Explain how geographical isolation can result in speciation

When two populations are geographically isolated they can no longer interbreed. There is no mixing of genes between the groups and over generations differences build up between the populations. This is caused by mutations, genetic drift, and the founder effect, especially if the population is small. The populations also become adapted to their different environments and natural selection takes place, causing different individuals to survive and reproduce depending on their environment. If the genetic differences are great enough, the two populations will no longer be able to interbreed, even if they were in the same location. Allopatric speciation has occured and the two populations have become seperate species.