OXFORD, England, July 27 (UPI) -- Poor light in long winters and cloudy days in Earth's higher latitudes have given people who evolved there bigger eyes and bigger brains, U.K. researchers say.
However, they say, bigger brains do not make people smarter because the extra size is almost all made up of larger vision processing areas.
Scientists at Oxford University measured the size of eye sockets and the brain volumes of 55 museum skulls from 12 indigenous populations ranging from Scandinavia to Australia, Micronesia and North America, the BBC reported Wednesday.
The results were plotted against the latitudes occupied by each population.
"We found a positive relationship between absolute latitude and both eye socket size and cranial capacity," Eiluned Pearce said.
"Both the amount of light hitting the Earth's surface and winter day-lengths get shorter as you go further north or south from the equator.
"We found that as light levels decrease, humans are getting bigger eye sockets, which suggests that their eyeballs are getting bigger," she said.
The largest were found in skulls from Scandinavia while the smallest were from Micronesia, the researchers said.
"Humans have only lived at high latitudes in Europe and Asia for a few tens of thousands of years, yet they seem to have adapted their visual systems surprisingly rapidly to the cloudy skies, dull weather and long winters we experience at these latitudes," study co-author Robin Durbar said.