I recently had a discussion with a student of biology about the implications of the human-Neanderthal interbreeding hypothesis. She suggested that I was putting too much emphasis on the issue of a genetic basis for intelligence, and informed me that a professor in her school made the statement, “From what I’ve read, it seems unlikely that Neaderthals contributed significantly to modern humans.”
Once again, my little BS detector lit up as I realized the game that her instructor was playing with words. “Contribute significantly” is a loaded phrase. There isn’t a 1:1 relationship between the quantity of genetic material transferred and every measure of “significance”. A single gene, for example, could make all the difference in terms of cognitive function, or the ability to use language and speech. These happen to be precisely the kind of contributions being looked at, by the way.
In discussion of the D allele in particular, there is a model of gene transfer in place already which predicts that a gene which confers even slightly higher advantage to its bearer could rise to high frequencies within a population. The D allele just happens to fit that model. Anyway, I haven’t seen any proof that it confers greater “intelligence”, as I also think that word is too ambiguous. The authors of the HHMI study were ambiguous themselves, but they did use a phrase like “more efficient brain function”, which does touch on cognition, but in a non-specific way.
Isn’t it interesting how scientists can use language to be precise and yet, sometimes, they simply refuse to do so?
Even the most orthodox academics admit that something happened in terms of brain chemistry to precipitate the advent of the rise of culture. They also have to admit that it happened in Europe. It turns out that narrative is sometimes the natural enemy of the scientist. Controversy is easy to avoid if you simply focus on the measurements and minutia… all the way up until it isn’t. Until very recently, they have had n layers of uncertainty to rest behind and no pressing need to provide a narrative of how it all happened. Now, they have n-1 layers between them and certainty, and there is a host of complementary data which is going to reduce that number further.
For example, it appears that East Asians and Europeans developed pale skin independently, probably due to local adaptations in response to ultraviolet radiation densities at similar clines. Interestingly, the genes identified in the pigmentation path which correspond to pale skin in Europeans are similar to the same coloration in Neanderthals. Have you seen many ginger Chinese? Probably not. Natural selection models are in competition with sexual selection models for explaining the variations in pigmentation, eye color, and hair form in Europeans, but the evidence is beginning to show that the ultra-pale skin did not make its way into our gene pool until the Holocene.
When you lay out the time line and map, the most parsimonious answer begins to look like an initial wave of Africans meeting up an pairing, perhaps infrequently, with Neanderthals in the Levant. This was followed by some changes in behavior and then an explosion outwards into Europe and western Asia. Here, again, the tan-colored species went on divergent paths, and the group who made it to Europe probably interbred again and more frequently with Neanderthals there. More variation in pigmentation occurred, and the skull measurements of Early Europeans (formerly known as Cro-Magnon) indicate that they were longer – two phenotypical expressions that you would expect to find if the distinct populations were interbreeding.
Now, the Out of Africa view has been dominant, and most academics are smart but not very rebellious. I have recently discovered that the multi-regional hypothesis has actually always been far more accepted in scientific circles than the textbooks and journalists would have you believe, however. I predict that a hard core of politically-inclined researchers (or researchers dependent on money from the politically inclined) will begin to veer into more complex modeling to compensate for the fact that the most parsimonious explanation for the very visible and measurable differences among “populations” today happens to be perhaps the most politically dangerous one.
It’s a great time to be alive.