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Denisovans, Neandertals, Immunity, Anthropology, Sex


25 August 2011: The day Denisovans hit the big time. They still needed to piggyback on the Neandertals, but got a big boost from the immune system study. And sex.

Small selection of some wonderful headlines:

All this from the report version in Science of a drab-titled “The Shaping of Modern Human Immune Systems by Multiregional Admixture with Archaic Humans” by Laurent Abi-Rached and many colleagues.

My previous posts and content (see boxes above) have been some of the most referenced on Living Anthropologically. For a long time these posts held a top-10 place in search results for “Denisovans” just from a short discussion. It is interesting that Denisovans now hit the mainstream with the article on immunity. Some comments on how this is breaking:

First, John Hawks’s analysis of the paper is a must-read: “HLA class-I loci in Neandertals and Denisova.” Hawks has been working on this stuff for a long time, without the sensationalistic headlines. He adds important notes of caution and qualification. For another post that explicitly consider Hawks’s points, see “Did sex with Neanderthals and Denisovans shape our immune systems? The jury’s still out.”

Second, as Rosemary Joyce explores in “A Neanderthal Tragedy of Shakespearean Dimensions” and “Neanderthal/sapiens: a stormy love affair?” there is just a lot of strange romance, love, and sex going on in these accounts–and that was before the August 25 headlines!

Update 30 August 2011: Rosemary Joyce has just tackled this specific study and the press implications in “Irresistible Neanderthals: Sex in Human Ancestry.” Joyce notes it is not just media reports sensationalizing the sex–it was in the first sentence of the Stanford University press release.

Third, it is striking that one of the more complete accounts of Denisovans, “Who Were the Denisovans?” by Ann Gibbons is now behind a paywall at Science. At the end of the article, John Hawks gets quoted (indirectly) as thinking that “even small amounts of interbreeding confirm the regional continuity model, and that there was more mixing in the past, but its traces were erased by later waves of immigrants who swamped out the archaic genes.” Somewhat ironically, Hawks has also recently been urging action on scientific journals, to “Make journals work better.”

Finally, I remain worried about racist interpretations of admixture data. Fortunately the main headlines seem about advantages conferred to modern humans as a whole or “us.” But lurking in the text is almost always the idea that these genes are “absent in Africans” or “never in Africans” or the constant talk of “non-Africans.” Racist websites and commenters have picked this up, claiming Neandertal admixture led to an IQ advantage for Europeans but Denisovan admixture led to IQ disadvantage for people in the Papua New Guinea region. I’ve even seen comments relating Neandertal admixture to the UK riots–I wish I were making this up.

One mainstream headline that opens this door: “The downside of sex with Neanderthals” which takes up some points unmentioned in other news reports:

The scientists think there was a downside. Inheriting Denisovan or Neanderthal immunity genes will have helped modern humans to fight the diseases of the day, but beyond the age of reproductive maturity they might have a more harmful effect, turning our immune systems on ourselves.

Another blog headline makes this even more explicit: “Neanderthal Sex Gave Europeans and Asians Stronger Immune Systems.” However, this blog also has one of the more interesting paragraphs about African immune system:

Africans, who never personally interbred with the Denisovans and Neanderthals did receive a bit of these genes second hand, from migrants who returned to the region around 10,000 years ago. And they are thought to have an even stronger and more diverse immune system, as they bred with other species of archaic hominids, which were native to Africa.

At least this mentions return migration, but I’m not sure about those archaic African hominids–the link seems to be to the Australopithecus afarensis which at 3.6mya would put it out of the range of the kind of admixture under discussion with Neandertals and Denisovans. This post also has some pretty ugly stuff in the comment thread.

Update 7 September 2011: This study from PNAS is a better reference for possible “Genetic evidence for archaic admixture in Africa” with lead author Michael Hammer from the University of Arizona. This article seems to be getting described as “Ancient humans were just having sex with everyone,” which leads back to the Rosemary Joyce comments above.

Yet another article, this time very silly, tries to combine this news with Warren Buffett and Steve Jobs: “Steve Jobs, Warren Buffett and a ‘Neanderthal edge.’” Once again, I sometimes wish I were just imagining things or making this stuff up.

It’s too early to tell how this reporting will emerge–will it be more of upsides and downsides? For whom? But it is worth anthropological vigilance. As I discuss in related material (see boxes below), we need to

  1. Recapture the multiregional trellis of Franz Weidenreich.
  2. Insist that “never in Africa” means “relatively rare in Africa” and does not apply across the continent or to persons of African descent in other areas.
  3. Show how it is contemporary inequality and social conditions that shape social outcomes, not ancient genetic flows.