Formation of new species in nature. Formation of new species. Links and notes

Competition and other interspecific interactions can stimulate rapid speciation when combined with natural selection to improve the mechanisms that ensure successful mating within a species. Australian scientists came to this conclusion based on studying different natural populations of one species of tropical tree frogs.

Even Charles Darwin drew attention to the fact that in some species-rich systematic groups (genera, families), the most closely related species differ primarily in characteristics associated with the choice of a mating partner and mating. These can be both structural features of the genital organs and specific signals to attract a partner - for example, the croaking of a male frog or odorous substances (attractants) secreted by females (and sometimes males) of some insects. If in some part of the population there is selection for changes in such characteristics, then it may become reproductively isolated (sometimes called “sexually isolated”) from the maternal population. This happens especially quickly when hybrids between individuals from the separated group and the maternal population are characterized by reduced viability. This increase in the degree of sexual isolation and, accordingly, the acceleration of the formation of a new species received a special name in English literature - “reinforcement” (which literally means “strengthening”).

Currently, specialists in the field of evolutionary biology are intensively studying “reinforcement” and often associate it with such a long-described phenomenon as “character displacement” - a change in a trait not in all populations of a species, but only in those that are in contact with the ecological close competing species. Thus, two species of Galapagos finches living on different islands (under allopatric conditions) have beaks of approximately the same size, but when the same species live on the same island (under sympatry conditions), the average sizes of their beaks differ significantly, which leads us to assume and whether there are differences in the food they consume. If a trait that is displaced in the presence of a competitor is responsible for ensuring a meeting with a sexual partner, then this can lead to very rapid speciation, since the exchange of genes between the budding and maternal populations ceases.

In the journal " Ecology Letters» A review article recently appeared by two Australian researchers, Conrad Hoskin and Megan Higgie, who detail how a population of one species can change by changing the traits responsible for mating behavior, may separate the new kind. The object of their research is green-eyed tree frog(Green-eyed tree frog), Litoria genimaculata(Fig. 1), a species quite widespread in the tropical rainforests of Australia and New Guinea. Where the work was directly carried out, in the area of ​​the Barron River (Barron, northeastern part state of Queensland, Australia), there are two (this has been proven by molecular genetic methods) allopatric - that is, occupying different territories - populations of green-eyed frogs, conventionally designated as “northern” and “southern” (Fig. 2). These populations apparently formed sometime in the Pleistocene, during a period of colder and drier climate, when rainforests remained only as isolated islands among the open landscape.

Later, around 6,500 years ago, as the climate became warmer and wetter and the rainforests reappeared, the ranges of these frog populations converged. Hybrids between them in the border area are possible, although they are characterized by reduced viability. A peculiar situation arose, however, in the north of the surveyed territory, where surrounded by the “northern” population there was a small “enclave” represented by individuals of the “southern” population (in Fig. 2 it is marked as iS). It was in this “enclave” that an unusually rapid shift in the characteristics responsible for the meeting of the sexes was discovered (characteristics of the calling cry of the males and the response of the female). As a result of this displacement, individuals of this group lost the ability to normally interbreed with individuals of the maternal (main “southern” population). How this could happen is shown schematically in Figures 3 and 4 below.

Rice. 3 illustrates three possible options for evolutionary changes in individual genetic lines of the population: in the “southern” ( S) and "northern" ( N). Each circle corresponds to a specific line at a specific point in time. The upper half of the circle is postzygotic (occurring after fertilization) isolation. If for coexisting populations these halves are the same color, then the hybrids are viable; if they are different, they are not viable. The lower half of the circle corresponds to prezygotic (that is, existing even before fertilization) isolation: mating of individuals of different lines is possible if they are the same color, impossible if they are different. The scale of time (and, accordingly, evolution) is directed from top to bottom. Barriers that prevent individuals of different genetic lines from meeting are shown as black vertical lines and labeled with the word “Barrier.” Red horizontal arrows show the possibility of contact between individuals of different lines. Black thin arrow down - crossing individuals of different lines. The red cross indicates the impossibility of hybridization.

Three cases are considered: a- classical allopatric speciation (gradual accumulation of differences in populations isolated from each other and loss of the ability to interbreed); b- the beginning of allopatric speciation ends with “reinforcement” (although individuals are still able to mate, their hybrids are sterile or have reduced viability); c- the beginning of allopatric speciation changes its course due to new system barriers: the population of the “southern” line turns out to be subdivided by a new barrier, while part of it ends up on the same side of the barrier along with the “northern” line; it is in this part of the southern population (shown by a small circle with an index S') there is a selection aimed at isolating from the “northern” population as quickly as possible (this is possible due to behavioral mechanisms that ensure the meeting of marriage partners); in this case, selection goes so far that individuals of the new line ( S') lose the ability to interbreed with individuals of the mother southern line (S), actually leading to the formation of a new species.

In Fig. 4. The option of shifting reproductive characteristics in a population of frogs is illustrated in more detail A in case of living next to a competing species. Selection for reproductive traits, aimed at enhancing differences from a competitor, leads to the fact that individuals of a given part of the population ( B) may lose the ability to interbreed with the parent population and, in fact, give rise to a new species. Thus, interspecific interactions can stimulate speciation within one species.

Detecting in nature shifts in the reproductive traits of one species (which can lead to the formation of a new species) caused by interactions with other species is actually very difficult. And one of the complicating circumstances is the extraordinary speed of these changes. The results of research by Australian scientists are further confirmation that our inability to see with our own eyes the process of speciation is not due to the fact that this process is extremely long (as was believed in Darwin’s time), but on the contrary, it is very fast.

The formation of species is an important stage of evolution. It begins in populations saturated with constantly occurring mutations, which, when freely crossed, form new genotypes and phenotypes (see the chapter “Fundamentals of Genetics and Selection”). This leads to divergence of characteristics among individuals of a given population - divergence(55). The initial population forms a group of forms that have varying degrees sign deviations.

Organisms with altered characteristics are able to colonize new habitats and increase their numbers. Individuals with extreme contrasting deviations have the greatest opportunities to survive and leave fertile offspring. Intermediate forms compete more and die out faster. Thus, new groups 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. Darwin explained the formation of genera, families, orders, etc. in a similar way.

There are two methods of speciation: geographical and ecological.

Geographic speciation is associated with the expansion of the range of the original species or its division into isolated parts by various natural barriers (rivers, mountains, etc.). As the range of a species expands, individuals in populations encounter new soil and climatic conditions and different flora and fauna. In new unusual conditions, those individuals whose genotypes are most consistent with these conditions will survive and leave offspring. This leads to a change in the gene pool, the formation of new populations, and subsequently to the emergence of subspecies and species.

Isolation of populations, which prevents free crossing, also leads to changes in the gene pool of populations, and then to the creation of new populations, subspecies and species. An example of geographic isolation is centers of origin cultivated plants(see section “Selection”). The separation of these centers from each other by ridges, deserts, and oceans contributed to their isolation and the autonomous formation of flora in them, which led to an exceptional diversity of related plants in them.

Ecological speciation associated with the colonization of new habitats (ecological niches) within the range of its species. At the same time, small groups of one population may fall into unusual for them environmental conditions within the range of its species. New conditions will help identify and consolidate new mutations and change direction natural selection, which will lead to a change in the gene pool, to even greater isolation of populations, and then to the formation of new populations, subspecies and species adapted to new specific conditions.

An example of this is the five species of buttercups that have evolved in different habitats (56):

1. buttercup is an aquatic plant;
2. pimple buttercup grows in moist soils;
3. golden buttercup - in meadows, gardens, along roads;
4. buttercup Kassubian (Kashubian) - in forests and parks;
5. poisonous buttercup - in very damp places.

Elementary evolutionary factors.

The evolutionary process occurring in a population, leading to a change in the genetic structure of the population and directed by natural selection, is called microevolution. It begins in a population consisting of individuals with unequal genotypes. The totality of all genotypes in a population is called gene pool. When exposed to various elementary factors evolution, the gene pool of a population changes.

Such factors may include the following:

1. the emergence of new hereditary changes - mutations and combinations leading to the emergence of new genotypes in populations;
2. fluctuations in population numbers, called population waves. They may arise due to seasonal changes(annual plants, insects), with food supply (mass reproduction of rodents), with natural disasters (droughts, floods, fires). Population waves change the concentration of individual genes. During a population decline, some genes may disappear, and with a new population increase, other genes may increase in concentration;
3. geographical or biological isolation populations that create barriers to free interbreeding, leading to differences in genetic composition different populations and to their isolation.

All these changes in the gene pool are random in nature, they are multidirectional. The only selecting and directing factor of evolution is natural selection, which, under changed conditions, selects and increases the number of individuals whose genotype is more suitable for specific environmental conditions and reduces the number of individuals with a genotype less appropriate for this environment. The diversity of species is the result of the divergence of characteristics and the directing creative role of natural selection.

Natural selection usually leads to a gradual complication and increase in the organization of living forms, their relative adaptability to the conditions of existence and the diversity of species.

Species participate in evolutionary processes in the formation of higher systematic groups. This process is called macroevolution, or supraspecific evolution. In macroevolution, the same processes occur as during speciation - divergence of characters, struggle for existence and natural selection.

As living conditions change, the direction of natural selection also changes. If groups of individuals of the same widely distributed species fall into different conditions or begin, for example, to hunt for different prey, then selection in these groups will go in different directions. This will lead to the formation of various adaptations in them. As a result, from one type through natural selection several new species are formed, i.e., the process of speciation will take place. To illustrate this, Darwin gives a diagram of divergence or divergence of characters.

In the diagram, capital letters (A, B, C, D, etc.) under the bottom line conventionally indicate individual species one kind. Parallel lines from bottom to top (from I to XIV) symbolize the change of generations over time. Darwin conventionally accepts that from one line to the next there is a change of a thousand generations. The dotted lines directed from bottom to top illustrate the historical fate of these generations at different stages of development. The greater the distance between the dotted lines crossing one parallel line, the greater the difference between divergent groups of individuals in the corresponding generation (II line) than between points a5 and m5 (V line). This means that the initial divergence (difference) between two groups of descendants (a2 and m2) of the common original species A that arose over 2000 generations is less than the differences that developed after 5000 generations (a5 and m5). Therefore, says Darwin, we can accept that groups a2 and m2 are two more varieties of one common species, and groups a5 and m5 will already be two new species having a common ancestor (species A).

Thus, according to Darwin, new species arise through a series of intermediate steps: first, two (or more) varieties arise within one species; these varieties, continuing to diverge in their characters, gradually become subspecies and, finally, new species. A variety is a step towards the formation of a new species. Moreover, according to the divergence scheme, as a rule, one old look gives not one, but several types.

Divergent character Speciation occurs because the initial difference of organisms within a species increases its number. Darwin illustrates this point with this example: total number wolves begin to grow as different families This predator begins to hunt for different prey. Some wolves “specialize” in livestock, while others specialize in wild animals. As a result, the total number of wolves increases. Different directions of natural selection arise among them and, as a consequence, divergence.

Let's return to the divergence scheme. In the course of evolution, new directions of selection also arise (the dotted lines from species A and species I branch repeatedly). Some of these lines turn out to be dead ends: their descendants do not survive to modern times (XIV line) and die out, replaced by more adapted species. Many of the original species also do not leave offspring behind (i.e., they die out). And some (line F in the diagram) survive to the present day, almost without changing their characteristics.

At the final stage of the process considered, the newly emerged species exhibit varying degrees of similarity. On line XIV, 5 groups of species closest to each other are clearly visible. The reason for this proximity, as can be clearly seen from the diagram, is the close relationship of such species. Taxonomist, combining closely related species into one genus, thereby reflecting the kinship and common origin of these species.

Childbirth in turn, they unite into families, families into orders, etc. The divergence diagram shows that in this case, the basis of such associations is the process of evolution itself. If they are very closely related, species will belong to the same genus; if they are more distantly related, they will belong to the same family. Finally, very distant species will fall into different classes of the same type. This would mean that all species of the same type ultimately have one common ancestor, only this ancestor is unusually ancient.

So, modern systems plants and animals reflect a certain stage of evolution. At the same time, it is important to remember that modern views, described by taxonomists, are real now, but historically temporary: once upon a time they were only subspecies; in some distant future they may become genera, uniting groups of new related species; these new future species in modern times are only subspecies or varieties. The divergence diagram thus explains how evolution is the basis of modern taxonomy. At the same time, it shows that divergence inevitably leads to the emergence of a variety of organic forms in nature.

The divergence diagram helps to understand another important issue. The general increase in the diversity of organic forms greatly complicates the relationships that arise between organisms in nature. Therefore, during historical development As a rule, the most highly organized forms receive the greatest benefits. Thus, the general progressive development of the plant and animal world on Earth is carried out from lower forms to higher ones.

However, in those cases when living conditions do not become more complicated, but remain practically unchanged, and organisms are preserved without further complication.

Along with divergence, the result of evolution can also be the opposite result - convergence, or convergence of characteristics. Convergence occurs due to the unidirectional action of natural selection in organisms that are systematically distant from each other, when these organisms live in similar conditions. An example of convergent similarity is the streamlined body shape of a shark (fish), ichthyosaur (extinct, necked aquatic reptile) and dolphin ( aquatic mammal). The similarity of body shapes here is not caused by close genus. ity, but the unidirectionality of the action of natural selection in the same aquatic environment, where this form is useful for both fish and dolphin.

Thus, on the basis of the action of natural selection, relative fitness is formed, new species are formed, and general diversity organic forms in nature and carried out progressive development animal and plant life on Earth.

The formation of new species in nature is the final stage of microevolution. Under the influence of evolutionary factors with the leading role of natural selection, the process of transformation of genetically open intraspecific populations into genetically stable species systems is underway. Between individuals of different populations within a species, the process of crossing and leaving fertile offspring is possible. As long as there is gene flow between populations within a species, the species gene pool is unified system. As a result of the isolation of populations, crossing between divergent forms stops, there is no exchange of hereditary information, and populations or groups of populations become independent genetic systems.

A species is considered a qualitative stage in the evolutionary process, since it is the smallest genetically stable supraorganismal system in living nature. During speciation, mainly two processes occur: the emergence of adaptations to changing environmental conditions and the separation based on the isolation of new species. Based on the territory of settlement of the original species, we can distinguish two main paths of speciation: allopatric and sympatric.

Allopatric or geographic speciation is associated with the spatial isolation of divergent groups and can be carried out mainly through migration or dismemberment of the range by various barriers (rivers, mountains, soils, climate, etc.). When moving beyond the range of the original species, populations find themselves in different environmental conditions, which through microevolutionary processes can lead to the formation of new species. An example of species differentiation in the process of migration can be the complex complex of populations and subspecies of the great tit species. The spread of this species from Europe to the East took two routes: northern to Far East and southern around the Central Asian Plateau. In the Far East there are Eurasian and East Asian subspecies, which do not produce hybrids when living together. During the settlement process, a reproductive barrier arose between them.

Speciation through fragmentation of the range of the parent species can be traced using the example of the emergence of lily of the valley species. Forest lily of the valley was widespread in Eurasia several million years ago, but due to glaciation its range split into several territories. To date, several new species have formed.

Sympatric speciation occurs within the range of the original species. Several methods can be distinguished: by polyploidy (in the tobacco genus the initial number of chromosomes is 12, but there are forms with 24, 48, 72 chromosomes); by hybridization followed by chromosome doubling ( interspecific hybrids common among plants: raspberry, wormwood, mountain ash), through seasonal isolation (trout from Lake Sevan, according to the timing of their reproduction, forms winter and spring races).

End of work -

This topic belongs to the section:

Biology course of lectures for students studying in Russian

State educational institution.. higher vocational education.. Ryazan State Medical University..

If you need additional material on this topic, or you did not find what you were looking for, we recommend using the search in our database of works:

What will we do with the received material:

If this material was useful to you, you can save it to your page on social networks:

All topics in this section:

Biology
course of lectures for students studying in Russian Ryazan Compiled by: Associate Professor, Ph.D. Kalygina T.A.

Basic properties of living things
Living beings differ from non-living bodies in a number of properties. The main properties of living things include: Specific organization. Living organisms have

Levels of organization of living beings
Life on Earth is whole system, consisting of various structural levels organization of biological beings. There are several main levels of organization (the division has

Cell theory
In 1665 R. Hooke first discovered plant cells. In 1674 A. Leeuwenhoek discovered the animal cell. In 1839 T. Schwann and M. Schleiden formulated the cell theory. The main tenet of cell theory

Cell structure
Based on their structure, there are 2 types of cells: - prokaryotes - eukaryotes Prokaryotes include bacteria and blue-green algae. Prokaryotes differ from eukaryotes in the following ways: they

Outer cell membrane
1 – polar head of the phospholipid molecule 2 – fatty acid tail of the phospholipid molecule 3 – integral protein

Cell evolution
There are two stages in the evolution of a cell: 1. Chemical. 2.Biological. The chemical stage began about 4.5 billion years ago. Under the influence of ultraviolet radiation, radiation

Structure and functions of the cell nucleus
The nucleus is an essential part of a eukaryotic cell. Main function nucleus - storage of genetic material in the form of DNA and transfer it to daughter cells during cell division. Besides

Chromatin and chromosomes
Chromatin is a despiralized form of chromosome existence. In a despiralized state, chromatin is found in the nucleus of a nondividing cell. Chromatin and chromosomes interchange into each other

Cell life cycle
G1 – presynthetic period S – synthetic period G2 – postsynthetic period G0 –

Cell proliferation
Proliferation is an increase in the number of cells through mitosis, which leads to tissue growth and renewal. The intensity of proliferation is regulated by substances that are produced both inside cells,

Forms of reproduction of living organisms
Reproduction is the property of living organisms to reproduce their own kind. There are two main forms of reproduction: asexual and sexual. Asexual reproduction contributes to the preservation of the greatest

Spermatogenesis
Section of the cross-section of the convoluted tubule of the testis (see page 27) Cellules germinales primordiales – p

Types and periods of ontogenesis
Ontogenesis is the process of individual development of an individual from a zygote during sexual reproduction (or the appearance of a daughter during asexual reproduction) until the end of life. The term "ontogenesis" in 1866 suggested by German scientists

Structural features and types of eggs
Ovules (or eggs) are highly specialized female reproductive cells, relatively large and immobile. There are no fundamental differences in the structure of the egg and somatic cells

Embryonic period of development, its stages
The period of embryonic development is the most complex in higher animals and consists of several stages: 1. Formation of the zygote 2. Fragmentation 3. Formation of the blastula

Crushing in chordates
A – lancelet (completely uniform) B – amphibians (completely uneven) C – birds (incomplete discoidal)

Histogenesis and organogenesis
Histogenesis is the process of tissue formation in embryogenesis. Organogenesis is the process of formation of organ systems in embryogenesis. At this stage of embryonic development, two phases are distinguished.

Embryonic induction
Clarifying the mechanisms of development is one of the complex problems of biological science. Embryogenesis as a whole is determined by the hereditary apparatus of cells (as already mentioned, during ontogenesis

Embryonic development of birds
The egg cell of birds is sharply telolecithal; the vegetative pole contains a lot of yolk. As a result of fertilization, a one-celled embryo is formed - a zygote, which is characterized by

Extraembryonic provisional organs
In the embryonic development of vertebrates, a major role is played by provisional organs that function in the embryo and are absent in adulthood. These include: yolk sac, amnion, serous

Characteristics of postembryonic development
Postembryonic (postnatal) ontogenesis begins from the moment of birth, upon exit from the embryonic membranes (during intrauterine development) or upon exit from the egg membranes and ends with death

Effort. Clinical and biological death
Aging is a general biological pattern of decline of the body, characteristic of all living beings. Old age is the final natural stage of ontogenesis, ending with death.

Regeneration of organs and tissues, its types
Regeneration is the process of restoring lost or damaged tissues or organs. There are two types of regeneration: - physiological - reparative Physiological

Transplantation
Transplantation is the engraftment and development of transplanted tissues in a new location. The organism from which the material for transplantation is taken is called a donor, and the one to which the transplant is performed is called

Homeostasis in living organisms
Homeostasis is the property of living beings to maintain the constancy of their internal environment, despite the variability of factors environment Despite significant fluctuations

Biological rhythms. Chronobiology
Biological rhythms - regularly repeating changes in intensity biological processes. Biological rhythms are found in all living beings, they are hereditarily fixed and are factors

Community
Any type of organized beings and any population of any species does not exist in isolation from other beings, but form a complex and contradictory unity called a biotic community. Bi

Monohybrid cross
Mendel conducted experiments on peas. When crossing pea varieties with yellow and green seeds (crossed homozygous organisms or pure lines), all offspring (i.e. first generation hybrids

Di- and polyhybrid crossing. Mendel's third law
In a dihybrid cross, the parent organisms are analyzed for two pairs of alternative traits. Mendel studied such characteristics as the color of seeds and their shape. When crossing peas with yellow

Determination of gender
In most organisms, sex is determined at the time of fertilization (syngamous) and is regulated by the chromosome complement of the zygote; it is called the chromosomal type of sex determination. In humans and mammals

Inheritance of sex-linked and sex-limited traits
Sex-linked traits are those whose development is determined by genes located on the sex chromosomes. If the gene is located on the Y chromosome, then it is inherited in humans, mammals

Linkage of genes. Experiments and Morgan's Rule
The study of sex-linked inheritance has stimulated the study of linkage between genes located on autosomes. Any organism is characterized by species constancy of chromosomes in the karyotype.

Basic provisions of the chromosomal theory of heredity
The main provisions of the chromosomal theory of heredity boil down to the following: - the carriers of hereditary information are chromosomes and the genes located in them, - genetic

Stages of development of molecular genetics
Molecular genetics emerged from biochemistry and emerged as an independent science in the 50s of the last century. The birth of this science is associated with a number of important biological discoveries: 1

Functional gene activity or gene expression
In prokaryotes, it is carried out in two stages: transcription and translation. In eukaryotes there is also a processing stage. Gene expression involves the synthesis of an mRNA molecule on a DNA molecule, the complex

Regulation of gene expression in prokaryotes
Scheme of regulation of transcription of structural genes of a prokaryotic cell according to the type of repression

Definition and forms of variability
Genetics studies two basic properties of living beings - heredity and variability. Variability is the property of organisms to acquire new characteristics and features of individual development

Mutagenic factors
Factors that cause mutations are called mutagenic factors (mutagens) and are divided into: 1. Physical; 2. Chemical; 3. Biological. To physical m

Stability and repair of genetic material
Resistance to changes in genetic material is ensured by: 1. A diploid set of chromosomes. 2. DNA double helix. 3. Degeneracy (redundancy

Law of homological series of hereditary variability N.I. Vavilov
It is known that mutation occurs in various directions. However, this diversity is subject to a certain pattern, discovered in 1920 by N.I. Vavilov. He formulated the law homol

Genealogical method
The types of inheritance and forms of manifestation of genetic inclinations in humans are very diverse and differentiation between them requires special methods analysis, primarily genealogical, p

Twin research method
Twin studies are one of the main methods of human genetics. There are identical twins, which arise from one egg fertilized by one sperm. They arise due to

Dermatoglyphics method
This is a science that studies the hereditary determination of the patterns that form the lines of the skin on the tips of the fingers, palms and soles of a person. It turned out that every nation

Somatic cell hybridization
Hybrid cells have certain properties that make it possible to determine gene localization or gene linkage. Loss of human chromosomes from certain types of hybrid cells allows obtaining a clone

Ontogenetic method
Allows you to study the patterns of manifestation of any sign or disease in the process of individual development. There are several periods of human development. Antenatal (development before birth)

Simulation method
N.I. Vavilov’s law of homological series (species and genera that are genetically close have similar series of hereditary variability) allows us to extrapolate experimental data with certain restrictions

Immunological research method
This method is based on the study of the antigenic composition of cells and fluids human body– blood, saliva, gastric juice, etc. The most frequently tested antigens of blood cells are erythro

Gene diseases
1) An autosomal dominant type of inheritance is characterized by a violation of the synthesis of structural proteins or proteins that perform specific functions (for example, hemoglobin). Phenotypically, in this case, t

Chromosomal diseases caused by autosomal abnormalities
Chromosomal diseases are a group of hereditary pathological conditions caused by a change in the number of chromosomes or a violation of their structure. The most common trisomies are dir.

Chromosomal diseases caused by abnormalities of sex chromosomes
Sex chromosomes are the main carriers of genes that control the development of sex, therefore their numerical or structural abnormalities determine various deviations in sexual development.

J.B. Lamarck's theory of evolution
J.B. Lamarck in “Philosophy of Zoology” (1809), in which the foundations of an integral evolutionary concept were first outlined, formulated two laws: 1) on the influence of the use and disuse of an organ on its

Charles Darwin's theory of evolution
In 1858, Charles Darwin and, independently of him, A.R. Wallace substantiated the principle of natural selection and the idea of ​​the struggle for existence as a mechanism of this selection. Theory of evolution by eating

Microevolution. Criteria and structure of the species. Population
Microevolution is the initial stage of evolutionary transformations of a population: from the occurrence of hereditary changes to the formation of adaptation and the emergence of new species on their basis. Study

Factors of evolution
Changes in the genotypic composition of populations occur under the influence of many events that are able to transform populations in one way or another. Nevertheless, it is possible to distinguish the following basic

Human animal origin concept
At the core modern ideas about the origin of man lies the concept according to which man came out of the animal world, and the first scientific evidence in favor of this concept was

Differences between humans and animals
The man has significant differences from animals, which was also noted by the ancients, for example Anaxagoras (500-428 BC) and Socrates (469-399 BC) believed that sp

Driving factors of anthropogenesis
There are social and biological factors of anthropogenesis. Anthropogenesis is the origin of man and his formation as a species in the process of formation of society. A person has a number of specific

Remember why a population of organisms is considered the basic unit of evolution. Describe isolation as an elementary factor of evolution. What forms of isolation exist between populations of organisms in nature?

The main condition for the formation of new species of organisms is isolation. As a result, the exchange of genes between individuals of the isolated population and the rest of the population stops. This leads to a gradual change in characteristics in individuals of an isolated population, which leads to its transformation into one or more new species (Fig. 166).

Rice. 166. Scheme of speciation: individual branches - populations

Consequently, the formation of new species of organisms, or speciation, is the process of transforming individual genetically isolated populations of the original species into new species. Depending on the nature of the barriers preventing the interbreeding of individuals, two methods of speciation are distinguished - geographical and ecological.

Geographic speciation. Associated with a change in the range of the original ancestral species. Various geographical physical objects act as barriers to the crossing of individuals: land or sea spaces, mountain ranges, deserts, etc. Geographic speciation is carried out in two ways: the resettlement of individuals of a population to new territories or the division of the previous habitat of the population into separate isolated parts. As a result of this, geographical subspecies of the original species are formed, which become the ancestors of independent new species of organisms.

An example of geographic speciation through the dispersal of individuals into new habitats is the appearance of two species of gulls: herring and black-billed gulls (Fig. 167). The ancestral form of these two species was a single species of gull that existed several hundred thousand years ago in the area of ​​​​the modern Bering Strait (indicated by a cross in the figure). From it, through settlement to the east and west, several geographical subspecies of gulls were formed (areas of the subspecies are indicated in the figure), from which two new species were formed.

Rice. 167. Geographic speciation of two species of gulls: herring and black-billed gulls

An example of geographic speciation by dividing the former range of a species into several isolated parts is the appearance of three species of lilies of the valley (Fig. 168). The original ancestral type existed several million years ago in deciduous forests Eurasia. Due to glaciation, the single habitat of this species was torn into several parts. Lily of the valley is preserved only in forest areas that escaped glaciation: in the center and south of Europe, in Transcaucasia and in the south of the Far East. From these surviving populations, three independent species of lilies of the valley subsequently formed, differing in the size of the leaves and the color of the flower corollas.

Rice. 168. Geographic speciation of three species of lilies of the valley

Ecological speciation. Associated with changes in the living conditions of the original ancestral species. Differences in the living conditions of isolated populations act as barriers to the crossing of individuals. As a result, ecological subspecies are formed, which become the ancestors of new species of organisms.

An example of ecological speciation is the appearance of several species in the genus Buttercup, growing in places with different humidity (Fig. 169).

Rice. 169. Ecological speciation in the genus Buttercup

Rice. 170. Coloring of egg shells in ecological subspecies of the common cuckoo

Thus, the formation of new species of organisms follows the following scheme: populations of the original species of organism >> geographic or ecological subspecies >> new species of organisms

Evolution does not stop with the formation of new species. It leads to the emergence of new and new species of plants, animals and other organisms, forming over-species systematic groups- genera, families, orders, orders, classes, divisions, types.

Exercises based on the material covered

1. What is speciation?
2. What factor is the main one for the formation of new species of organisms?
3. According to what scheme do new species of organisms form from the original ancestral species?