Scans tell gripping tale of possible ancient tool use

Members of the human evolutionary family possessed hands capable of making and using tools at least 200,000 years before the earliest evidence of stone implements, scientists say.

Fossil hand bones of Australopithecus africanus previously excavated at South Africa’s Swartkrans Cave, which date to as early as 2.8 million years ago, display an inner structure associated with grips needed for wielding tools, anthropologist Matthew Skinner of the University of Kent in England and his colleagues report in the Jan. 23 Science. A. africanus lived in Africa from roughly 3 million to 2 million years ago.

The oldest known stone artifacts come from a 2.6-million-year-old site in East Africa. Either Homo habilis, known as handy man, or another species called Australopithecus garhi may have created those cutting implements. Due to the relative skill involved in making the 2.6-million-year-old tools, though, anthropologists generally assume that toolmaking originated considerably earlier than that.

“We finally have evidence of what was long suspected, that australopithecines used humanlike hand proportions to handle objects in humanlike ways,” comments anthropologist Brian Richmond of the American Museum of Natural History in New York City.

The problem in proving this suspicion has been finding ways to identify fossil markers of the potential for toolmaking. Skinner’s team used a special scanning device to analyze the 3-D structure and density of spongy trabecular tissue that grows beneath bones’ hard outer layers. Spongy tissue gets molded by pressure produced during manual activities.

To know what wear pattern to look for, researchers compared scans of A. africanus and modern ape hand bones with scans of hand bones from more modern peoples. They included a 90,000-year-old H. sapiens, two roughly 60,000-year-old Neandertals, Romans and Egyptian Nubians who lived between about 1,500 and 2,000 years ago, and 19th century Europeans and South Americans. All humans and Neandertals had hands capable of holding items between the thumb and fingertips and gripping objects such as hammers with the thumb and palm, the researchers say.

The A. africanus fossils display concentrations of spongy bone at the base of the thumb and in the knuckles of the third and fifth fingers, a pattern also observed in hand fossils of ancient H. sapiens and Neandertals, Skinner’s team reports. Stone Age people and Neandertals regularly crafted and used stone implements.

Chimpanzees, gorillas, orangutans and gibbons show a different pattern of spongy bone distribution in their hands, consistent with tree climbing and knuckle-walking, the researchers find.

Along with four fossil hand bones of A. africanus, three hand bones from a 1.9-million- to 1.8-million-year-old Swartkrans hominid also bear an anatomical signature of a humanlike grip, the researchers say. Anthropologists designate those finds either as Australopithecus robustus or an early Homo species. Until now, this species had not been regarded as a tool user.

 “Our findings are exciting because you cannot detect this signal of a humanlike grip from studying the outsides of hand bones,” Skinner says.

A. africanus could have used those grips to gather and manipulate fruit or other foods, Richmond says. But he suspects the ancient hominid used stone tools as well. Two 3.4-million-year-old animal bones found in Ethiopia bear butchery marks made by stone tools (SN: 9/11/10, p. 8).

Further research needs to address whether australopithecines other than A. africanus had humanlike grips, Richmond says. The answer may come soon. Skinner’s team plans to study a complete fossil hand from Australopithecus sediba, a nearly 2-million-year-old South African hominid (SN: 8/10/13, p. 26).