Scientists used to think that human evolution happened steadily and gradually, over millions of years, but they couldn?t explain why certain early hominids, such as Neanderthals, seemed to mysteriously die out. Now two researchers have decided that these die-outs are due to asteroid impacts and that we are the lucky survivors, who managed somehow not to become extinct.

Dr. Brian Peiser, an anthropologist at John Moores University in Liverpool, and Michael Paine, an impact researcher from the Planetary Society in Australia, say the most likely cause of hominid extinctions may be more than two globally devastating catastrophes that occurred over the last five million years. ?It is sobering to realize that we are alive due to cosmic luck rather than our genetic make-up,? says Dr. Peiser. ?After all, the populations of 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.?

The two researchers created a computer simulation of cosmic impacts over a five million year period in order to determine the degree of environmental disruption that may have occurred during the evolution of our species. The simulation looked at the worst event in each of the preceding 5,000 millennia. They found that over the period of the simulation, 57% of millennia suffered an impact that would potentially have had devastating consequences for land-dwelling creatures.

Michael Paine says, ?Just over two million years ago, an asteroid estimated to be 1.2 miles in diameter struck the Southern Ocean, southwest 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.?

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