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Skull suggests there weren’t so many different human species

By John Noble Wilford
New York Times

After eight years spent studying a 1.8million-year-old skull uncovered in the republic of Georgia, scientists have made a discovery that may rewrite the evolutionary history of our human genus Homo.

It would be a simpler story with fewer ancestral species. Early, diverse fossils – those currently recognized as coming from distinct species like Homo habilis, Homo erectus and others – may represent variations within a single, evolving lineage. In other words, just as people look different from one another today, early hominids looked different from one another, and the dissimilarity of the bones they left behind may have fooled scientists into thinking that they came from different species.

This conclusion was reached by an international team of scientists led by David Lordkipanidze, a paleoanthropologist at the Georgian National Museum in Tbilisi, as reported Thursday in the journal Science.

The key to this revelatory conclusion was a cranium excavated in 2005 known as Skull 5, which scientists described as “the world’s first completely preserved adult hominid skull” of such antiquity. Unlike other Homo fossils, it had a number of primitive features: a long, apelike face, large teeth and a tiny braincase, about one-third the size of that of a modern human being. This confirmed that, contrary to some conjecture, early hominids did not need big brains to make their way out of Africa.

The discovery of Skull 5 alongside the remains of four other hominids at Dmanisi, a site in Georgia rich in material of the earliest hominid travels into Eurasia, gave the scientists an opportunity to compare and contrast the physical traits of ancestors that apparently lived at the same location and around the same time.

Lordkipanidze and his colleagues said the differences among these fossils were no more pronounced than those among any given five modern humans or five chimpanzees. The hominids who left the fossils, they noted, were quite different from one another but still members of one species.

“Had the braincase and the face of Skull 5 been found as separate fossils at different sites in Africa, they might have been attributed to different species,” Christoph Zollikofer of the University of Zurich, a co-author of the journal report, said in a statement.

Zollikofer and Marcia Ponce de Len, his Zurich colleague, conducted the comparative analysis of the Dmanisi specimens.

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