Thursday, October 19, 2006

The likelihood of more recent genetic evolution

... the capacity for innovation in behaviorally modern humans materially speeded up evolution, because it led to frequent innovation, and every significant innovation created a mismatch with the environment and, therefore, new selective pressures. Look at the Bushmen: they're 4' 8" and hunt big game. They couldn't do it without poisoned arrows and, back before missile weapons, no one did: early humans were bigger and built like linebackers. The bow begat the Bushmen.

Take agriculture: the switch to reliance upon cereals cut protein intake almost threefold while reducing protein quality and greatly increasing the percentage of high-glycemic carbohydrates in the diet (along with other changes) That put huge areas of metabolism under selective pressure - towards more robust glucose regulation, towards changes that conserve protein, especially essential/scarce amino acids. Check out the distribution of diabetes - it's not 'thrifty genes', it's pre- and post agricutlural adaptations.

... Female-farming systems would seem likely to select for reduced paternal investment and increased intermale competition and display: the selected myostatin mutations, along with the regional differences in the androgen receptor may fit into this picture.

...A more complex and hierarchical society (with far greater reproductive skew) must have selected for different cognitive and personality profiles - not just among the Ashkenazi or the Chinese, but in all civilized populations. Look, all those personality and cognitive traits have substantial heritability, so selection happened.... For that matter, different kinds of hunter-gatherer ecology selected for different traits; Eskimoes are not Bushmen are not Negritos.

...without modern medical care, Amerindian and other long-isolated peoples are incredibly vulnerable to Old World infectious diseases, enormously more so than Eurasians and Africans. The domestication of cows turned Northern Europeans into mampires that live off the milk of another species.

Sewing, the atlatl, pottery, writing - all changed peoples.

The recent adaptations to agriculture are of course not even found in hunter-gatherers, but agriculturalists in different parts of the world have mostly experienced different genetic changes... For example, the genetic basis of skeletal gracilization in Europe/Middle East appears to be fundamentally different than that in China, lactose tolerance in the Masai is caused by a different allele than in Europe, while the genetic basis of light skin color is entirely different in China and Europe.

Which implies that the causal mechanism, the nuts and bolts of >100 IQ, likely a consequence of post-agricultural adaptation, probably differ significantly between East and West, just as the details of skin color do. The psychometric subtructure sure looks different.

Greg Cochran, commenting on the Gene Expression blog, disagreeing with the prevalent assumption that evolution stopped well over 10,000 years ago .

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