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

The amount of polymorphism in DNA sequences should be higher in larger populations, to be more precise, in populations with large effective sizes (N_e) (Kimura 1983b).This is a result of the fact that, in small populations, a greater fraction of mutations falls in the category of effectively neutral mutations, i.e. mutations for which the absolute value of the selection coefficient (s) is less than or equal to 1/N_e.On the other hand, in large populations, a major part of the mutations fall in the category of selectively significant mutations, primarily in the category of selectively negative mutations, and are thus are quite rapidly eliminated from the population (Nevo, Filippucci, & Beiles 1994; Takahata 1996).However, empirical data indicate that the dependence of the amount of intra-population polymorphism on the size of the population is actually much less than would follow from the models assuming fundamental participation of genetic drift.A possible explanation is provided by Gillespie's model of molecular evolution through the action of genetic draft, described in Chapter IX.4.4.1.