First Stage: Separation
Speciation usually begins when a part of a population becomes separated from the rest of their species.
Second Stage: Adaptation
Adaptation in speciation is quite similar, though the groups may evolve different sets of traits if the environmental conditions differ for each group.
Third Stage: Reproductive Isolation
Reproductive isolation is when groups of a same species are reunited and cannot interbreed with each other anymore, so they are now identified as different species.