Dmanisi Skulls 1-5, from left. Researchers have discovered the first complete skull of an adult early hominid, the class of apes that would eventually give rise to modern humans. Skull 5, as researchers have classified the fossil, was a mature male with a tiny brain, massive lower jaw and jutting brow who lived 1.8 million years ago in what is now the nation of Georgia.
(Photo: M. Ponce de Leon and Ch. Zollikofe, University of Zurich, Switzerland)
Scientists trying to unravel the origins of humanity mostly study scraps - some ancient teeth here, a damaged bone there. But now a lucky research team has uncovered a fossil superstar: the first complete skull of an early human adult from the distant past.
The 1.8 million-year-old fossil, known as Skull 5, is like nothing seen before. It has a small brain case and a heavy, jutting jaw, as did some of humanity's older, more ape-like ancestors. But other bones linked to Skull 5 show its owner had relatively short arms and long legs, as does our own species, Homo sapiens. Those who've studied Skull 5 say it also provides support for the provocative idea that, 1.8 million years ago, only one kind of early human held sway, rather than the throng of different species listed in today's textbooks.
"We're not against the idea that there might have been more than one species at some point about 2 million years ago," Christoph Zollikofer of the Anthropological Institute and Museum in Switzerland, who helped analyze the new fossil, said at a news conference Wednesday. "But we simply say ... we don't have sufficient fossil evidence."
That's a controversial claim, but no one is disputing that Skull 5, discovered in pieces in 2000 and 2005 at the village of Dmanisi in the nation of Georgia, is a treasure. Never before have researchers found an adult skull of the early Homo family that was so exquisitely preserved. Scientists have dug up a few other skulls similar in age and condition to Skull 5, but all belonged to individuals who were either too old or too young to be very useful representatives of their species. Skull 5, on the other hand, is a mature adult - exactly what's needed.
Generally, "you have to wait until humans bury their dead before you get something as good as this," says George Washington University paleoanthropologist Bernard Wood, who was not part of the team. Dmanisi, he says, is "the FAO Schwarz of hominin paleontology."
In addition to Skull 5, four other full or partial skulls have been found at Dmanisi, and all five come from individuals who died within a few centuries of each other at most. Outside Dmanisi, researchers have never found a cluster of fairly complete early skeletons from one sliver of time. That means the Dmanisi skeletons give scientists an unprecedented look at the full range of anatomy within a single population.
By analyzing the shape of the Dmanisi skulls, the team members found that even though they seem to vary widely they're no more different from each other than the skulls of a group of modern-day humans or a group of chimpanzees. The parallel suggests that all five Dmanisi individuals belonged to the same species of early human, probably Homo erectus, which many scientists think spawned the lineage that led to us.
Then the team analyzed skull shape among a grab-bag of early-human species such as Homo habilis and Homo rudolfensis, all known from fossils from Africa. By some measures these skulls, too, were no more different from each other than a selection of chimpanzee skulls or a group of human skulls. So the differences thought to demarcate species are actually differences within a species, the team reports in this week's Science.
Other scientists disagree. Paleoanthropologist Susan Antón of New York University, while praising the new analysis, says the Dmanisi team didn't compare fossil features, such as the anatomy around the front teeth, that differ most starkly between two different species of early humans. So the Dmanisi team's hypothesis that there was only one lineage is not totally convincing, she says.
Wood also has doubts, but he agrees with the Dmanisi researchers that they have an exceptional resource on their hands, most of it still awaiting excavation.
"The fossil is interesting, and the site is tremendously interesting," he says. "For all we know, it's going to be the richest early hominin site there has ever been."