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Source: PA|Published: Tuesday January 23, 9:35 AM
LONDON - Early human evolution was driven by a sudden and dramatic change in the weather, scientists said today.
British researchers have found evidence that the world has become 10 degrees Celsius chillier in the last 3.2 million years.
The cooling off is five times greater than experts had previously believed, enough to bring about changes that have sent human evolution into overdrive, it is claimed.
Cooling was especially rapid about two million years ago, according to the findings reported in the journal Science.
Jeremy Marlow, of Newcastle University, who led the team of British, American and German scientists, said: "People have been looking for a climate event that could explain what is seen in the geological record.
"We postulate that this dramatic cooling could be it. Up to two million years ago the vegetation across southern Africa was fairly rich and typical of a temperate climate where evolutionary pressures were not that great.
"Then you get this sudden cooling. There's less evaporation from the sea, less rain, and you start to see a build up of savannah appearing.
"Resources become limited; food is harder to get and there's less tree cover, increasing the danger from wild animals. The hominids around then would have been under greater pressure to survive, and they would have switched from gathering to hunting."
This would have provided the spur needed to push human evolution forward, said Mr Marlow, a Phd student at the university.
The scientists discovered tell-tale signs of the fall in temperature in the molecular fossils of microscopic marine algae.
Examining the pattern of deposition of algae sediments revealed evidence of a climate change cycle spanning thousands or even millions of years.
It showed that the Earth has been cooling for about five million years. During this time threshold points were reached which saw sudden and pronounced temperature dips. However the cycle could be rapidly reversed by man-made global warming, the researchers said.
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