THEORY OF EVOLUTION

From Big Medical Encyclopedia

THEORY OF EVOLUTION —

set of knowledge of historical development (evolution) of wildlife. This science studies formation of adaptations (devices), features of an ontogeny of organisms (ontogenesis), factors directing to evolution, and specific ways of historical development (phylogenesis) of separate groups of organisms and the organic world in general. Basis E. at. theory of evolution makes. Also concepts of an origin of life and an origin of the person belong to theory of evolution.

The first ideas of development of life stated in works of Empedocles, Democritus, Lucretius and other antique philosophers had character of ingenious guesses and were not proved biol. facts. In 18 century in biology the transformism — the doctrine about convertibility of animal species and plants, opposite to the creationism based on the concept of divine creation and an invariance of types was created. The most visible transformist of the second half of 18 century and the first half of 19 century —

G. L. L. Buffon and E. G. Saint-Hilaire in France, Darwin (E. Darwin) in England, J. W. Goetlie in Germany, K. F. Rulye in Russia — considered that

existence of transitional forms between close types and unity of the plan of a structure of organisms of big groups of animals and plants testifies to convertibility of types. However they did not consider the reasons and factors causing changes of types.

The first attempt of creation of complete theory of evolution belongs to the fr. scientist Ge. Lamarck who stated in «Philosophy of zoology» (1809) of idea of motive powers of evolution. Ge. Lamarck claimed that transition from the lowest life forms to the highest — gradation — results from commitment to excellence inherent in organisms. A variety of types at each level of the organization Zh. Lamarck explained with influence of conditions of the environment. According to first «law» of Lamarck exercise of bodies leads to their progressive development, and not exercise — to a reduction; according to second «law» results of exercise and not exercise of bodies at the sufficient duration of influence are fixed in heredity of organisms and further pass from father to son already regardless of the influences of the environment which caused them (see the Lamarckism). Lamarck's «laws» are based on wrong idea that are inherent to the nature aspiration to improvement and inheritance by organisms of acquired properties.

Opening of true factors of evolution belongs to Ch. Darwin, to-ry created evidence-based theory of evolution (it is stated in the book «The Origin of Species by Natural Selection, or Preservation of Favourable Breeds in Struggle for Life», 1859). Motive powers of evolution, across Darwin (see Darwinism), are uncertain variability — the caused variety of organisms of each population of any kind, fight for existence is hereditary, in the course a cut less adapted organisms, and natural selection — survival of fittest individuals perish or keep from reproduction, as a result to-rogo useful hereditary changes collect and summed up and there are new adaptations. There is a number of the concepts denying value of selection as motive power of evolution. Development of biology validated the Darvinian theory. Therefore in modern biology the terms «Darwinism» and «theory of evolution» are often used as synonyms. Closely to them the concept «neodarvinism» which arose from A. Veysman's concept that the only factor of evolution is natural selection. Further, in process of accumulation of data in the field of genetics, this representation was developed in the synthetic theory of evolution, edges began to reflect thus a combination (synthesis) of original positions of the theory of Darwin, genetics and a number of evolutionary generalizations of other fields of modern biology.

Development of genetics (see) allowed to understand origins of the uncertain hereditary variability providing material for evolution. This phenomenon permanent changes of hereditary structures — mutations (see the Mutation), and also the diverse changes of quantity and sequence of nucleotides of DNA arising at an unequal crossing-over (see the Recombination of chromosomes) are the cornerstone, of a transposition, at introduction of alien DNA viruses or plasmids and other processes at molecular level. Mutational variability is not directed:

again arising mutations are not adequate to conditions of the environment and, as a rule, break already existing adaptations. For the organisms which do not have the issued kernel (see Prokariotny organisms), mutational variability serves as base material of evolution.

In mechanisms of variability of organisms, cells to-rykh a soder

it is reaped the issued kernel (see Euka-riotny organisms), the large

role is played by combinative variability — a combination of genes in the course of a syngenesis.

Elementary unit of evolution Is population (see). Relative isolation of populations leads to their reproductive isolation — restriction of freedom of crossing of individuals of different populations. Reproductive isolation provides uniqueness of a gene pool of each population and by that a possibility of its autonomous evolution. In the course of fight for existence it is shown biol. the heterogeneity of the individuals making population determined by kokhmbinativny and mutational variability. At the same time a part of individuals perishes, and others survive and breed. As a result of natural selection (see) again arising mutant combinations of genes are combined from a gene lie the individuals who already underwent selection and their phenotypical expression changes that is a basis of emergence of new adaptations (see). Thus, selection serves as the main driving factor of evolution causing emergence of new adaptations, transformation of organisms and speciation (see the Look). Selection can be stabilizing (providing preservation in invariable conditions of the environment of already created adaptations), moving, or the leader (leading to elaboration of new adaptations), and balancing or the equilibratings (causing emergence of polymorphism and increasing heterozygosity of individuals of population). In modern E. at. idea of factors of evolution was enriched thanks to allocation of population as elementary unit of evolution, to creation of the theory of isolation and deepening of the theory of natural selection. Studying of isolation as the factor providing increase in a variety of life-forms is the cornerstone of modern ideas of speciation and structure of a look. The allopatric speciation connected with resettlement of a look and geographic isolation of suburban populations is fullestly investigated. The sympatric speciation caused by ecological, chronological or ethological (behavioural) isolation is less studied. The evolutionary processes proceeding in a look and which are coming to the end with speciation combine under the general name «microevolution». Macroevolution call historical to a razvitrkha of groups of organisms (taxons) of a nadvidovy rank. Evolution of nadvidovy taxons is result of the speciation happening under the influence of natural selection. However the analysis of different spans (evolution of big taxons consists of many stages of speciation) and use of various methods of studying (given to paleontology, comparative morphology, embryology, etc.) allow to reveal the patterns escaping during the studying of microevolution. The most important tasks of the concept of macroevolution are the research of a ratio of individual and historical development of organisms, the analysis of patterns of phylogenesis and the main directions of evolutionary process. In 1866 it is mute. scientist Gekkel (E. Haeckel) formulated biogenetic law, according to Krom in ontogenesis (see) stages of phylogenesis briefly repeat (see) this systematic group. Mutations are shown in a phenotype of an adult organism as a result they change processes of its ontogenesis. Therefore natural selection of adult individuals leads to evolution of processes of ontogenesis — interdependence of the developing bodies called by I. I. Shmaljgauzen ontogenetic correlations. Reorganization of system of ontogenetic correlation as a result of driving selection leads to emergence of changes — filembrioge-not call, owing to-rykh during phylogenesis new signs of organisms form. If change happens at a final stage of an organogeny, further evolution of bodies of ancestors is carried out; there are also deviations of ontogenesis at intermediate stages that leads to reorganization of bodies; change of a bookmark and development of early rudiments can cause emergence of the bodies which were absent at ancestors. However evolution of ontogenetic correlations under the influence of the stabilizing selection leads to preservation only of those correlations, to-rye most reliably provide processes of ontogenesis. These correlations are reconciliation — repetitions in ontogenesis of descendants of phylogenetic conditions of ancestors; thanks to them biogenetic law is provided. The direction of phylogenesis of each systematic group is defined by a specific ratio of conditions of the environment, in a cut evolution of this taxon, and its organization proceeds. Divergence (divergence of characters) of two and several taxons arising from the general ancestor is caused by distinctions in the conditions of Wednesday. It begins at the population level, leads to increase in number of types and proceeds at the level of nadvidovy taxons. Divergent evolution caused a taxonomical variety of living beings. Parallel evolution arises when initially diverging taxons remain in similar conditions of the environment and develop similar devices on the basis of the similar, inherited from the general ancestor organization. Convergence (a convergence of signs) happens when unrelated taxons adapt to identical conditions. Biol. progress can be made by the general increase in the level of the organization providing adaptation of organisms to more various conditions of the environment than those, in to-rykh their ancestors lived. Such changes — aromorfoza — arise seldom and surely are replaced by allomorphisms — divergence and adaptation to more specific conditions in the course of development of the new habitat. Elaboration of narrow adaptations in phylogenesis of group leads to specialization. 4 main types of specialization allocated with Shmalgauzen — telomorfoz, a hypopestilence-foz, hyper morphosis and katamorfoz — differ on character of devices, but all of them cause delay of rates of evolution, in connection with loss of specialized animals of multifunctionality by bodies, decrease in evolutionary plasticity. At preservation of stable conditions of the environment specialized types can exist beyond all bounds long. So there were «living fossils», napr, many childbirth of mollusks and Brachiopoda, the existing hundreds of millions years. At jumps of living conditions specialized types die out whereas more plastic manage to adapt to these changes. AA. at. and its theoretical kernel — theory of evolution — serve as important natural-science justification of dialectic materialism and one of methodological fundamentals of modern biology.

542 THEORY OF EVOLUTION


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