Geographic isolation refers to two population of the same species being separated due to some type of physical barrier. This separation of population occurs when a body of water or land forms and divides a habitat. Geographic isolation of a species also can occur when animals migrate to an isolated island.
An example of a separated population to geographic isolation are the American finches that migrated to the Hawaiian islands. From this original finch population, 23 new species of honeycreepers are evidence of speciation due to geographic isolation.
However, geographic isolation also can lead to reduction of gene flow as these separated populations of animals or organisms cannot mate and exchange genetic material. Scientists believe that geographic and reproductive isolation are the causes for new species forming.