How Ice Ages increased our brainpower

Extreme climate change has been linked to humanity's giant mental leap forward

Robin McKie

Sunday April 14, 2002

Scientists believe climate catastrophes that triggered droughts and forest fires in mankind's African homeland two million years ago were responsible for the evolution of our large brains.

Faced with massive, rapid changes to their woodland homes, early humans had rapidly to learn to live in a changing landscape. Only those with the most flexible, adaptive minds survived.

'Climate change is the engine of evolutionary change, and it drove the development of our brains,' said US brain expert William Calvin, of the University of Washington School of Medicine.

Scientists have long known that mankind began using stone tools 2.5 million years ago and that around this time the world entered a period of considerable climatic instability. Ice ages brought major weather changes to all parts of the globe.

However, researchers had thought that these changes took decades or even centuries to take effect. 'It has only recently become apparent that climate change would have struck very quickly, producing major changes in one or two years,' said Calvin, who outlines his theory in Brain for All Seasons (Chicago University Press), which is published this week.

Although Africa - home of our Homo erectus ancestors - would have been protected against the worst effects of global cooling, it would have suffered severe droughts. Vast tracts of forest would have dried to tinder within a couple of years to be destroyed by fires sweeping the woodlands. Over succeeding decades, the environment would have recovered, only for the process to be repeated a century or two later.

With the destruction of our ancestors' woodland homes, most of their food sources would have been swept away, leaving them with little to eat except grass and large animals, such as antelopes. They would have had little alternative than to hunt these creatures, in the process creating a problem: each big kill would have produced far too much meat for each group of hunters, so they started sharing with others, in the expectation of being given food when someone else succeeded.

Thus the idea of sharing and trust, the linchpins of human society, would have been born as our ancestors tried to survive. 'In effect, we are the children of the Phoenix generation,' said Calvin.

Slowly our brains grew, partly to cope with the pressures of dealing with societies and cultures that were becoming more and more complex, but also to develop the means to adapt to the different ecological niches that were being created at the time, an idea that is also backed by Richard Potts of the Smithsonian Institute in Washington.

'About 2.5 million years ago, hominids encountered great fluctuations in the climate,' he said. 'At the same time, we see the appearance of stone tools. That is no coincidence. They indicate that that at least one species of hominid was responding to these changes by becoming even more adaptable.'

The end result was Homo sapiens, a creature marked by its ability to make tools and instruments - harpoons, guns, spears, and fishing nets - that allow us to exploit all sorts of varying ecological niches, and which give us unprecedented flexibility as a species.

'Essentially, we now carry our environments around with us, in the form of tools and clothes,' said Professor Chris Stringer of the Natural History Museum, in London. 'We had to learn to do that because the environment we evolved in was unpredictable and changeable. Climate made us what we are today.'

Whether humanity can continue to evolve in, or even survive further climatic mayhem, is a different matter, as Calvin acknowledges.

'Were a cold flip to happen in our now crowded world, dependent on agricultural productivity and efficient supply lines, much of civilisation would be ruined in a series of wars over the shrinking food supply,' he said.

· Additional research by Hannah Richards.

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