The thinking hominid

We are a species capable of remarkable technological and cultural achievements thanks to our big brains and our extended cooperative social networks. Of course, it has not always been this way. Our first upright, ape-like ancestors lived between 7 and 6 million years ago, and perhaps a half dozen human-like species with increasing cognitive abilities span the evolutionary period to the present-day Homo sapiens.

Palaeoanthropologists like Dr Michael Petraglia in the Department of Biological Anthropology are interested in documenting and explaining our evolutionary history, and particularly in examining the cognitive and behavioural changes that have occurred along the way. One fundamental question has always been: how did advanced levels of human cognition evolve in our early ancestors? In searching for clues, Dr Petraglia is using the artefactual record left behind by early hominids.

Acheulean tools

One particular period, known as the Acheulean, has fascinated palaeoanthropologists and archaeologists alike because it is the longest enduring time of technology and manufacture, and therefore of comparatively rich artefactual record, in our evolutionary history. Beginning in Africa at about 1.6 million years ago, and lasting until about 250,000 years ago, the Acheulean is characterised by the manufacture of pear- and oval-shaped stone handaxes and cleavers. Often found in association with animal carcasses, these tools were probably used as efficient cutting devices for detaching and slicing meat for food.

During the prolonged period of this dominant technology, Acheulean tool users migrated from Africa and colonised Eurasia. Examples of tools have been found from Arabia to Asia, and in Europe from the Mediterranean to central Britain.

Discovering debris

The long-lasting and supposedly unchanging technological tradition of the Acheulean has been thought of as demonstrating a period of biological and cultural stasis. But did it also denote a mentally and behaviourally conservative Acheulean mind? Since the mid-1990s, Dr Petraglia has been looking at new ways of evaluating the evolution of cognition in Acheulean hominids by closely analysing the evidence of their manufacturing and landscape practices used to create these tools.

An opportunity to do this presented itself when he and Professor K Paddayya of Deccan College (Pune, India) discovered a well-preserved Acheulean site in the semi-arid Hunsgi Valley of southern India. The Isampur Quarry was uncovered when the local Irrigation Department cleared much of the metre-deep thick black silt; extensive excavations since that time have exposed an extremely well-preserved Acheulean quarry, the first to be discovered on the Indian subcontinent.

Crucially, the site was found to be littered not just with tools but with tool-making debris: here was a rare chance to examine tool-making procedures and landscape behaviours of a million years ago.

The quarriers’ tale

Our ancestors came to the quarry to prise up the limestone bedrock to make their handaxes and cleavers. Research is showing that the tools they made were not the end result of chance and serendipity but were the outcome of intention, thought, planning and memory.

The quarriers understood the mechanical properties of their materials and they approached the natural rock slabs with specific goals in mind: handaxes were crafted from tabular slabs; cleavers from flakes struck from large boulder-sized slabs. As they worked, the remnants of their endeavours littered the occupation area, some 60 square metres in excavations, as chipped stone cores, flakes and chunks. They planned and anticipated events – making cleavers from large flakes needed complex procedures to achieve the desired result; hammerstones of different sizes and raw materials had to be brought into the quarry from sources more than a kilometre away. All of this suggests the hominids were capable of deliberate calculation, adjusting techniques to circumstances, remembering activities and solving problems. Intriguingly, what it also suggests is that socially learned and transmitted behaviours were passed from individual to individual: in short, some form of communication was occurring.

Interestingly, though, these hominids practised behaviours that are unfamiliar – once tools were used, they were quickly abandoned. Stone tools found at sites away from the quarry showed limited evidence of resharpening. It seems that early humans made tools, carried them across the landscape for an intended goal, and then discarded them. This discard behaviour has few analogies among modern foragers, who typically retain and repair their toolkits over the long-term.

Thinking hominids

Acheulean hominids lived in a range of ecological settings with an assortment of different resources available to them – limestone, flint, quartzite, and so on. A comparison of Indian tool-making procedures and landscape behaviours with other sites around the globe shows that groups adapted to novel circumstances in different ways and yet still employed the same technology. Such evidence implies a learned behaviour revolving around a set of conventions or rules in tool-making. Some of the abilities that we see in the artefactual record are also found in the tool-making and tool-using capabilities of some primates and certain bird species. However, there are also relative differences in tool-using behaviours, suggesting that early hominids had an extended ability for planning beyond the immediate future, relying on abstraction and memory for satisfying future needs over space and time. While this may be the case, the hominids were not as innovative as we might expect, producing similar tool forms over hundreds of thousands of years, perhaps lacking the planning depth to anticipate conditions in the far-off future.

Comparative research should allow us to interpret how the mind evolved in hominids and how their behaviour diverged from other intelligent animals. Further detailed archaeological and palaeoanthropological studies of the Acheulean record will continue to shed light on cognition in these early hominids, whose brains were three-quarters the size of our own.

For more information, please contact the author Dr Michael Petraglia(mp341@cam.ac.uk) at the Leverhulme Centre for Human Evolutionary Studies (www.human-evol.cam.ac.uk).