Frozen Evolution. Or, that’s not the way it is, Mr. Darwin. A Farewell to Selfish Gene.

The original concept of sexual reproduction as a source of evolutionary variability of the species continues to appear frequently in the biological literature.An important cause of this inertia apparently lies in the changing meaning of the term variability.This term is now generally understood to mean polymorphism, the simultaneous existence of several alleles of a single gene in a single population, rather that changeability in time.In this sense, sexual reproduction and the processes connected with it truly  constitute one of the basic mechanisms maintaining intrapopulation and intraspecies variability.

            Primarily the effect of genetic segregation andrecombination can be cited as an example of a mechanism through which sexual reproduction can contribute to maintenance of polymorphism.In each generation, these processes create new combinations of genes, new and old-new genotypes, including those that are disadvantageous for their carrier at the given moment and that are thus repeatedly removed from the population.In asexually reproducing organisms, these disadvantageous genes would be eliminated once and for all, together with the alleles of the genes that cause them.

            Of other mechanisms, mention should be made of ineffective selection against recessive homozygotes or maintenance of the presence of two alleles of a single gene through selection in favour of heterozygotes.A great many of the mechanisms of maintenance of polymorphism in the population, e.g. selection in favour of heterozygotes, are connected with the existence of diploidy.As will be demonstrated below, the existence of diploidy is, in itself, also a consequence of the existence of sexual reproduction.

            The permanent existence of polymorphism provides several fundamental advantages for sexually reproducing species.It allows the members of a single population and the members of a single family to better utilize the heterogeneity of the environment and the related heterogeneity of resources.It should be emphasized that this is an advantage not at the level of the species, but at the level of individuals.The relevant model will be described elsewhere (theelbow room hypothesis (XIII.3.2.2.1) and the lottery model (XIII.3.2.2.2).The advantage of the persistence of polymorphism at the level of a population and species is described by the tangled bank hypothesis (XIII.3.2.2.2) and the advantage of  an expanded genotype and phenotype variability of species is described by the Sisyphean genotypes model (XIII.3.1.2.2).

            The existence of polymorphism and the related ability of rapid microevolutionary adaptation to changing or locally heterogeneous conditions are very useful properties from the standpoint of evolutionary potential.Especially in a varying and heterogeneous environment, they can provide not only a population but also species with a substantial advantage.Consequently, it can be expected that species that have created mechanisms for maintenance of polymorphism (for example, sexuality) will be less endangered by extinction and will thus be more successful, in the long term, than species that do not have such mechanisms (Williams 1975).It is thus possible that sexuality could be maintained in the long term by species selection on a macroevolutionary scale.