Asteroids 'affected human evolution'

A threat to our early ancestors?

By BBC News Online science editor Dr David Whitehouse

Impacts by asteroids may have affected the course of human evolution, according to two researchers studying how often the Earth has been struck in the past.

They say that rather than gradual and uninterrupted human evolution, the ascent of mankind could have been influenced by frequent cosmic catastrophes.

It is sobering to realise that we are alive due to cosmic luck rather than our genetic make-up

Dr Benny Peiser, John Moores University, UK

Their work, they say, explains one of the biggest problems that has puzzled researchers for generations: why almost all human-like creatures or hominids, have become extinct during the past five million years.

According to traditional theories of evolution, our early ancestors were slowly and gradually replaced because they failed to compete with other human species that had superior "fitness".

But according to Dr Benny Peiser, a social anthropologist at John Moores University in Liverpool, UK, and Michael Paine, an impact researcher from the Planetary Society in Australia, the most likely cause of hominid extinctions may be more than 20 globally devastating catastrophes that occurred over the last five million years.

There may be more threatening objects in space than once thought

"The reason that Homo sapiens has survived in spite of these global disasters has little to do with the traditional explanations given by Neo-Darwinists," Dr Peiser told BBC News Online.

"It is sobering to realise that we are alive due to cosmic luck rather than our genetic make-up," he added.

"After all, the populations of hominids and early modern humans were extremely small. Had any of these impacts occurred in the proximity of these population groups, we might also have gone the way of the dodo."

Michael Paine of the Planetary Society agrees: "Just over two million years ago an asteroid estimated to be 2 km (1.2 miles) in diameter struck the Southern Ocean, south west of Chile. Had it struck land the environmental consequences might have been much worse.

"If the collision had occurred a few hours earlier, southern Africa might have been wiped out, along with our ancestors."

Simulation

The researchers performed a computer simulation of cosmic impacts over a five million year period to give an indication of the environmental disruption that may have occurred during the evolution of our species.

The simulation looked at the worst event in each of the preceeding 5,000 millennia.

They found that over the period of the simulation some 57% of millennia suffered an impact that would potentially have had consequences for land-dwelling creatures.