Fossils May Mark Human Migration Out of Africa
Two fossil skulls found beneath a medieval castle in the former Soviet republic of Georgia may be the remains of the first human species to journey out of Africa, an international research team said Thursday.
Reliably dated to 1.7 million years ago, the bones offer the earliest known anatomical evidence of the direct link between humanity’s ancestral birthplace in Africa and the primitive human forebears who colonized much of the rest of the world. They provide concrete evidence for the widely accepted theory that the human species originated in Africa, then migrated elsewhere, the researchers said.
The fragmented skulls belong to a young male and a female from a species of relatively tall, agile tool users called Homo ergaster who lived among the elephants, hyenas and rhinos along the lush riverbanks of prehistoric Dmanisi about 60 miles southwest of the present-day Georgian capital of Tbilisi.
The fossils and the many simple stone tools discovered with them reveal not only when humanity’s forebears first ventured from the place where they evolved, but also offer a suggestion as to why they might have left Africa, several experts said.
Many experts have speculated that the invention of more advanced stone tools, such as double-edged hand axes, gave primitive people a new ability to brave the challenges of new homelands. At Dmanisi, however, only the crudest stone choppers, flakes and scrapers have been discovered.
That suggests to some experts that it perhaps was hunger, not new technology, that opened the world to the primitive hominids. Experts estimate that the Homo ergaster were about one-third larger than earlier hominid species and might have needed at least 40% more energy to maintain themselves. Under the spur of their voracious appetites, they may have foraged ever more widely to sustain the high-protein energy demands of their large bodies and evolving brains, eventually ranging into Asia.
The discovery by a team of Georgian, German, French and American scientists led by the Georgia National Academy of Sciences is documented in research published today in Science.
“This is one of the most important finds in a long time,” said Carl C. Swisher III, a dating expert at the Berkeley Geochronology Center who helped determine the fossils’ age. “It looks like we have representatives of that first early migration out of Africa.”
Paleoanthropologist Susan C. Anton at the University of Florida in Gainesville, a member of the research group, said there was no mistaking the fossils’ distinctive features or their kinship with other hominids in Africa from the same period. “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 actually left the African continent to go into other parts of the world.”
Anthropologist F. Clark Howell at UC Berkeley called the discovery “a miracle” and said, “I think this is the beginning of a real revolution in human evolutionary studies.”
Ian Tattersall, an expert on human origins at the American Museum of Natural History in New York, said, “I think these specimens will dominate discussion of the identity of the first humans to have left Africa.”
The bones were discovered last May by a team excavating the grounds of a castle set high on a promontory overlooking two 260-foot-deep gorges carved by the Masavera and Pinezaouri Rivers. The skull fragments, along with hundreds of stone tools, were preserved in ancient river and lake sediments underlying the courtyards of the castle and its surrounding village walls. They were only a few feet away from the spot where, in 1991, researchers had found a jawbone from an unidentified hominid species.
“It was a very nice surprise to find these skulls,” said co-investigator David Lordkipanidze of the Georgia State Museum.
The researchers uncovered two partial skulls, crushed and distorted by the inexorable pressure of geologic burial. The larger skull has a brain case of about 775 cubic centimeters, about half the size of a modern human. The smaller and more complete skull has a cranium of about 650 cubic centimeters in volume.
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.
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 discovered in East Africa. And the ergaster species is almost identical to Homo erectus hominids found throughout ancient Asia during the same period, showing the full extent of the journey that the creatures and their descendants made.
Based on the few partial skeletons discovered elsewhere so far, Homo ergaster may have weighed about 110 pounds on average and been about 5 feet tall, much taller and heavier than the more primitive hominids the species displaced.
Indeed, that dramatic increase in body size may have been enough by itself to lead to the migration out of Africa, without any advances in toolmaking abilities, the researchers concluded.
“There were other things going on besides technology that enabled them to leave Africa,” said Anton. “It is a bigger animal, and that requires more food of higher quality to feed that body. You may end up having a bigger home range, covering much bigger areas.”
Tattersall, however, suggested that beyond the size increase, the evolutionary advance of the modern body form made the journey inevitable.
Earlier pre-human species were not as adept at upright walking as hominids like Homo ergaster and therefore may have kept closer to the deep forests, venturing more rarely into the open grasslands, he said.
“Modern body form meant an emancipation from this kind of environment,” Tattersall said. “They became creatures well adapted to the savannas. As soon as this happens, they seem to move out of Africa.”
(BEGIN TEXT OF INFOBOX / INFOGRAPHIC)
Out of Africa
Two fossil skulls of Homo ergaster discovered in Georgia may belong to the first human species to journey out of Africa, where humanity originally evolved. Dating from 1.7 million years ago, the bones link primitive humans who once inhabited Africa to Asia, researchers said. *
Source: Science
Researched by ROBERT LEE HOTZ
