Gregory Cochran and Razib Khan: The Speed of Human Evolution

[giblets]

Could hunters get calcium from bone marrow, or some similar hunting related source? I mean, is there a reason why a lactose intolerant population would get more calcium from hunting than from farming?

Bone marrow? Probably not.
http://nutritiondata.self.com/facts/ethnic-foods/8088/2

That's only for marrow from one type of animal, though.

[Heraclitus]

Hera, what? Are you ignoring my counter-points?

Sorry I'm trying to spend less time online and I saw the discussion was heading a mostly productive direction anyway and didn't feel I would have much to add.

The talking about helmets is at ~24 minutes. They don't say much about it, though. How much selection pressure can the wearing of helmets have on the thickness of skulls? Seems a little odd. Do American Indians who never developed helmets, as far I know, have thicker skulls? They say nothing of that.

No it doesn't add up though. Same thing as with Amerindians not having especially thick skulls (as far as I know) but never having developed helmets is a criticism for the claim that helmets lowered the selection pressure for thicker skulls.

With calcium, why is it that rates of lactose intolerance is nearly 100% among Sub-Saharan Africans yet I've always read that 'Negroids' tend towards bigger bone structure and have far lower rates of osteoporosis than Whites and Asians?

I don't think Native Americans have thicker skulls. However it may be that before the Bronze Age Europeans or Middle Easterners had thicker skulls than East Asians and Native Americans (perhaps due to other factors).

Also I always assumed that the Aztecs and Incans did use helmets going from the depictions of their armies. Also many sub-Saharan peoples are lactose tolerant, the Beja people in Sudan and various other tribes in East Africa.

I do recall something vague about Negroids tending towards a bigger bone structure, but don't recall ever reading a paper on this issue. I have however heard of higher bone density and you are right on osteoporosis rates.

Keep in mind however that while lactose tolerance does make it easier to afford a more robust skeleton things like farming without easy access to diary products (a situation that lasted millennia in some regions) might make it more expensive (farmers where generally malnourished compared to hunter gatherers). Western Eurasians do seem more robust compared to East Eurasians, this seems likely the result of a greater proportion of pastoral ancestors (I have no data on this but I have a hunch the Mongols are more robust than the Japanese).

By the way, with the skull issue, the other things, besides helmets, that Cochran mentioned that may have contributed to higher survival of those predisposed for less thick skulls included a change in warfare towards 'distance' warfare with the invention of the bow and, presumably, throwing spear, and the organization of government having lowered the incidence of violence (and probably distributed it from population-wide to a warrior class).

Like with helmets, these don't add up, though. Yes, the thick-skulled Aborigines didn't develop helmets and the government didn't monopolize and limit violence but they did having ranged weapons (such as the Woomera throwing spear); the Amerindians don't have thicker skulls though they also didn't develop helmets and most ethnic groups didn't develop government, though they had ranged weapons.

Government imposing a monopoly on violence seems a plausible hypothesis considering the most common cause of death for males in many hunter gatherer societies and even some simple tropical agriculture societies is murder/warfare (this of course is far from conclusive because of differences between ancient HG and modern ones).

Overall your counterexamples regarding Helmets and ranged warfare seem good, but its hard to say what is really going on. Helmets and Arrows might contribute towards thinner skulls, but the effects could easily be swamped by other selective forces.

Note I didn't embrace this as the explanation for the unique shape of Australian skulls, just one of the many possibilities.