October 24, 2006

"The Bow Begat the Bushmen"

Greg Cochran explains how cultural change speeds up genetic change in the comments section of GNXP.

There are 47 ways in which culture accelerates rather than retards evolution. I keep thinking that this is all obvious, but clearly the word 'obvious' has no meaning.

More exactly, 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 agricultural adaptations. Agriculture allowed closer spacing of births and so selection increased the frequency of (probably ancient) r-strategy alleles of LH and FSH (along with new variants, natch). Female-farming systems [found mostly in the tropics] would seem likely to select for reduced paternal investment and increased inter-male competition and display: the selected myostatin mutations, along with the regional differences in the androgen receptor may fit into this picture.

Sedentism, changes in workloads, and reduced dietary calcium apparently selected for more gracile skeletons (intensifying an ongoing trend originated by the development of missile weapons). 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, probably more in the direction of pointy-haired bosses [a la Dilbert] than big heads and six fingers. For that matter, different kinds of hunter-gatherer ecology selected for different traits; Eskimos are not Bushmen are not Negritos.

The increased disease load associated the high-density agricultural societies (and the domestication of animals) put selection into high gear: 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 [a spear-throwing enhancer], pottery, writing - all changed peoples.

Change has been so rapid, some 300 times the supposed Haldane limit, that it has far outpaced gene flow. 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 even when phenotypic changes are convergent. 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 substructure sure looks different.

My published articles are archived at iSteve.com -- Steve Sailer

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