Abstract
BackgroundDarwin's evolutionary theory could easily explain the evolution of adaptive traits (organs and behavioral patterns) in asexual but not in sexual organisms. Two models, the selfish gene theory and frozen plasticity theory were suggested to explain evolution of adaptive traits in sexual organisms in past 30 years.ResultsThe frozen plasticity theory suggests that sexual species can evolve new adaptations only when their members are genetically uniform, i.e. only after a portion of the population of the original species had split off, balanced on the edge of extinction for several generations, and then undergone rapid expansion. After a short period of time, estimated on the basis of paleontological data to correspond to 1-2% of the duration of the species, polymorphism accumulates in the gene pool due to frequency-dependent selection; and thus, in each generation, new mutations occur in the presence of different alleles and therefore change their selection coefficients from generation to generation. The species ceases to behave in an evolutionarily plastic manner and becomes evolutionarily elastic on a microevolutionary time-scale and evolutionarily frozen on a macroevolutionary time-scale. It then exists in this state until such changes accumulate in the environment that the species becomes extinct.ConclusionFrozen plasticity theory, which includes the Darwinian model of evolution as a special case - the evolution of species in a plastic state, not only offers plenty of new predictions to be tested, but also provides explanations for a much broader spectrum of known biological phenomena than classic evolutionary theories.ReviewersThis article was reviewed by Rob Knight, Fyodor Kondrashov and Massimo Di Giulio (nominated by David H. Ardell).
Highlights
Darwin’s evolutionary theory could explain the evolution of adaptive traits in asexual but not in sexual organisms
Epistasis and context dependence of the influence of a trait on fitness, which critics of the Darwinian/Fisherian model of evolution consider to be the main constraints to evolutionary response to selection, just slow down the adaptive evolution in sexual organisms
The frozen plasticity theory[14,46] is a complex theory, based on many particular hypotheses concerning the mechanisms of evolutionary stasis and evolutionary change - most of which were suggested in some form by different students of evolution during the 20th century
Summary
Mechanism of Adaptive Evolution in Sexual Organisms It was argued above that adaptive evolution by means of Darwinian selection of individuals in a population, as well as by means of Dawkinsian competition between alleles in individual loci, is very difficult, if not impossible, in populations of sexual organisms. The mutation in all loci is highly improbable especially if, due to pleiotropy, the genes in particular loci influence other traits Another source of the evolutionary stability of a trait is frequency-dependent selection, the steep dependence of fitness on the frequency of a particular allele. The rate could even be proportional to a higher power of the trait frequency This kind of trait probably survives peripatric speciation in a polymorphic state, or polymorphism in such a trait is restored very quickly in the originating new species due to mutations. Only some species retain this capacity and even in these species some traits had a highly limited capacity to respond to selection after peripatric speciation
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