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May 18, 2006
Our Life Together - With Our Primate Ancestors
Carl Zimmer and John Hawks and others report on an interesting article that appeared in Nature's advanced on line publication on the possibility of hybridization between the common ancestors of chimpanzees and our human ancestors over a very long period of time. The paper is by Nick Patterson and team.
Here is the short version of Zimmer's synopsis of the article.
. . . The Broad Institute scientists lined up millions of bases of DNA in humans and chimps and measured their differences. Humans and chimpanzees both inherited each segment of DNA from a common ancestor. Over time, the copies of that ancestral segment picked up mutations. The differences between them can offer clues to how long they've been evolving along separate paths. It turns out that the ancestors for some of those segments are much older than others. The only way to make sense of these results, according to the scientists, is to conclude that hominids and the ancestors of chimpanzees were interbreeding--to some extent at least--for four million years.
Or as the abstract says,
The genetic divergence time between two species varies substantially across the genome, conveying important information about the timing and process of speciation. Here we develop a framework for studying this variation and apply it to about 20 million base pairs of aligned sequence from humans, chimpanzees, gorillas and more distantly related primates. Human–chimpanzee genetic divergence varies from less than 84% to more than 147% of the average, a range of more than 4 million years. Our analysis also shows that human–chimpanzee speciation occurred less than 6.3 million years ago and probably more recently, conflicting with some interpretations of ancient fossils. Most strikingly, chromosome X shows an extremely young genetic divergence time, close to the genome minimum along nearly its entire length. These unexpected features would be explained if the human and chimpanzee lineages initially diverged, then later exchanged genes before separating permanently.
Zimmer, one of the best science writers around, raises a few important questions about the article but is generally favorably impressed; Hawks, a practicing paleoanthropologist, is very critical. Both their posts make for abnormally interesting reads as do the comments from Gene Expression and Evolgen (twice). While I've read the article, I think it best to leave the commentary to the professions until a scientific consensus is reached. This will likely be a controversial subject for some time.
Via Pharyngula: I hope PZ has more to say on this later and it would be good to hear from afarensis on this also.
Posted by Duane Smith at May 18, 2006 9:15 AM | Read more on Paleoanthropology |
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