Origins of mankind reviewed

Hunting for meat and the use of stone tools by our ancestors seems to have started much earlier than was thought – as far back as 3.4 million years ago, writes DICK AHLSTROM

OUR EARLY ancestors may have looked decidedly ape-like, but they were already beginning to act like humans as much as 3.4 million years ago. New fossil discoveries in Africa show they were using stone tools and began eating large game much earlier than scientists had realised.

An international team, working in the Afar region of Ethiopia, found fossilised bones showing clear evidence of stone tool use. Sharp-edged stones were used to slice meat and sinew off the bone and large rocks were used to smash open bones so the marrow could be freed.

Palaeoanthropologists have long believed that stone tool use only arose when our own genus, Homo, began to appear. The oldest fossil bone finds that carry evidence of tool use date to between 2.6 and 2.5 million years ago and were linked to an early ancestor, Homo habilisor "Handy Man".

But this latest discovery pushes stone tool use back another 800,000 years to about 3.4 million years ago.

“Tool use fundamentally altered the way our early ancestors interacted with nature, allowing them to eat new types of food and exploit new territories,” said research team leader Dr Zeresenay Alemseged from the California Academy of Sciences.

This find reaches back before the evolution of Homo to an even earlier “hominin” or member of the human lineage.

The animal bones were most likely scavenged by an Australophithecus afarensis, a hominin species that includes the famous fossil Lucy (see photograph) and a juvenile A afarensisfound in 2000 called Selam and dubbed "Lucy's Daughter".

Scientists view this as a particularly important find given the implications of what was found in this dig, which was part of Alemseged's "Dikika Research Project" in Ethiopia's Lower Awash Valley. Details of the discoveries are revealed this morning in the journal Nature, which uses it as the cover story.

The all-important bones came from different animals, a rib from a hoofed animal about the size of a cow and the other an upper leg bone from a goat-sized animal.

The team quickly proved that the bone damage was caused by a sharp-edged stone tool. It left behind obvious grooves but also evidence of thin bone layers sliced away with the flesh as the hominins butchered the animals. A tiny stone fragment left behind in one cut offered more evidence of intentional stone tool use.

While the researchers, including lead author Dr Shannon McPherron of the Max Planck Institute for Evolutionary Anthropology, could not say whether the hominins made the tools or collected them, they were certain about who used the tools.

A afarensiswas the only hominin in the region during the period when these animal bones were still fresh about 3.4 million years ago. So Lucy and her peers were the only creatures present and able to have made these cuts. And the animal bones were found close to where Selam's nearcomplete skeleton was located.

The find’s importance is emphasised in an accompanying commentary by Dr David Braun of the University of Cape Town. It pushes back hominin tool use by almost one million years and attributes it to a creature that was considered human-like only because it walked on two legs. Tool use implies activity of a much more human kind.

Equally important is the fact that the sharp stones and hammering stones used by the A afarensisto harvest scraps of meat were not found nearby and had to have been brought to where animals were butchered.

McPherron and colleagues showed that the nearest place where such stones could be found was at least six kilometres away. The meat and marrow “must have been a valued resource” to these hominins, says Braun, particularly because the hominins faced extra dangers.

The assumption is that the butchered animals were carrion left behind by large carnivores, and this would have put the hominins in direct competition with dangerous predators. Then there was the risk of exposure to parasites and bacteria that would multiply quickly on the abandoned carrion.

Yet it opened up a highly nutritious food source and may have paved the way to more sophisticated stone tool production, says Braun. It could have given this early human ancestor survival advantages that carried through to later generations as the behaviour was passed on.