August 25, 2011

Adaptive archaic admixture in HLA human immune system gene

Link to supplement (pdf). I haven't read the paper yet, but this bit from a story on it seems to gel well with my Palaeoafrican admixture theory:
While Europe and Asia might now be viewed as a hotbed of interbreeding, modern humans who stayed in Africa appear to have been active interbreeders as well. Neanderthals and Denisovans weren't present, but other archaic human groups likely were.

"Well established is that modern Africans have greater genetic diversity, overall, than the modern populations of other continents," Parham said. "This greater diversity is likely due to what was inherited from earlier forms of Homo, combined with interbreeding between different forms of Homo."

The early ancestors of all modern people, then, did not seem to shy away from breeding with different human species, actions that strengthened our immune systems and likely resulted in other benefits yet to be revealed.
It seems that multiregional evolution isn't dead, after all, as I suggested recently, and the explicit use of the word "multiregional" in the paper's title is probably indicative of the shifting atmosphere.

UPDATE: John Hawks post on the subject.

Science DOI: 10.1126/science.1209202

The Shaping of Modern Human Immune Systems by Multiregional Admixture with Archaic Humans

Laurent Abi-Rached et al.


Whole-genome comparisons identified introgression from archaic to modern humans. Our analysis of highly polymorphic HLA class I, vital immune system components subject to strong balancing selection, shows how modern humans acquired the HLA-B*73 allele in west Asia through admixture with archaic humans called Denisovans, a likely sister group to the Neandertals. Virtual genotyping of Denisovan and Neandertal genomes identified archaic HLA haplotypes carrying functionally distinctive alleles that have introgressed into modern Eurasian and Oceanian populations. These alleles, of which several encode unique or strong ligands for natural killer cell receptors, now represent more than half the HLA alleles of modern Eurasians and also appear to have been later introduced into Africans. Thus, adaptive introgression of archaic alleles has significantly shaped modern human immune systems.


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