Speciation is the evolutionary process by which new biological species arise. 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.There are four geographic modes of speciation in nature, based on the extent to which speciating populations are isolated from one another: allopatric, peripatric, parapatric, and sympatric. Speciation may also be induced artificially, through animal husbandry, agriculture, or laboratory experiments. Whether genetic drift is a minor or major contributor to speciation is the subject matter of much ongoing discussion.