Species concepts and species identification in human evolution

Abstract

Little is known about the process of speciation. However, while this process is clearly independent of morphological differentiation, if one species arises from (and thus within) another, anatomical differentiation associated with speciation cannot initially exceed that possible within a species. Beyond this, however, theory provides no help in the practical business of species recognition in the fossil record. The “biological” species concept, whilst having the merit of stressing the historical importance of genetic disjunction, provides no general guidelines for identifying species either in the living biota or in the fossil record. For paleontological purposes, the same is also broadly true for the “recognition” concept. The “phylogenetic” species concept, which views species as the minimum diagnosable unit, remedies this deficiency but blurs the distinction, critical in the living biota, between species, which are both taxically and morphologically differentiated, and subspecies, which are only differentiated morphologically. Empirical appraisal of closely related extant species suggests, however, that intraspecific variants are rarely recognizable on the basis of hard-tissue morphology, and that distinctive hard-tissue “morphs” will almost certainly correspond to disjunct species or even to closely related groups. This has major implications for interpreting the human fossil record, especially over the last half million years, where use of the term Homo sapiens to cover a spectrum of morphologies has served to obscure evolutionary patterns.