An earlier article quoting the original opinion on which the current round of news was at http://www.cnn.com/2006/TECH/science/05/17/human.chimp.split.ap/index.html: DNA study: Human-chimp split was messy, but appears to be no longer available. It may be archived at cnn, but they require a registration for "deep searches."

[extracted quotes]

Wednesday, May 17, 2006; Posted: 1:03 p.m. EDT (17:03 GMT)

NEW YORK (AP) -- Humans and chimps diverged from a single ancestral population through a complex process that took 4 million years, according to a new study comparing DNA from the two species.

By analyzing about 800 times more DNA than previous studies of the human-chimp split, researchers from the Broad Institute of MIT and Harvard were able to learn not just when, but a little bit about how the sister species arose.

"For the first time we're able to see the details written out in the DNA," said Eric Lander, founding director of the Broad Institute. "What they tell us at the least is that the human-chimp speciation was very unusual."

The researchers hypothesize that an ancestral ape species split into two isolated populations about 10 million years ago, then got back together after a few thousand millennia. At that time the two groups, though somewhat genetically different, would have mated to form a third, hybrid population. That population could have interbred with one or both of its parent populations. Then, at some point after 6.3 million years ago, two distinct lines arose.

... ... ...

Past studies that compared human and chimp DNA could only offer a point estimate of how long ago the two species split by averaging the amount of divergence in their genes. Generally, those studies come up with a figure of about 7 million years ago.

But since the completion of the chimpanzee genome project in September it is possible to look at how specific sections of the genetic code have evolved. The Broad Institute study, which will be published in a future issue of the journal Nature, is one of the first to do that.

... ... ...

The data also show that the human-chimp split probably took millions of years. That's because in some parts of the DNA sequence the genetic difference between humans and chimps is so large that those genes must have been isolated from each other nearly 10 million years ago. But in other places the human and chimp lines are so close that they appear to have still been swapping genetic material at least until 6.3 million years ago.

One of those areas is the X-chromosome, which is intriguing.

"The genes that are a barrier to speciation tend to be on the X-chromosome," said David Reich, the main author of the study.

[end quotes]

Does anyone have a subscription to Nature to let us know when the report is published?

John