Human and chimp genomes reveal new twist on origin of species

The evolutionary split between human and chimpanzee is much more recent -- and more complicated -- than previously thought, according to a new study by scientists at the Broad Institute of MIT and Harvard and at Harvard Medical School published in the May 17 online edition of Nature.

The results show that the two species split no more than 6.3 million years ago and probably less than 5.4 million years ago. Moreover, the speciation process was unusual -- possibly involving an initial split followed by later hybridization before a final separation.

"The study gave unexpected results about how we separated from our closest relatives, the chimpanzees. We found that the population structure that existed around the time of human-chimpanzee speciation was unlike any modern ape population. Something very unusual happened at the time of speciation", said David Reich, the senior author of the Nature paper, and an associate member of the Broad Institute and assistant professor at Harvard Medical School's Department of Genetics.