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Направленность эволюции - Северцов А.С.

Северцов А.С. Направленность эволюции — M.: Изд-во МГУ, 1990. — 272 c.
ISSN 5—211—00917—7
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Furthermore, the impossibility of determination of selective coefficients, as well as the relative adaptive value and (or) fitness, is due to the fact that the stability of morphogenesis is higher then that of genotypes.
Nevertheless, the prediction of the direction of evolution is of great practical importance. Remind for example phenomena of the «antropogenic evolution» — the adaptations of pests to the pesticides, resulting in the accumulation of these substances at the higer trophic levels in the ecosystems; or arising of the antibiotic — dependent pathogenic myco — and microflora in people, domestic animals and cultured plants; or synantrophisation of wild animal and plant species e. t. c. The consequences of the evolutionary processes of this kind have to be predicted first of all clue to their harmful environmental impact which require the significant Investments to mitigate them.
This book is concerned with the analysis of causes that allow for the direction of micro — and macroevolution as well as for the correlation between the •evolution of organism and evolution of ecosystems.
The direction of microevolution is guided by two main agencies: variability and environmental conditions. The common idea, that it is selection that determines the direction of evolution is not to be fairly true. In fact, the direction of the selection is to be derived from the variability and environmental impact, the last being brought about through the stress of the struggle for life. The pheno-typical variability, more exactly its genotypical component, which affords both the material and gidance of evolution, is extremely diverse. In every given generation the evolution is concerned with only those part of genofond, which are manifested of the phenotipic level of the individuals without making the selection to act against them. The ways of expression of variability, as well as their chao
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ges in the process of evolution, depend on the lot of parameters determining the fate of the evolving characters. ,
There occurs the continuous range of shifts between the stable genotypically determined phenotypic characters and the phenotypical characters with the wide reaction norm. Characters of these two opposite types imply fairly different mechanisms of the evolution. The evolution of the strictly determined characters is based on the elimination of the unfavorable inheritable deviations (i. е., deviations which does not fit the direction of the environmental changes), as well on the combinations of those deviations which fit the direction of the selection. The evolution of characters with wide reaction norm is based on the formation of geno-copies of favourable phenotypes, i. e. phenotypic adaptation procedes the genotypic one. In the last case the genotypic variability cannot be considered as guiding factor of evolution. The plastic phenotypical characters arise when the population falls under the non-specific environmental deterioration which stimulates, the selection favouring the wider reaction norm. When falling under new environmental conditions, or under the unusual extent of the environmental pressure, the individuals with the widest reaction norm will posesses of the best chances to survive. In general, the essential body of progressive evolution in plants and animals may be attributed to the increase of the flaxibility in the phenotypic reactions. The essential proportions of ontogenetic and inorphophysiological reactions, being designated by the uncertain term «adaptive modifications», as well as tlie essential part of physiological and behavioral reactions are characterized by more or less prominent flexibility. In other words, the main part of characters which seem to determine the level of adaptation posess the wide reaction norm. When we are considering the correspondence between the organism and its environment, processes of this kind display more prominent evolutionary trend than processes based on the stable genetically determined characters.
The evolutionary environment is, first of all, the ecological niche, occupide by the population of the certain species in the certain biogeocoenosis. Therefore, the communities canalize the evolution of their populations. This is manifested in the most prominent way when we are considering the coadaptive complexes — the groups of species with the most tight ecological linkages in limits of biogeocoenosis At the same time, the community as a whole changes in coherence with the evolution of its populations. In fact, although the community delimits the direction of evolution of these population, these limitations are not strict: the adaptation to the conditions of a given ecosystem may not contradict to the adaptation of the other populations of the same species which belong to other ecosystems. Contradictions of this kind seem to lead to the intraspecific differentiation and. finally, to the formation of species thus leading to the evolution of the ecosystems itself. The control of the composition of the population by the community may be brought about in two opposite ways: in the preservence of the existing adaptations (the stabilizing selection), and in the formation of the new ones (the directional selection). As far as every sertain population, being controlled by the ecosystem (as regulator) at the same time appears to be a part of a regulatory system for other populations of the same community, the evolution of ecosystems is based on the coadaptive evolution of their components. The species, being considered as a system of interconnected populations, is included into several communities which may be fairly different in their composition. The adaptation of a given population in frames of one or another ecosystem (dependent on its everybiontness) effects all the other populations of the same species. As a result, the otheres species of the given ecosystem have to adapt to the changes which occur in the former species and thus constitute a part of the regulatory system of their evolution. For example the specialization of the species is hindered by the fact that they are involved into different communities. At the same time, as far as every species is adapted to the certain environmental range of conditions, the communities of the species (in spite of the fact that their structure is reproducible under given abiotic conditions) are always formed from the existing species, which replace one another, the course of this replacement being dependent on the biotopic peculiarities and the succession stage. Each population of the ecosystem develops under the influence of the complexion of environmental conditions. The adaptive requirements of this complex are full of contradictions thus preventing the complete adaptation to them. This is
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