure, flora and fauna of many countries, and sent a huge number of collections from England. Having compared the found remains of plants and animals with modern ones (at that time), Charles Darwin made an assumption about a historical, evolutionary relationship.
In the book “Changes in Domestic Animals and Cultivated Plants” (vol. 1-2, 1868), he presented additional factual material to the main work. In the book “The Descent of Man and Sexual Selection” (1871), he put forward the hypothesis of the origin of man from an ape-like ancestor.
1 . The concept of "evolution"
The term “evolution” was first used in one of the embryological works by the Swiss naturalist Charles Bonnet in 1762. Currently, evolution is understood as an irreversible process of change in any system occurring over time, due to which something new, heterogeneous, and more valuable appears. high stage of development.
The process of evolution concerns many phenomena occurring in nature. For example, an astronomer talks about the evolution of planetary systems and stars, a geologist talks about the evolution of the Earth, a biologist talks about the evolution of living beings. At the same time, the term “evolution” is often applied to phenomena that are not directly related to nature in the narrow sense of the word. For example, they talk about the evolution of social systems, views, some machines or materials, etc.
The concept of evolution takes on special meaning in natural science, where biological evolution is studied primarily.
Biological evolution is an irreversible and, to a certain extent, directed historical development of living nature, accompanied by changes in the genetic composition of populations, the formation of adaptations, the formation and extinction of species, transformations of biogeocenoses and the biosphere as a whole. In other words, biological evolution should be understood as the process of adaptive historical development of living forms at all levels of organization of living things.
2. Prerequisites for the emergence of the theory of natural selection
Darwin sought the answer to the question of how new species arise in the practical activities of man. He studied the work of livestock breeders and plant breeders, he himself was involved in breeding chickens and pigeons, observed the feeding of insects and pollination of plants, conducted extensive correspondence with people of science and practice, and read many books.
Studying the history of the development of different breeds of horses, chickens, and sheep, Darwin found that numerous breeds originated from one or a few wild species. Their changes are associated with changes in living conditions: nutrition, climate, etc. Man selects animals and plants with changes that are beneficial to him. Man himself, as Darwin thought, cannot create these changes, nature causes them, and man only combines these gifts of nature and selects them. Thanks to selection, changes useful to humans accumulate and intensify, and this leads to the improvement of old breeds and varieties and to the development of new ones.
But how do new species arise in nature? Selection can proceed not only according to a predetermined plan, but also without it, without a clearly realized goal. At the same time, a person not only selects the best, but also destroys those that do not meet his needs or tastes. Consequently, not every creature that is born can survive and give the world offspring.
But what about in natural conditions? Will every sprout that emerges from the ground develop into a plant? Will every chick that appears in the nest become an adult bird? No. But who will survive? Obviously, the one who turns out to be more adapted to living conditions. But there is no rejector in nature. Who selects?
Selection occurs by itself, naturally.
In the economy, the hand of man selects - this is artificial selection, in nature - the hand of time - natural selection. In nature, animals and plants also change under the pressure of changing living conditions. But not all individuals of the same species change equally, and those of them that have at least some, however slight, advantage over the rest survive as a result of natural selection, leave offspring and eventually displace the less adapted. Natural selection leads to the gradual accumulation and intensification of changes beneficial to the body, to the improvement of organisms and their adaptation to changing environmental conditions, and as a result to the emergence of new species.
3. Basic provisions of evolutionary theory
Using the results of his own observations collected during his travels, Darwin worked hard for 20 years to create the theory of evolution.
The theory of evolution by Charles Darwin is outlined in the book “The Origin of Species by Means of Natural Selection, or the Preservation of Favored Breeds in the Struggle for Life” (1859).
The main provisions of the evolutionary teachings of Charles Darwin boil down to the following:
1. The diversity of animal and plant species is the result of the historical development of the organic world.
2. The main driving forces of evolution are the struggle for existence and natural selection. The material for natural selection is provided by hereditary variability. The stability of the species is ensured by heredity.
3. The evolution of the organic world mainly followed the path of increasing the complexity of the organization of living beings.
4.The adaptation of organisms to environmental conditions is the result of the action of natural selection.
5. Both favorable and unfavorable changes can be inherited.
6. The diversity of modern breeds of domestic animals and varieties of agricultural plants is the result of artificial selection.
7.Human evolution is connected with the historical development of ancient apes. The evolutionary teaching of Charles Darwin can be considered as a revolution in the field of natural science.
4. Results of natural selection
Natural selection is the inevitable result of the struggle for existence and hereditary variability of organisms.
Charles Darwin drew attention to the fact that although any living creature changes during life, individuals of the same species are not born the same. He wrote that an experienced farmer can distinguish each of the sheep even in a large herd. For example, their fur may be lighter or darker, thicker or thinner, etc. Under normal environmental conditions, such differences are insignificant. But when living conditions change, these small hereditary changes can give advantages to their owners. Among the many useless and harmful changes, there may also be useful ones. Reasoning in this way, Darwin came to the idea of natural selection. Individuals with useful differences survive and reproduce better, and pass on their characteristics to their offspring. Therefore, in the next generation the percentage of such individuals will become larger, after a generation even larger, etc. This is the mechanism of evolution. Darwin wrote: “It may be said that natural selection daily and hourly investigates throughout the world the smallest changes, discarding the bad, preserving and adding the good, working silently and unseen...” The evolution of different species proceeds at different speeds.
According to Darwin, natural selection is the most important creative force that directs the evolutionary process and naturally determines the emergence of adaptations of organisms, progressive evolution and an increase in the diversity of species.
The emergence of adaptations of organisms to the conditions of their existence, which gives the structure of living beings the features of “expediency”, is a direct result of natural selection, since its very essence is differentiated survival and the preferential leaving of offspring by precisely those individuals who, due to their individual characteristics, are better adapted than others to environmental conditions.
The accumulation by selection from generation to generation of those characteristics that provide an advantage in the struggle for existence.
The theory of natural selection makes it possible to explain the development of the most complex and perfect adaptations, including such as the mutual adaptation of two different species to each other, the interaction of which is beneficial for both. Such, for example, are the mutual adaptations of flowering plants and the insects that pollinate them.
Acting in species populations, natural selection contributes to the formation and spread of characteristics that are important and useful for the species as a whole: in this case, a contradiction may arise between the “interests” of the species and individual individuals. In this case, traits that are useful for the species are fixed, despite their negative role for individual individuals.
The second (after the emergence of adaptation) most important consequence of the struggle for existence and natural selection is, according to Darwin, a natural increase in the diversity of forms of organisms, which has the character of divergent evolution. Since the most intense competition is expected between the most similar individuals of a given species due to the similarity of their vital needs, in more favorable conditions there will be individuals who deviate most from the average state.
These latter get an advantage in surviving and leaving offspring, to whom the characteristics of the parents and the tendency to change further in the same direction are transmitted. With the predominant preservation of the most extreme variants of variability in each generation, it is obvious that evolution will move in the direction of dividing the species into varieties, which over time will turn into new (daughter) species.
According to Darwin, the ancestral and intermediate forms have worse chances of survival than the most deviant daughter forms, since the former are more similar to each other, and competition between them should be the most fierce. As a result, more and more diverse and different descendants should come from a common ancestor in the course of evolution.
5. Examples of natural selection
Examples of natural selection were described by scientists only in the 20th century.
The most famous of these examples is with the birch moth butterfly in England. Inspecting collections of butterflies collected over the previous hundred years in 1950, biologists discovered that butterflies with black wings were becoming more common, and butterflies with gray wings becoming increasingly rare. It turns out that during the day moths sit motionless on tree trunks, relying on their camouflage coloration. In the 19th century, gray coloring perfectly hid butterflies against the backdrop of lichens that covered the trees.
But as air pollution in England worsened, the lichens died and the trunks became black with soot. Against a dark background, gray butterflies became noticeable to their main enemies, birds. The black uniform turned out to be well camouflaged. As a result, the ratio of black to gray butterflies has steadily shifted in favor of blacks. (Note that the unit of evolution is always not an individual, but a population, i.e. a group of individuals (in this case, moths) living next to each other and interbreeding with each other).
Another example of natural selection is the emergence of resistance to pesticides in insects. Professor K. Williams wrote that in the early 40s. XX century “a powerful weapon ended up in the hands of man. It was the toxic chemical DDT, which, like an almighty avenging angel, attacked harmful insects. After the first contact with it, mosquitoes, flies, almost all insects went into a tailspin, fell, buzzed for an hour or two, lying on their backs, and then died.” The first reports of insect resistance to DDT appeared in 1947. and touched a housefly. Of the hordes of harmful insects, only a few systematically survived, having accidentally turned out to be more resistant to the poison. But every subsequent year, more and more resilient offspring remained alive. “A few years later,” Williams wrote, “mosquitoes, fleas, flies and other insects no longer paid attention to DDT. Soon they began to assimilate it, then they fell in love with it.” Such resistance has been found in more than 200 insect species, and the list continues to grow.
The story of the “addiction” of pathogenic bacteria to antibiotics and many other drugs is completely similar.
6. Scientists’ opinions on Charles Darwin’s theory
Some scientists compared the impression of a book to a flash of lightning, which suddenly illuminates the way for a person lost on a dark night. Others - with a bomb that Darwin threw from his peaceful rural home into the enemy camp.
In France, scientists treated the theory with contempt. German anti-Darwinists produced a lead medal on which Darwin was depicted in an offensive caricature with donkey ears.
The English geologist Sedgwick said with indignation that this theory was nothing more than a chain of soap bubbles, and he ended his letter to Darwin like this: “Now - one of the descendants of the monkey, in the past - your old friend.” Since Darwin's teachings undermined the foundations of religion, reactionary scientists set the clergy against him.
“Science and Christ have nothing in common” - this is the conclusion that Darwin himself drew from his teaching. This explains the fact that Darwin's teaching met with furious resistance from all the reactionary forces of bourgeois society and, above all, from the church.
Already in the first review of the book “On the Origin of Species,” Darwin’s teaching was criticized from the standpoint of theology, as fundamentally hostile to religion and irreconcilable with it. Darwin's materialistic theory of the origin of man aroused particular anger among theologians and scientists of the old school.
About one critic, Darwin wrote to friends that the critic himself, perhaps, would not have burned him at the stake, but he would have brought him some brushwood and would have shown the black beasts how to catch him. Catholic priests organized a special academy to combat evolutionary teaching, calling it “bestial philosophy.”
The abuse and contempt of ignorant people upset Darwin, but he did not answer them. He valued only the opinions of people he respected.
Advanced scientists greeted Darwin's theory with great enthusiasm. The German biologist E. Haeckel wrote that after reading this brilliant book, he felt like “a curtain fell from his eyes.” The young Professor Huxley was ready to “go to the stake” for a new idea. The path along which Darwin proposed to follow himself seemed to him not like an airy path of spider web threads, but like a wide bridge along which one could cross many abysses.
F. Engels noted that Darwin dealt a severe blow to idealistic ideas about nature, proving that the modern organic world is a product of historical development that lasted millions of years. He compared Darwin's merits in discovering the laws of the development of nature with the merits of Marx, who discovered the laws of the development of society.
The Russian translation of “The Origin of Species” appeared in 1864. The spread of Darwinism in Russia coincided with the rise of the revolutionary movement, with the awakening public consciousness after the Crimean War, with the spread of the ideas of the great Russian democrats N. G. Chernyshevsky, A. I. Herzen, D. I. Pisarev. And although here too there were attempts to turn the theory into an “incoherent heap of garbage,” but with the help of numerous popularizers, Darwin’s teachings became available to wide reading circles and were met with sympathy.
D.I. Pisarev called Darwin a brilliant thinker and wrote that Darwin talks about the laws of organic nature so simply and proves so irrefutably that anyone who reads his book is surprised how he himself did not come up with such clear conclusions a long time ago. But the main fighter in this battle of ideas was Darwin's book itself. Years passed, and Darwin's teachings spread like a stormy stream, sweeping away all obstacles along the way. Darwin was lucky during his lifetime to see the triumph of his ideas: not a year passed without him receiving some kind of award.
7. Confirmation of the evolutionary theory of C. R. Darwin.
With the emergence of Darwinism, several tasks came to the fore in biological research:
· collecting evidence of the very fact of evolution;
· accumulation of data on the adaptive nature of evolution;
· experimental study of the interaction of hereditary variability, the struggle for existence and natural selection as the driving force of evolution;
· study of patterns of speciation and macroevolution.
Information confirming Darwin's theory of evolution was obtained from a variety of sources, among which the most important are paleontology, biogeography, systematics, plant and animal breeding, morphology, comparative embryology and biochemistry.
1. Paleontology . This science deals with the study of fossil remains, i.e. any preserved in earth's crust traces of previously living organisms. These include whole organisms, hard skeletal structures, fossils, and prints.
In the 19th century these findings were interpreted from the point of view of the theory of evolution. The fact is that in the most ancient rocks there are traces of very few simple organisms. In young rocks, various organisms with a more complex structure are found. In addition, there are quite a lot of examples of the existence of species only at one stage of the geological history of the Earth, after which they disappear. This is understood as the emergence and extinction of species over time.
Gradually, scientists began to find traces of more and more “missing links” in the evolution of life: either in the form of fossils (for example, Archeopteryx - a transitional form between reptile and bird), or in the form of living organisms close in structure to fossil forms (for example, Coelacanth , referring to long-extinct lobe-finned fish). Of course, scientists have not been able to find all the transitional forms, so the fossil record of our planet is not continuous, and opponents of evolutionary theory use this argument. However, scientists find convincing explanations for this fact. In particular, it is believed that not all dead organisms find themselves in conditions favorable for their preservation. Most of the dead individuals are eaten by scavengers, decompose without leaving any traces, and return to the cycle of substances in nature.
Paleontologists managed to discover some patterns of evolution. In particular, as the complexity of an organism increases, the duration of existence of a species decreases, and the rate of evolution increases. Thus, bird species exist on average for 2 million years, mammals - 800 thousand years, human ancestors - about 200 thousand years. It was also possible to find out that the lifespan of a species depends on the size of its representatives.
2. Geographical distribution (biogeography) . All organisms are adapted to their environment. Therefore, all species arose in a specific area, and from there they could spread to areas with similar natural conditions. The degree of dispersal depends on how successfully these organisms can settle in new places and how complex the natural barriers are that stand in the way of the dispersal of this species (oceans, mountains, deserts). Therefore, species usually spread only if suitable areas are located close to each other. Thus, in the distant past, land masses were located closer to each other than they are now, and this contributed to the widespread dispersal of many species. If in some area there are no more developed species, then this indicates an early separation of this territory from the place of original origin of the species. That is why Australia has preserved a large number of marsupials that are absent in Europe, Africa and Asia.
These facts do not explain the mechanism of the emergence of new species, but indicate that different groups arose in different time and in different areas, which confirms the theory of evolution.
3. Biological classification (systematics) . K. Linnaeus created the first classification, which included the taxon units he identified, which were in a relationship of hierarchical subordination. He distinguished: species, genus, family, order, class, type and kingdom. Linnaeus based his classification on the structural similarity between organisms, which can be represented as the result of their adaptation to certain environmental conditions over a certain period. Thus, this classification fits well into evolutionary theory, illustrating the process of evolution on Earth.
4.Plant and Animal Breeding . In addition to natural selection, there is artificial selection associated with purposeful activities human conservation the right types. This is exactly how, through selection, all animals were bred from wild ancestors. cultivars plants and breeds of domestic animals.
With the creation of genetics, it became clear that during artificial selection, those genes that are useful for human purposes are preserved, and those that do not suit him are removed.
5. Comparative anatomy (morphology) . It deals with comparing groups of plants and animals with each other. At the same time, common structural features inherent in them are revealed. As a result, it becomes clear that they are fundamentally similar.
Thus, comparative anatomy reveals organs built according to the same plan, occupying a similar position and developing from the same rudiments. The existence of such organs, as well as the appearance of rudimentary organs that remain in organisms but do not perform any function, can only be explained by the theory of evolution.
6. Comparative embryology . One of the founders of this science was the Russian scientist K. M. Baer, who studied embryonic development in representatives of different groups of vertebrates. At the same time, he discovered a striking similarity in the development of embryos of all groups, especially in the early stages of their development.
After this, E. Haeckel expressed the idea that the early stages of embryo development repeat the evolutionary history of their group. He formulated the law of recapitulation, according to which the individual development of an organism repeats the development of the entire species. Thus, the vertebrate embryo at different stages of its development has the characteristics of a fish, amphibian, reptile, bird and mammal. Therefore, in the early stages of embryo development, it can be very difficult to determine which species it belongs to. Only at later stages does the embryo acquire resemblance to the adult form.
The law of recapitulation can only be explained by the presence of common ancestors in all living organisms, which confirms the evolutionary theory.
8. The meaning of evolutionary theory. conclusions
The significance of evolutionary theory is as follows:
1. The patterns of transformation of one organic form into another have been identified.
2. The reasons for the expediency of organic forms are explained.
3. The law of natural selection was discovered.
4. The essence of artificial selection is clarified.
5. The forces of evolution have been clarified.
Developed by Darwin evolutionary theory was a great achievement for mankind in the knowledge of living nature, a huge victory for the advanced, progressive forces of society in the struggle for a materialistic, atheistic worldview, against superstitions and religious prejudices.
Darwin was the first to prove the reality of evolutionary changes in organisms. The relationship between the organism and the external environment in his theory has the character of a dialectical interaction: Darwin emphasized the role of environmental changes as a stimulus for the variability of organisms, but, on the other hand, the specificity of these changes is determined by the organisms themselves, and the divergent evolution of organisms changes their habitat.
The doctrine of natural selection and the struggle for existence is, in essence, an analysis of these complex relationships between the organism and the environment, in which the organism is not opposed to the environment as a self-developing autonomous unit, but also does not passively follow changes in the environment (as the relationship between the organism and the environment is interpreted in the theory Lamarck). According to Darwin's theory, evolution is the result of the interaction of an organism and a changing external environment.
Modern evolutionary theory developed on the basis of Darwin's theory. In principle, recognizing this and assessing the specific place of Darwin’s ideas in the totality of modern evolutionary and views, they often fall into one of two extremes: either they believe that now Darwin’s concept as such has only historical interest - from it to modern science only the idea of natural selection remained; or, on the contrary, they argue that since Darwin’s time the foundations of the theory have not undergone significant changes.
Thus, Darwin's theory provided a logically consistent and strictly materialistic explanation for the most important problems of the evolution of organisms and the general structure of the organic world that emerged as a result of the evolutionary process.
List of used literature
1. Biology: “A manual for preparatory departments and applicants to universities” / N.P. Sokolova, I.I. Andreeva, L.N. Katonova, L.S. Rodman; Edited by N.P. Sokolova. – 2nd ed., rev. and additional – M.: Higher school, 1994.
2. Iordansky N.N. "The Evolution of Life". – M.: “Academy”, 2001.
3. Ch. Darwin “The Origin of Species by Means of Natural Selection”, series “Classics of Science”, ed. "Science" 2001
4. Alimov A.F., Levchenko V.F., Starobogatov Ya.I., Biodiversity, its protection and monitoring // Biodiversity Monitoring.M. 1997
5. Vorobyov R.I. Evolutionary teaching yesterday, today and. – M., 1995
6. Vorontsov N.N. Development of evolutionary ideas in biology. – M., 1999
7. Danilova V.S., Kozhevnikov N.N. Basic concepts of natural science. – M.: Aspect Press, 2000. – 256 p.
8. Darwin Ch. Op. T.3. - M. -L., 1939
9. Naydysh V.M. Concepts of modern natural science. – M., 1999
