Researchers comparing the genomes, or genetic codes, of the two species found that the split took place no more than 6.3 million years ago and probably less than 5.4 million years ago.

It also found that the process of separation may have taken about four million years and that there could have been some inter-breeding before the final break.

David Reich of the Broad Institute and Harvard medical school department of genetics in the US, where the study was conducted, said: "The study gave unexpected results about how we separated from our closest relatives, the chimpanzees."

 

A final fling?

 

Previous genetic research has shown that chimpanzees and humans are sister species and split from a common ancestor about seven million years ago.

 

"My problem is imagining what it would be like to have a bipedal hominid and a chimpanzee viewing each other as appropriate mates"

Daniel Lieberman, biological anthropology professor at Harvard

However, the new study looked at 800 times more DNA than earlier efforts, and the extra data was able to show a more specific timeline.

 

The researchers say now that humans and chimpanzees first split up about 6.3 million years ago, more recently than previously thought.

 

Then, after evolving in different directions for about four million years, they got back together for a short time and produced a third, "hybrid" population which shared characteristics with both lines.

 

This hybrid probably then, in turn, created two separate branches, one leading to humans and the other to chimpanzees.

 

However, some scientists are not convinced that after splitting up for so long, humans and chimpanzees got back together for a "final fling".

 

Daniel Lieberman, a professor of biological anthropology at Harvard who was not involved in the study, said: "My problem is imagining what it would be like to have a bipedal hominid and a chimpanzee viewing each other as appropriate mates - not to put it too crudely."