A comparison of 14,000 human and chimpanzee genes by researchers at the  University of Michigan, U.S, shows that the forces of natural selection have had the greatest impact on our ape cousins. Humans and chimps followed different evolutionary paths from a common ape ancestor about 5 million years ago. Both underwent changes as the fittest survived to pass their genes on to future generations.

But the U.S study shows that the humans possess a "substantially smaller" number of positively-selected genes than chimps. This may be because the original human population was very small-which would have reduced the effectiveness of natural selection. Instead,"genetic drift" -the random survival of genetic mutations rather than their preservation by the laws of natural selection -was likely to have been more important for humans.

"These observations refute the anthropocentric view that a grand enhancement in Darwinian selection underlies human origins." scientists wrote in the Journal Proceedings of the National Academy of Sciences.

Source: Daily Mail, London