Development of new species as a result of the geographic separation of population called ?

That would be allopatric speciation.

In allopatric speciation, a part of the population becomes geographically isolated from the main popula­tion. The population becomes entirely separated and finally constitutes a new species. Thus geographic isolation brings about allopatric speciation.

An important example of this type of speciation is formation of Darwin’s finches that formed separate species in the Galapagos Islands.

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