Skull Details Suggest Neanderthals Were Not Humans

Ever since their discovery in the 19th century, Neanderthals have been like the uncomfortably odd relatives who show up at a family reunion. Should they be seated with the closest kin, sent to the back of the room with the distant cousins or tossed out as rank interlopers, despite a family resemblance?

In short, were the now-extinct Neanderthals of Europe full members of the modern human species, a subspecies or an entirely different species? The answer has implications for the ancestry of modern Europeans: whether some Neanderthal blood could flow in their veins.

Although many scientists think Neanderthals were a subspecies, which could have interbred with Homo sapiens, new research appears to confirm the more widely held view that Neanderthals and modern humans were significantly different, enough to qualify as separate species.

The findings were based on detailed measurements of variations in the skulls of modern humans and Neanderthals as well as 12 existing species of nonhuman primates. The research team, led by Dr. Katerina Harvati, a paleoanthropologist at New York University, reported its results yesterday in The Proceedings of the National Academy of Sciences.

"What we are really saying is that Neanderthals did not contribute to the ancestry of modern Europeans," Dr. Harvati said in an interview.

The research lends strong support for the single-origin theory of modern human evolution, one of two models that have split anthropology into warring camps. This theory holds that modern Homo sapiens is a new species that arose relatively recently in Africa — more than 100,000 years ago — and spread out to replace indigenous archaic populations around the world. Neanderthals were one such group, a separate species that did not breed with the newcomers before it vanished.

The opposing regional-continuity theory holds that the new migrants from Africa bred at least to some extent with the archaic populations they encountered, perhaps accounting for some superficial differences among people today in different regions. In this view, Neanderthals were a subspecies and at least partly ancestral to modern Europeans.

Dr. Eric Delson, a paleontologist at the American Museum of Natural History and Lehman College, both in New York City, said the new research was a mathematically rigorous approach to the question of Neanderthal-human relationships. "It's a very convincing piece of work," Dr. Delson said.

But not convincing enough, it seems, to put the controversy to rest.

"This research will not change many minds," said Dr. Erik Trinkaus, a specialist in Neanderthal studies at Washington University in St. Louis. His research has suggested that there was some interbreeding.

"We have known for a long time what these fossils look like," Dr. Trinkaus continued. "We know that Neanderthals are distinctive, but this research doesn't address their underlying biology."

In the new research, Dr. Harvati and her colleagues, Dr. Stephen R. Frost of the New York Institute of Technology in Old Westbury and Dr. Kieran P. McNulty of Baylor University in Waco, Tex., used a technique known as geometric morphometrics to measure the degree of variation between and among living primate species, including chimpanzees, gorillas, baboons, monkeys and humans.

The researchers focused their analysis on the same 15 "landmarks" on the cranium and face of each specimen. They were examined in 3-D to determine even the finest variations in shapes.

The purpose, Dr. Harvati said, "was to devise a quantitative method to determine what degree of difference justified classifying specimens as different species."

The differences measured between modern humans and Neanderthals were found to be significantly greater than those found between subspecies or populations of the other species studied. The two living species of chimpanzees, for example, appear to be more closely related to each other than Neanderthals are to humans, the scientists concluded.

In a statement about the findings, Dr. Harvati said the research provided "the most concrete evidence to date that Neanderthals are indeed a separate species within the genus Homo."

NY Times

Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0308085100

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

Katerina Harvati et al.

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.

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Posted by Dienekes at January 26, 2004 04:42 PM | PermaLink