Fig. 4
From: Views from Understanding Evolution: Parsimonious Explanations for Punctuated Patterns
A hypothetical example of peripatric speciation. Just a few fruit flies from a mainland population are carried to an island in a hurricane. These flies happen to have an unusually high frequency of two genes that are rare in the mainland population. Those rare genes happen to drift to fixation in the island population. Over time, this precipitates other evolutionary changes in the island population, and they evolve into a separate species from the mainland flies