Evolutionary history and the species problem

Abstract

Systematics has transformed itself from a discipline concerned with classification into a discipline concerned with reconstructing the evolutionary history of life. This transformation has been driven by cladistic analysis, a set of techniques for reconstructing evolutionary trees. Long interested in the large-scale structure of evolutionary history, cladistically oriented systematists have recently begun to apply "tree thinking' to problems near the species level. In any local situation, species are usually well-defined, but across space and time the grouping of organisms into species is often problematic. Three views of species are in common use today: the biological, and phylogenetic species concepts. No matter which is applied, exact counts of the number of species in any extended area will always be ambiguous no matter how much factual information is available. This ambiguity arises because evolution is a historical process, and the grouping of organisms into species always depends to some extent upon expectations of the future behaviour of those organisms and their descendants, expectations that cannot be evaluated in the present. The existence and special character of the species problem is itself a central piece of evidence for the fact of evolution. -from Author