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Skepticism Towards Santa Rosalia, or Why are There so Few Kinds of Animals?

Joseph Felsenstein
Evolution
Vol. 35, No. 1 (Jan., 1981), pp. 124-138
DOI: 10.2307/2407946
Stable URL: http://www.jstor.org/stable/2407946
Page Count: 15
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Skepticism Towards Santa Rosalia, or Why are There so Few Kinds of Animals?
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Abstract

A model of speciation has been constructed involving two loci under natural selection in two subpopulations, with different alleles adapted to the different subpopulations. Progress toward speciation in this model consists of association of a third locus, at which there is assortative mating, with the original two loci. Cases can be found in which speciation cannot occur. The evolutionary force acting against speciation turns out to be recombination, which acts to randomize the association between the prezygotic isolating mechanism (assortative mating) and the adaptations to the two environments. This model suggests that there is an important distinction between two kinds of speciation. One involves speciation by substitution of the same alleles in the two nascent species, the other by substitution of different alleles. Only in the latter case does recombination act as a force retarding or blocking speciation.

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