How Lucy's meat-eating made us what we are now

The point in prehistory when our early ancestors first picked up a sharp-edged stone to butcher animals has been pushed much further back in time with the discovery of ancient bones.

Scientists working at an archaeological site in Ethiopia have discovered two animal bones with the distinctive cut marks of stone tools that the researchers believe were used to scrape or slice chunks of meat from carcasses some 3.4 million years ago.

The bones, which also show evidence of being broken open to extract highly nutritious marrow, are evidence that our ancestors were organised carnivores a million years earlier than previously understood.

The butchery of animals in such a deliberate manner with stone tools has never been observed in such ancient fossils. Until now, the oldest evidence of butchery comes from the discovery of similar cut marks on animal bones about 2.5 million years old, which is nearly as old as the oldest stone tools, dated to about 2.4 million years ago.

The scientists who made the discovery, led by Zeresenay Alemseged of the California Academy of Sciences, believe that the find shows that the ancestors of humans developed a taste for meat eating and butchery that long predated the point at which it was thought that man shifted to a largely carnivorous diet in order to feed the high-energy demands of a bigger brain.

Dr Alemseged and his colleagues believe that the butchery at the site of Dikika in the Afar region of Ethiopia was probably carried out by the only known hominin to be living in the area at the time, a small-brained, bipedal creature called Australopithecus afarensis, of which the most famous member is "Lucy", a female whose remains were discovered in 1974.

"This discovery dramatically shifts the known timeframe of a game-changing behaviour for our ancestors. Tool use fundamentally altered the way our early ancestors interacted with nature, allowing them to eat new types of food and exploit new territories," Dr Alemseged said.

"This find will definitely force us to revise our textbooks on human evolution since it pushes the evidence for tool use and meat-eating in our family back by nearly a million years. These developments had a huge impact on the story of humanity," he said.

The butchered bones – a fragment of rib and a shaft of a femur, or thigh bone – belong to two ungulate mammals, possibly goat or bison, which the scientists suspect had died of other causes and were then scavenged by a band of hominins. The bones were found between two volcanic layers in the ground, respectively dated at 3.42 and 3.24 million years old, but were lying closer to the older volcanic layer, suggesting they were nearer to 3.4 million years old.

In addition to the distinctive cut marks, the scientists found evidence that the bones had been pounded to extract the marrow. They also found a microscopic piece of stone embedded in one of the cut marks, which is possibly a remnant of the stone tool itself. A detailed analysis ruled out other possible causes of the marks, such as the teeth of a carnivore.

Shannon McPherron of the Max Planck Institute for Evolutionary Anthropology in Leipzig said that the source of the stone tools, which were made from volcanic rock, was likely to be several kilometres away. "The hominins at this site probably carried their stone tools with them from better raw material sources elsewhere," Dr McPherron said.

The site of the discovery is just 200 metres from the place where in 2006 Dr Alemseged and colleagues found the fossilised skeleton of an infant A. afarensis girl, known as "Lucy's baby". "The only hominin species we have in this part of Africa at this time period is A. afarensis, and so we think this species inflicted these cut marks on the bones we discovered," Dr Alemseged said.

The study is published in the journal Nature.