Planet Earth

Interbreeding With Other Human Species Helped Our Ancestors Spread Worldwide

80beatsBy Joseph CastroJun 20, 2011 8:24 PM

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Could Neanderthal DNA have protected our ancestors from diseases?

What’s the News: While we humans have certainly outlasted our hominin cousins, new research shows that Neanderthal and Denisovan

genes may have helped us spread far and wide. By mating with the two species, our ancestors acquired genes that allowed them to adapt to diseases outside of Africa far quicker than would have been otherwise possible, according to Peter Parham, a professor of microbiology and immunology at Stanford University. How the Heck:

  • Parham began by taking a close look at a family of genes called human leukocyte antigens (HLAs), which play a central role in our body’s immune responses. We are able to react to a wide array of diseases because our HLA genes are highly variable, each containing dozens of alleles (forms of genes).

  • Our ancestors in Africa, however, would have had a small number of HLA alleles because they likely traveled in small bands and had little contact with other groups. Moreover, their HLAs would have only protected them against African diseases.

  • When Parham compared the HLAs of modern humans with those of Neanderthals and Denisovans, he noticed some overlaps. In particular, he found that HLA-C*0702, an allele common in Europeans and Asians but nonexistent in Africans, was also present in the Neanderthal genome. Similarly, HLA-A*11, which is found in modern Asians but not in Africans, popped up in Denisovan DNA.

  • Overall, about 50 percent of HLA Class I alleles in Europeans seemed to come from Neanderthals, 70 to 80 percent in East Asians from Denisovans, and 90 to 95 percent in Papuans from Denisovans, Parham said at a recent Royal Society meeting.

What’s the Context:

Not So Fast: It is unclear what the research means for the various models of human evolution, and some questions still linger. Does the overlapping of HLA alleles reflect a single massive migration out of Africa, where humans ran into Neanderthals and Denisovans all at once, or is it somehow a product of multiple migrations? And how essential was the interbreeding for our ancestors’ survival? (via New Scientist

)

Image: Wikimedia Commons / Ökologix

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