Neanderthal taxonomy reconsidered: implications of 3D primate models of intra- and interspecific differences

The taxonomic status of Neanderthals lies at the center of the modern human origins debate. Proponents of the single-origin model often view this group as a distinct species with little or no contribution to the evolution of modern humans. Adherents to the regional continuity model consider Neanderthals a subspecies or population of Homo sapiens, which contributed significantly to the evolution of early modern Europeans. Paleontologists generally agree that fossil species should be equivalent to extant ones in the amount of their morphological variation. Recognition of fossil species therefore hinges on analogy to living species. A previous study by one of the authors and recent work by other researchers [Schillachi, M. A. & Froelich, J. W. (2001) Am. J. Phys. Anthropol. 115, 157-166] have supported specific status for Neanderthals based on analogy to chimpanzees and Sulawesi macaques, respectively. However, these taxa may not be the most appropriate models for Pleistocene humans. Here we test the hypothesis that Neanderthals represent a subspecies of H. sapiens by comparing the degree of their morphological differentiation from modern humans to that found within and between 12 species of extant primates. The model taxa comprised >1,000 specimens, including phylogenetic (modern humans and African apes) and ecological (eight papionin taxa) models for Pleistocene humans. Morphological distances between model taxon pairs were compared to the distances between Neanderthals and modern humans obtained by using a randomization technique. Results strongly support a specific distinction for Neanderthals.