March 19, 2013

Ancient hybridization in Africa between archaic and modern humans

I've been putting together a theory about the origin of prehistoric art (and in a way, of all art), but one thing kept bugging me. The theory required there to be an archaic form of the genus Homo in Africa that Homo sapiens would have run into, possibly interbred with, sometime between 20 and 40,000 years ago.

I don't stay as up-to-the-minute on human genetic evolution as I used to, so I went to check, and there it was: "Genetic evidence for archaic admixture in Africa." The interbreeding probably occurred around 35 to 40,000 years ago, with some other group that had split off from Homo sapiens around 700,000 years ago. Well goddamn. Better reading it a year and a half late than never, I guess. Two follow-up articles, which I have not read (here and here), all by separate teams, confirm that hunter-gatherers in Africa show signs of their ancestors having interbred with some archaic form of human (i.e., not Homo sapiens) tens of thousands of years ago.

Correction: the last article linked only discusses admixture among various sapiens groups in Africa, not with archaics as well.

This is analogous to the sapiens-Neanderthal and sapiens-Denisovan interbreedings, whose signs show up in the genomes of living people today. (Denisovans were closer to Neanderthals than to us, though still distinct from each other.) Those interbreedings happened in Eurasia, while the ones reported above happened within Africa.

In a round-up of some of the main implications of the first article, Dienekes Pontikos wondered:

It is certainly counterintuitive that admixture with archaics would have happened in Africa after it happened in Eurasia. . . It is difficult to believe that Homo sapiens waited 160 [thousand years] to mix with his archaic neighbors in Africa... and yet started hooking up right away with Eurasian archaics.

My hunch is that Homo sapiens was already pretty well suited to Africa, no matter which of the many diverse environments they found themselves in. So, while this mystery archaic Homo must have been locally better adapted than sapiens in some way (hence why we picked up and kept some of its genes), it wasn't a huge difference. Not so pressing of a need to get their genes.

Once sapiens left Africa, though, all bets were off -- we needed all the help we could get, and fast, by picking up whatever genes the Neanderthals had that adapted them to the strange new world that we had stumbled into. It was colder, had a different mix of infectious diseases, etc.

Hopefully I'll be able to throw together a post soon on what this all has to do with the birth of art. In the meantime, just mull over the idea that hunter-gatherers from sub-Saharan Africa aren't a 100% window into our primeval past. Some things unique to them, not shared with hunter-gatherers elsewhere in the world, could have come from the mystery archaic species in Africa. I wonder about linguistic clicks (or something related to it). Or "steatopygia," i.e. having a butt big enough that your baby can stand on it when you're upright.

4 comments:

  1. Anonymous11:54 AM

    Clicks are a tricky topic in linguistics - their rarity and exoticism leads to many wild speculations about their origin. However, we do know that they accompanied humans after their exit from Africa. The aboriginal ritual language Damil, spoken by the Lardil people , has clicks. Moreover, words from click languages have been adopted quite liberally by humans who are at a significant genetic distance from the San. The Bantu, who originate in West Africa and migrated South, incorporated click sounds into their language, the most famous example being Zulu. There are click loanwords found in Languages as far North as Kenya and the Sudan. This suggests that they are fully incorporable into human phonology, and thus, their most likely explanation is that they are a fully human development - not the result of a strictly genetic import which affected some human populations, but not others. Their rarity outside of Africa is attributable to the simple fact that feature structures of languages deteriorate and simplify as people have more contact with one another (and become complex again when they become isolated), and the phonological codification of clicks is quite complex. Think of Indo-European ... older versions of the language are much more morphologically rich, since an ingroup of pastoralists will have a lot to do with one another, an not as much with the outside world. Then, go from Sanskrit to Hindi, simpler, more chopped up, less morphologically rich ... spoken by a vast agrarian civilization. And then compare that to the phonological, grammatical, an morphological simplicity of a language like Chinese ... Even simpler.

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  2. I wasn't thinking so much of a direct genetic import to a group that had previously lacked them, or been incapable of them. More like genes related to vocal physiology that made it easier to keep them among the ancient African groups, and less so among others. I recall something like that for genes related to pitch perception in East Asians who speak tone languages.

    Or maybe all sapiens groups were capable of clicks, but they caught on primarily after the various non-African groups left Africa. (Ritual use in Damil doesn't show that clicks used to be part of ancient languages of the Australians.) If the African H-G's communicated with the mystery archaics, maybe clicks were easier for the archaics to perceive and produce.

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  3. steatopygia. i knew u'd bring that up....

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  4. Heh, it is one of the most bizarre distinctions between them and everyone else, including all other H-G's. Small stature, epicanthic fold, yellowy skin -- not so weird. Having proportionally more junk in the trunk than two black girls put together -- that's weird.

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