Neandertal origins, Middle Pleistocene systematics, and tests of current taxonomic and phylogenetic hypotheses

The "Neandertal problem" is paleoanthropology's oldest question. Although the debate over the position of the Neandertals in human phylogeny has historically considered their fate rather than their origin, recent discussions focus on the composition and relationships of European and African Middle Pleistocene fossil taxa that precede them chronologically. These taxa, previously referred to as "archaic Homo sapiens ," include H. antecessor and H. heidelbergensis . Researchers who accept these named paleospecies as valid taxa also elevate the Neandertals to specific status (H. neanderthalensis). There is, of course, disagreement about these taxonomic hypotheses. This discourse reflects the broader debate over the pattern of evolution that culminated in the origin of modern humans and the place of the Neandertals in that pattern.; The purpose of this study is to evaluate systematic hypotheses concerning the Middle to Late Pleistocene fossil sample from an explicitly phylogenetic perspective. Discrete and continuous characters, emphasizing those previously identified as taxonomically or phylogenetically significant, were recorded for a diverse fossil sample that consisted primarily of European, Middle Eastern, and African specimens. Individuals and site samples ("exemplars") were employed as operational taxonomic units (OTUs). By using only "natural" groups as terminal taxa, it is possible to explicitly test taxonomic hypotheses because conspecifics should reflect their close relationship in the results of a phylogenetic analysis. Phylogenetic analyses were conducted using cladistic methods that yield hypotheses about relative recency of common ancestry and order of divergence. Clades that were supported across a wide range of analyses that differed in terms of taxa, characters, and coding schemes, were identified. The composition of these clades, and their relationships to each other, were evaluated for congruence with taxonomic and phylogenetic hypotheses concerning these fossils.; The results of these analyses support the taxonomic unity of Neandertals. H. heidelbergensis is identified as a probable grade taxon. The hypothesis that Neandertals played a major role in modern human ancestry is not supported. The present study yields explicit, testable hypotheses about the natural groups present in this enigmatic assemblage. This information will allow paleoanthropologists to better understand the nature and pattern of human evolution during this important time period.