© 1994 by The Society for Integrative and Comparative Biology
Evolutionary History and the Species Problem1
Center for Critical Inquiry in the Liberal Arts and Department of Biology, University of North Carolina at Greensboro Greensboro, North Carolina 27412-5001
SYNOPSIS. In the last thirty years 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 ("non-dimensional") situation, species are usually welldefined, 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 species concept, the evolutionary species concept, and the phylogenetic species concept. Each of these has strengths and weaknesses, but 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 behavior 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 one of the central pieces of evidence for the fact of evolution.