Explain how two different species can arise from allopatric speciation.

Allopatric speciation occurs when two different species arise from a population that has been split due to geographical factors. The two portions of the population live in different environments, hence they are exposed to different environmental factors (selection pressures). A random mutation can make some organisms better adapted to the new conditions. This allele gives them a higher survival and reproductive probability, hence it is more likely that the new allele is passed on the next generations. Allele frequencies change and as a result, over the course of many years the two populations are reproductively isolated. They cannot reproduce to give a fertile offspring. Hence two new species are created.