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

Variability is constantly generated within any species through random mutations. The genotype and thus also the phenotype spectrum of each species should be constantly expanding, which should also lead to gradual reduction of phenetic distances and thus to obscuring of the boundaries between different species. However, such processes do not seem to occur in nature. So far, no example is known where two phenotypically identical species would be formed by gradual convergence of two phylogenetically unrelated species. One of the possible explanations could be that mechanisms of species cohesion exist for the individual species, i.e. mechanisms that act against the broadening of the phenotype and apparently also the genotype spectra of the relevant species and that prevent the fusion and merging of two species (Templeton 1989; Templeton 2001). Several possible mechanisms of species cohesion have been proposed up to the present time. They have the common property that they are responsible for the active process of maintenance of the similarity between the members of a single species and simultaneously indirectly for the existence of differences between the members of different species.