Speciation

Abstract

Speciation is the central event of evolution. With the isolation of a new species, two closely related forms acquire evolutionary independence. The basic criterion of species, which systematics has elaborated in its long development, is still in force. This is the so-called “triple criterion”: species are genetically isolated (i.e., unable to interbreed); a hiatus is always found between very near species; species possess independent ranges. In the majority of cases, this criterion works in the resolution of the most complex taxonomic problems. Difficult cases do not compromise the triple criterion, since practical difficulties are unavoidable in the application of any theory to the boundlessly diverse phenomena of the living world.