From today's New York Times:
Skull 5; a rendering of the original owner After eight years spent studying a 1.8-million-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 actually represent variation among members of a single, evolving lineage.
This was the conclusion 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 revelation was a cranium excavated in 2005 and known simply 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. ...
“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,” a co-author of the journal report, Christoph Zollikofer of the University of Zurich, said in a statement. Such was often the practice of researchers, using variations in traits to define new species.
Although the Dmanisi finds look quite different from one another, Dr. Zollikofer said, the hominids who left them were living at the same time and place, and “so could, in principle, represent a single population of a single species.” He and his Zurich colleague, Marcia Ponce de León, conducted the comparative analysis of the Dmanisi specimens.
“Since we see a similar pattern and range of variation in the African fossil record,” Dr. Zollikofer continued, “it is sensible to assume that there was a single Homo species at that time in Africa.” Moreover, he added, “since the Dmanisi hominids are so similar to the African ones, we further assume that they both represent the same species.”
