As an alternative to the traditional belief about evolution, Mayr (1963), and Elrdridge and Gould (1972) argue that geographic distribution plays a greater importance in determining the fate of a species than previously thought. Mayr (1963) and Moore (1954) show the increased influence of geographic barriers on the species living near the extremeties of their communities.

Because of the extreme difficulty of speciation within a large population, allopatrick speciation emphasizes the importance of geographic barriers in isolating gene pools, thus greatly increasing the chances of speciation. This diagram illustrates how isolation, migration, and geographic barriers aid in speciation.

Source: Eldredge and Gould (Kauffman and Hazel 1977) p45