Inheritance Variability and Natural Selection

For Darwinian self-organization, life must be structured for discrete generations and lifetime of each generation must be limited. To be effective, transfer of hereditary information from a previous generation to the next one cannot be absolutely free. Each species is divided into more or less isolated populations, where panmixia takes place. New specimens' characters are examined at the level of populations; only in the case of success, they spread for the whole species. Sometimes there are additional levels of such hierarchy: subspecies, races, subpopulations, etc. Structural units of species, uniting closely related individuals, are partly reproductively isolated. It is still not clear whether it is a natural result of hereditary remoteness or it is a manifestation of special isolation mechanisms forming an optimal structure of the hereditary field.

An important fact is discreteness of the hereditary code; genes are indivisible. This consideration eliminates Jenkin's nightmare: a useful character cannot resolve in descendants of reiterative coenobium.

Inherited characters cannot be absolutely independent; some of them are more or less correlated. On the one hand, it is a destabilizing factor; characters are selected in the context of other ones. On the other hand, it leads to tendentiousness of genes' variability, joint manifestation of correlated characters in accordance with the homologous series law of N. I. Vavilov (1920).

Darwinian variability is a principally random phenomenon. It is impossible to predict dynamics of external conditions; evolutionary perspective living forms must have multidirectional hereditary deviations. Initially directed evolution (as Berg's nomogenesis) is not sufficiently flexible to be effective.

Genes' variability (mutations) must be within reasonable limits. If it is too small, the progress will be too slow and can stop far from a local extremum. If the variability is too big, it will lead to system's chaotic behavior. These parametric effects are well illustrated by mathematical models based on the well-known 'genetic algorithm' (see Evolutionary Algorithms).

Darwinian natural selection examines the character of different specimens: stability, amativeness, reproductive potential, etc. It is not always a struggle for existence; often it is a struggle for leaving sufficient number of descendants. The main criterion is birth rate. If it is less than one, the species is doomed.

There are three levels of natural selection; only such forms of life can exist, which: (1) are stable and can physiologically give a breed; (2) allow origin of intellectual man (the anthropic principle); and (3) survive in the course of competition with other species (Darwinian selection). Evolution eliminates evidently defective individuals; other ones are not really exterminated, but rather 'squeezed' from the ecosystem because of low birth rate.

Natural selection can be classified into three forms: stabilizing (supporting existing adaptations in stable environment); motivating (producing new adaptations); and disruptive (leading to separation of the population in condition of heterogenic environment).

Selection leads to harmony of the organism and its environment. Similar conditions produce similar organism's forms of adaptation to them. This effect is called 'convergence'. Adaptation can follow a limited number of ways; in particular cases, it is not evident whether this form is a result of selection, or it is a direct consequence of physical laws.

Evolution can be divided into micro- and macroevolu-tion. Microevolution consists in accumulation of hereditary changes in the population. At this stage, the most essential effects are the change of statistical distribution of different genes within the population and a search for their optimal combinations. The main factors of population evolution are maintenance of genetic heterogeneity, population size fluctuations, reproductive isolation, and natural selection.

Macroevolution is the evolution at the level of ecosystems; its result is the origin of new species. Its nature is not absolutely clear yet. It can be explained by either multistep microevolution or a random essential change, appearance of 'perspective freaks'.

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