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Irresistible Neanderthals: Sex in Human Ancestry

Why are we fascinated by Neanderthal sex?

Canoodling. Nookie. Hanky panky. Dalliances. Hookups.

Yes, it's Neanderthal sex, again.

Caveman's Sexy Bonus, the UK's Daily Express headlined their version of the story, summarizing the key points with a totally anachronistic set of images:

Cavemen made us healthier by having sex with primitive Neanderthals...One night stands between them and our ancestors boosted the human genome.

There is something that the press cannot resist about the idea of sex between early modern humans and the human populations that preceded them in Europe and Central Asia.

Even the less lurid news reports seem more focused on imagined sexual acts than on details about immunity and disease.

Indeed, it was the original press release from Stanford University that introduced "canoodling" into the story. From the first sentence the tone is coy and teasing:

For a few years now, scientists have known that humans and their evolutionary cousins had some casual flings, but now it appears that these liaisons led to a more meaningful relationship.

Casual flings? One night stands?

The research, reported in the journal Science, is about variants of the HLA class I gene series, described by the research team as "critical for our body's ability to recognize and destroy pathogens". One variant, HLA-B*73, was interpreted as passing into ancestral modern humans from Denisovans, in West Asia. Another variant, HLA-A*11, making up as much 64% of HLA in East Asia and Oceania, was also identified as crossing from another lineage into the modern human ancestral genome.

But the imagined story is less about disease resistance than about sex. About what the press thinks of as "primitive" forms of human ancestors having sex with what they seem to imagine as much more advanced ancestral forms-- early modern humans.

What resonates here is an older idea of Neanderthals that should have been thoroughly superseded by now. Neanderthals, Denisovans, and early modern humans were contemporaries. But the imagery being employed is all about forbidden affairs across an imagined gulf.

These sexual relations are visualized as rare: "the sexual encounters of modern and archaic humans may have been few and far between", the Globe and Mail assures us.

The Daily Telegraph writer openly admits that there is no way to be sure about "the nature of those relationships - whether violent or consensual, short or long-term".

But the press consensus seems to be that sexual relations across the lineages must have been rare-- despite there being no way to actually determine that.

The Daily Tech cites Svante Pääbo arguing that

one of two possibilities occurred. Either migrants to Asian and Europe broadly had sex with Neanderthals or just a few did, but whose progeny survived in greater numbers, passing on the early hominids' genetic material.

Without explanation, the story says the scenario of fewer sexual encounters is most likely. It preserves the implication that these different ancestral groups would have been so unlikely to experience sexual attraction that such events would have been rare.

The focus on sex-- who had it, where, and how often-- leads most of the press to ignore the fact that there are serious objections to the new argument for a hybrid immune system.

Discover online, among other science-related outlets, reports on the doubts. Anthropologist John Hawkes provides a lucid commentary. The HLA variants could be old enough to have been inherited by all three human populations that left Africa. Any one of them could have conferred adaptive advantage in a specific context.

But that only matters if the story is about resistance to disease. For most of the media, the story is about irresistable Neanderthals and their sexual liaisons.

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