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

The frozen plasticity theory was developed to explain the evolution of adaptive traits in sexual species. The phenomenon of frequency-dependent selection plays a very important role in the resistance of a genetically polymorphic population to adaptive evolution in sexual organisms where in every generation the alleles of two parents meet each other in new zygotes. The selective value of an allele depends, for example, on the probability that the same allele is present in the chromosomes of both paternal and maternal origin, which depends on the frequency of the allele in the population. This source of frequency dependence of the selective value of alleles does not exist in asexual organisms; however, some sources of frequency dependence are present even here. Frequency dependence could take part in ecological interactions between host and parasite. A parasite is often specialized for exploitation of the most common form of its host, for example, a host with the most common MHC alleles. Similarly, the immune system of a host is usually adapted to the most common strain of a parasite. An asexual species can be a mixture of phenotypically and genetically different strains with differing strategies to exploit resources from their environment. The frequencies of particular strains could change in response to changes in the environment: They will probably express a tendency to return to some state of equilibrium. The long-term competition of strains with selective values dependent on their frequency in the population could be an important source of species cohesion and resistance of the population to adaptive evolution even in asexual species.