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. Last Updated: 07/27/2016

Skull Find Alters View of Human Migration

Two fossil skulls unearthed in Georgia are the oldest human ancestor remains ever found on the Eurasian land mass and probably represent part of the first migration out of Africa by human ancestors, researchers reported Thursday.

An international team of scientists said the two skulls are 1.7 million years old and show close similarities to contemporary fossils from East Africa, while having little in common with remains found later in Europe and Asia.

"They were able to leave Africa by the Levantine corridor, travel through the Near East and into Georgia," said Georgia State Museum paleontologist David Lordkipandze, who leads the excavation at Dmanisi, 80 kilometers southwest of Georgia's capital, Tbilisi. Results of the team's research were to be reported in Friday's edition of Science.

The Dmanisi find is the best evidence yet of an early departure from humankind's point of origin in Africa at a time when ancestors there had just evolved into long-legged species capable of walking long distances.

By their brow ridges, teeth and other anatomical characteristics, the skulls were clearly those of Homo ergaster, the research team reported. The bones closely resemble other early human fossils found in East Africa. And the ergaster species is almost identical to Homo erectus hominids found throughout ancient Asia during the same period, showing the extent of the journey the creatures and their descendants made.

Team member Susan Anton, a University of Florida anthropologist, said the two fossils - one "skullcap" and one nearly intact skull - "look very much like" contemporary remains of a species known as Homo ergaster that were found at the famous East African site of Koobi Fora.

"The anatomy is very clear," Anton said. "And the anatomy is telling us that this is something that came from Africa.

"We are talking about the very first time that hominids [human ancestors] actually left the African continent to go into other parts of the world."

Anthropologist F. Clark Howell at the University of California, Berkeley, called the discovery "a miracle," and said, "I think this is the beginning of a real revolution in human evolutionary studies."

Rick Potts, director of the Smithsonian's Human Origins program, suggested that "what's neat" about the Dmanisi find is that it confirms events in Africa, where early humans lived "very close to water, but starting around 1.7 million years ago, you found them dispersing into new environments."

Potts noted that East Africa had a lot of volcanic activity beginning 1.7 million years ago. Lakes and rivers shrank and expanded, endangering food supplies: "One way to respond to these changes is become more mobile," Potts said. "A biped totally committed to walking finds a greater diversity of settings. The Dmanisi finding says they could range far enough to get out of Africa."

Besides the skulls and some animal bones, the team also recovered more than 1,000 stone artifacts, most of them chunks of basalt used for chopping and scraping. Until Dmanisi, it was thought that human ancestors left Africa only when they had developed more sophisticated, double-faced tools, noted geologist Carl Swisher of the Berkeley Geochronology Center.

"So the reason for the [Dmanisi] emigration and expansion is not technologically driven," Swisher said. "It is biological," he said, suggesting that the migrants may have departed in pursuit of large animal herds heading north.

"The interesting thing is that this is the first hominid species who looks modern," Swisher said. "He's long-legged, short-armed, 5 feet 6 inches [1.7 meters] tall. He's a carnivore now and a runner. He's got more range."

But with only crudely crafted stones to use as tools and weapons - and a brain capacity about half that of modern humans - the migrants were probably poor hunters. Swisher suggested they may have been scavengers, stalking herds of antelope as they headed north and swooping down on crippled animals - "the Pleistocene equivalent of road kill."

While the new discovery moves early humans into Eurasia, it sheds little light on other vexing evolutionary questions, among them the origin of the human ancestors known as Homo erectus, whose earliest examples from the Indonesian island of Java are roughly contemporary with Dmanisi, or perhaps earlier.

Also, the new data are unlikely to resolve the debate over whether modern Europeans evolved from an early migration from Dmanisi or somewhere else, or from a second African migration about 1 million years ago: "The fossil record just isn't there," Potts said.

The bones were discovered last May by a team excavating the grounds of a castle set high on a promontory overlooking two 78-meter-deep gorges carved by the Masavera and Pinezaouri rivers. The skull fragments, along with hundreds of stone tools, were preserved in river and lake sediments. They were only a meter from the spot where, in 1991, researchers had found a jawbone from an unidentified hominid species.

The researchers dated the fossil deposits by precise argon isotope measurements of lava flows directly underneath the site, the paleomagnetic signature of the surrounding rocks, and by analyzing the fossil plants and animals found with the bones. The fossils predate what had been the first known appearance of humans in Europe by about 500,000 years.