Published in The Hindu on August 12, 2010

So when did hominins (members of human lineage) start using stone tools for the first time? Until recently, based on available evidence, it was presumed that the use of stone tools by hominins dates back to about 2.5 million years ago.

But a paper published online today (Aug 12) in Nature has pushed the date back by about 8,00,000 years to make it nearly 3.4 million years ago. “Our discovery extends by approximately 800,000 years the antiquity of stone tools,” note the authors.

The actual stone tools used by hominins 3.4 million years ago have not been found. The inference is therefore drawn based on tool marks found on bones.

Earlier record

The discovery was made from bones found in sedimentary deposits near Gona, Ethiopia. Earlier record of stone tools usage, some 2.6 million years ago, came from several localities in Ethiopia and Kenya.

The sand deposits where the bones were found were not strongly cemented, and this had enabled the tools marks to be well preserved. Scientific evidence clearly indicates the tool marks were formed prior to fossilisation of bones.

Three types of stones

Three different types of tool marks — cutting, scraping, and percussion are found on the bones. Interestingly, the marks are found on the bones of large mammals — a femur shaft fragment of a goat-sized mammal, and a right rib fragment of a cow-sized animal.

The researchers have, based on the morphology of the marks, ruled out the possibility of tooth-inflicted cuts. In fact, the marks indicate two different shaped stones used by hominins.

For instance, the cut marks indicate that sharp-edged stones were used for cutting and scraping the animal flesh, and blunt stones (producing the percussion marks) for crushing the bones to probably gain access to bone marrow.

What does the discovery mean for human evolution? Hominins, unlike what was believed till now, had started using stone tools nearly one million years earlier, and had become carnivorous and competed with other such animals for food.

“The bones presented here are the earliest evidence for meat and [bone] marrow consumption in the hominin lineage, pre-dating the known evidence by over 800,000 years,” note the authors.

Lucy used stone tools?

The age of the bones with tool marks coincides with the age when Australopithecus afarensis roamed east Africa. In all probability, Lucy and Selam, the most complete skeletons of A. afarensis discovered so far, would have walked around with such stone tools to eat animal flesh.

There is already sufficient scientific evidence to show that A. afarensis was not a relatively primitive hominin.

In fact, this species had body proportions similar to those of humans and apes, its fingers were relatively short, which would have “allow[ed] the kind of fine-scale manipulations necessary for tool-use,” notes a piece published in the News and Views section of Nature.

Earlier conclusion

The latest discovery of bones with stone tool marks reaffirms the earlier conclusion based on the study of another A. afarensis fossil — this hominin species surely did not eat a low-quality diet.

“Until now, there has been no direct evidence that meat and marrow formed a part of the diet of hominins at this early age. …It is notable that these early humans departed from the typical primate pattern of disregarding relatively large animals as food,” notes the News and Views piece.

Unknown fact

But what is not known is whether this hominin species made sharp-edged stone tools by chipping the rocks or just used some naturally occurring ones. But one thing is clear — the hominins did not find such sharp-edged stones at the site where the bones were found.

The sedimentary environment from where the tool-marked bones were recovered had pebbles that are too small to create sharp-edged stones. The authors thus envisage that the A. afarensis species carried these stone tools with them.