A test of the single species hypothesis in the Upper Pleistocene Levant using multivariate analysis of mandibular measurements

Recently, craniometric and morphological studies have attempted to determine whether the Late Pleistocene Levant was inhabited by one highly variable or two distinct hominid species. However, the mandible has rarely been employed in this endeavor, which is surprising as it is the skeletal element most often represented in the fossil record and is responsive to both behavioral and genetic changes.

This study uses metric measurements of male mandibles in both non-hierarchical cluster and principal coordinates analyses to test the two species hypothesis. If this hypothesis is correct, then it is expected that the Levantine hominids generally classified as "Neandertals" (Amud I, Tabun 11, Kebara 2) would distinctly cluster with the European Neandertal sample (N=8) while the Levantine "modem humans" (Qafzeh 9, Skhūl IV and V) would cluster with a modem human sample (represented by Predmost 5, two Mesolithic mandibles and 24 Native American mandibles).

This analysis reveals two significantly distinct clusters, one predominately Neandertal and the other modem human. As expected, in the two species model, Amud 1, Tabun 11 and Kebara 2 cluster with the European Neandertals and Skhul V clusters with the modern human sample. However, Skhul IV and Qafzeh 9 cluster with the Neandertals instead of with the modern humans.

Because the Levant sample does not cluster according to a two species model, the single species hypothesis is not rejected. An explanation of the variability of this single species is that the Levant was a contact zone where two different populations, one from Europe and one from Africa interbred.