Executive summary for those who don't like long posts: the Inuit and Arctic Siberians were found to have larger skulls and therefore brains than average. The complex interplay of a challenging Arctic environment with a rich brain resource--fats of land and sea creatures--may have resulted in larger human brains.
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Tyler originally tipped me off about Inuit skull/brain size and I found a confirmation here:
"The French cranium measurers ran into serious problems in Greenland. They were working from the theory that there was a linear relation between a person's intelligence and the size of his skull. They discovered that the [Inuit] Greenlanders, whom they regarded as a transitional form of ape, had the largest skulls in the world." --Peter Hoeg, Smilla's Sense of Snow, pp. 17-18
I would add that Siberians also tend to have larger than average skull/brain sizes, as this map shows:
(the darker an area, the larger the average skull size). Note: there were some graphical extrapolations used in creating the map, so it's mainly useful in giving an overall rough impression rather than details.
Meat/fat also tends to be a major part of the diet in Siberia, and there are other hypothesized factors for skull/brain growth, such as greater diversity of environments requiring more foresight and wider dispersal of foods requiring larger brain maps. Many phenomena in nature are complex and multifactorial. This could be the case with evolution of larger human brains. It could involve an interplay between environmental pressures and raw material food sources. Perhaps the greater challenges of Arctic environments applied selective pressure for larger brains and fat from land and sea mammals and fish was the fuel that enabled the brain growth (as human brains, like all mammal brains, are composed largely of fat). Meat and fat are probably also easier to chew and digest than heavily fibrous foods like the wild legume tubers and nuts of Africa (there are tubers and other underground storage organs in the Arctic too, but they probably provided a smaller proportion of the diet than in tropical areas), which may also have contributed to downsizing of jaw and gut and upsizing of skull/brain. I'm just speculating, of course, but the information we do have suggests that excluding all animal foods from the diet is a risky proposition. Here are a couple sources:
> Northerners' brains are bigger, scientists find - Good news for our readers from the north: you are likely to have a bigger brain than your southern counterparts. By Nick Collins, Science Correspondent,
http://www.telegraph.co.uk/science/science-news/8662850/Northerners-brains-are-bigger-scientists-find.html (thanks to Tyler for this link)
> Beals, K.L., C.L. Smith, and S.M. Dodd (1984). Brain size, cranial morphology, climate, and time machines, Current Anthropology, 25, 301–330 (via Brain size and latitude: Why the correlation?
http://evoandproud.blogspot.com/2011/07/brain-size-and-latitude-why-correlation.html).
It's not politically correct, I know, to say that some peoples brains are larger than others, but I've never given a shit about political correctness. As David Brudnoy, a politically incorrect host of a Boston talk radio show of the recent past, once said, politically correct usually means incorrect in any other context. Granted, he had a few incidents where he splurted out racist whoppers, so that was perhaps a bit self-serving, but nonetheless on the mark. If a fact happens to be politically correct, so be it, but I'm not going to ignore facts merely because they're unpalatable.
