I reproduce below the results of a small study of an old skull collection. Given the limits of the basic data, the generalizability of the findings is uncertain but they are interesting nonetheless -- in that they confirm other findings about the effect of latitude on IQ.
The authors were apparently rather embarrassed by their findings so they have presented their findings in a very politically correct way. A lot of the presentation is blatantly speculative and certainly over-interpreted. They talk, for instance, about Arctic brains in blithe indifference to the fact that they had zero data on Arctic brains! So I reproduce below only the more factual bits.
The finding that eyes are bigger in Northern latitudes is a genuine contribution to knowledge but saying that bigger eyes lie behind larger brain size is tendentious. The larger brain of the North is much more likely to be a result of the generally greater survival challenge in Northern latitudes.
In support of that it may be noted that the spectacular visual acuity of Australian Aborigines is found among a people who tend to have somewhat smaller brains than Europeans.
It should be noted that the present "native" population of the British Isles is of peri-Baltic origin (North German and Scandinavian) so should be at the high end of brain size. The authors below deny that greater brain size indicates greater intelligence but ignore most of the literature on the subject in doing so. Most research indicates a positive correlation of .30+
Students of ancient history will also be aware that Northerners have been invading the South for a very long time -- and usually leaving some genes behind. Germans have been invading Italy since the days of the Roman Republic (i.e. before the Roman empire) so Teutonic genes are undoubtedly widely spread throughout Europe today. So Northern brains too are undoubtably to be found throughout Europe these days.
People who live in high latitude regions have bigger eyeballs and brains than other individuals, according to new research.
The increase in brain and eye size allows people to see better in places that receive less light than areas closer to the equator, according to the new study, published in the latest issue of the journal Royal Society Biology Letters.
"People living at high latitudes have greater visual acuity than those who live at the equator," added Dunbar, who is head of the Institute of Cognitive & Evolutionary Anthropology at the University of Oxford.
"The whole point is that they need to have better vision to compensate for the lower light levels at high latitudes, as indicated by the evidence we provide that visual acuity under ambient/natural light conditions remains constant with latitude."
For the study, Dunbar and colleague Eiluned Pearce measured the skulls of 55 individuals from 12 different populations, focusing on the dimensions for orbital volume and cranial capacity. The people lived about 200 years ago. Their skulls are now part of collections housed at the Oxford University Museum of Natural History and the University of Cambridge's Duckworth Collection.
The researchers found significant positive relationships between absolute latitude, orbital volume and brain size. Eyeballs varied in size from around a quarter to a third of an ounce in volume.
The brains, in turn, ranged from about 40.6 ounces for Micronesians, on the low end of the size spectrum, and 50.2 ounces for Scandinavians on the high end.
As for the larger eyeballs, they permit smaller proportions of images to fall upon each photoreceptor field so that more details can be distinguished. The amount of light hitting Earth's surface as well as minimum day length decrease with increasing absolute latitude, so people living in such areas need the visual boost.