NEW YORK: The beetle-browed skull of an early human who died a million years ago on the grasslands of Ethiopia is further evidence that modern humans evolved from a common African ancestor, scientists say.

The skull was discovered by a fossil-hunting American graduate student in December 1997. But it took two more years of meticulous scraping with dental tools to extract it from its resting place in the silty sand of what is now a hard-baked desert.

The value of the find is less its age and remarkable preservation - there are East African fossils of early humans dating back 1.8 million years - than the fact that it represents a continuum in the fossil record, researchers say.

Scientists generally agree that Homo erectus was the direct ancestor of peoples in Africa, Asia and Europe. Most believe that H. erectus emerged on the savannahs of Africa some two million years ago, eventually populating other continents thanks to superior technology like bone tools.

But in the 1980s, some anthropologists decided that early African fossils were not H. erectus at all, but a distinct species they dubbed Homo ergaster. They pointed to differences in facial and skull bones, and theorised that H. ergaster was in fact an ancestor of Homo sapiens - modern humans.

The Ethiopian skull will not lay this argument to rest, but it does tip the scales toward those who assert that the two-species theory is false, says Tim White, a paleoanthropologist at the University of California, Berkeley, who led the team of US and Ethiopian researchers. “The findings are significant because they are so well dated and so complete and so similar to the Asian forms from China and Java,” he said. “I’d say that the debate is far from over, but every fossil discovered helps to better understand where we came from.”

Homo erectus is thought to have emigrated to Asia and Europe between a million and 500,000 years ago - although this estimate, too, is contentious. What is certain is that starting in the late 1800s, scientists began to unearth fossils in China, Indonesia and parts of Africa that seemed to share striking similarities. In the 1950s, the legendary evolutionary biologist Ernst Mayr proposed that they be grouped into one category - H. erectus.

The new find, reported in the journal Nature, is important because it helps fill a gap between the oldest H. erectus fossils and the later ones - showing, its proponents say, that H. erectus has maintained a constant presence in Africa.

“It is a good intermediate between these African specimens and the Asian ones - thus it answers many questions about H. erectus,” said C. Owen Lovejoy, an anthropologist at Kent State University in Ohio who has examined the Ethiopian find. “It now appears,” adds Lovejoy, that “erectus was a world-wide species that at some point gave rise to primitive forms of H. sapiens - almost certainly, it would now seem, in Africa,” he explained. “Therefore the new specimen greatly simplifies our view of erectus evolution, and paves the way, as these authors point out, for new analyses of how and why erectus eventually gave rise to H. sapiens.”

The skull was found near the village of Bouri in the Afar depression, a northern continuation of the Rift Valley, about 230 kilometres from Ethiopia’s capital of Addis Ababa. Because the teeth and lower jaw were missing, researchers were unable to determine the individual’s gender - although they did detect signs of gnawing by animals.

All fossils found in the country are curated and studied at the National Museum of Ethiopia in Addis Ababa. Last year, the same team of researchers found 4.4 million-year-old teeth and bones in the Afar from an ancient chimpanzee-like species that represents the earliest known hominids. They named the find Australopithicus ramidus. “This species is the oldest known link in the evolutionary chain that connected us to our common ancestor with the living African apes,” White said at the time. “Clearly, Darwin was right - humans evolved from an African ape.”

More and more evidence is piling up that Africa was indeed the cradle of both human evolution and civilisation. The discovery of bone tools in a seaside cave in South Africa has also bolstered the “Out of Africa” theory - this time, regarding the onset of so-called modern human behaviour.—Dawn/InterPress Service.