for National Geographic News
An exquisitely preserved skull of a tiny-brained human ancestor has been recovered from excavations beneath the ruins of a medieval castle in the republic of Georgia. The skull is about 1.8 million years old and belongs to the first group of humans to migrate out of Africa, reports an international team of archaeologists.
The find calls into question a widely held hypothesis that the evolution of big brains propelled the exodus of early humans out of Africa.
The fossil evidence from Dmanisi now includes three skulls, several jaw fragments, and hundreds of stone tools and animal remains. All of the material has been recovered from the same layer of sediment. It is forcing scientists to come up with alternative explanations for why humans were able to leave Africa.
"Before this find, the main reason was that at least these humans had big brains," said David Lordkipanidze, a paleoanthropologist at the Georgian State Museum in Tbilisi who led the excavation team. "Now this shows that [their brains] were quite small."
The brain of the new specimen from Dmanisi is about half the size of a modern human's brain. The two skulls found in 1999 at the site are also about 1.8 million years old and had room for substantially larger brains.
The research by Lordkipanidze and colleagues is published in the July 5 issue of the journal Science and is the subject of the cover story of the August issue of National Geographic magazine.
Dmanisi sits on a promontory formed by the confluence of two rivers between the Black Sea and the Caspian Sea about 50 miles (80 kilometers) southwest of Tbilisi. Archaeologists first began excavating the remains of a 1,000-year-old castle located on the site in 1936.
In 1983, while examining an ancient garbage pit, one of the archaeologists uncovered what Abesalom Vekua, a team member from the Georgian State Museum, identified as a tooth of a rhinoceros, an odd creature to have been wandering the Caucasus Mountains. Speculation about what lay in the sediments beneath the castle spurred further excavations.
Stone tools recovered in 1984 and the two skulls discovered in 1999 were all dated to 1.8 million years ago, making the site a rare treasure trove for scientists interested in human evolution.
"We can say this is the richest material from this time period from one site and from one strata," said Lordkipanidze. "Usually we have isolated finds. Now on one geological level you have three skulls and three mandibles. We have a chance to study isolated specimens and to study populations."
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