Speciation

Speciation is the formation of new species from an existing species. It can happen when populations of the original species become separated and gradually develop inherited differences.

When separated populations exchange few or no alleles—different versions of genes—changes in one population are unlikely to be shared with the other. Over many generations, inherited differences can accumulate. If the populations live in different environments, natural selection may favour different inherited characteristics in each population. Their phenotypes, or observable characteristics, may therefore become increasingly different.

If the populations change so much that they can no longer interbreed to produce fertile offspring, they are regarded as distinct species. Two populations of an original species can therefore form two new species. A difference in appearance alone does not establish that speciation has occurred: the populations must no longer be able to produce fertile offspring together.