From Big Medical Encyclopedia

DARWINISM — the theory of organic evolution constructed on Ch. Darvin's views; in wide value D. — this theory of evolution in general, i.e. the doctrine about historical development of the organic nature, about continuous reorganization of live forms in the course of adaptation to the habitat. In narrower understanding of D. is a theory of natural selection or survival of fittest organisms in fight for existence.

The idea of evolutionary development of the organic world expressed also to Ch. Darvin — - G. L. Buffon, Ge. Lamarck, R. Chambers, Geoffroi St E. Geoffroy Saint-Hilaire and many other evolutionists 18 and 19 centuries), however only Ch. Darwin managed to prove objective existence biol, evolutions and created the theory of this process.

Succeeded the lamarkistsky ideas of evolution allowing emergence of new, reasonable signs by direct adaptation to the changed living conditions, in particular by means of inheritance of results «exercises or not exercises of bodies» (see. Lamarckism ). Opposed to a lamarckism theory of evolution on the basis of uncertain (nondirectional) changes and natural selection (see), providing survival in the conditions of fight for existence of fittest individuals.

In the works «The Origin of Species by Natural Selection, or Preservation of the Favoured Breeds in Struggle for Life» (1859), «Change of domestic animals and cultivated plants» (1868), «An origin of the person and sexual selection» (1871) and others Darwin offered a scientific explanation for the phenomenon of variability of live organisms as under natural conditions, and under the influence of domestication and cultivation.

Ch. Darwin established that the main operating factors of evolution are variability (see), heredity (see) and natural selection. In the theory Darwin proceeded from existence of two types of variability — certain and uncertain (hereditary). In that case when these or those environmental factors equally affect change of all or the majority of individuals, a certain variability takes place (e.g., dependence between climate and thickness of skin or a wool cover). A certain variability at elimination of the operating factor hereditarily is not fixed. Uncertain changes arise under the influence of those environmental factors, to the Crimea organisms did not adapt during evolution (e.g., radiation, cellular poisons, etc.), have accidental character and are hereditary by the nature. In that case when the arisen uncertain changes are useful to this look, in the course of natural selection they are fixed and can give rise to a new look; e.g., if in group of plants of one look under the influence of the accidental reasons there were frigostable plants, then at hit during a frigid climate frigostable plants survive, giving thus rise to new frigostable plants. Ch. Darwin considered natural selection and fight for existence the major driving factors of evolution by means of which organisms with changes harmful or useless for the sake of appearances are eliminated and there are forms possessing more or less useful signs. Selection creates fitness through destruction of unadapted. As in the course of fight for existence survive and those organisms which more correspond to conditions of the environment surrounding them, degree of their fitness from generation to generation give posterity increases. By this way, across Darwin, the property which received the name expediency is developed at organisms. Expediency at the same time has relative character (i.e. fitness of organisms to the environment is imperfect), causing a possibility of further evolution.

Thanks to continuous action of natural selection animals or plants, getting to new conditions, adapt to them by divergence, i.e. they gradually change diversely and become more and more various on the signs. Divergence leads to formation of new forms which will also diverge. Thus, from one initial form there are new forms (types or versions).

Lack of direct proofs of existence of the natural selection which is central position of D. led to revival of various lamarkistsky currents upholding the principle of direct adequate adaptation due to inheritance of the acquired changes — a mechanolamarckism (see. Lamarckism ), and even frankly idealistic teleologic views — a psycholamarkizm (see. Vitalism ). Further the fact of natural selection was proved by direct experiments on the example of protective coloration and other adaptive signs.

During the studying of influence of selection on structure of populations it was established that in the conditions of a relative invariance of conditions of the environment natural selection eliminates all a little considerable deviations from the typiform which is already fixed by natural selection in the previous generations and keeps the individuals possessing adaptive signs, typical for this population. I. I. Shmalgauzen (1968) called this form of selection the stabilizing selection, unlike «driving», or «leader», selection, for the account to-rogo in population change of typical signs owing to the changed conditions of abiotic or biotic environment is carried out. Further development of the theory of the stabilizing selection is connected with M. M. Kamshilov, A. L experimental works. Zelikmana, etc.

D.'s development is connected with the analysis of interaction of all levels of the organization of live — from molecular and cellular to organismal, population and specific and biogeotsenotichesky. This relationship was studied in detail by I. I. Shmalgauzen who made, in particular, the first successful attempt of studying of patterns of evolution by means of receptions and methods of the theory of information and cybernetics.

As proof of the theory Darwin presented the numerous facts taken from the field of paleontology, a comparative anatomy, embryology, biogeography, etc. In turn Darwin ideas promoted further development of these sciences and emergence of the new, actively using evolutionary approach at an explanation new facts and creation on their basis of theoretical generalizations.

So, clarification of phylogenetic development of separate groups of animals and plants became a problem of the paleontology reformed under the influence of D. In creation of evolutionary paleontology V. O. Kowalewski (1842 — 1883) works in which on a historical basis not only relationship and phylogenetic succession between fossil forms was established had the greatest value, but also the mechanism of evolutionary changes as result of the changing ratio morfol, signs with functional features of organisms and with conditions of their existence became clear. Further development of the evolutionary paleontology which is based on the principles D. is connected with a name of Dollo (L. Dolio, 1857 — 1931) who set for himself the task of clarification of devices, i.e. the signs depending on a way of life of animals in certain living conditions. Called this direction of theory of evolution of Dollo ethology and illustrated applicability of an ethological method to studying of evolution of fishes, reptiles and mollusks. Dollo belongs also important theoretical generalization known as the law of irreversibility of evolution, or Dollo's law. Dollo followed Darwin which claimed that once the disappeared look will never appear again even if former living conditions will be recovered. Much later Shmalgauzen wrote that the law of irreversibility of evolution confirms value of historically developed structure of an organism for it further evolution. If the organism is returned on Wednesday, in a cut there lived his ancestors, then it reacts for this Wednesday differently; the previous history of an organism was reflected in it morfol, and biochemical, signs, i.e. in ability to change under the influence of living conditions.

From all morfol, disciplines the greatest influence of D. was come by a comparative anatomy. To replace the theory of the English anatomist and paleontologist R. Owen, according to a cut the existing animals are variations of initially created ideal form (archetype), Darwin put forward the doctrine about the ancient primogenitor of extant forms and phylogenetic understanding of a homology (see. Homologous bodies , Morphogenesis ). The formal doctrine of Owen about analogy and various types of a homology — the general, serial and private — in evolutionary comparative morphology was replaced with phylogenetic understanding of these signs of similarity, and analogy, i.e. functional similarity, was considered as the certificate of an origin from the remote ancestors, and a homology, i.e. morfol, similarity as the evidence of closer relationship.

Embryologists till the Darvinian period used almost exclusively descriptive method; their comparative embriol. generalizations were based on the theory of types. The Darwinism allowed to turn comparative embryology into evolutionary. Date of origin of evolutionary comparative embryology should be considered the middle of the 60th — the beginning embriol, A. O. Kowalewski and I. I. Mechnikov's researches. Their works, and also works of other embryologists laid the foundation of evolutionary comparative embryology (see); achievement it was the proof of a homology of germinal leaves at all animals — vertebrata and invertebrates. After X. I. Pander and K. M. Ber created the topographical theory of germinal leaves, having shown that their mutual situation at all vertebrata in principle is identical and that from each leaf at all classes of vertebrata the same systems of bodies develop, A. O. Kowalewski and I. I. Mechnikov introduced the idea that to cellular layers of which germs of vertebrata consist the corresponding nucleating of the most various types of invertebrates is quite homologous. So contents was enclosed in the theory of germinal leaves genealogical, or phylogenetic. Gekkel (E. Haeckel) created the theory of a gastrea — the hypothetical gastrulopodobny ancestor of all metazoans, edges became widely known and excited brisk discussions.

On the basis of the data obtained in the field of comparative embryology the evolutionary generalizations establishing connection between were made ontogenesis (see) and phylogenesis (see). Müller (F. Muller, 1864), proceeding from a comparative embriol. studying of Crustacea, came to a conclusion that new signs arise in phylogenesis or by change of any stage of ontogenesis, or owing to accession of a new stage to ontogenesis of ancestors. The law of reproduction (reconciliation) of signs of ancestors in ontogenesis of descendants established by Darwin, detailed by Müller and developed by Gekkel was called the basic biogenetic law (see). Ontogenesis, according to Gekkel, is short and bystry repetition of phylogenesis; the gekkelevsky doctrine about reconciliation provides at extant organisms two types of signs — palingeneza, i.e. the signs inherited from far ancestors, and cenogenesises, again arising signs which were absent at ancestors. Studying of palingenez promotes, across Gekkel, to clarification of the phylogenetic relations whereas cenogenesises darken manifestation of palingenez by desequencing of reproduction of phylogenetic stages in time (geterokhroniya) or displace their emergence in space (heterotopy). Further most reasonable development of a problem of a ratio between ontogenesis and phylogeny belongs to A. N. Severtsov who developed classification of the phenomena of reconciliation and created the theory of a filembriogenez. Filembriogenezami A. N. Severtsov called the embryonal changes connected with phylogenetic development of adult organisms; natural selection of evasion from former process leads to reorganizations of ontogenesis. A. N. Severtsov created morfofiziol. theory of evolutionary process. That direction of evolutionary process, a cut leads to survival and preservation of this systematic group, to increase in its number, to resettlement and division into new versions and types, A. N. Severtsov called biol, progress, and the reverse leading eventually to extinction, biol, regress. Biol, progress is not necessarily connected with morfofiziol. progress. Example biol, the progress which was carried out by means of morfofiziol. regress (secondary simplification of the organization), change of organisms upon transition to parasitic or to a sedentary life is. Biol, the progress which is followed morfofiziol. progress, A. N. Severtsov called an aromorphosis, and private biologically progressive changes — idioadaptation.

Also the main idea of theory of evolution of Darwin — the doctrine about natural selection underwent development. Value of this doctrine, and in particular an explanation biol, expediency, were noted by K. Marx who wrote that in Darwin book «The origin of species...» «not only the mortal blow of „teleology" in natural sciences is struck, but also its rational sense is found empirically out» (K. Marx and F. Engels, Izbr. letters, 1953, page 121). G. Helmholtz also stopped on this essentially important party of Darwinism, noting that Darwin theory showed how expediency of a structure of organisms can arise without any intervention of reason, blind action of the law of nature. H. W. Bates investigated the phenomena of a mimicry at butterflies and showed that development of imitative drawings of a wing can be explained only with natural selection. In more detail these phenomena were analyzed by A. Wallace and especially A. Veysman. Date the beginning of 20 century the first works in which real existence of natural selection on the example of a mimicry was proved not by simple observation And logical conclusions, and much more evidential, experimental method yutsyatsya. Studying of ratios of organisms with the habitat led to creation of special field of biology, a cut Gekkel gave the name ecology (see).

One of cornerstones of theory of evolution of Darwin yav-j lyatsya heredity. Nevertheless within at least first two decades 20 century of generalization of genetics it was not possible to combine with original positions of theory of evolution. And in biology speculative theories of heredity, in particular theory of germ plasm of Veysman continued to dominate (see. Veysmana theory ).

1900 there was critical in the history of D. V this year of X. de Fris, Korrens (S. of Correns) and E. Tschermak confirmed Mendel's laws (see. Mendel laws ). From this point theory of evolution rose by higher step of development. Iogansen (W. Johannsen, 1909) for the first time noted value of the fact of a wide spread occurance of mutational variability, having shown that within a look set of individuals: in a certain area forms population — i.e. genetically diverse posterity of originally homogeneous initial forms in the hereditary relation; heterogeneity of individuals of the same population | is a consequence of a large number of spontaneously arising mutations. This direction scientific, researches gained further development in works of S. S. Chetverikov and his pupils (1926 — 1929). On the example of natural populations of a drosophila existence of their genetic heterogeneity forming a basis of evolutionary process is shown. Recessive mutations in a heterozygous state do not change a phenotype of the individuals who are a part of population, edges is more and more sated with various mutations. In the conditions of free crossings; emergence homozygous (phenotypical shown) the mutants serving as material for selection in the conditions of dwelling at which mutants can be more adapted, than an initial form is possible. It is favored by disintegration of a view of a number of the isolated colonies, napr, in oceans on close located islands. Isolation together with continuously I continue be sewed by genotypic variability is, according to S. S. Chetverikov, a major factor of intraspecific and trans-species differentiation. More widely researches in which synthesis of genetics and D. taking into account patterns biogeographical and ekol, character with use of the latest methods of the experimental and mathematical analysis of the studied phenomena was carried out began to be developed. Progresses of genetics at the beginning of 20 century were made its one of the major bases modern D. Byl the possibility of artificial receiving hereditary changes (mutations) under the influence of X-ray [G. A. Nadson and G. E. Filippov, is shown 1925; Meller (N. J. Muller), 1927] and chemicals (N. A. Rapoport, 1939). The data showing that mutations, as a rule, have character of insignificant deviations from a base type collected. Detection of a flow of mutational variability confirmed Darwin idea about a preferential role in evolutionary process of uncertain hereditary variability (see. Mutation ). An important stage in modern D.'s development, or as it is called, the synthetic theory of evolution (see. Theory of evolution ), finding out patterns of the microevolution proceeding in populations issue of works of R. Fisher «The genetic theory of natural selection», Haldane was (J. Century of S. Haldane) «Reasons of evolution», Dobzhansky (Th. Dobzhansky) «Genetics and origin of species», I. I. Shmalgauzena (number of special works and monographs of 1938 — 1964), N. V. Timofeev-Resovsky, etc.

Development of theory of evolution in postdarvinian time led along with the analysis of microevolutionary processes at the level of populations to detailed studying of the sets of the populations living in one land area or a reservoir and forming system — biocenosis (see). Biocenoses, just as types which are their part, arise in the course of evolution by natural selection; in each historically developed biocenosis separate types borrow inherent to their vital needs ekol, niches (see. Ecology ) also are connected among themselves rather difficult ekol, the relations, most often in the form of mains circuits. Since each biocenosis inhabits a certain territory or the water area with combinations of geographical conditions inherent in them (nature of the soil, climate, a relief, chemical composition of water, etc.), was to study quite naturally a combination of a certain biocenosis with set of these fi-ziko-geographical conditions — i.e. biogeocenosis (see). Based on the found patterns, V. N. Sukachyov created the new section of biology — the biogeocenology representing further development of Darwinism about difficult ratios of organisms with the environment of their dwelling and about value of these ratios for evolution. Clarification of the processes proceeding in a biogeocenosis defines ways of active influence of the person for preservation and increase in economic value of a biogeocenosis.

In addition to influence on structure of biocenoses, i.e. indirect impact on evolutionary process, the person influences evolution of animals and plants by creation of new forms, managing variability and heredity and applying artificial selection, or selection (see. Artificial selection ). According to N. I. Vavilov, methods of selection promote further development of theory of evolution, enriching it with an experiment. Addressing specially selection of plants, Vavilov noted that the doctrine about the initial high-quality, specific and patrimonial potential (botanikogeografichesky bases of selection), about hereditary variability, about a role of the environment in identification of high-quality signs, the theory of hybridization of the close and remote types and the theory of the most selection process is the cornerstone of it. For increase in a variety of a starting material of selection N. I. Vavilov studied geographical distribution of various grades of cultivated plants and established the geographical centers of their origin. At the same time it was open important obshchebiol. pattern of parallelism in emergence of similar mutations not only in close types, but also in forms systematically far from each other (e.g., albinism, giantism, dwarfism, a form of fruits, coloring of flowers and fruits). These observations were generalized in the form of the law of homologous series in hereditary variability, i.e. existence of a homologous genes is established (see. Genetic analysis ).

For selection artificial strengthening of hereditary variability under the influence of ionizing radiation or chemical mutagens is of great importance (see. Mutagenesis ); X-ray mutations are successfully applied in selection of the microorganisms producing antibiotics; also the polyploidy which is artificially caused by influence of the substances stopping a mitosis in metaphase, napr, colchicine is used (see. Chromosomal complement ). Source of variation at selection is also hybridization both intraspecific, and trans-species. Overcoming infertility of interspecies hybrids is carried out. by artificial doubling of chromosome number. Modern selection, i.e. management of evolution of microorganisms, cultivated plants and domestic animals, leads to creation of the new organic forms possessing necessary for practical use morfol, and fiziol, signs. Scientific selection is further development of D. since the motive powers of organic evolution established by Ch. Darwin — variability, heredity and selection are the cornerstone of it.

The main medico-biol. D.'s aspect consists that fitness of types to conditions of the environment and the expediency based on it are not absolute; evolution selects optimum structures of organisms of this look for some statistically average conditions, however it means that in principle there cannot be ideal designs for various conditions in general. Darwin recognized premises that organisms of one look, being similar on ancestral features, differ due to the variability having uncertain character. Distinctions of individuals of one look are premises of natural selection. This idea of genetic distinctions of organisms within population is very important for theoretical developments in the field of medicine. Such distinctions exist objectively, being not the certificate of initially biological inequality of organisms, but the law of adaptation of a look to the changing conditions of the environment.

See also Natural selection , Theory of evolution .

Bibliography: Berman 3. And., etc. History of theories of evolution in biology, M. — L., 1966; Zavadsky K. M. Development of theory of evolution after Darwin, L., 1973, bibliogr.; Medical nicknames B. M. Darvinizm in the 20th century, M., 1975; Paramonov A. A. Fundamentals of Darwinism, M., 1946; Timofeev-Resovsky H. Century, In about r about N of c about in H. N and I - l about to about in A. V. Short sketch of the theory of evolution, M., 1969, bibliogr.; Shmad-gauzen I. I. Problems of Darwinism, M., 1969, bibliogr.

L. Ya. Blyakher.