A survey of 55 skulls from the 1800s and regions across the globe finds that people who lived in high latitudes had bigger eyes and brains. Researchers at Oxford University say the variations are not due to differences in intelligence but are instead related to ambient light:
"Lead author Eiluned Pearce, from the Institute of Cognitive and Evolutionary Anthropology in the School of Anthropology, said: 'As you move away from the equator, there's less and less light available, so humans have had to evolve bigger and bigger eyes. Their brains also need to be bigger to deal with the extra visual input. Having bigger brains doesn't mean that higher latitude humans are smarter, it just means they need bigger brains to be able to see well where they live.'"
Oxford's bulletin on the research fills in the details.