Remarkable skull hints at dramatically simpler view of human evolution
A 1.8-million-year-old skull suggests that several species of early humans might not be different species at all, meaning the tree of human evolution might have fewer branches than previously thought.
Five remarkably preserved, 1.8-million-year-old skulls are are opening a unique window on early human evolution. In the process, they hint that several early human fossils found elsewhere and identified as different species may actually all be members of this same species, according to a new study.Skip to next paragraph
Scientists discovered the skulls and other skeletal remains as they were excavating a long-studied site at the small town of Dmanisi on the southern border of the Republic of Georgia.
All the specimens represent individuals who lived at various times within the same roughly 100-year span, suggesting they belong to the same species, the researchers say.
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An analysis of the skulls shows a range of features whose variety falls within the range of different looks found in modern humans, chimpanzees, and bonobos. This further reinforces the notion that these early humans were members of the same species, researchers say.
Armed with information on these individuals' range of looks, scientists may be able to prune some limbs from the human family tree if the team's analysis – that more fragmentary early-human fossils scientists have found in Africa may belong to the same species as the Dmanisi Five – holds up, the researchers suggest.
The discovery represents "a significant contribution to our understanding of the origins and evolution of our own genus, homo," says Donald Johanson, founding director of the Institute for Human Origins at Arizona State University in Tempe.
Scientists have worked for decades to uncover well-preserved specimens from the same geological period and same location, he says. It's a bit surprising that such a find was discovered on the Eurasian continent, given that Africa is widely seen as the birthplace of the genus Homo. This discovery does not challenge that view of human origin, but enriches it, Dr. Johanson says.
The five individuals the skulls represent "are the earliest representatives of our own genus outside of Africa," says David Lordkipanidze, a Georgian anthropologist who led the international team reporting the results in Friday's issue of the journal Science.
Of special interest is a virtually complete skull, which the team has dubbed Skull 5. Scientists discovered the lower jaw in 2000 and found the rest of the skull five years later and seven feet away. The team undertook painstaking analysis to establish that the two belong together.
The skull is "an extraordinary find in many respects," says Marcia Ponce de Leon, an anthropologist from the Anthropological Institute and Museum in Zurich and a member of Dr. Lordkipanidze's team.
Unlike other fossilized skulls from this period found elsewhere, Skull 5 is well-preserved, remains perfectly formed, and hasn't been broken into fragments.
The skull's odd proportions were unexpected, Dr. Ponce de Leon notes. The skull's brain case is much smaller than expected, but the face is large, with large, thick jaws that jut forward, large teeth, and thick bony ridges crossing the face just above the eye sockets.
"This is really an important specimen," writes Ian Tattersall, anthropologist and curator emeritus at the American Museum of Natural History in New York, in an e-mail. "It underscores that the history of the hominid family was one of vigorous evolutionary experimentation."