Razib Khan One-stop-shopping for all of my content

September 14, 2010

By our genes, though not alone

Filed under: Behavior Genetics,David Dobbs — Razib Khan @ 10:31 am

David Dobbs over at his new digs has a massive post on the relationship between behavior genetics, genomics, neuroscience, environment, and culture. It’s titled The depression map: genes, culture, serotonin, and a side of pathogens, and he concludes:

In a sense, these studies are looking not at gene-x-environment interactions, or GxE, but at genes x (immediate) environment x culture — GxExC. The third variable can make all the difference. Gene-by-environment studies over the last 20 years have contributed enormously to our understanding of mood and behavior. Without them we would not have studies, like these led by Chiao and Way and Kim, that suggest broader and deeper dimensions to what makes us struggle, thrive, or just act differently in different situations. GxE is clearly important. But when we leave out variations in culture, we risk profoundly misunderstanding how these genes — and the people who carry them — actually operate in the big wide world.

One of the things I harp on on this weblog is that I see more potential for group selection dynamics at the level of the evolution of culture than the domain of evolutionary genetics. The reasoning is that the power of selection is proportional to heritable variation at the level you’re evaluating. So, of you have two adjacent demes “competing” you’d have to have group-level heritable variation. Basically, the between group component of genetic variation which can’t be reducible to within group variance. Recall that Fst values, the between group component of genetic variance, at the maximal scale of genetic distance is on the order of ~0.15, 15% of the total (the rest being within group). But in real human societies over most of evolutionary history the conflict has been between groups which are genetically much closer, in fact, groups which probably “trade” in women as a byproduct of conflicts or even when at peace, and so diminish extant variation to nearly nothing.

The same issues are not as operative when it comes to culture. Two tribes can speak different dialects or languages. If a woman moves from one tribe to another her children don’t necessarily speak a mixture of languages, rather, they may speak the language of their fathers. The nature of cultural inheritance is more flexible, and so allows for the persistence of more heritable variation at different levels of organization. Differences of religion, language, dress, and values, can be very strong between two groups who have long lived near each other and may be genetically similar.

Over the course of human history our norms may have been shaped by these sorts of cultural dynamics. But over time the norms themselves may have had an impact on the gene frequencies within the populations, as some variants may have been fitter in some cultures than in others. And, within those societies there is still a fair amount of variation and ability to construct “niches,” the “environment” which David speaks of. It’s complex, and I’m glad David is starting the conversation.

On an unrelated note, I find the registration system over at Wired Science a touch onerous. If they want to force registration something which is hooked into twitter or Facebook would be convenient, but as it is, the Ajax was broken on Chrome/Windows 7 for me, in case the tech people are curious. So I never left a comment, which was my intention, because I couldn’t login after registering.

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