In his paper “Art, Brains and Shellfish” presented to the Human Genome Conference in March 2003, Professor Parkington examined the phenomenon in which modern humans broke through the traditional barriers of body weight and brain size. The case in most animals is that the larger the body, the smaller – in relative terms – is the size of the brain.

“How did we manage to keep our brains while all those around us were losing theirs” asked Professor Parkington, showing that this leap in brain size correlated with periods of environmental stress. The most convincing explanation, he said, was that tough times forced Homo sapiens towards a marine diet.

He said that Africa had undergone several dry periods during the past 100 000 years which generally coincided with ice ages. This had the effect of making large tracts of the interior uninhabitable and early human populations were forced into coastal pockets. Here they supplemented their traditional hunting lifestyles by gathering seafood.

The limiting factor in developing large brain sizes is the availability of long chain fatty acids which are not common in terrestrial foodstuffs, said Professor Parkington. However, these fatty acids, such as docosahexaeroic acid (DHA) are common in marine animals. DHA is particularly important for unborn babies and those in their first year out of the womb.

“It’s not difficult to imagine pregnant or lactating women walking along the sea shore gathering shell fish to eat which their menfolk were out trying to hunt wildebeest” said Professor Parkington, pointing out that in evolutionary terms the former action was more beneficial than the latter.

There is particularly convincing evidence of the widespread use of marine resources along the south-western Cape, which would have been cut off from the rest of Africa during arid times by the expansion of the Kalahari and Karoo deserts. Hundreds of shell middens have been discovered and in many of these are the remains of artifacts that indicate a shift in human behaviour towards a more culturally aware state of being.

Among the artifacts are the now famous Blombos piece of ochre which is one of the oldest artworks in the world and decorated ostrich egg shells which may have been used as water containers.

Earlier in the session, Professor Jean Jaques Hublin from the University of Bordeaux said that he had found similar middens on the North African coast which were also the probable result of early humans being pushed into coastal pockets during periods of extreme aridity.