By David Brown
Washington Post Staff Writer
Thursday, May 18, 2006; Page A01
When the ancestors of human beings and the ancestors of chimpanzees parted ways 6.3 million years ago, it was probably a very long goodbye. Some of their descendants may even have gone back for a final tryst.
That is the conclusion a group of scientists has reached, using a comparison of the genes of humans and their closest animal relatives to sketch a picture of human origins far more detailed than what fossil bones have revealed.
According to the new theory, chimps and humans shared a common apelike ancestor much more recently than was thought. Furthermore, when the two emerging species split from each other, it was not a clean break. Some members of the two groups seem to have interbred about 1.2 million years after they first diverged -- before going their separate ways for good.
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