key concept
22.3
Speciation May Occur through Geographic Isolation or in Sympatry
Many biologists who study speciation have concentrated on geographic processes that can result in the division of an ancestral species. Splitting of the geographic range of a species is one obvious way of achieving such a division, but it is not the only way.
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Speciation can be allopatric (resulting from the physical division of a population) or sympatric (due to disruptive selection or polyploidy).