The Unz Review - Mobile
A Collection of Interesting, Important, and Controversial Perspectives Largely Excluded from the American Mainstream Media
Email This Page to Someone

 Remember My Information



=>
Authors Filter?
Razib Khan
Nothing found
 TeasersGene Expression Blog
/
Neandertal admixture

Bookmark Toggle AllToCAdd to LibraryRemove from Library • BShow CommentNext New CommentNext New Reply
🔊 Listen RSS

Ed Yong has a good good review of a new Neandertal introgression/admixture paper in PNAS. It’s not live on the web yet, so let me quote Ed:

Even if the odds of successful interbreeding were just 5 percent, Neanderthal genes would make up the majority of the human genome today. As it is, a lack of viable sex explains why none of the Neanderthals’ mitochondrial DNA made its way into modern humans, and why so little of their main genome did.

Currat and Excoffier suggest that either modern humans and Neanderthals didn’t have sex very often, or their hybrids weren’t very fit. They favour the first idea. According to their model, it would only have taken between 197 and 430 liaisons between ancient humans and Neanderthals to fill 1-3 percent of modern Eurasian genomes with Neanderthal DNA. Considering that they two groups probably interacted for 10,000 years or so, it would have been enough for one human to sleep with one Neanderthal every 23 to 50 years.

From what I gather in the comments this is due to the fact that if there was a wave of advance very small levels of admixture per unit of advance can build up rather rapidly. I think this is easy to express in temporal rather than spatial terms.

For example, let’s imagine a population of modern humans expanding into a population of Neandertals. The original source population doesn’t receive any more contributions after the initial push, so you have a series of admixture events over time. Assuming 5% admixture per generation, this is the dilution of the “original ancestry” which would occur over 30 generations, or 750 years:


The model outlined in Ed Yong’s post needs to be examined with care though. No doubt there are all sorts of assumptions which can be disputed. Though I think I accept the final result as entirely plausible.

(Republished from Discover/GNXP by permission of author or representative)
 
🔊 Listen RSS

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.

(Republished from Discover/GNXP by permission of author or representative)
 
No Items Found
Razib Khan
About Razib Khan

"I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. If you want to know more, see the links at http://www.razib.com"