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

Calculations show that, if the diversification of subpopulations is the result of natural selection and not genetic drift, the number of migrants required to maintain the genetic cohesion of the metapopulation is substantially higher (Gavrilets 2000; Rieseberg & Burke 2001). If a dominant allele is being eliminated in a given local subpopulation by natural selection with intensity s, i.e. at the rate of ps per generation (p corresponds to the frequency of the allele in the subpopulation, s – selection coefficient) and, at the same time, it enters that subpopulation via gene flow at a rate of  (P – p)m from surrounding subpopulations (P corresponds to the frequency of the allele in the surrounding subpopulations, m – the intensity of gene flow), any particular ratio of the selection and gene flow intensity can ultimately result in a balanced frequency of the given allele in the subpopulation

p^*= P [.m/(s-m)].

If selection is much stronger than gene flow, the allele can practically disappear from the local subpopulation and, analogously, if gene flow is much stronger than selection, the frequency of the allele in the local subpopulation can very closely resemble its frequency in the surrounding subpopulations.

            The intensity of gene flows detected in real populations is so high that, even in the case of plants, a useful allele can spread quite rapidly to all the subpopulations within the whole range of the given species, allowing the species to behave as an evolutionary unit in terms of adaptive evolution. Subpopulations tend to differ in non-adaptive traits or in traits expressing low additive heritability that are difficult to select (Rieseberg & Burke 2001).