The Pattern of Phyletic Speciation

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Abstract
Phyletic speciation arising from a shift between adaptive peaks in the selective surface is modeled. At a locus initially monomorphic, a new allele is introduced that triggers phenotypic evolution by making a new adaptive peak available. A phenotypic model is used to describe the evolution of a quantitative character that is important for fitness but not directly affected by the new allele. Recursion equations are derived for both the allele frequency and the mean of the quantitative character. It is shown that the dynamics of the quantitative trait fit a “punctuated equilibrium” pattern of evolution. Phyletic speciation is seen to occur over a time span so short as to make observation of the transition in the fossil record unlikely.