Final answer:
Allopatric speciation is achieved through geographic isolation, which prevents gene flow between groups of the same species, leading them to evolve new genetic traits that can eventually result in the formation of a new species.
Step-by-step explanation:
In the process of allopatric speciation, genetic isolation is accomplished through geographic isolation, where groups from the same species are separated by physical barriers. This separation leads to a disruption in gene flow between the divided groups, allowing them to evolve independently. Over time, the genetic differences that accumulate may be sufficient to prevent interbreeding between these populations, leading to the formation of new species.
Examples of geographic barriers causing allopatric speciation include the formation of a new river branch, erosion creating a new valley, or organisms moving to a new location from which they cannot return. A classic case of allopatric speciation is observed in rodent populations that become divided by a new lake. Unlike flying insects that can easily overcome small geographical separations, these rodents are unable to maintain gene flow across the body of water, resulting in distinct evolutionary paths for each population.