USA Biology Olympiad (USABO) Practice Exam

Allopatric speciation occurs when populations of a species become geographically isolated from one another, which prevents gene flow between the groups. This type of separation often occurs due to physical barriers like mountains, rivers, or distances that lead to the populations evolving separately over time. The lack of interbreeding allows for the accumulation of genetic differences, eventually resulting in the formation of new species. In contrast, behavioral and temporal speciation relate to differences in mating behaviors and timing of reproduction, respectively, while sympatric speciation refers to the emergence of new species within the same geographic area, typically through mechanisms like polyploidy or behavioral changes. These types of speciation do not involve the geographic isolation that is fundamental to allopatric speciation. Therefore, geographic separation is the key element that distinguishes allopatric speciation from the other mechanisms of speciation.