Thanks to evolution, the modern organic world is diverse and unique. Scientists suggest that today there are over 10 million species of living organisms living on our planet. Therefore, the task of classifying known species into groups in a certain sequence and system is very important. This will ultimately make it possible to establish for each organism its place in the world of living nature.

The need to classify living organisms was understood by scientists of Ancient Greece. However, the proposed classifications of that time were based only on a few characteristics. They concerned mainly the external and internal structure of organisms and practically did not take into account the family ties between them. The evolutionary theory of Charles Darwin laid the foundation for the creation of modern classification.

Classification of organisms is a conditional distribution of the entire population of living beings into hierarchically subordinate groups in accordance with any common characteristics.

Today, the classification of the living world is carried out by systematics - the science of the diversity of species and family relationships between organisms. In modern taxonomy, when assigning a particular rank to any organism, it is based on a number of characteristics. For example, on the features of origin and historical development, morphological and anatomical structure, reproduction, embryonic development. Physiological and biochemical characteristics, type of reserve nutrients, chemical composition of cells, number and composition of chromosomes, etc. are also taken into account.

Principles of taxonomy

You already know that he created the first scientific system of living nature in the middle of the 18th century. Swedish natural scientist Carl Linnaeus. The author based this system on two basic principles: binary nomenclature and hierarchy (subordination). These principles are still relevant today. By binary nomenclature Each species has two words in its name: a noun and an adjective. The noun means the name of the genus to which the species belongs, and the adjective means the specific epithet. For example, a forest cat ( Felis silvestris), domestic apple tree ( Malus domestica).

According to modern rules, after the specific epithet the surname of the scientist who first described the species is usually placed. For example, the Linnaeus grape snail ( Helix pomatia Linnaeus or Helix pomatia L.).

Just as in a textbook the questions studied are combined into paragraphs, and paragraphs into chapters, organisms are united into systematic taxa. In taxonomy this is called the principle hierarchy (subordination). In total, there are seven most common systematic taxa:

So kinds animals are combined into childbirth, childbirth- V families, families- V squads, squads- V classes, classes- V types, types- V kingdoms. It should be remembered that when classifying bacteria, fungi and plants, instead of taxon squad use order, and instead of taxon type — Department.

Sometimes in taxonomy such categories as superkingdom and empire are used. There are two superkingdoms - eukaryotes (nuclear) and prokaryotes (prenuclear), which are included in the empire of cellular organisms. The second empire is represented by non-cellular life forms - viruses.

Biological system

Currently, the most widespread biological system divides all living organisms into five kingdoms: Bacteria, Protists, Fungi, Plants and Animals. At the same time, it is impossible to draw a sharp line between individual kingdoms based on only a few characteristics. For example, representatives of the kingdoms Fungi and Plants are characterized by similar characteristics. These are a sedentary lifestyle, aerobic respiration, the presence of a cell wall, the same structure of the genetic apparatus and most cellular organelles, etc. At the same time, they have a number of significant differences. For example, photosynthesis in plants.

Only a deep analysis of the set of characters, based on their origin, patterns of structure and life activity, as well as a thorough study of phylogenetic relationships between different groups of organisms, allows us to assign a species or a larger taxon to one or another kingdom.

The classification of the living world is carried out by systematics - the science of the diversity of organisms and the family relationships between them. The fundamental principles of taxonomy are binary nomenclature and hierarchy. Currently, all living organisms are divided into five kingdoms: Bacteria, Protists, Fungi, Plants and Animals.

Taxonomy- a branch of biology that deals with the classification (grouping) of modern and fossil organisms based on similarity and relatedness.

The purpose of taxonomy is to describe, name, classify and construct an evolutionary ( phylogenetic ) a system of organisms that allows us to display family relationships between different classification groups of organisms, as well as the directions and paths of evolution of the organic world.

Systematic features- the most significant signs of external and internal structure, by which taxonomy establishes the similarity and relatedness of organisms.

When classifying living organisms, the following are taken into account:
■ features of their morphological and anatomical structure;
■ features of reproduction, embryonic development and life activity;
■ physiological and biochemical characteristics;
■ type of reserve nutrients;
■ the origin and historical development of a group of living organisms, determined from fossil remains;
■ distribution and habitat (ecological niche);
■ structure and chemical composition of cells;
■ number of chromosomes in the karyotype, etc.

The classification of organisms is based on the identification of certain systematic systems subordinate to each other ( taxonomic ) categories.

Taxonomic(or systematic) categories- These are designations for groups of organisms that differ in the degree of relatedness.

There are taxonomic categories of different levels (see below) assigned to specific groups of organisms - taxa .

Taxon- a group of related organisms that can be assigned a specific taxonomic category. Examples of taxa: chordates, mammals, domestic dog.

❖ Taxonomic categories (in order of decreasing subordination):
■ view,
■ gender,
■ family,
■ order (order - for plants),
■ class,
■ type (department - for plants),
■ kingdom,
■ supremacy.

There are also intermediate categories - subkingdom, subtype, superclass, subclass, etc. Within a species, subspecies, varieties, forms, etc. are distinguished.

Elementary systematic unit- view.

A species is a historically established set of populations, individuals of which are similar in morphological, physiological and biochemical characteristics, are adapted to certain living conditions, occupy a certain area in nature and are capable of interbreeding with each other to form fertile offspring.

Binary nomenclature of the form(introduced by C. Linnaeus in 1753): the name of each species is formed from two words, the first of which means the name of the genus to which the species belongs, and the second is the specific epithet (examples: Scots pine, magnolia grandiflora, brown bear). Next to the name of the organism (in Latin) in the scientific literature, the name of the scientist who first named or described this species is indicated in abbreviated form.

Currently, two superkingdoms and five kingdoms of organisms are distinguished (see table).

This system of organisms does not include viruses, which are non-cellular life forms.

Brief characteristics of prokaryotes and eukaryotes

Prokaryotes- organisms whose cells do not have a formed nucleus.

Prokaryotes include bacteria, cyanobacteria and some other organisms.

Prokaryotes lack, except for the nucleus, all organelles known in eukaryotes (mitochondria, chloroplasts, endoplasmic reticulum, lysosomes, Golgi complex); there are only numerous (up to 20 thousand) ribosomes and one large circular DNA molecule associated with a very small amount of protein. Most bacteria also contain small circular DNA molecules called plasmids.

The basis of the cell wall of all prokaryotes is murein- a polysaccharide with several amino acids attached.

In a number of bacterial species, the plasmalemma forms mesosomes- invaginations into the cytoplasm, on the folded membranes of which there are enzymes and photosynthetic pigments, due to which mesosomes are able to perform the functions of mitochondria, chloroplasts and other organelles.

Eukaryotes- organisms whose cells contain a formed nucleus surrounded by a nuclear envelope.

Eukaryotes include both unicellular (protists) and multicellular (fungi, plants and animals) organisms.

The genetic material of eukaryotes is localized in chromosomes, consisting of DNA and protein. In addition to the nucleus, eukaryotes have membrane-bound cellular organelles (sometimes with their own DNA) - mitochondria, endoplasmic reticulum, lysosomes, Golgi complex, and in plants there are also plastids and large vacuoles.

Kingdoms of organisms

Bacteria- single-celled prokaryotic organisms.

Protista- eukaryotic unicellular or colonial organisms with a cellular level of organization (examples: green euglena, volvox, common amoeba).

Mushrooms- non-motile eukaryotic organisms, the body of which consists of thin intertwining threads that form mycelium (in some types of fungi there is no mycelium).

Plants- multicellular, eukaryotic, autotrophic organisms leading an attached lifestyle, capable of synthesizing organic substances from inorganic ones in the process of photosynthesis.

Animals- multicellular, eukaryotic, heterotrophic organisms, most species of which are capable of active movement.

Diversity of the organic world

Principles of taxonomy. Classification of living organisms

The organic world of the Earth is currently extremely diverse. However, more than 4 billion years ago, life did not exist on Earth, since the conditions were not suitable for it. As our planet cooled, simple organic substances were formed from inorganic gaseous substances in the atmosphere under the influence of electrical discharges, solar ultraviolet rays, and water vapor. They accumulated in the primordial ocean. Over the course of many millions of years, the first simply structured living organisms arose from these organic substances, which fed heterotrophically and could grow and divide.

About another billion years later, green organisms capable of photosynthesis appeared. Using solar energy, they synthesized organic substances from inorganic ones and saturated the earth's atmosphere with oxygen. In the process of further evolution, organisms changed and became more complex, conquering land and air habitats. Some organisms were transformed into others, some of them, not adapting to changing conditions on Earth, died out.
Since most of the ancient organisms are extinct, their existence can only be judged by paleontological remains– prints and fossils. By studying them, scientists reproduce the appearance of ancient plants and animals. The deeper the geological layer is located in the earth’s crust, the more ancient remains it contains and the more significantly the restored appearance of ancient organisms differs from modern ones.

Currently, there are about 5 million different species of living organisms on Earth, and new species are being discovered. Much more of them died out in the process of evolution.

Living organisms are of great importance in nature and in human life. Their diversity is very great. In order not to get confused in all these forms and species, scientists combine all organisms into groups using signs of their similarities and differences. Such groups were called units of systematics, or taxonomic units.
Classification of organisms, i.e. combining them into groups is the science of taxonomy. The main taxonomic units are: species, genus, family, order (in plants) or order (in animals), class, division (in plants) or phylum (in animals), kingdom. With great diversity, intermediate taxonomic units can be introduced: suborder, superorder, subclass, etc.
The main unit of taxonomy is species, since any organism belongs to some species. One species includes individuals similar in structure and vital activity, inhabiting a certain area, interbreeding freely and producing fertile offspring similar to their parents.
In different countries, the same organism may be called differently. The Swedish scientist Carl Linnaeus introduced the scientific names of species of organisms in Latin, consisting of two words (double, or binary, nomenclature). For example, creeping wheatgrass, field chamomile. The first word in this double name denotes the genus, and the second the species of the plant. The genus unites species that are similar in origin and structure. For example, peach-leaved bellflower and campanula latifolia are two species belonging to the same genus - campanula.
Several closely related genera form a family. For example, the genus rye, the genus wheat, the genus barley and others make up the family of cereals. Plant families are grouped into orders, orders into classes, classes into divisions, and divisions into kingdoms.
Close families of animals are grouped into orders. For example, the families Feline, Wolf, Bear and others belong to the order Predatory. Related orders form classes. Thus, the orders Carnivora, Rodents, Primates and others make up the class Mammals.
Classes of animals are combined into types. For example, the classes Mammals, Birds, Reptiles and others are included in the phylum Chordata.

All plants of the class Dicotyledons and class Monocots have flowers, so they are combined into the department Angiosperms, or Flowering plants. In addition to the department Angiosperms, there are departments Gymnosperms, Ferns, Mosses, etc. The departments also include classes of fungi and bacteria.
An even larger unit of taxonomy is the kingdom. All divisions of plants form the kingdom of Plants, in which there are about 500 thousand species. All types of animals form the kingdom Animals, which includes over 1.5 million species. According to the most common classification system of the Austrian scientist R. Whittaker, in addition to the kingdoms of Plants and Animals, the kingdoms of Bacteria, Protists and Fungi are distinguished.
The highest unit of taxonomy is the superkingdom. All organisms of the kingdoms Protists, Fungi, Plants and Animals have a formed nucleus in their cells. These kingdoms are united into the superkingdom Eukaryotes, or nuclear organisms. The kingdoms of Bacteria (Drobyanka) and Archaebacteria form the superkingdom of Prokaryotes, or prenuclear organisms, since they do not have a formed nucleus and many other typical cellular organelles.

Key words of the abstract: diversity of living organisms, systematics, biological nomenclature, classification of organisms, biological classification, taxonomy.

Currently, more than 2.5 million species of living organisms have been described on Earth. To organize the diversity of living organisms, they serve taxonomy, classification And taxonomy.

Taxonomy - a branch of biology, the task of which is to describe and divide into groups (taxa) all existing and extinct organisms, establish family relationships between them, and clarify their general and particular properties and characteristics.

The branches of biological systematics are biological nomenclature And biological classification.

Biological nomenclature

Biological nomenclature is that each species receives a name consisting of a generic and specific name. The rules for assigning appropriate names to species are governed by international nomenclature codes.

For international species names it is used Latin language . The full name of the species also includes the name of the scientist who described the species, as well as the year the description was published. For example, international name house sparrow - Passer domesticus(Linnaeus, 1758), A tree sparrow - Passer montanus(Linnaeus, 1758). Typically, in printed text, species names are italicized, but the name of the describer and the year of the description are not.

The requirements of the codes apply only to international names of species. In Russian you can also write “ field sparrow " And " tree sparrow ».

Biological classification

Classification of organisms uses hierarchical taxa(systematic groups). Taxa have different ranks(levels). The ranks of taxa can be divided into two groups: obligatory (any classified organism belongs to taxa of these ranks) and additional (used to clarify the relative position of the main taxa). When systematizing different groups, a different set of additional taxon ranks is used.

Taxonomy- a section of taxonomy that develops the theoretical foundations of classification. Taxon a group of organisms artificially isolated by man, related by one degree or another of kinship, etc. at the same time, sufficiently isolated so that it can be assigned a certain taxonomic category of one or another rank.

In the modern classification there is the following taxon hierarchy: kingdom, division (type in the taxonomy of animals), class, order (order in the taxonomy of animals), family, genus, species. In addition, they highlight intermediate taxa : over- and subkingdoms, over- and subdivisions, over- and subclasses, etc.

Table “Diversity of living organisms”

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At first glance, it may seem that the world of living beings consists of an unimaginable variety of plants and animals, different from each other and each going their own way. However, a more detailed study shows that all organisms, both plant and animal, have the same basic life needs, they face the same problems: obtaining food as a source of energy, conquering living space, reproduction, etc. In the course of solving these problems, plants and animals formed a huge variety of different forms, each of which is adapted to life in given environmental conditions. Each form has adapted not only to the physical conditions of the environment - it has acquired resistance to fluctuations within certain limits of humidity, wind, lighting, temperature, gravity, etc., but also to the biotic environment - to all plants and animals living in the same zone.

In order to study and describe the characteristics of this infinite variety of life forms, the biologist had first of all to name them and classify, systematize, and organize them.

Currently, the field of knowledge within which the problems of orderly designation and description of the entire set of objects (in our case, the organic world) are solved is called “Systematics” (from the Greek systematikos - ordered, related to the system). Taking into account the specifics, i.e. the need to describe and place in a system all existing and extinct organisms and plants - this area can be called “Biological systematics”. Biological systematics itself studies the diversity of the organic world, the elements of which correspond to taxa (as they came up with, see below “Some thoughts on systematics and taxonomy”)

Systematics is based on the principles of typology - classification according to existing stable characteristics of the objects that form the system. The principles of typology, which can be very diverse, have been used at all times. In the pre-Darwinian period, taxonomy was based on structural similarity, usefulness or uselessness to humans, etc. For example, in the 4th century. St. Augustine divided animals into useful, harmful and indifferent to humans. Medieval herbalists classified plants according to whether they produced fruit (edible), fiber, or wood.

Objects can also be systematized according to other characteristics: properties, functions, connections. In this case, the characteristic of the object must be sufficient to distinguish it from other objects and allow the object to occupy a single place in the system. You can arrange objects according to a purely formal criterion, for example, by assigning serial numbers to objects, and end up creating a system based on an objective law. An example and standard of such a system is the periodic table of elements in chemistry.

Systems whose objects are ordered without objective justification based on proven facts are artificial. An example of an artificial system is the classification of plants and animals based on visual similarity of structure, which was created by the Swedish biologist Carl Linnaeus. He cataloged and described plants in Species Plantarum (1753) and animals in Systema Naturae (1758). Despite the artificiality of Linnaeus' system, it played a major role in the development of modern taxonomy.

The system of the organic world is a systematic description of fossil and living organisms.

With the recognition of the theory of evolution, the development of science and the accumulation of factual data on biological objects of the fossil and modern periods, the approach to constructing the classification has also changed. Currently, botanists and zoologists, when constructing a classification of animals and plants, are based on their natural phylogenetic relationship, placing organisms with similar evolutionary origins in the same group. The degree of relatedness of the compared objects is established on the basis of their morphological, anatomical, biochemical, genetic, etc. similarities and differences. Such a classification is a natural system of the organic world, the construction of which is a continuous process in connection with an endless series of ever-deepening and more complex studies. Thanks to systematics, the diversity of life is presented not as a chaotic accumulation of organisms, but as a certain ordered system, changing from simple to complex.

The system of the organic world is a systematic description of fossil and currently existing organisms in accordance with the principles, methods and rules of classification of organisms developed by the branch of systematics called "Taxonomy". The term “taxonomy” was introduced in 1813 by the Swiss botanist O. Decandolle, who developed plant classifications.

For a long time, botanists and zoologists used the term "taxonomy" as a synonym for taxonomy, and only in the 60-70s. XX century There has been a tendency to define biological systematics more broadly - as the science of the diversity of living organisms and related relationships between them, and taxonomy (the theory of classification of complexly organized areas of reality, usually having a hierarchical structure) - as a narrower discipline (or section of systematics) dealing with principles, methods and rules for the classification of organisms (this point of view is shared by American zoologists-taxonomists J. Simpson and E. Mayr, Soviet botanist A.L. Takhtadzhyan, etc.).

Thus, biological systematics deals with the study of real groups of organisms - taxa, and biological taxonomy develops the doctrine of taxonomic categories and their definition into a system that best corresponds to the natural system of organisms.

The system is built on a hierarchical principle (subordination), i.e. according to the principle of multi-level structural organization of animal communities or plant systems, consisting in ordering between levels from lower to higher (evolution). Individuals at each level have essential and fundamental characteristics by which they are grouped at a given level. Moreover, the lower the level, the more subordinate the characteristics by which individuals are grouped.

Species as a specific form of existence of the organic world
and the basic concept of systematics

All organisms belong to one species or another (Latin species). It is difficult to give a universal definition of a species that would be completely acceptable for both animals and plants, including those that during their life cycle are represented by two or more completely different forms (such as mosses, ferns, some algae, many coelenterates) , worms, insects or amphibians).

The concept of species has changed significantly throughout the history of biology. There are still some disagreements among taxonomists on the question of what a species is, but to a large extent, unanimity has been achieved on this cardinal issue.

From the standpoint of modern taxonomy, a species is a genetically limited group of individuals, similar to each other in their morphological, embryological and physiological characteristics, occupying a certain geographical space - an area, having common ancestors, interbreeding in nature only with each other and producing fertile offspring. Rare cases of interspecific crossings in nature do not violate the independence and isolation of each species, which are maintained through reproductive isolation.

Each species is the result of long-term evolution and comes from another species by turning it into a new one (phyletic evolution) or from part of a species (a separate population) by divergence (division into two or more species). The current species is relatively stable over time, and this stability goes far beyond the scope of human history.

The Swedish naturalist K. Linnaeus (1707-1778), who is rightfully considered one of the creators of scientific taxonomy and systematics, at one time adopted the species as the main unit of classification; he introduced into scientific use such concepts as “genus”, “family”, “order” and “class”; finally approved the binary nomenclature and the hierarchical principle of constructing a system (which are still used in biology).

In accordance with the binary nomenclature, each individual is assigned a Latin name consisting of two words: the first is a noun - the name of a genus that unites a group of closely related species; the second is an adjective - the name of the species itself.

According to this system, the scientific name of, for example, the domestic cat, Felis domestica, refers to all breeds of domestic cats - Persian, Siamese, tailless, Abyssinian and tabby - since they all belong to the same species.

Related species of the same genus are the lion (Felis leo), tiger (Felis tigris) and leopard (Felis pardus). A dog belonging to a different genus is called Canis familiaris. Note that in all of the examples given, the genus name comes first and is capitalized, and the species name comes second and is capitalized (with the exception of some plant species names).

You may ask, why is it so difficult to give Latin names to plants and animals? Why call the sugar maple Acer (maple) saccharum (sugar)? First of all, to be precise and avoid confusion [show] , since in some areas of America this same tree is called hard, or stone, maple. The tree that most of us call white pine is Pinus strobus. However, in some countries white pine is also called Pinus flexilis and Pinus glabra, while in other countries Pinus strobus is called northern pine, soft pine or Weymouth pine. There are thousands of other reasons for confusion in everyday names, but the examples given clearly show that precise scientific names are really necessary, and are not a scientific duplication of generally accepted ones.

The scientific names of organisms cannot be considered immutable, since sometimes new research shows that the related relationships of some genera and species do not fit into the framework of our previous ideas about them. It may be necessary to change the name of a particular organism, to the chagrin of other biologists who are accustomed to calling the animal by a certain scientific name.

In a discussion of biochemical evolution, Georges Wald (Problems of Physiology and Biochemistry, Academic press, New York, 1952) described the difficulties he had encountered in a paper published in 1904 in determining which animals belonged to essentially the names Cynocephalus mormon and Cynocephalus sphinx.

"Until that time I believed that one of them was a mandrill, the other a baboon. After Natol published his work in 1904, these names underwent the following amazing transformations: Cynocephalus mormon became Papio mormon or Papio majmon, which turned into Papio sphinx. This name could easily have been confused with Cynocephalus, which now became Papio sphinx, if the latter had not meanwhile turned into Papio papio. Having barely eliminated this danger, Papio sphinx was renamed Mandrillus sphinx, and Papio papio - Papio comatus. All "What I can say about this is - thank God that one animal is called a mandrill, and the other a Guinea baboon."

Table 1. The position of man and the “white oak” plant in the system of the organic world
White oak		Human
kingdom	Plants	kingdom	Animals
Department	Tracheophyta	type	Chordata
subdepartment	Pteropsida	subtype	Vertebrata
Class	Angiospermae	Class	Mammalia
subclass	Dicotyledonae	subclass	Eutheria
order	Sapindales	squad	Primates
family	Fagaceae	family	Hominidae
genus	Quercus	genus	Homo
view	alba	view	sapiens

According to the hierarchical principle of constructing a system of the organic world (Table 1.), animal species - as a systematic unit of classification - began to be grouped into the next, higher systematic unit - genus (genus, plural genera), genera - into families, families - into orders, orders - into classes, classes - into types (phyla). When classifying bacteria, fungi and plants, instead of the concept of “order”, “order” is used, and instead of “type” - “division”. Type and department are combined into kingdoms. In microbiology, terms such as “strain” and “clone” are used. Often, to emphasize the diversity in a group, subordinate categories are used, for example, subspecies, subgenus, suborder, subclass or superfamily, superclass.

The concept of “over-kingdom” is relatively new, which introduced the division of the entire biomass of the Earth into:

• eukaryotes (contain a nucleus);
• prokaryotes (non-nucleated)

The fact that living beings, based on their characteristics, can be arranged into a hierarchical system - species, genera, families, orders, classes and types - can be interpreted as evidence of the existence of evolutionary relationships between them. If different “varieties” of plants and animals were not related to each other phylogenetically, their characteristics would be random and the establishment of such a hierarchy would be impossible.

The elimination of extinct intermediate forms of organisms from the system made it possible to split the organic world into clearly defined living species, which someone called “islands of life in the ocean of death.” They are also likened to the terminal shoots of a tree whose trunk and main branches have disappeared [show] .

As is known, the first classification systems introduced into zoology and botany were created at a time when the biological sciences were inseparably dominated by the theory of the constancy of species, owing their existence to an act or acts of creation. However, taxonomists have noticed that each system has a certain order and hierarchy, and is not chaotic. Systematics groups species that are very similar to each other into one genus, similar genera into families, families into orders, and orders into classes. Finally, classes that have certain similarities are classified by taxonomy as one type. However, only the principle of evolution explains why this, and not another order, characterizes the classification system.

Species assigned to the same genus, or those that are closely related, evolved through evolution from a common ancestral trunk. The same is true with other higher categories of zoological and botanical systematics. All vertebrate animals share some basic common features. These similarities indicate a common origin, an evolutionary development from some group of animals that were the ancestors of all vertebrates. The more the systematics approaches natural, that is, based on kinship, the more such a system will reflect true evolutionary relationships.

In striving to create a natural system, the modern taxonomist cannot rely solely on currently living forms, but must also take into account fossil forms. If we imagine the entire phylogenetic development of the animal world in the form of a rapidly branching tree, the branches at the top of which represent the currently living species, then on the basis of anatomical and embryological data it would be possible to easily understand the relationship between individual families.

However, we should not forget that in the process of evolution the overwhelming majority of forms completely died out, that large branches and large branches disappeared, as well as an innumerable number of smaller branches. Therefore, studying only modern fauna, without taking into account paleontological data, cannot give us a complete picture and cannot lead to a correct understanding of all related relationships between currently living organisms.

In the process of evolution, newly emerged organisms, better adapted to new conditions, inevitably lead to the extinction of old archaic and less adapted forms. Therefore, among modern fauna we most often do not see transitional forms connecting animal forms that are currently isolated from each other. Transitional or archaic forms could survive only in exceptional cases, in environments in which not only physical conditions did not undergo significant changes, but in which they did not find new competitors better adapted to life. Such forms are, as it were, living fossils, and their presence serves as the next proof of evolution that taxonomy presents.

Archaic forms are also of interest because they have been preserved almost unchanged from ancient times. For example, the hatteria (Sphenodon) has lived almost unchanged since the Jurassic period, and possums since the Cretaceous. Lingula, belonging to the brachiopods, are completely similar to the forms that lived in the Ordovician approximately 400 million years ago. Oysters have also lived for about 200 million years, having undergone only minor changes. Recently, valuable discoveries have been made in this area.

We have already indicated above that in the sea, near Madagascar, representatives of seemingly long-extinct lobe-finned fish (Latimeria), which once gave rise to the evolution of amphibians, were discovered. In 1952, representatives of ancient mollusks (Monoplacophora) were caught from the depths of the ocean, west of Costa Rica, and in 1958 the following exhibits of this group were caught in the northern part of the Peruvian-Chilean Basin. These forms belong to the genus Neopilina. While lobe-finned fish were thought to have gone extinct about 70 million years ago, members of Monoplacophora were known fossils dating back to about 300 million years ago.

Relict forms also include representatives of a very interesting order of mammals from the point of view of evolution, the so-called cloacals (Monotremata). The two currently living representatives of this order, that is, the platypus and the echidna, are distinguished by a number of anatomical and physiological characteristics that bring them closer to reptiles. Cloacals are the only mammals that lay eggs. However, their body is covered with hair, and young animals initially feed on their mother’s milk. The echidna is found in Australia, Tasmania and New Guinea, the platypus - in Australia.

In almost every organ system of cloacal animals one can find features that make them similar to reptiles. As the name itself indicates, they have a cloaca, that is, a common excretory duct of the genitourinary organs and intestines. Milk floats out from the glands on the abdominal surface of the body, but the ducts of these glands do not merge into one common one, which would open at the top of the mammary gland. Cloacal eggs are quite large and contain a large amount of yolk.

The origin of the cloacae remains quite mysterious. The first fossil forms are found in the Pleistocene. Simpson believes that they are rather highly modified mammalian reptiles, which "we classify as mammals by the definition of mammals rather than by their origin."

The preservation of relict forms alive almost unchanged from such ancient times can provide us with certain data regarding the very pace of the evolutionary process. This is a very difficult question to which it is difficult to find a satisfactory answer. Paleontological evidence suggests that the evolutionary process occurs at different rates in different groups of animals. Some groups of animals undergo rapid changes, others do not change over long periods of time.

Source: S.Skovron. Development of the theory of evolution.
Translation by Lozova R.M., ed. Vorontsova N.N. - Polish State Medical Publishing House. Warsaw, 1965

The task of taxonomy is to complement modern classifications , mostly created on the basis of the cladistic method, or cladistics (from the Greek klados - branch) - a variant of constructing a family tree of the organic world, based on the degree of relationship, but without taking into account the geochronological sequence, restore the missing branches and place each shoot on the corresponding branch .

In general, such a system, based on the cladistics method, quite objectively reflects the levels of evolution and the degree of relatedness of groups thanks to embryological, cytological and other studies, but without taking into account paleontological data (geochronology, analysis of “ancestor-descendant” and “sibling” characteristics, the main link of development etc.) is still phylogenetically unstable. Its stability will be ensured by placing fossil and modern plants and animals in one continuous series of forms - from lower to higher.

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Some thoughts on systematics and taxonomy [show]

According to the literature of the modern period, it seems that since the time of Linnaeus, naturalists have been so carried away by dismemberment that they have probably already forgotten why they did it and concentrated all their efforts on introducing new terminology, which, due to its redundancy, began to cause confusion, imho. The founder of this process was O. Decandolle with his taxonomy.

The Great Soviet Encyclopedia defines the taxon as a group of discrete objects connected by one or another degree of commonality of properties and characteristics and, due to this, giving grounds for assigning them a certain taxonomic category. The identification of a taxon can be based on different properties and characteristics of objects - on the common origin, structure, composition, form, functions, etc., but in each case the set of characteristics and properties must be necessary and sufficient for a given taxon to occupy the only place in the system and did not overlap with other taxa. When solving problems of systematics and taxonomy, it is sometimes important to clearly distinguish between the terms “taxon” and “taxonomic category”. A taxon always characterizes a specific set of objects (the organic world, units of geographical description, language, etc.), while a taxonomic category expresses only the designation and logical conditions for identifying a given level of hierarchy or rank of system organization. Therefore, for example, in biology, where these categories are most commonly used, the concepts “species”, “genus”, “family” belong to the category of taxonomic categories, and the taxon is formed by the species “Scots pine” or the order of rodents.

Consider this jumble of beautiful words:

Taxon- a group of discrete objects connected by varying degrees of commonality of properties and characteristics. Moreover, a species is also a set (group) of organisms (objects) of common origin, similar morphologically and physiologically. Their identification is based on different properties and characteristics, while the set of these characteristics allows them to occupy a single place in the system and not overlap with other species or taxa. Thus, according to the definition of taxon and species, we can say that a taxon is a species.	Taxonomic unit- this is a classification unit taken as a basis by Linnaeus. And, as is known, Linnaeus took the form as the basis for classification. He combined species into a higher-ranking taxonomic unit - genus, etc.
So the whole heap looks something like this: (similar for genus, family, etc.) This is simply some kind of trinity of the word “species”: a taxon is a species, a taxonomic unit is a species, a taxonomic (systematic) category (rank) is a species.

Conclusion: although the Russian language is “broad,” there are not enough words to describe it. However, naturalists themselves admit that they really lack words. Nevertheless, a unity of views is gradually being achieved and, therefore, there is a real possibility of building a natural, generally accepted system of the organic world.