Evolution is regarded as a branching process, whereby populations are altered over time and may speciate into separate branches, hybridize together, or terminate by extinction. 进化被视为一个分枝过程;随着时间的推移,种群发生改变,种群也可能进化成为分枝,也可能相互杂交或灭绝终止。
Speciation is the evolutionary process by which reproductively isolated biological populations evolve to become distinct species. The biologist Orator F. Cook was the first to coin the term 'speciation' for the splitting of lineages or "cladogenesis," as opposed to "anagenesis" or "phyletic evolution" occurring within lineages. Charles Darwin was the first to describe the role of natural selection in speciation. There is research comparing the intensity of sexual selection in different clades with their number of species.