Four Speciations Explained: Allopatric and Peripatric
Allopatric occurs when a species population separates into two different, isolated subpopulations. Kind of like a group of jocks in school that separate from the nerds. Once this particular separation happens, genetic drift and especially natural selection will result in independently produced evolutionary outcomes.
Peripatric occurs when a smaller subpopulation ends up becoming isolated from its larger majority group. Due to the small nature of the group, divergent evolution can happen in such a way that there will be connections to the previous group. Yet the changes in the subpopulation will result in changes that could wildly differ from their majority group. This is due to the “Founder Effect,” where the subpopulation is more receptive to rapid change due to the lack of a majority group nearby.