Speciation

Abstract

Speciation is the evolutionary emergence of species, and all of the taxonomic diversity of life is ultimately the result of this process. Speciation can be either anagenetic (within a single lineage, although many do not accept this as true speciation) or cladogenetic (branching speciation, in which a parental species gives rise to two or more daughter species). Cladogenesis is subdivided based on the geographical relationships between the daughter species: (1) sympatric speciation, for which the daughter species inhabit the same area; (2) parapatric speciation, for which the daughter species inhabit contiguous areas; and (3) allopatric speciation, in which the daughter species inhabit different geographic areas. Sympatric speciation is more common in plants than in animals, and some plant species evolve via hybrid speciation in which the hybrid (and often polyploid) offspring of two hybridizing species become a new, third species. Most cladogenetic events are thought to be allopatric. As speciation is the production of species, a single methodology for defining species would be desirable, but remains elusive. As a result, there is much debate surrounding the identification of extant species taxa, and determining the bounds of fossil species is more difficult still.