Hominids may be state-of-the-art tool makers 2.6 million years ago

The discoveries in East Africa of what could be the oldest instrument of expertly cut stone suggest that the first members of the human race, Homo, invented these tools about 2.6 million years ago, according to the researchers. But their conclusions are controversial.

New discoveries at a site in Ethiopia called Ledi-Geraru fit into a scenario in Homo Groups have devised ways to sharpen hand-held stones, said archaeologist David Braun of George Washington University in Washington, DC, and his colleagues. The artifacts of Ledi-Geraru date from 2.58 million to 2.61 million years, the team publishes its report online June 3 in the Proceedings of the National Academy of Sciences.

Another team had previously discovered sharp stones dating from 2.55 to 2.58 million years ago in Gona, a nearby Ethiopian site (SN: 17/04/04, p. 254). Until now, these were the oldest examples of cutting and digging devices with consistently sharpened edges. Archaeologists describe these types of Oldowan artifacts as early examples were found in Olduvai Gorge in East Africa.

Age estimates of Ledi-Geraru artifacts were determined based on where they were found, between a dated layer of volcanic ash and sediments preserving a known inversion of the Earth's magnetic field. The stone tools at Ledi-Geraru "are probably older than 50,000 years, but they could be 100,000 years older than Gona's artifacts," says Braun. His team recovered 300 stone artifacts, including sharp-edged rocks and larger rocks from which these tools were struck. These discoveries were scattered among 330 fossilized bones of nonhuman animals.

Older stone tools have been discovered. For example, large stone tools found in Kenya on a site called Lomekwi 3, some of which are perhaps best suited for pounding objects, could date back 3.3 million years (SN: 13/06/15, p. 6). Contested evidence, based on possible incisions using stone tools on two animal bones aged 3.4 million years, suggests that Australopithecus afarensis, former hominids better known for the partial skeleton of Lucy, the animals skinned before the Homo appeared (SN: 9/11/10, p. 8). And today's chimpanzees and monkeys break nuts with stones, a sign that this behavior dates back far in the evolution of primates (SN: 26/11/16, p. 16).

But the Ledi-Geraru artifacts indicate that Homo, whose origin probably dates back to 2.8 million years ago and which relies on a jaw already found in Ledi-Geraru (SN: 04/04/15, p. 8The Braun Group claims that the manufacture of stone tools has reached a new level, characterized by qualified edge sharpening.

The archeologist Ignacio de la Torre from University College London, who did not participate in the new study, agrees. "The combination of Oldowan tools in the early Homo can be best explained by changes in diet and access to animal meat by cleaning, "he says.

The animal bones discovered with the Ledi-Geraru artifacts came from creatures such as gazelles and giraffes that would have inhabited open grasslands with few trees, according to the Braun team. Researchers suspect that this landscape is likely to have frequent recovery opportunities. Lucy's species would have seen fewer fresh animal carcasses, she said, because the same part of East Africa included shrubs with occasional stands of trees and woodlands in her day.

The ability to cut meat and other foods with stone tools may have influenced the transition to smaller teeth seen early in pregnancy. Homo specimens, Braun's group is titular.

The archaeologist Sonia Harmand, of Stony Brook University in New York, found no stone tools dating from 3.3 to 2.6 million years ago. It is therefore unclear whether the Ledi-Geraru artifacts represented a rapid change in tool making or a development of earlier techniques. Sharp-edged flakes hit by larger rocks have been discovered in Kenya in Lomekwi 3, so the precursors of Oldowan's techniques may have begun to develop as early as 3.3 million years ago, says Harmand. who led the excavations of the site.

Other researchers question the conclusions of Braun and Harmand. The discoveries of Ledi-Geraru add to an increasingly confusing image of the early days of stone tool making, explains archaeologist Manuel Domínguez-Rodrigo of the Complutense University of Madrid. Until a detailed analysis of sediment formation at the Ledi-Geraru site is published, he remains skeptical about the claim that recently discovered artifacts have been found where they occur. have been deposited or are as old as they have been reported. Similarly, Domínguez-Rodrigo suspects that the artifacts of Harmand Lomekwi 3 originally rested in much younger sediments, before erosion and water led them down a slope of 3, 3 million years. And the trampling of animals probably created the incisions reported on animal bones from Lucy's time, he argues.

The Ledi-Geraru artifacts were also found on a slope where they could have settled in sediments after 2.6 million years, said archaeologist Yonatan Sahle of the University of Tübingen in Germany. Sahle has already participated in field work in Ledi-Geraru with the Braun group, but is not part of the new document. It is "simply unjustified" to mark the stone tools discovered in Ledi-Geraru as the oldest specimens of Oldowan without further analysis of the sediments, says Sahle. Even the evolutionary identity and age of Ledi-Geraru's jaw initially attributed to Homo are up for grabs, he says.

The microscopic study of Ledi-Geraru sediments indicates that stone artifacts were deposited at the edge of a lake and quickly covered by the earth that kept the finds in their original position, says Braun .

For the moment, the divergent positions of scientists on the reliability and implications of old evidence in tool making also seem to be maintained or even engraved in stone.