Planet Earth

The hunt for ancient DNA

Gene ExpressionBy Razib KhanAug 9, 2011 3:59 PM

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Ewen Callaway has a good survey of what's been going down in ancient human genomics over the past year in Nature, Ancient DNA reveals secrets of human history. It's not paywalled, so read the whole thing. Most of it won't be too surprising for close readers of this weblog, but this part is new:

By comparing individual DNA letters in multiple modern human genomes with those in the Neanderthal genome, the date of that interbreeding has now been pinned down to 65,000–90,000 years ago. Montgomery Slatkin and Anna-Sapfo Malaspinas, theoretical geneticists from the University of California, Berkeley, presented the finding at the Society for Molecular Biology and Evolution meeting in Kyoto, Japan, held on 26–30 July. Slatkin says that their result agrees with another study presented at the meeting that came from the group of David Reich, a geneticist at Harvard Medical School in Boston, Massachusetts, who was involved in sequencing both the Neanderthal and Denisova genomes. The dates also mesh with archaeological finds bookending early human migrations out of Africa to between about 50,000 and 100,000 years ago. Reich's team is now developing tools to find signs of more recent interbreeding that might have occurred after humans arrived in Asia and Europe.

Remember that the Neandertal admixture seems present in all non-Africans. That pegs the admixture event very early, before the diversification of modern human populations. I wouldn't put too much stock in any one value presented at a conference with a large confidence interval. From what I hear there will be much more on statistical genetic inferences of admixture timing over the next year, but if there's one thing that the enormous yield from genomes constructed from ancient DNA has convinced me is that we should be really cautious of results which we can't cross-check easily because of their time depth. I read a lot of papers by high-powered teams before 2010 on how the genomic evidence implied no admixture between modern human and archaic lineages, and gave them great weight. There's only so much power in working back to the past from the present.

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