Where Does the Genus Homo Begin, and How Would We Know?

Abstract

Genus defi nitions use four criteria, two lines of evidence (phenotypic and genetic) and fall into two categories. The four criteria are the relationships among taxa, information about their adaptive grade, estimates of the genetic distance that separates them, and the estimated time of divergence. At least one researcher (Dubois, 1988) has suggested that a fi fth criterion, evidence of hybridization between species, should be the primary criterion for grouping species into genera. However, even if this suggestion had any merit, it is not clear how evidence of hybridization could be obtained from the fossil record of extinct taxa. One, or more, of the criteria has been used, or combined, to generate genus defi nitions that belong to two categories. The fi rst category draws upon phenotypic evidence to make inferences about adaptive grade, and uses both phenotypic and molecular evidence (if the latter is available) to make inferences about relationships. Defi nitions in the second category rely solely on genetic evidence for either estimates of genetic distance, or for generating estimates about the timing of evolutionary events, which are then converted into criteria for recognizing genera.