Friday, May 19, 2006

Climate sensitivities   posted by Razib @ 5/19/2006 03:23:00 PM

I was going to mention this before, but I forgot. Recently I went to a talk given by a physical anthropologist, and he mentioned how humans are superior as far as large mammals go in maintaining a high level of function during the heat of the day. Offhand, he offered that if you took a 'cold adapted' Inuit and placed them in a subtropical desert they could acclimate pretty quickly. On the other hand, he suggested that the reverse was not true, that if you took a person from a tropical climate they won't adjust as well physiologically in a frigid clime. One could say this shouldn't be surprising, the hominin lineage has been predominantly a tropical one, and H. sapiens are presumably a recent arrival from Africa to much of the world. So one might accept that our heat adaptations are ancestral characters that non-tropical peoples have retained because of the vicissitudes of phylogeny. I doubt it is that simple, I suspect that there are other benefits of our heat adaptations, probably relating to cognitive function, which constrains the loss of these traits in non-tropical people. Of course the addition of adaptations to the cold as derived characters makes sense. When I asked for the source, I was told that this sort of information could be found in Human Biology. I haven't been able to get a hold of this text, but he told me that most of the references are to studies from the earlier half of the 20th century done by the US military (probably black-white comparisons?).

In any case, these findings shouldn't surprise too much, though the asymmetry was something I hadn't expected. But, it seems likely that disease was a much better trick at keeping northern peoples out of places like Africa than climate. But, this might have some bearing on why northern peoples invaded southern regions more than vice versa. Mind you, I don't think simple biological explanations are the predominant underlying component here. I've already pointed out the World Island tends to taper along many of its peninsulas in a north-south fashion so a form of geographic determinism probably plays a role. Additionally, a great deal of the conquest over the past 4,000 years has likely been in the form of steppe barbarians who descended upon civilized peoples whose martial skills were not up to par. The Central Asian steppe is in a northern clime, but the history of peoples like the Oirat Mongols or Jurched/Manchu also suggests they ventured north and displaced hunter-gathers in Siberia during some periods of history. Of course, the encroachment upon circumpolar peoples is not as notable because circumpolar peoples, like the rat-eating Finns, didn't have an indigenous literate civilization to record the onslaught from the peoples to the south. The reality is that it seems steppe peoples have periodically overwhelmed cultures to the west, east, south and north. Nomadism seems to occupy a "happy" martial medium between the hunter-gathering lifestyle and settled farming.