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Human and Chimp Ancestors Might Have Interbred

21-05-2006 8:38pm

#1

Capt'n Midnight

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http://www.broad.mit.edu/cgi-bin/news/display_news.cgi?id=1003

Hybridization, that is, the interbreeding of two different species, could also reconcile a second surprising finding. While the DNA that makes up the human autosomes shows the expected age range (the 4 million-year interval noted in the initial phase of the study) the researchers found that the nearly all of the DNA on the X chromosome sits at the youthful extreme of this spectrum. In fact, they predict the X chromosome to be younger on average than the others by some 1.2 million years. Such a stark age difference can signify a particularly unusual evolutionary past, and hybridization, which exposes the sex chromosomes to stronger evolutionary selection than its autosomal counterparts, could be a likely explanation.

From their findings, the scientists propose that ancestral humans initially separated from chimps, but that the two populations continued to interbreed before finally splitting from each other, less than 5.4 million years ago. Future efforts, including the completion of the gorilla genome as well as sequencing of other more distantly related primates, will help scientists at the Broad and elsewhere to further test the timing and proposed mechanisms of human speciation put forth in the Nature paper
...
Paper cited:
Patterson N et al. Genetic evidence for complex speciation of humans and chimpanzees. Nature (advance online publication); doi: 10.1038/nature04789

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