Dr Groves said that even today it could be possible for humans and chimps to have sex and produce offspring, although there would be ethical problems.
The very roots of the human family tree have been redrawn thanks to a groundbreaking study that has compared the genetic codes of humans and chimpanzees.
The US research, published in Nature, shows that the evolutionary split between humans and chimpanzees was not clean and sudden 7 million years ago, as previously suspected.
The split happened 6.3 million years ago at the earliest, say the scientists. But more importantly, the genetic analysis shows that chimpanzees and the earliest hominids continued to have sex with each other and swap genes for another 1.2 million years before the final break.
This finding sheds new light on the earliest hominid fossils, all of which have been found in Africa over the past 15 years. The fossils have puzzled scientists with their inconsistent and unusual blend of human and chimpanzee characteristics.
The scientists, working at Harvard University and the Massachusetts Institute of Technology, completed an exhaustive analysis of human, chimpanzee and gorilla genomes to find out the evolutionary history of each.
“The genome analysis revealed big surprises, with major implications for human evolution,” said the paper’s co-author, Harvard biologist Eric Lander. “First, human-chimp speciation occurred more recently than previous estimates. Second, the speciation itself occurred in a more unusual manner that left a striking impact across (the female chromosome) chromosome X.”
The paper says “the two species split no more than 6.3 million years ago and probably less than 5.4 million years ago”.