Health

The point mutation which made humanity

Gene ExpressionBy Razib KhanAug 16, 2011 10:30 AM

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Steve Hsu points me to a piece in The New Yorker on the science and personality of Svante Pääbo. The personality part includes references to Pääbo's bisexuality, which to me seemed to be literally dropped into the prose to spice it up. Of course it was the science which I found interesting. There are many more bisexuals than there are heterodox scientists. And yet like many researchers of yore it seems that Pääbo is out to find the genes which make humanity distinctive as we understand it (if the reporting is accurate, which I don't take as a given). There are some interesting tantalizing clues littered about; some genes implicated in autism seem to exhibit Neandertal vs. modern human differences (with the Neandertals carrying the autism-implicated variants). But here's a consideration: what if the premise that there are a set of traits which are disjoint between Neandertals and modern humans is false? What I'm saying here is that there are traits which are fixed and universal within a species, and totally differentiate species x from species y. Anatomically and behaviorally modern humans seem to be exceptionally strange creatures. As noted in The New Yorker this lineage was the one responsible for many of the megafaunal extinctions and the push into Oceania and the New World. And yet do we have to presume that whatever characteristics differentiated behaviorally modern humans from other human lineages were universal to all of the former and totally absent from the latter? It may be that the difference is not one of quality/kind, but of quantity/degree. In other words, a particularly novel personality type may have transitioned to critical mass amongst the neo-Africans ~50,000 years before the present, but that personality type may not have been universal, and may even have been present at far lower frequencies across the other branches of humankind. If the above proposition is assumed, then the quest to find the "gene which made humanity" is going to be much harder. You can't just compare a few Neandertals to humans, but would need many more Neandertal samples. That's because there may not have been a gene which made humanity, but a subtle complex of numerous genetic and cultural changes which transitioned at a critical point. Do remember also that it may be the nature of statistical genetics that there are some loci where Neandertals and modern humans differ in totality, but these are the "genes which make us human" only if you presume that there are some genes which make all modern humans human and all Neandertals not quite human. To be concrete about this idea, what if the archetype of the visionary/mystical leader with charisma is responsible for the distinctiveness of modern human groups? This is not a common individual, but not exceptionally rare. Most humans are not particular visionary, nor are they prone to mysticism. Perhaps the difference between Neandertals and behaviorally modern humans was less about large between group differences in individual level traits, and more about the fact than Neandertals simply lacked the leadership cadre which behaviorally modern humans possessed. In this scenario most modern humans are just like Neandertals, lacking vision, drive, and proximate insanity. Neandertals would not have had their Alexander the Greats, but perhaps they would not have had their Adolf Hitlers.

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