A new, more extensive study of DNA variations between humans and chimps seems to indicate that the speciation between the two (or their respective ancestors) was an on-again, off-again matter.
One of the most detailed comparisons yet of human and chimp DNA shows that the split between the two species was a long, messy affair that may even have featured an unusual evolutionary version of breakup sex.
Previous genetic research has shown that chimpanzees and humans are sister species, having split off from a common ancestor about 7 million years ago. The new study goes farther by looking at approximately 800 times more DNA than earlier efforts. That additional data make it possible to determine not just when, but how the split happened.
[…] The researchers, from the Broad Institute of MIT and Harvard, propose that humans and chimpanzees first split up about 10 million years ago. Then, after evolving in different directions for about 4 million years, they got back together for a brief fling that produced a third, hybrid population with characteristics of both lines. That genetic collaboration then gave rise to two separate branches – one leading to humans and the other to chimps.
The analysis is based on varying degrees of genetic differentiation in separate gene sequences. Some genes indicate a break of around 10 million years ago; others point to a split closer to 6 million years. Thus the hypothesis, which has a few paleontologists raising their academic eyebrows.
The work has inspired both admiration and skepticism. Many paleontologists have a hard time believing that some of the fossil humans that are known to have lived during that era could have been pairing up with apes.
“It’s a totally cool and extremely clever analysis,” said Daniel Lieberman, a professor of biological anthropology at Harvard who wasn’t involved in the study. “My problem is imagining what it would be like to have a bipedal hominid and a chimpanzee viewing each other as appropriate mates – not to put it too crudely.”
It does seem improbable enough (cross-species mating is pretty darned unusual, and viable mating in that fashion even moreso) that I suspect there’s another interpretation of the data that’s waiting discovery, perhaps a rescaling of how the gene differences track over time.
But it’s an interesting news item all the same. Ook-ook!