One, at a million. This skull suggests that only one human species lived 1 million years ago.

African Skull Points to One Human Ancestor

Almost 1.8 million years ago, a new kind of human appeared in Africa and Eurasia. It stood tall and had a relatively large brain and slender hips. These early humans used stone tools adeptly, scavenged meat on the open savanna, and colonized more than one continent. But anthropologists have been divided for 2 decades about their identity.

Until the mid-1980s, most anthropologists embraced the view that these early humans all belonged to a species known as Homo erectus, making it the direct ancestor of living humans. But then several scientists proposed that fossils found in Africa--called Homo ergaster--differed from the classic specimens of H. erectus from Java, Indonesia, which appeared between 200,000 and 750,000 years later (Science, 2 March 2001, p. 1735). That meant that H. ergaster was the human ancestor--and H. erectus was an Asian dead-end.

Now a team of researchers argues that the earlier view was right after all. The team compared a 1-million-year-old skull from Ethiopia with other fossils from Africa, Europe, and Asia and used numerical methods to rank 22 characteristics in the skulls, sorting them on an evolutionary tree. The Ethiopian skull, along with another skull from Olduvai in Tanzania, overlapped extensively with Asian forms and later African fossils, the team reports in the 20 March issue of Nature.

"This [Ethiopian] fossil is a crucial piece of evidence showing that the splitting of H. erectus into two species is not justified," says one of the paper's authors, paleoanthropologist Tim White of the University of California, Berkeley. If White and his colleagues are right, there was a single species that spread from Africa to Europe to Asia 1 million years ago, rather than several different species alive at once.

But others say it is premature to write a death notice for H. ergaster. "I don't think it takes the wind out of the sails of H. ergaster," says Bernard Wood of George Washington University in Washington, D.C., who still thinks more than one species was alive 2 million to 1 million years ago. Jeff Schwartz of the University of Pittsburgh agrees: "To me, it says there was more diversity in these hominids." And the debate continues.

Related links
White's page
Human family tree with additional information about H. ergaster and H. erectus