African discovery yields new hominid clues.

Anthropologists have revealed the 1991 discovery of a group of archaeological sites in southern Ethiopia, known collectively as Konso-Gardula, that so far has yielded a partial lower jaw and several teeth assigned to Homo erectus, as well as stone tools closely resembling those found with H. erectus remains at other African sites.

Deposits at Konso-Gardula may eventually yield fossils and artifacts rivaling those from the most fertile African sites, such as Tanzania's Olduvia Gorge, assert Berhane Asfaw of the Ministry of Culture in Addis Ababa, Ethiopia, and his colleagues.

Konso-Gardula sediments span the period from about 1.9 million to 1.3 million years ago, based on dating of volcanic ash layers deposited above and below the remnants of human ancestors, Asfaw's team reports in the Dec. 24/31 NATURE.

"This site should shine much new light on the evolution of hominids [members of the human evolutionary family]," remarks anthropologist F. Clark Howell of the University of California, Berkeley, who did not participate in the project but has seen some of the Konso-Gardula artifacts. "It will undoubtedly also help us realize how complicated hominid evolution really was."

Initial excavations uncovered two main types of tools: pear-shaped stones with edges sharpened on both sides and thinner "picks" with triangular points. Large mammal bones, including those of saber-toothed cats, appear among the stone implements and contain marks produced by hominids, such as thin incisions near joints. The investigators offer no opinion, however, as to whether human ancestors at Konso-Gardula hunted animals or scavenged their carcasses.

Excavations also revealed a lower left jaw containing four cheek teeth and a separate molar tooth, all of which the scientists classify as from H. erectus. Some anthropologists now place East African specimens formerly dubbed H. erectus, which would include those from Konso-Gardula, in a different species they consider directly ancestral to modern humans (SN: 6/20/92, p.408).

Stone tools and fossils unearthed at Konso-Gardula, date to approximately 1.4 million years ago.

Asfaw's team obtained this estimate through a dating technique that gradually heats grains of ash and then exposes them to a laser beam that identifies different forms of the element argon. Comparing the abundance of these argon variations enables scientists to calculate when the ash formed.

Dates from Konso-Gardula support earlier suspicions that the distinctive sharpened tools favored by H. erectus in East Africa -- which also turn up at Asian and European sites extending to as recently as 200,000 years ago -- abruptly appeared for the first time around 1.4 million years ago, the researchers note. Konso-Gardula artifacts required considerable skill to produce, and they appear in large numbers at the several sites, indicating intensive occupation of the area by H. erectus, they argue.

The new Ethiopian finds also call into question the theory that periods of global cooling -- which sparked savanna expansion and the shrinkage of woodlands in Africa -- promoted the evolution of H. erectus and its eventual migration out of Africa. Another African site provides the earliest H. erectus fossil, about 1.7 million years old, and Konso-Gardula establishes the emergence of sophisticated stone tools 300,000 years later, Asfaw's team asserts. These dates fall between major ice ages that occurred around 2.4 million and 900,000 years ago.

Uncertainty also surrounds hominid evolution prior to 1.4 million years ago in Asia, the Middle East, and Europe, the investigators hold, because anthropologists have explored those regions far less intensively than East Africa.

For now, scientists cannot conclude with certainty that H. erectus originated only in Africa and later migrated elsewhere, the researchers note.