Posted by: Patrick Allen Foster | October 24, 2014

Genome from 45,000-Year-Old Leg Bone Tells us Some Things About our Neanderthal Inheritance

NPR: “Researchers have successfully decoded the genes of a 45,000-year-old man from Siberia. The results offer clues about early human life outside of Africa as well as how humans interacted with Neanderthals and other groups around at the time.”

Ars Technica (emphasis added):

Based on Y chromosome and mitochondrial genome, the Ust’-Ishim DNA appears to reside at the base of a broad group of populations that exist in current Eurasia. The rest of the genome indicates that it lacks many of the individual DNA changes that have appeared in current populations. All of which suggests that the population it belongs to is ancestral to Europeans and Asians.

But if you look at overall relatedness, the genome is slightly closer to current Asian populations than it is to Europeans. The authors note that other data has led researchers to hypothesize that Europeans have had an influx of DNA from a population that did not participate in the initial migration out of Africa—perhaps a second wave out of Africa.

Another source of DNA present in non-African populations that was not involved in that initial migration comes from archaic humans, the Neanderthals and Denisovans. The Ust’-Ishim skeleton has no indications of any Denisovan DNA, which furthers indications that this DNA might have been picked up somewhere along the southern coast of Asia.

Neanderthal DNA is present, and in roughly the same percentage that’s found in current human populations: about 2.3 percent. If you assume that interbreeding was common during the years of our coexistence with Neanderthals, then you might have expected that number to be higher, so this argues against it.

While the same fraction of Neanderthal DNA is present, there is a key difference: the stretches of Neanderthal DNA are quite a bit longer. You’d actually expect that, since recombination with the modern human genome will gradually break up the Neanderthal sequences over time. The authors of the paper use this process as a clock and date the time of our interbreeding with Neanderthals to about 50 to 60,000 years ago. That’s on the high end of previous estimates and places the interbreeding at a time where modern humans had just left Africa and were sharing the Mid-East with Neanderthals.

See also this New York Times story.

(For my previous blogging on this topic, see here.)

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Responses

  1. Reblogged this on Conversations I Wish I Had.

  2. Looks like Neandertals were popular only while the dating pool was limited.


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