Not only did the evolutionary parting of human from chimpanzee ancestors occur more recently than had been indicated by previous data, but it also played out over an extended period during which forerunners of people and chimps interbred.
That controversial possibility arises from a new genetic comparison of people, chimps, gorillas, orangutans, and macaque monkeys.
Various parts of the human genome diverged from those of chimps at times that span at least 4 million years, concludes a team led by geneticist David Reich of Harvard Medical School in Boston. A final genetic split, yielding reproductively separate ancestral species of humans and chimps, transpired between 6.3 million and 5.4 million years ago, the scientists report in the June 29 Nature.
Most scientists had held that hominids and ancient chimps branched off from a common ancestor roughly 7 million years ago, with no interbreeding.
Clues to ancient interbreeding lie on the X chromosome,