There is simply no evidence that speciation occurs as the result of a single point mutatio

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There is simply no evidence that speciation occurs as the result of a single point mutation, or even that it occurs in a single generation. As a general rule, except for fatal mutations and mutations causing sterility, individuals with mutations breed quite successfully with other members of the same species. This leads to a certain mixing of the genes, and to the presence of a number of individuals with any given variant. (The number depends somewhat on the reproductive potential of the mutant). Thus mutation, per se, is unrelated to speciation, it just increases the amount of variability in a given population. Just that, nothing more. The currently favored model of speciation is the one developed by Ernst Mayr in the 1940's, often called the peripatric model. The key event in this model is the establishment of a small, isolated population in a marginal habitat for the prospective parent species. Several effects are enhanced, or enabled, by this situation. They are genetic drift, differential selection, and release from pressure to conform. In combination these factors can cause *relatively* rapid divergence in these isolated populations [that is divergence in periods of only a few hundred generations]. This level of divergence can easily lead to reproductive barriers between the local isolate and the original species. When this point is reached a new species is said to have formed. (although the exact degree of isolation necessary to qualify as a species is uncertain - and almost all intermediate degrees of reproductive isolation are known from real populations). Other modes of speciation do occur, but are generally held to be rare, and thus unimportant in the long run.


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