An Early Journey Out of Africa

Ann is a contributing correspondent for Science

Two fossil skulls, unearthed near a medieval castle in Eastern Europe, provide a glimpse of the faces of the first wanderers. The fossils show that ancient humans left Africa to colonize the world about 1.7 million years ago--hundreds of thousands of years earlier than many scientists had assumed. And they used only simple stone tools to accomplish their journey.

The finds--an almost complete cranium, most likely belonging to a female adolescent, and a skullcap, probably from a young adult male--were found in May 1999 at an archaeological site in Dmanisi, 85 kilometers southwest of the Georgian capital of Tbilisi. In 1991, scientists had already found a hominid jawbone here, just above a deposit of volcanic rock dated to at least 1.8 million years old. Yet a number of researchers argued that the bone's shape suggested a younger date, and that it might have been deposited much later than the volcanic layer.

In the 12 May issue of Science, however, a team of Georgian, German, French, and U.S. researchers present fresh evidence that the jaw and the newly found fossils are indeed very old. New radiometric dates put the volcanic layer at 1.85 million years ago. New paleomagnetic measurements, as well as associated fossils found nearby, show that the layer that held the fossils themselves is about 1.7 million years old.

The age is further supported by the skulls' small size and several other features, such as high temporal lines and prominent brow ridges, which resemble those of an early species of human called Homo ergaster, which lived in Africa between 1.9 million and 1.4 million years ago.

So far, the oldest traces of early humans outside Africa--except for a disputed site in Java--are primitive stone tools at 'Ubeidiya, Israel, dated to as early as 1.5 million years ago. These tools are an early stage of the relatively advanced Acheulean technology, which includes "handaxes" and other carefully crafted tools. Similar tools began to show up in Africa at about 1.6 million years ago, and some researchers proposed that the invention of the tools spurred colonization out of Africa at that time.

But the Dmanisi results may shatter that theory. Not only are the Georgian fossils older than the earliest known Acheulean tools in Africa, but the Dmanisi people had only simple stone tools, the Georgian scientists report; they resemble the Oldowan tools found in East Africa's Olduvai Gorge as early as 2.5 million years ago.

Apparently, it wasn't tools but biology that helped early hominids make the leap from Africa, the researchers say. "As soon as you get larger body sizes (and brains), you see shifts in what they eat and how far they range that ultimately lead them out of Africa," says team member Susan Antón at the University of Florida, Gainesville.

Ian Tattersall, a paleoanthropologist at the American Museum of Natural History in New York City, agrees: "The story is looking strong that up until 1.9 million years ago the only hominids were archaic [types] restricted to the forest fringes" of Africa, he says. "Somehow, a modern body was acquired, then all hell broke loose and this strutting biped ... was mobile enough to set out of the forest fringes and walk out of Africa."

Posted in Archaeology, Paleontology