Speciation

Natural selection can also help explain speciation. Imagine two populations of the same species becoming separated so that they no longer breed together. If they face different conditions, different inherited phenotypes may be favoured in each population.

Independently, he arrived at an explanation of evolution based on natural selection that was similar to Darwin’s. His work on warning colouration, particularly in butterflies, showed how a characteristic that helps deter predators could be favoured. He also did pioneering work on speciation, the formation of new species.

As differences accumulate over many generations, the populations may eventually become so different that their members can no longer interbreed to produce fertile offspring. They are then classified as separate species, and speciation has occurred.

Speciation has occurred if the organisms have evolved to be so different from their ancestors that they could no longer mate with them to produce fertile offspring. Isolation makes this outcome more likely, but it does not guarantee it: merely living apart or looking different does not, by itself, make two populations separate species.