Which type criterion is the most accurate and why. Type and its criteria. Morphological criterion of the species

The belonging of individuals to a particular species is determined based on a number of criteria.

Type criteria- these are various taxonomic (diagnostic) characters that are characteristic of one species, but absent in other species. A set of characteristics by which one species can be reliably distinguished from other species is called a species radical (N.I. Vavilov).

Species criteria are divided into basic (which are used for almost all species) and additional (which are difficult to use for all species).

Basic criteria of the type

1. Morphological criterion of the species. Based on existence morphological characteristics, characteristic of one species, but absent in other species.

For example: in the common viper, the nostril is located in the center of the nasal shield, and in all other vipers (nosed, Asia Minor, steppe, Caucasian, viper) the nostril is shifted to the edge of the nasal shield.

Twin species. Thus, closely related species may differ in subtle characteristics. There are twin species that are so similar that it is very difficult to use a morphological criterion to distinguish them. For example, the malaria mosquito species is actually represented by nine very similar species. These species differ morphologically only in the structure of the reproductive structures (for example, the color of the eggs in some species is smooth gray, in others - with spots or stripes), in the number and branching of hairs on the limbs of the larvae, in the size and shape of the wing scales.

In animals, twin species are found among rodents, birds, many lower vertebrates (fish, amphibians, reptiles), many arthropods (crustaceans, mites, butterflies, dipterans, orthoptera, hymenoptera), mollusks, worms, coelenterates, sponges, etc.

Notes on sibling species (Mayr, 1968).

1. There is no clear distinction between common species(“morphospecies”) and twin species: simply in twin species, morphological differences are expressed to a minimal extent. Obviously, the formation of sibling species is subject to the same laws as speciation in general, and evolutionary changes in groups of sibling species occur at the same rate as in morphospecies.

2. Sibling species, when subjected to careful study, usually show differences in a number of small morphological characters (for example, male insects belonging to different species clearly differ in the structure of their copulatory organs).

3. Restructuring of the genotype (more precisely, the gene pool), leading to mutual reproductive isolation, is not necessarily accompanied by visible changes in morphology.

4. In animals, sibling species are more common if morphological differences have less impact on the formation of mating pairs (for example, if recognition uses smell or hearing); if animals rely more on vision (most birds), then twin species are less common.

5. The stability of the morphological similarity of twin species is due to the existence of certain mechanisms of morphogenetic homeostasis.

At the same time, there are significant individual morphological differences within species. For example, the common viper is represented by many color forms (black, gray, bluish, greenish, reddish and other shades). These characteristics cannot be used to distinguish species.

2. Geographical criterion. It is based on the fact that each species occupies a certain territory (or water area) - geographical range. For example, in Europe some species malarial mosquito(genus Anopheles) inhabit the Mediterranean, others - the mountains of Europe, Northern Europe, Southern Europe.

However, the geographical criterion is not always applicable. The ranges of different species can overlap, and then one species smoothly passes into another. In this case, a chain of vicariating species is formed (superspecies, or series), the boundaries between which can often be established only through special research (for example, herring gull, black-billed gull, western gull, Californian gull).

3. Ecological criterion. It is based on the fact that two species cannot occupy the same ecological niche. Consequently, each species is characterized by its own relationship with its environment.

For animals, instead of the concept of “ecological niche,” the concept of “adaptive zone” is often used. For plants, the concept of “edapho-phytocenotic area” is often used.

Adaptive zone- this is a certain type of habitat with a characteristic set of specific environmental conditions, including the type of habitat (aquatic, land-air, soil, organism) and its particular features (for example, in a land-air habitat - the total amount solar radiation, precipitation, relief, atmospheric circulation, distribution of these factors by season, etc.). In the biogeographical aspect, adaptive zones correspond to the largest divisions of the biosphere - biomes, which are a collection of living organisms in combination with certain living conditions in vast landscape-geographical zones. However, different groups of organisms use environmental resources differently and adapt to them differently. Therefore, within the biome of the coniferous-deciduous forest zone temperate zone One can distinguish adaptive zones of large guarding predators (lynx), large overtaking predators (wolf), small tree-climbing predators (marten), small terrestrial predators (weasel), etc. Thus, the adaptive zone is ecological concept, occupying an intermediate position between habitat and ecological niche.

Edapho-phytocenotic area- this is a set of bioinert factors (primarily soil, which are an integral function of the mechanical composition of soils, topography, the nature of moisture, the influence of vegetation and microorganism activity) and biotic factors (primarily the totality of plant species) of nature that make up the immediate environment of the area of ​​interest kind of us.

However, within the same species, different individuals can occupy different ecological niches. Groups of such individuals are called ecotypes. For example, one ecotype of Scots pine inhabits swamps (swamp pine), another - sand dunes, and a third - leveled areas of pine forest terraces.

A set of ecotypes that form a single genetic system (for example, capable of interbreeding with each other to form full-fledged offspring) is often called an ecospecies.

Additional type criteria

4. Physiological-biochemical criterion. Based on the fact that different species may differ in the amino acid composition of proteins. Based on this criterion, for example, some species of gulls are distinguished (herring, black-billed, western, Californian).

At the same time, within a species there is variability in the structure of many enzymes (protein polymorphism), and different species may have similar proteins.

5. Cytogenetic (karyotypic) criterion. It is based on the fact that each species is characterized by a certain karyotype - the number and shape of metaphase chromosomes. For example, all durum wheats have 28 chromosomes in their diploid set, and all soft wheats have 42 chromosomes.

However, different species can have very similar karyotypes: for example, most species of the cat family have 2n=38. At the same time, chromosomal polymorphism can be observed within one species. For example, moose of Eurasian subspecies have 2n=68, and moose of North American species have 2n=70 (in the karyotype of North American moose there are 2 less metacentrics and 4 more acrocentrics). Some species have chromosomal races, for example, the black rat has 42 chromosomes (Asia, Mauritius), 40 chromosomes (Ceylon) and 38 chromosomes (Oceania).

6. Physiological and reproductive criterion. It is based on the fact that individuals of the same species can interbreed with each other to form fertile offspring similar to their parents, and individuals of different species living together do not interbreed, or their offspring are infertile.

However, it is known that interspecific hybridization is often common in nature: in many plants (for example, willow), a number of species of fish, amphibians, birds and mammals (for example, wolves and dogs). At the same time, within the same species there can be groups that are reproductively isolated from each other.

Pacific salmon (pink salmon, chum salmon, etc.) live for two years and spawn only before dying. Consequently, the descendants of individuals that spawned in 1990 will breed only in 1992, 1994, 1996 (“even” race), and the descendants of individuals that spawned in 1991 will breed only in 1993, 1995, 1997 (“even” race). odd" race). An “even” race cannot interbreed with an “odd” race.

7. Ethological criterion. Associated with interspecific differences in behavior in animals. In birds, song analysis is widely used to recognize species. Depending on the nature of the sounds produced, different types of insects differ. Different types North American fireflies vary in the frequency and color of their light flashes.

8. Historical criterion. Based on the study of the history of a species or group of species. This criterion is complex in nature, since it includes comparative analysis modern ranges of species, analysis

To study the diversity of life, man needed to develop a system of classifying organisms to divide them into groups. As you already know, the smallest structural unit in the taxonomy of living organisms is the species.

A species is a historically established set of individuals that are similar in morphological, physiological and biochemical characteristics, interbreed freely and produce fertile offspring, are adapted to certain environmental conditions and occupy a common territory in nature - a range.

In order to classify individuals as the same or different species, they are compared with each other according to a number of certain characteristic features— criteria.

Type criteria

The set of characteristic characteristics of the same type, in which individuals of the same species are similar, and individuals of different species differ from each other, is called a species criterion. IN modern biology The following main criteria for the species are distinguished: morphological, physiological, biochemical, genetic, environmental, geographical.

Morphological criterion reflects a set of characteristic features external structure. For example, types of clover differ in the color of the inflorescences, the shape and color of the leaves. This criterion is relative. Within a species, individuals can differ markedly in structure. These differences depend on gender ( sexual dimorphism), stage of development, stage in the reproduction cycle, environmental conditions, belonging to varieties or breeds.

For example, in a mallard the male is brightly colored, and the female is dark brown; in the red deer, the males have antlers, but the females do not. The cabbage white butterfly has a caterpillar different from adult outward signs. In the male shield fern, the sporophyte has leaves and roots, and the gametophyte is represented by a green plate with rhizoids. At the same time, some species are so similar in morphological characteristics that they are called twin species. For example, some types malarial mosquitoes, fruit flies, and North American crickets do not differ in appearance, but do not interbreed.

Thus, on the basis of one morphological criterion it is impossible to judge whether an individual belongs to a particular species.

Physiological criterion- a set of characteristic features of life processes (reproduction, digestion, excretion, etc.). One of the important characteristics is the ability of individuals to interbreed. Individuals of different species cannot interbreed due to incompatibility of germ cells and mismatch of genital organs. This criterion is relative, since individuals of the same species sometimes cannot interbreed. In Drosophila flies, the inability to mate may be due to differences in the structure of the reproductive apparatus. This leads to disruption of reproduction processes. Conversely, there are known species whose representatives can interbreed. For example, a horse and a donkey, representatives of some species of willows, poplars, hares, and canaries. It follows from this that to determine the species identity of individuals, it is not enough to compare them only according to physiological criteria.

Biochemical criterion reflects the characteristic chemical composition body and metabolism. This is the most unreliable criterion. There are no substances or biochemical reactions that are unique to a particular species. Individuals of the same species can differ significantly in these indicators. Whereas in individuals of different species, protein synthesis and nucleic acids happens the same way. A number of biologically active substances play similar roles in metabolism in different species. For example, chlorophyll in all green plants is involved in photosynthesis. This means that determining the species identity of individuals based on one biochemical criterion also impossible.

Genetic criterion characterized by a certain set of chromosomes, similar in size, shape and composition. This is the most reliable criterion, since it is a factor in reproductive isolation that maintains the genetic integrity of the species. However, this criterion is not absolute. In individuals of the same species, the number, size, shape and composition of chromosomes may differ as a result of genomic, chromosomal and gene mutations. At the same time, when crossing some species, viable fertile interspecific hybrids sometimes appear. For example, a dog and a wolf, a poplar and a willow, a canary and a finch, when crossed, produce fertile offspring. Thus, the similarity according to this criterion is also not enough to classify individuals as one species.

Ecological criterion is a set of characteristic environmental factors necessary for the existence of a species. Each species can live in an environment where climatic conditions, soil characteristics, topography and food sources correspond to its tolerance limits. But organisms of other species can also live in the same environmental conditions. The development of new animal breeds and plant varieties by humans has shown that individuals of the same species (wild and domesticated) can live in very different environmental conditions. It proves relative nature ecological criterion. Consequently, there is a need to use other criteria when determining whether individuals belong to certain kind.

Geographical criterion characterizes the ability of individuals of one species to inhabit a certain part of nature earth's surface(area).

For example, Siberian larch is common in Siberia (Trans-Urals), and Dahurian larch is common in the Primorsky Territory ( Far East), cloudberries are in the tundra, and blueberries are in the temperate zone.

This criterion indicates that the species is confined to a specific habitat. But there are species that do not have clear boundaries of distribution, but live almost everywhere (lichens, bacteria). In some species, the range coincides with the range of humans. These types are called synanthropic(housefly, bedbug, house mouse, gray rat). Different species may have overlapping habitats. This means that this criterion is relative. It cannot be used as the only one to determine the species identity of individuals.

Thus, none of the described criteria is absolute and universal. Therefore, when determining whether an individual belongs to a certain species, all its criteria should be taken into account.

Species range. The concept of endemics and cosmopolitans

According to the geographical criterion, each species in nature occupies a certain territory - range.

area(from lat. area- area, space) - part of the earth's surface within which they are distributed and pass full cycle its development of an individual of a given species.

Range may be solid or intermittent, extensive or limited. Species that have a wide range across different continents are called cosmopolitan species(some types of protists, bacteria, fungi, lichens). When the distribution area is very narrow and is located within a small region, the species inhabiting it is called endemic(from Greek. endemos- local).

For example, kangaroos, echidnas and platypus live only in Australia. Ginkgo grows naturally only in China, rhododendron acuminate and Daurian lily - only in the Far East.

A species is a set of individuals that are similar in morphological, physiological and biochemical characteristics, interbreed freely and produce fertile offspring, are adapted to certain environmental conditions and occupy a common territory in nature - a range. Each species is characterized by the following criteria: morphological, physiological, biochemical, genetic, environmental, geographical. All of them are relative in nature, therefore, when determining the species affiliation of individuals, all possible criteria are used.

1. Biological species and its criteria.

All life on the planet is represented by individual species.

A species is a historically established collection of individuals with hereditary similarities in morphological, physiological and biochemical characteristics; capable of freely interbreeding and producing fertile offspring; adapted to certain environmental conditions and occupying a certain area.

Each type of organism can be described by a set of characteristic features and properties, which are called signs of the species. Characteristics of a species by which one species can be distinguished from another are called species criteria.

The following general criteria of the type are most often used: morphological, physiological, genetic, biochemical, geographical and environmental.

Morphological criterion - based on the external and internal similarity of individuals of the same species.

The morphological criterion is the most convenient and is therefore widely used in species taxonomy.

However, the morphological criterion is insufficient to determine the difference sibling species with significant morphological similarity.

Twin species practically do not differ in appearance, but individuals of such species do not interbreed.

Twin species are quite common in nature. About 5% of all species of insects, birds, fish, etc. have twin species:

- black rats have two twin species;

- the malaria mosquito has six twin species.

The use of a morphological criterion is also difficult in cases where individuals of the same species differ sharply from each other in appearance, the so-called polymorphic species.

The simplest example of polymorphism is sexual dimorphism, when morphological differences are observed between males and females of the same species.

It is difficult to use a morphological criterion when diagnosing domestic animal species. Breeds bred by man can differ significantly from each other, remaining within the same species (breeds of cats, dogs, pigeons).

Thus, the morphological criterion is insufficient to determine the species identity of individuals.

The physiological criterion characterizes the similarity of life processes in individuals of the same species, primarily the similarity of reproduction.

There is physiological isolation between individuals of different species, which manifests itself in the fact that individuals of different species almost never interbreed. This is explained by differences in the structure of the reproductive apparatus, timing and places of reproduction, behavioral rituals during mating, etc.

If interspecific crossing does occur, the result is interspecific hybrids that are characterized by reduced viability or are infertile and do not produce offspring:

For example, There is a known hybrid of a horse and a donkey - a mule, which is quite viable, but sterile.

However, in nature there are species that can interbreed and produce fertile offspring (for example, some species of canaries, finches, poplars, willows, etc.).

Consequently, the physiological criterion is insufficient to characterize the species.

The genetic criterion is a set of chromosomes characteristic of each species, their strictly defined number, size and shape.

Individuals of different species cannot interbreed, since they have different sets of chromosomes and differ in number, size and shape:

- for example, two closely related species of black rats differ in the number of chromosomes (one species has 38 chromosomes, the other 48) and therefore do not interbreed.

However, this criterion is not universal:

- firstly, in many different species the number of chromosomes can be the same (for example, many species of the legume family have 22 chromosomes);

- secondly, within the same species there can be individuals with different numbers of chromosomes, which is the result of mutations (for example, in silver crucian carp there are populations with a set of chromosomes 100, 150, 200, while their normal number is 50).

Thus, based on genetic criterion It is also impossible to reliably determine whether individuals belong to a specific species.

The biochemical criterion allows one to distinguish between species based on biochemical parameters (the composition and structure of certain proteins, nucleic acids and other substances).

It is known that the synthesis of certain high-molecular substances is characteristic only of certain species ( for example, many plant species differ in their ability to form and accumulate certain alkaloids).

However, there is significant intraspecific variability in almost all biochemical parameters, down to the sequence of amino acids in molecules of proteins and nucleic acids.

Therefore, the biochemical criterion is also not universal. In addition, it is not widely used, as it is very labor-intensive.

The geographical criterion is based on the fact that each species occupies a certain territory or water area.

In other words, Each species is characterized by a specific geographic range.

Many species occupy different habitats, but most species have overlapping habitats.

There are species that do not have a specific geographical range, i.e. living over vast expanses of land or ocean, the so-called cosmopolitan species :

- some inhabitants of inland water bodies - rivers and freshwater lakes (many species of fish, reeds);

- cosmopolitans also include dandelion, shepherd's purse, etc.;

- cosmopolitans are found among synanthropic animals - species that live near a person or his home (lice, bedbugs, cockroaches, flies, rats, mice, etc.);

- cosmopolitans also include indoor and cultivated plants, weeds, and domestic animals that are under human care.

In addition, there are species that do not have clear boundaries of distribution or have a broken geographic range.

Due to these circumstances, the geographical criterion, like others, is not absolute.

The ecological criterion is based on the fact that each species can exist only in certain conditions, fulfilling its functional role in a specific biogeocenosis.

In other words:

Each species occupies a specific ecological niche in complex system ecological relationships with other organisms and inanimate factors.

An ecological niche is the totality of all factors and environmental conditions within which the existence of a species in nature is possible.

It includes the entire complex of abiotic and biotic environmental factors necessary for an organism to live, and is determined by its morphological fitness, physiological reactions and behavior.

The classic definition of an ecological niche was given by the American ecologist J. Hutchinson (1957).

According to the concept he formulated, an ecological niche is a part of an imaginary multidimensional space (hypervolume), the individual dimensions of which correspond to the factors necessary for the normal existence of a species (Fig. 1).

two-dimensional niche three-dimensional niche

Rice. 1. Hutchinson’s ecological niche model

(F 1, F 2, F 3 – intensity of various factors).

For example:

- for the existence of a terrestrial plant, a certain combination of temperature and importance is sufficient (two-dimensional niche);

- for a marine animal, the following are necessary: ​​temperature, salinity, oxygen concentration (three-dimensional niche).

It is important to emphasize that an ecological niche is not just the physical space occupied by a species, but also its place in the community, determined by its ecological functions and its position relative to abiotic conditions of existence.

According to the figurative expression of Yu. Odum, an “ecological niche” is the “profession” of a species, its way of life, and “habitat” is its “address” ”

For example, a mixed forest is a habitat for hundreds of species of plants and animals, but each of them has its own and only one “profession” - an ecological niche. Elk and squirrel share the same habitat, but their ecological niches are completely different.

Consequently, an ecological niche is not a spatial, but a functional category.

It is important to recognize that an ecological niche is not something that can be seen. An ecological niche is an abstract abstract concept.

An ecological niche determined only by the physiological characteristics of organisms is called fundamental, and the one within which the species actually occurs in nature - realized.

However, the ecological criterion is also insufficient to characterize the species.

Some different species in different habitats can occupy the same ecological niches:

- antelopes in the savannas of Africa, bison in the prairies of America, kangaroos in the savannas of Australia, The marten in the European taiga and the sable in the Asian taiga lead the same lifestyle and have a similar type of diet, i.e. in different biogeocenoses they perform the same functions and occupy similar ecological niches.

It often happens the other way around - the same species in different habitats is characterized by different ecological niches. Most often this is due to the availability of food and the presence of competitors:

Moreover, the same view in different periods its development can occupy various ecological niches:

- Thus, a tadpole feeds on plant foods, and an adult frog is a typical carnivore, so they are characterized by different ecological niches;

- migratory birds, in connection with migrations, are also characterized by different ecological niches in winter and summer;

- among algae there are species that function either as autotrophs or as heterotrophs. As a result, at certain periods of their lives they occupy certain ecological niches.

Thus, none of these criteria can be used to determine whether an individual belongs to a specific species. A species can be characterized only by a combination of all or most criteria.

A species is a collection of individuals that have similar genetic, morphological, physiological signs, are capable of crossing with the formation of fertile offspring, inhabit a specific area, have a common origin and similar behavior. A species is a basic systematic unit. It is reproductively isolated and has its own historical destiny. Species characteristics ensure the survival of both the individual and the species as a whole. At the same time, behavior that is beneficial for the species can even suppress the instinct of self-preservation (bees die defending the family).

Basic criteria of the type

1. Morphological criterion of the species. Based on the existence of morphological characters characteristic of one species, but absent in other species. For example: in the common viper, the nostril is located in the center of the nasal shield, and in all other vipers (nosed, Asia Minor, steppe, Caucasian, viper) the nostril is shifted to the edge of the nasal shield.

2. Geographical criterion. It is based on the fact that each species occupies a certain territory (or water area) - a geographic range. For example, in Europe, some species of malaria mosquito inhabit the Mediterranean, others - the mountains of Europe, Northern Europe, Southern Europe.

3. Ecological criterion. It is based on the fact that two species cannot occupy the same ecological niche. Consequently, each species is characterized by its own relationship with its environment.

Additional type criteria

4. Physiological-biochemical criterion. Based on the fact that different species may differ in the amino acid composition of proteins. Based on this criterion, for example, some species of gulls are distinguished (herring, black-billed, western, Californian).

At the same time, within a species there is variability in the structure of many enzymes (protein polymorphism), and different species may have similar proteins.

5. Genetic-karyotypic criterion. It is based on the fact that each species is characterized by a certain karyotype - the number and shape of metaphase chromosomes. For example, all durum wheat has 28 chromosomes in the diploid set, and all soft wheat has 42 chromosomes.

However, different species can have very similar karyotypes: for example, most species of the cat family have 2n=38. At the same time, chromosomal polymorphism can be observed within one species. For example, moose of Eurasian subspecies have 2n=68, and moose of North American species have 2n=70 (in the karyotype of North American moose there are 2 less metacentrics and 4 more acrocentrics). Some species have chromosomal races, for example, the black rat has 42 chromosomes (Asia, Mauritius), 40 chromosomes (Ceylon) and 38 chromosomes (Oceania).

6. Physiological and reproductive criterion. It is based on the fact that individuals of the same species can interbreed with each other to form fertile offspring similar to their parents, and individuals of different species living together do not interbreed, or their offspring are infertile.

However, it is known that interspecific hybridization is often common in nature: in many plants (for example, willow), a number of species of fish, amphibians, birds and mammals (for example, wolves and dogs). At the same time, within the same species there can be groups that are reproductively isolated from each other.

Some Pacific salmon (pink salmon, chum salmon, etc.) live for two years and spawn only before dying. Consequently, the descendants of individuals that spawned in 1990 will breed only in 1992, 1994, 1996 (“even” race), and the descendants of individuals that spawned in 1991 will breed only in 1993, 1995, 1997 (“ odd" race). An "even" race cannot interbreed with an "odd" race.

7. Ethological criterion. Associated with interspecific differences in behavior in animals. In birds, song analysis is widely used to recognize species. Depending on the nature of the sounds produced, different types of insects differ. Different species of North American fireflies vary in the frequency and color of their light flashes.

8. Historical criterion. Based on the study of the history of a species or group of species. This criterion is complex in nature, since it includes a comparative analysis of the modern ranges of species, analysis

None of the considered species criteria is the main or most important. To clearly separate species, it is necessary to carefully study them according to all criteria.

On planet Earth there is living matter. When talking about it, scientists immediately identify the biological species into which it is divided. Any organism has its own characteristics, name and characteristics. This is what allows it to be classified as a specific group of animals.

In this case, only hybrids can be added to the exceptions. They are one biological (see below) mixed with another. However, on this moment Such mutations are quite rare, so real life a common person is unlikely to encounter something like this. But it should be noted interesting fact: Some unusual subspecies are bred artificially by scientists. An example would be a mule (the offspring of a donkey and a mare) and a hinny (the result of crossing a donkey and a stallion).

Today, the species includes more than 1 million animals and plants, not counting those that have not yet been studied. Every year this figure is growing rapidly, as new representatives of flora and fauna are constantly being discovered.

Types of living matter

So, in essence, a species is a collection of similar individuals in functions, behavior, general characteristics, appearance and other properties inherent in a given plant or animal.

The formation of the concept began closer to the 17th century. It was then that a sufficient number of representatives of living organisms were already known. But at that time, the concept of “biological species” was used as a collective name (wheat, oak, oats, dog, fox, crow, tit, etc.). With the study of more organisms, the need arose for the ordering of names and the formation of a hierarchy. In 1735, Linnaeus's work appeared, which made some adjustments. Representatives closer to each other were collected into clans, and the latter were divided into orders and classes. By the end of the 18th century, the world's leading biologists accepted these provisions as fundamental.

For quite a long time, biological species were a closed system for scientists. Previously, this phrase meant the impossibility of transferring genes from one organism to another (subject to belonging to different groups of living matter). More often, crossbreeds of species are found in plants. This process easier to reproduce, if only because they are able to “exchange” genes themselves without the intervention of a human hand. That is why the biological species of plants is so rich.

However, today there are also animal hybrids, which have already been mentioned above. Some of them are able to reproduce their offspring (for example, female ligers and tigons are fertile). But others are not endowed with such a function (we are talking about mules and hinnies).

Birds

The class of vertebrates is commonly called birds. characteristic feature which is the feather cover. Previously, there were species that were born wingless. However, they became extinct long ago, and kiwis are considered their descendants.

Some species are capable of flying, however, for example, ostriches and penguins lack this function.

Archaeological expeditions have revealed that dinosaurs are the direct ancestors of birds. There is also a version that, perhaps, it is the feathered animals that are the only surviving representatives of the Mesozoic era in the world.

Thanks to classifications, organisms are divided into domestic and wild. Each of these stages is divided into types. Birds differ from other representatives of living matter by the presence of feathers, the absence of teeth, a skeleton that is very light in weight (but quite strong), a 4-chambered heart, etc.

Human

Many people believe that humans are the highest stage of animal evolution. However, some scientists, citing various facts, refute this statement. Neoanthropes belong to the class of mammals and the order of primates.

Humans as a biological species are capable of having a strong impact on the environment. However, the main difference this representative What distinguishes the animal world from others, less developed, is the presence of a strong intellect. Thanks to him, many questions were answered. But the process of development of the species is quite thorny. Just 1.5 million years ago, human life expectancy was about 20 years, and the population did not exceed 500 thousand.

Signs

Any characteristic of a biological species begins with the presentation of signs of belonging to a certain set of individuals. There are several similar criteria:

• Morphological. It allows you to distinguish one species from another, taking into account only external characteristics.
• Physiological-biochemical. Thanks to this criterion, scientists distinguish between different Chemical properties and functions of individuals.
• Geographical. The sign indicates where a particular species can live, as well as where exactly it is distributed and localized at the moment.
• Ecological. This criterion allows you to learn about attempts to establish in an area, as well as learn more about which habitat zone is more suitable for certain organisms.
• Reproductive. He talks about so-called reproductive isolation. It's about about factors that prevent the transfer of genes even from closely related individuals.

The listed signs are generally accepted and basic. However, in addition to them, there are others: chromosomal criterion, etc.

Each species has an individual genetic system, which, in turn, is closed. This indicates the inability of natural mating between representatives of different populations.

Due to the fact that any biological species (examples are in the article) is dependent on climatic conditions and other factors, individuals in one area are distributed unevenly. They unite in populations.

Species are also divided into subspecies. The latter are united due to a common geographical location or environmental factor.

Species criteria: morphological

Biological species have common features, manifested in appearance. It allows you to combine non-closely related individuals into one group. Every person, even Small child, will be able to distinguish a cat from a dog, an older person will be able to distinguish a dog from a fox, but it will be difficult to separate a fox from an arctic fox without the appropriate knowledge.

However, the morphological criterion is not sufficiently competent in all cases. There are biological species in the world that are too similar to each other. When faced with such problems, scientists convene consultations and closely analyze the proposed representatives. Twin species are not very common, but they still exist and should be distinguished. Otherwise, chaos will ensue.

Cytogenetic and molecular biological characteristics

To describe this criterion, it is necessary to recall the school biology course. The teachers explained that each representative of a particular biological species has a certain set of chromosomes, called a karyotype. Related individuals have the same structure, functions, number, and size of structures containing genes. It is thanks to this feature that the so-called twin species can be distinguished from each other.

Using the example of a vole, we can show exactly how assemblages differ from each other. The common one has 46 chromosomes, the Eastern European and Kyrgyz ones have 54 (they differ in the structure of the structural unit), and the Trans-Caspian one has 52.

However, even in this case there are exceptions. The described method is not always particularly accurate. For example, ancient cats had exactly the same karyotype, although they belonged to different species.

Reproductive isolation

This factor indicates the presence of a closed genetic system. This criterion should be understood correctly. Representatives of one species from different populations are able to interbreed with individuals from another population. Thanks to this, genes move to completely different places of residence.

It also occurs due to different structures of the genital organs, sizes and colors. This applies not only to animals, but also to plants. You should look into botany - “foreign” pollen is rejected by the flower and is not perceived by the stigmas.

Species names

All species names are added up according to general scheme and are usually recorded on Latin. In order to highlight certain representatives, it is taken common name genus, then the specific epithet is added to it.

Examples include Petasites fragrans or Petasites fominii. As you can see, the first word is always written with a capital letter, and the second - with a lowercase letter. The names are translated into Russian as “fragrant butterbur” and “Fomina’s butterbur”, respectively.

Variability of a biological species

Any species is capable of genetic change. This can affect the entire population or be individual. There are also modifications. The first has the ability to affect genes and chromosomes, thereby changing the standard karyotype of the animal. This problem it cannot be eliminated, and the body lives with it throughout the entire time. does not affect further offspring in any way, since it does not affect genes and chromosome set. The problem arises under the influence of certain factors. Once you get rid of them, the changes will immediately disappear.

Genetic and modification changes

Each variability is divided into several types. Genetic problems are characterized by the following processes: mutations and gene connections.

For modifications - the reaction rate. This process means the influence environment on the genotype, due to which various changes in the karyotype occur. If the body adapts to it, then no problems for existence will arise.