What is evolution in biology? Driving forces, laws, examples. Development of evolutionary concepts

There are three main directions of evolution - aromorphosis, idioadaptation and general degeneration. All of them lead to biological progress, i.e. the prosperity of species and larger taxa, when a group increases its number and species diversity, expands its range.

Biological progress is contrasted with biological regression, when the number, range of species (s), as well as the number of species of a taxon decrease as a result of the group's inability to adapt to changing environmental conditions. In other words, biological regression occurs when historical development the taxon does not follow any direction of evolution.

Aromorphosis

Aromorphosis refers to major evolutionary transformations, usually leading to the emergence of large taxa, for example, classes in animals. Aromorphoses increase the general level of organization, make it more complex, are the main path of evolution. They occur rarely, significantly change the morphophysiology of organisms, and allow the colonization of new habitats.

Aromorphosis is complex and affects different organ systems. So the appearance of the lungs "pulled" the appearance of a three-chambered heart. The emergence of the four-chambered heart and the complete separation of the circulatory circles played an important role in the appearance of warm-bloodedness.

Examples of aromorphoses: the appearance of photosynthesis, multicellularity, sexual reproduction, internal skeleton, development of the lungs, the appearance of warm-bloodedness in animals, the formation of roots and conductive tissues in plants, the appearance of a flower and a fetus.

The appearance of the lungs allowed organisms to come out onto land, that is, to populate the habitat with new environmental conditions. The warm-bloodedness that arose in birds and mammals made it possible for them to be less dependent on temperature and populate habitats inaccessible to amphibians and reptiles.

Thanks to the appearance of roots that anchor the plant in the soil and absorb water, as well as a conductive system that delivers water to all cells, plants were able to grow on land. Their biomass has reached enormous values ​​here.

Idioadaptation

Idioadaptation is a small evolutionary change that allows a species to adapt to specific features of its habitat and a narrow ecological niche. These are private adaptations that do not change the general level of organization.

Idioadaptation provides the emergence of a variety of adaptive forms within the same level of organization.

So all mammals have a similar internal structure. However, the diversity of species adapted to different habitats, feeding methods was achieved by such a direction of evolution as idioadaptation.

Angiosperms have many different species, a number of life forms (grasses, shrubs, trees). They differ greatly in outward appearance, but their morphology and physiology have the same level of organization.

As a result of idioadaptation, characters that are insignificant for a large taxon change. For example, all birds have a beak; aromorphosis provided its appearance. But each species has its own shape and size of the beak, adapted to specific feeding methods. This was provided by idio adaptations.

General degeneration

An example of degeneration in the plant world is dodder, which does not have its own chlorophyll and feeds on other angiosperms.

Apparently, general degeneration in importance should be put on a par with aromorphosis, and not idioadaptation, since it usually affects significant changes in the body. For example, the loss of an entire system, or even organ systems, is a major change.

Small partial degenerations leading to a simplification of the structure of any organ, for example, loss of good vision in animals leading an underground lifestyle, should be considered as idioadaptation.

Evolutionary doctrine

Evolutionary doctrine (theory of evolution)- a science that studies the historical development of life: causes, patterns and mechanisms. Distinguish between micro- and macroevolution.

Microevolution- evolutionary processes at the level of populations, leading to the formation of new species.

Macroevolution- evolution of supraspecific taxa, as a result of which larger systematic groups are formed. They are based on the same principles and mechanisms.

Development of evolutionary ideas

Heraclitus, Empidocles, Democritus, Lucretius, Hippocrates, Aristotle and other ancient philosophers formulated the first ideas about the development of living nature.
Carl Linnaeus believed in the creation of nature by God and the constancy of species, but admitted the possibility of the emergence of new species by crossing or under the influence of environmental conditions. In the book "The System of Nature" K. Linnaeus substantiated the species as a universal unit and the main form of existence of living things; each species of animals and plants assigned a double designation, where the noun is the name of the genus, the adjective is the name of the species (for example, Homo sapiens); described great amount plants and animals; developed the basic principles of the taxonomy of plants and animals and created their first classification.
Jean Baptiste Lamarck created the first holistic evolutionary teaching. In the work "Philosophy of Zoology" (1809), he identified the main direction of the evolutionary process - the gradual complication of organization from lower to higher forms. He also developed a hypothesis about the natural origin of man from ape-like ancestors who switched to a terrestrial lifestyle. Lamarck considered the striving of organisms for perfection as the driving force of evolution and asserted the inheritance of acquired traits. That is, the organs necessary in the new conditions develop as a result of exercise (the neck of a giraffe), and unnecessary organs atrophy as a result of non-exercise (the eyes of a mole). However, Lamarck was unable to reveal the mechanisms of the evolutionary process. His hypothesis about the inheritance of acquired traits turned out to be untenable, and his statement about the internal striving of organisms for improvement was unscientific.
Charles Darwin created an evolutionary theory based on the concepts of the struggle for existence and natural selection. The prerequisites for the emergence of Charles Darwin's doctrine were the following: accumulation by that time of rich material on paleontology, geography, geology, biology; development of selection; advances in taxonomy; the emergence of cell theory; the scientist's own observations during circumnavigation on the ship "Beagle". Charles Darwin outlined his evolutionary ideas in a number of works: "The origin of species by natural selection", "Change of domestic animals and cultivated plants under the influence of domestication "," The origin of man and sexual selection ", etc.

Darwin's teachings boil down to the following:

• each individual of a particular species has individuality (variability);
• personality traits (although not all) can be inherited (heredity);
• individuals produce a greater number of offspring than they survive to puberty and the beginning of reproduction, that is, there is a struggle for existence in nature;
• the advantage in the struggle for existence remains with the fittest individuals, which are more likely to leave behind offspring ( natural selection);
• as a result of natural selection, there is a gradual complication of the levels of organization of life and the emergence of species.

Evolution factors according to Charles Darwin- it

• heredity,
• variability,
• struggle for existence,
• natural selection.

Heredity - the ability of organisms to transmit their characteristics (features of structure, development, function) from generation to generation.
Variability - the ability of organisms to acquire new characteristics.
Struggle for existence - the whole range of relationships between organisms and environmental conditions: with inanimate nature(abiotic factors) and with other organisms (biotic factors). The struggle for existence is not a "struggle" in the literal sense of the word; in fact, it is a survival strategy and a way of the organism's existence. Distinguish between intraspecific struggle, interspecific struggle and struggle with unfavorable environmental factors. Intraspecific struggle- struggle between individuals of the same population. It is always very stressful, as individuals of the same species need the same resources. Interspecies struggle- struggle between individuals of populations of different species. It occurs when species compete for the same resources or when they are linked by a predator-prey relationship. Fight with unfavorable abiotic environmental factors especially manifests itself when environmental conditions deteriorate; enhances intraspecific struggle. In the struggle for existence, the individuals most adapted to the given habitat conditions are revealed. The struggle for existence leads to natural selection.
Natural selection- a process as a result of which predominantly individuals with hereditary changes that are useful under these conditions survive and leave behind offspring.

All biological and many other natural sciences were rebuilt on the basis of Darwinism.
Currently, the most generally accepted is synthetic theory of evolution (STE). Comparative characteristics basic provisions evolutionary teaching Ch. Darwin and STE are given in the table.

Comparative characteristics of the main provisions of the evolutionary teachings of Charles Darwin and the synthetic theory of evolution (STE)

The emergence of adaptations. Each adaptation is developed on the basis of hereditary variability in the process of struggle for existence and selection over a number of generations. Natural selection supports only appropriate adaptations that help the body to survive and reproduce.
The adaptability of organisms to the environment is not absolute, but relative, since environmental conditions can change. Many facts prove this. For example, fish are perfectly adapted to aquatic habitats, but all these adaptations are completely unsuitable for other habitats. Moths collect nectar from light-colored flowers, which are clearly visible at night, but often fly into the fire and die.

Elementary factors of evolution- factors that change the frequency of alleles and genotypes in the population (genetic structure of the population).

There are several basic elementary factors of evolution:
mutation process;
population waves and gene drift;
insulation;
natural selection.

Mutational and combinative variability.

Mutation process leads to the emergence of new alleles (or genes) and their combinations as a result of mutations. As a result of mutation, a gene can pass from one allelic state to another (A → a) or a gene change in general (A → C). The mutational process, due to the randomness of mutations, does not have directionality and, without the participation of other factors of evolution, cannot direct the change in the natural population. It only supplies the elementary evolutionary material for natural selection. Recessive mutations in a heterozygous state constitute a hidden reserve of variability that can be used by natural selection when the conditions of existence change.
Combinative variability arises as a result of the formation in offspring of new combinations of already existing genes inherited from their parents. The sources of combinative variability are the crossing of chromosomes (recombination), the random divergence of homologous chromosomes in meiosis, and the random combination of gametes during fertilization.

Population waves and gene drift.

Population waves(waves of life) - periodic and non-periodic fluctuations in the population size both upward and downward. The reasons for population waves can be periodic changes in environmental factors (seasonal fluctuations in temperature, humidity, etc.), non-periodic changes ( natural disasters), the settlement of new territories by the species (accompanied by a sharp outbreak in numbers).
Population waves act as an evolutionary factor in small populations where gene drift is possible. Gene drift- random undirected change in the frequencies of alleles and genotypes in populations. In small populations, the action of random processes leads to noticeable consequences. If the population is small in number, then as a result random events some individuals, regardless of their genetic constitution, may or may not leave offspring, as a result of which the frequencies of some alleles may change dramatically in one or several generations. So, with a sharp decrease in the population size (for example, due to seasonal fluctuations, a decrease in food resources, fire, etc.), rare genotypes may be among the few surviving individuals. If in the future the number is restored at the expense of these individuals, this will lead to a random change in the frequencies of alleles in the gene pool of the population. Thus, population waves are the supplier of evolutionary material.
Insulation due to the emergence of a variety of factors that impede free crossing. The exchange of genetic information between the formed populations stops, as a result of which the initial differences in the gene pools of these populations increase and become fixed. Isolated populations can undergo various evolutionary changes, gradually transform into different species.
Distinguish between spatial and biological isolation. Spatial (geographic) isolation associated with geographical obstacles (water barriers, mountains, deserts, etc.), and for sedentary populations, and simply with long distances. Biological isolation due to the impossibility of mating and fertilization (due to a change in the timing of reproduction, structure or other factors that prevent crossing), the death of zygotes (due to biochemical differences in gametes), sterility of the offspring (as a result of a violation of the conjugation of chromosomes during gametogenesis).
Evolutionary meaning isolation is that it reinforces and reinforces genetic differences between populations.
Natural selection. Changes in the frequencies of genes and genotypes caused by the evolutionary factors discussed above are random, undirected. Natural selection is the driving force behind evolution.

Natural selection- a process as a result of which predominantly individuals with useful properties for the population survive and leave behind their offspring.

Selection operates in populations; its objects are the phenotypes of individual individuals. However, selection for phenotypes is a selection of genotypes, since not traits, but genes are transmitted to offspring. As a result, an increase in the relative number of individuals with a certain property or quality occurs in the population. Thus, natural selection is a process of differential (selective) reproduction of genotypes.
Selection affects not only properties that increase the likelihood of leaving offspring, but also characters that are not directly related to reproduction. In some cases, selection can be aimed at creating mutual adaptations of species to each other (plant flowers and insects visiting them). Traits can also be created that are harmful to an individual individual, but ensure the survival of the species as a whole (a sting bee dies, but, attacking the enemy, it preserves the family). In general, selection plays a creative role in nature, since from undirected hereditary changes are fixed those that can lead to the formation of new groups of individuals that are more perfect in the given conditions of existence.
There are three main forms of natural selection: stabilizing, driving, and disruptive (disruptive) (table).

Forms of natural selection

A Brief History of the Evolution of the Organic World

The age of the Earth is about 4.6 billion years. Life on Earth originated in the ocean over 3.5 billion years ago.
A brief history of the development of the organic world is presented in the table. The phylogenesis of the main groups of organisms is shown in the figure.
The history of the development of life on Earth is studied from the fossil remains of organisms or traces of their vital activity. They are found in rocks of different ages.
The geochronological scale of the Earth's history is divided into eras and periods.

Geochronological scale and history of the development of living organisms

In the article, we will consider in detail the types of evolution, and also talk about this process in general, trying to comprehensively understand the topic. We will learn about how the doctrine of evolution was born, what ideas it presented and what role the species plays in it.

Introduction to the topic

The evolution of the organic world is a rather complex and lengthy process that simultaneously takes place at different levels of organization of living matter. However, he always touches on many areas. It so happened that the development of living nature occurs from lower forms to higher ones. Everything that is simple becomes more complex over time and takes on a more interesting form. In certain groups of organisms, adaptive skills are developed that allow living things to exist better in their specific conditions. For example, in some aquatic animals, membranes between the fingers evolved as a result of evolution.

Three directions

Before talking about the types of evolution, let us consider the three main directions identified by prominent Russian scientists I. Shmalgauzen and A. Severtsov. In their opinion, there is aromorphosis, idioadaptation, degeneration.

Aromorphosis

Aromorphosis, or arogenesis, is a serious evolutionary change that generally leads to the complication of the structure and functions of some organisms. This process allows you to fundamentally change some aspects of life, for example, habitats. Aromorphosis also helps to increase the competitiveness of specific organisms for survival in environment... The main essence of aromorphoses is the conquest of new adaptation zones. That is why such processes occur quite rarely, but if they do happen, then they are of a fundamental nature and have an impact on all further development.

In this case, it is necessary to deal with such a concept as the adaptation level. This is a specific area of ​​habitat with a characteristic climate and ecological conditions that are characteristic of a specific group of organisms. For example, for birds, an adaptive zone is airspace that protects them from predators and allows them to learn new ways of hunting. In addition, movement in the air makes it possible to overcome large obstacles and carry out long-distance migrations. That is why flight is rightfully considered an important evolutionary aromorphosis.

The most striking aromorphoses in nature are multicellularity and sexual reproduction. Due to its multicellularity, the process of complication of the anatomy and morphology of almost all organisms began. Thanks to sexual reproduction, the adaptive abilities have significantly expanded.

In animals, such processes contributed to the creation of more effective ways nutrition and improve metabolism. At the same time, warm-bloodedness is considered the most significant aromorphosis in the animal world, due to which the survival rate in different conditions has greatly increased.

In plants, similar processes are manifested in the appearance of a common and conducting systems that connect all their parts into a single whole. This increases the efficiency of pollination.

For bacteria, aromorphosis is an autotrophic way of feeding, thanks to which they were able to conquer a new adaptation zone, which may be deprived of organic food sources, but bacteria will still survive on it.

Idioadaptation

Without this process, it is impossible to imagine the evolution of biological species. It implies specific adaptations to specific environmental conditions. In order to better understand what this process is, let's think a little. Idioadaptation is small changes that significantly improve the life of organisms, but at the same time do not bring them to a new level of organization. Consider this information on the example of birds. The wing is a consequence of the aromorphosis process, but the shape of the wings and the ways of flight are already idioadaptations that do not change the anatomical structure of birds, but at the same time are responsible for their survival in a certain environment. These processes also include the color of animals. Due to the fact that they significantly affect only a group of organisms, they are considered signs of species and subspecies.

Degeneration, or catagenesis

Macro and microevolution

And now let's go directly to the topic of our article. What are the varieties of this process? This is micro and macro evolution. Let's talk about them in more detail. Macroevolution is the process of the formation of the largest systematic units: species, new families, and so on. The main driving forces behind macroevolution lie in microevolution.

The first is heredity, natural selection, variability, and reproductive isolation. Divergent character is characteristic of micro- and macroevolution. At the same time, these concepts, which we are talking about now, have received many different interpretations, but so far a final understanding has not been reached. One of the most popular is that macroevolution is a systemic change that does not require a large number time.

However, as far as the study of this process is concerned, it takes a very long time. Moreover, macroevolution is global in nature, so it is very difficult to master all its diversity. An important method for studying this direction is computer modeling, which began to develop especially actively in the 1980s.

Types of Evidence for Evolution

Now let's talk about what evidence exists for macroevolution. Firstly, this is a comparative anatomical system of inferences, which is based on the fact that all animals have a single type of structure. This is what indicates that we all have a common origin. Here, much attention is paid to homologous organs, also atavisms. Human atavisms are the appearance of a tail, many nipples and a continuous hairline. An important proof of macroevolution lies in the presence of vestigial organs that are no longer needed by humans and are gradually disappearing. Rudiments are the appendix, scalp, and remnants of the third century.

Now consider the embryological evidence that all vertebrates have similar embryos in their early stages of development. Of course, over time, this similarity becomes less and less noticeable, as the characteristic features for a particular species begin to prevail.

Paleontological evidence of the evolutionary process of species is that the remains of some organisms can be used to study the transitional forms of other extinct creatures. Thanks to the fossil remains, scientists can learn that there were transitional forms. For example, this form of life existed between reptiles and birds. Also, thanks to paleontology, scientists were able to build phylogenetic series in which one can clearly trace the sequence of successive species developing in the process of evolution.

Biochemical evidence is based on the fact that all living organisms on earth have a uniform chemical composition and genetic code, which should also be noted. Moreover, we are all similar in energy and plastic metabolism, as well as the enzymatic nature of some processes.

Biogeographic evidence is based on the fact that the process of evolution is perfectly reflected in the nature of the distribution of animals and plants on the surface of the Earth. So, scientists conditionally divided the array of the planet into 6 geographic areas... We will not consider them in detail here, but we will note that there is a very close connection between continents and related species of living organisms.

Thanks to macroevolution, we can understand that all species evolved from previously living organisms. Thus, the essence of the development process itself is revealed.

Transformations at the intraspecific level

Microevolution refers to small changes in alleles in a population over generations. It can also be said that these transformations occur at the intraspecific level. The reasons lie in mutational processes, artificial and natural drift and gene transfer. All these changes lead to speciation.

We have considered the main types of evolution, but we do not yet know that microevolution is divided into some branches. First, it is population genetics, thanks to which the mathematical calculations necessary to study many processes are performed. Secondly, it is ecological genetics, which allows observing development processes in reality. These 2 types of evolution (micro and macro) are of great importance and make their own contribution to the whole development process. It is worth noting that they are often opposed to each other.

Evolution of modern species

First, let's note that this is an ongoing process. In other words, it never stops. All living organisms evolve with different speed... However, the problem is that some animals live for a very long time, so it is very difficult to notice any changes. It takes hundreds or even thousands of years to track them.

V modern world there is an active evolution of African elephants. True, with the assistance of a person. So, in these animals, the length of the tusk is rapidly decreasing. The fact is that hunters have always hunted elephants that possessed massive tusks. At the same time, they were much less interested in other individuals. Thus, they have an increased chance of survival, as well as the transfer of their genes to other generations. That is why, over several decades, a decrease in the length of the tusks was gradually noted.

It is very important to understand that the absence of external signs does not mean the termination of the evolutionary process. For example, very often different researchers are mistaken about the coelacanth fish. It is believed that it has not evolved for millions of years, but it is not. We add that today the coelacanth is the only living representative of the Celacanthus order. If we compare the first representatives of this species and modern individuals, then you can find many significant differences... The only similarity is the appearance. That is why it is very important to take a comprehensive look at evolution, not to judge it solely by outward signs... Interestingly, modern coelacanth has more features in common with herring than with its progenitor, the celacanthus.

Factors

As we know, species originated through evolution, but what factors contributed to this? First, there is hereditary variation. The fact is that various mutations and new combinations of genes create the basis for hereditary diversity. Note: the more active the mutational process, the more effective natural selection will be.

The second factor is the accidental persistence of traits. To understand the essence of this phenomenon, let's look at concepts such as gene drift and population waves. The latter represent fluctuations that occur over periods and affect the size of the population. For example, every four years there are a lot of hares, and immediately after that their number drops sharply. But what exactly is gene drift? This implies the preservation or disappearance of any signs in a random order. That is, if, as a result of some events, the population greatly decreases, then some signs will remain completely or partially in a chaotic manner.

The third factor that we will consider is the struggle for existence. Its reason lies in the fact that a lot of organisms are born, but only some of them are able to survive. Moreover, there is not enough food and territory for everyone. In general, the concept of the struggle for existence can be described as a special relationship of an organism with the environment and other individuals. Moreover, there are several forms of struggle. It can be intraspecific, which occurs between individuals of the same species. The second form is interspecific, when representatives of different species are fighting for survival. The third form is to deal with environmental conditions, when animals need to adapt to them or die. At the same time, by right, the struggle within the species is considered the most cruel.

We now know that the role of the species in evolution is enormous. It is from one representative that mutation or degeneration can begin. However, the evolutionary process is regulated by itself, since the law of natural selection operates. So, if new traits are ineffective, then individuals with them will sooner or later die.

Consider another important concept that is characteristic of all driving types of evolution. This is isolation. This term implies the accumulation of certain differences between representatives of the same population, which has been isolated from each other for a long time. As a result, this can lead to the fact that individuals simply cannot interbreed with each other, thus two completely different species will appear.

Anthropogenesis

Now let's talk about the types of people. Evolution is a process characteristic of all living organisms. The part of biological evolution that led to the emergence of man is called anthropogenesis. Thanks to this, there was a separation human species from great apes, mammals and hominids. What types of people do we know? Evolutionary theory divides them into Australopithecus, Neanderthals, etc. The characteristics of each of these species are familiar to us from school.

So we got acquainted with the main types of evolution. Biology can sometimes tell a lot about the past and the present. That is why it is worth listening to it. Note: some scientists believe that 3 types of evolution should be distinguished: macro-, micro- and human evolution. However, such opinions are sporadic and subjective. In this material, we have presented to the attention of the reader 2 main types of evolution, thanks to which all living things develop.

Summing up the article, let's say that the evolutionary process is a real miracle of nature, which itself regulates and coordinates life. In the article, we covered the main theoretical concepts, but in practice, everything is much more interesting. Each species is a unique system capable of self-regulation, adaptation and evolution. This is the beauty of nature, which took care not only of the created species, but also of those into which they can mutate.

Evolution is a development process that consists of gradual changes, without sudden leaps (as opposed to revolution). Most often, speaking of evolution, they mean biological evolution.

Biological evolution is the irreversible and directed historical development of living nature, accompanied by a change in the genetic composition of populations, the formation of adaptations, the formation and extinction of species, the transformation of ecosystems and the biosphere as a whole. Biological evolution is studied by evolutionary biology.

There are several evolutionary theories that have in common the assertion that living forms of life are descendants of other forms of life that existed before. Evolutionary theories differ in the explanation of the mechanisms of evolution. V this moment the most common is the so-called. synthetic theory of evolution, which is a development of Darwin's theory.

Genes that are passed on to offspring, as a result of expression, form the sum of the characteristics of the organism (phenotype). When organisms reproduce, their descendants develop new or altered traits that arise as a result of mutation or when genes are transferred between populations or even species. In species that reproduce sexually, new combinations of genes arise through genetic recombination. Evolution occurs when hereditary differences become more frequent or rare in a population.

Evolutionary biology studies evolutionary processes and puts forward theories to explain their causes. The study of fossils and the diversity of species of living organisms by the middle of the 19th century convinced most scientists that species change over time. However, the mechanism of these changes remained unclear until the publication in 1859 of the book Origin of Species by the English scientist Charles Darwin on natural selection as a driving force of evolution. Darwin and Wallace's theory was ultimately accepted the scientific community... In the 1930s, the idea of ​​Darwinian natural selection was combined with Mendel's laws, which formed the basis of the synthetic theory of evolution (STE). STE made it possible to explain the relationship between the substrate of evolution (genes) and the mechanism of evolution (natural selection).

Heredity

Heredity, the inherent property of all organisms to repeat in a series of generations the same signs and features of development; due to the transfer in the process of reproduction from one generation to another of the material structures of the cell, containing programs for the development of new individuals from them. Thus, heredity ensures the continuity of the morphological, physiological and biochemical organization of living things, the nature of their individual development, or ontogenesis. As a general biological phenomenon, heredity - essential condition the existence of differentiated forms of life, impossible without the relative constancy of the characteristics of organisms, although it is disturbed by variability - the emergence of differences between organisms. Affecting the most diverse traits at all stages of ontogeny of organisms, heredity manifests itself in the patterns of inheritance of traits, that is, their transmission from parents to offspring.

Sometimes the term "Heredity" refers to the transmission from one generation to another of infectious principles (the so-called infectious heredity) or the skills of learning, education, traditions (the so-called social, or signal, heredity). Such an extension of the concept of heredity beyond its biological and evolutionary essence is controversial. Only in cases where infectious agents are able to interact with host cells up to inclusion in their genetic apparatus is it difficult to separate infectious inheritance from normal inheritance. Conditioned reflexes are not inherited, but are developed anew by each generation, however, the role of heredity in the speed of fixation of conditioned reflexes and behavioral features is indisputable. Therefore, the signaling heredity includes a component of biological heredity.

Variability

Variability is a variety of traits and properties in individuals and groups of individuals of any degree of relationship. It is inherent in all living organisms. Distinguish between hereditary and non-hereditary variability, individual and group, qualitative and quantitative, directed and undirected. Hereditary variability is due to the emergence of mutations, not hereditary - the impact of environmental factors. The phenomena of heredity and variability underlie evolution.

Mutation

Mutation is an accidental, persistent change in the genotype that affects whole chromosomes, their parts or individual genes. Mutations can be large, well noticeable, for example, lack of pigment (albinism), lack of plumage in chickens, short toes, etc. However, most often mutational changes are small, barely noticeable deviations from the norm.

Mutation is a rare event. The frequency of occurrence of individual spontaneous mutations is expressed by the number of gametes of one generation carrying a particular mutation in relation to the total gametes.

Mutations occur mainly as a result of two factors: spontaneous errors in the replication of the nucleotide sequence and the action of various mutagenic factors that cause replication errors.

Mutations caused by the action of mutagens (radiation, chemicals, temperature, etc.) are called induced, in contrast to spontaneous mutations that occur with random errors in the action of enzymes that ensure replication, and / or as a result of thermal vibrations of atoms in nucleotides.

Types of mutations. By the nature of the change in the genetic apparatus, mutations are divided into genomic, chromosomal and gene, or point. Genomic mutations involve changes in the number of chromosomes in the cells of the body. These include: polyploidy - an increase in the number of sets of chromosomes, when instead of the usual 2 sets of chromosomes for diploid organisms, there may be 3, 4, etc .; haploidy - instead of 2 sets of chromosomes, there is only one; aneuploidy - one or more pairs of homologous chromosomes are absent (nullisomy) or are represented not by a pair, but by only one chromosome (monosomy) or, on the contrary, by 3 or more homologous partners (trisomy, tetrasomy, etc.). Chromosomal mutations, or chromosomal rearrangements, include: inversions - a section of the chromosome is turned 180 °, so that the genes contained in it are located in the opposite order compared to normal; translocation - the exchange of sections of two or more non-homologous chromosomes; deletions - loss of a significant portion of the chromosome; shortages (small deletions) - loss small area chromosomes; duplications - duplication of a chromosome section; fragmentation - breaking a chromosome into 2 parts or more. Gene mutations are persistent changes in the chemical structure of individual genes and, as a rule, are not reflected in the morphology of chromosomes observed under a microscope. There are also known mutations of genes localized not only in chromosomes, but also in some self-reproducing organelles of the cytoplasm (for example, in mitochondria, plastids).

Causes of mutations and their artificial induction. Polyploidy often occurs when chromosomes at the beginning of cell division - mitosis - are divided, but cell division for some reason has not occurred. Artificially, polyploidy can be induced by acting on a cell that has entered mitosis with substances that disrupt cytotomy. Less often, polyploidy is the result of the fusion of 2 somatic cells or the participation of 2 sperm cells in the fertilization of the egg. Haploidy - for the most part a consequence of the development of the embryo without fertilization. It is artificially caused by pollinating plants with killed pollen or pollen of another species (distant). The main cause of aneuploidy is the accidental nondisjunction of a pair of homologous chromosomes during meiosis, as a result of which both chromosomes of this pair enter the same sex cell or none of them enter it. Less often, aneuploids arise from the few viable germ cells formed by unbalanced polyploids.

The causes of chromosomal rearrangements and the most important category of mutations - genes - have long remained unknown. This gave rise to erroneous autogenetic concepts, according to which spontaneous gene mutations occur in nature, supposedly without the participation of environmental influences. It was only after the development of methods for the quantitative accounting of gene mutations that it became clear that they can be caused by various physical and chemical factors- mutagens.

Recombination

Recombination is the redistribution of the genetic material of the parents in the offspring, leading to hereditary combinative variability of living organisms. In the case of unlinked genes (lying in different chromosomes), this redistribution can be carried out with free combination of chromosomes in meiosis, and in the case of linked genes - usually by crossing chromosomes - crossing over. Recombination is a universal biological mechanism inherent in all living systems - from viruses to higher plants, animals and humans. At the same time, depending on the level of organization of a living system, the Recombination (genetic) process has a number of features. The simplest way of recombination occurs in viruses: when a cell is co-infected with related viruses that differ in one or more features, after lysis of the cell, not only the original viral particles are found, but also recombinant particles with a certain average frequency with new gene combinations. In bacteria, there are several processes that end with recombination: conjugation, that is, the union of two bacterial cells by a protoplasmic bridge and the transfer of the chromosome from the donor cell to the recipient, after which individual sections of the recipient chromosome are replaced with the corresponding fragments of the donor; transformation - the transfer of signs by DNA molecules penetrating from the environment through the cell membrane; transduction - the transfer of genetic substance from a donor bacterium to a recipient bacterium, carried out by a bacteriophage. In higher organisms, recombination occurs in meiosis during the formation of gametes: homologous chromosomes approach and set side by side with great accuracy (so-called synapsis), then chromosomes break at strictly homologous points and reunification of fragments crosswise (crossing over). The result of recombination is detected by new combinations of traits in the offspring. The likelihood of crossing over between two chromosome points is roughly proportional to the physical distance between these points. This makes it possible, on the basis of experimental data on recombination, to build genetic maps of chromosomes, that is, to graphically arrange genes in a linear order in accordance with their location in chromosomes, and, moreover, on a certain scale. The molecular mechanism of recombination has not been studied in detail, but it has been established that the enzymatic systems that provide recombination are also involved in such an important process as the repair of damage that occurs in the genetic material. After synapse, endonuclease, an enzyme that makes primary breaks in DNA strands, comes into action. Apparently, these breaks in many organisms occur in structurally determined regions - recombiners. Further, there is an exchange of double or single DNA strands and, finally, special synthetic enzymes - DNA polymerases - fill the gaps in the chains, and the ligase enzyme closes the last covalent bonds. These enzymes have been isolated and studied only in some bacteria, which made it possible to approach the creation of a model of in vitro recombination (in vitro). One of the most important consequences of recombination is the formation of reciprocal offspring (i.e., in the presence of two allelic forms of genes AB and AB, two recombination products should be obtained - AB and AB in equal amounts). The principle of reciprocity is observed when recombination occurs between sufficiently distant points on the chromosome. With intragenic recombination, this rule is often violated. The latter phenomenon, studied mainly in lower fungi, is called gene conversion. The evolutionary significance of recombination lies in the fact that it is often not individual mutations that are favorable for the organism, but their combinations. However, the simultaneous occurrence in one cell of a favorable combination of two mutations is unlikely. As a result of recombination, a combination of mutations belonging to two independent organisms is carried out, and thereby the evolutionary process is accelerated.

Evolution mechanisms

Natural selection

There are two main evolutionary mechanisms. The first is natural selection, that is, the process by which hereditary traits favorable for survival and reproduction spread in the population, and unfavorable ones become more rare. This is because individuals with favorable traits are more likely to reproduce, so more individuals of the next generation have the same traits. Adaptations to the environment result from the accumulation of sequential, small, random changes and natural selection of the option best suited to the environment.

Genetic drift

The second major mechanism is genetic drift, an independent process of random change in the frequency of traits. Genetic drift occurs as a result of probabilistic processes that cause random changes in the frequency of traits in a population. Although the changes due to drift and selection during one generation are quite small, the differences in frequencies accumulate in each successive generation and lead to significant changes in living organisms over time. This process can end with the formation of a new species. Moreover, the biochemical unity of life points to the origin of all known species from a common ancestor (or pool of genes) as a result of a process of gradual divergence.

Nature is improving itself all the time. But evolutionary change is extremely slow. Compared to human life, of course. Only for billions of years of existence of the Earth, nature was able to achieve such perfection and diversity of life, which we see now.

Darwin suggested that the driving forces of evolution, or factors influencing the development of living nature, are:

• heredity and variability of individuals of the same species;

Heredity and variability

It is known that individuals of the same species are similar, but still not the same. They differ slightly in signs of external and internal structure, behavior. These differences can affect your ability to survive. More chances to survive and leave offspring have those special features which correspond to the habitat. These changes can be inherited by the offspring. As a result, the number of individuals with such traits increases in the next generation.

Struggle for existence

Natural selection

The struggle for existence leads to natural selection - predominant survival and reproduction of more adapted individuals of the species and the death of less adapted ones.

The action of natural selection throughout the life of many generations leads to the accumulation of small beneficial hereditary changes and the formation of adaptations of organisms to the habitat.

Inhabitant of European forests, the hedgehog has sharp thorns, which serve as protection from predators. Their occurrence is the result of the action of natural selection. Even slight skin roughness could survive distant ancestors hedgehog. For many generations, individuals with more developed thorns had the advantage in the struggle for existence. It was they who could leave offspring and pass on their hereditary changes to him. Gradually, new useful traits spread within the species, and all individuals European hedgehog became owners of thorns.

Acting long time, the driving forces of evolution lead to the formation of adaptations of living organisms to various environmental conditions, to the transformation of some species into others, to the emergence of more complex forms of life on the basis of simpler ones.

Adaptation (fitness)

Adaptations are the traits of living organisms, thanks to which they exist in nature. Beneficial traits, arising in individual organisms as a result of variability, help them survive in the struggle for existence. These traits are preserved as a result of natural selection and are inherited by descendants. So, generation after generation, the signs of animals and plants are gradually changing for the better for them. evolutionary changes. And that is why all living organisms are so well adapted to the conditions in which they live.

Speciation

Speciation is the result of evolution. A population throughout the life of many generations can be isolated from other populations of a given species (for example, be located on great distance). Acting for a long time, natural selection leads to the accumulation of many differences between the isolated and other populations.

As a result, individuals of different populations lose the ability to interbreed with each other and give offspring. The emergence of insurmountable biological barriers to crossing leads to the process of speciation.

Speciation led to the emergence of two species of foxes - the common fox and the corsac fox. In the north, natural selection contributed to the survival of the largest individuals (the larger the body size, the less heat loses the body). As a result, the species Common fox was formed. In the southern regions, on the contrary, natural selection was aimed at preserving the smallest individuals (the smaller the body size, the more heat the body gives off, while it does not overheat). As a result, the species of Fox-Korsak was formed.

To date, biological evolution has been fully confirmed on the basis of scientific facts accumulated in various industries biological science... Evidence for evolution is based on a comparative study of the external and internal structure, development and life processes of modern representatives of ancient extinct species. For this, there is a scientifically grounded cytological,