Men mated with chimps for 1m years (Filed: 18/05/2006) The human family tree has been thrown into disarray by evidence that the ancestors of man and chimpanzees kept on mating with each other for a million years or more. Studies of fossils have suggested that the ancestors of humans had started to walk upright seven million years ago. A study released today by Harvard Medical School and Massachusetts Institute of Technology suggests that men interbred with their ape cousins until at least 6.3 million years ago, making the boundaries between the species fuzzy. The evolutionary split between human and chimpanzee is much more recent - and more complicated - than previously thought, blurring the distiction between different branches of our family tree and also explaining the small difference in ape and human genetic codes today. The study, published in the journal Nature, shows that the speciation process was unusual - possibly involving an initial split followed by interbreeding before a final separation. john I'm saying Now't.