People up north have bigger eyes

People living in higher latitudes have bigger eyes and brains, according to a new study.

Scientists at Oxford University found that people living in countries with dull, grey, cloudy skies and long winters have evolved bigger eyes and brains to cope with the low light levels.

However, bigger brains don't make Northerners smarter; it's just that their brain needs to be bigger to deal with the extra visual processing needed to live in low light conditions.

The researchers measured the eye socket and brain capacity of 55 skulls from the Oxford University Natural History Museum collection, dating back to the 1800s. The skulls represented 12 different populations from across the world.

They then plotted the results against the latitude of the skull's country of origin.

Lead author Eiluned Pearce, at 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."

Worldwide, people have the same ability to see in natural daylight, which suggests that the human visual processing system has adapted to the different light conditions as human populations have migrated across the world.

Study co-author Professor Robin Dunbar 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."

The skulls used in the study came from the indigenous populations of England, Australia, Canary Islands, China, France, India, Kenya, Micronesia, Scandinavia, Somalia, Uganda and the United States.

From measuring the brain cavity, the research suggests that the biggest brains belonged to populations who lived in Scandinavia with the smallest being Micronesians.

The study also confirms past research in animals that has looked at the links between eye size and light levels, the researchers said.

Birds with relatively bigger eyes are the first to sing at dawn in low light and animal species with the largest eyes are usually those that are active at night.

The study is published in the journal Biology Letters.

This article was published on Wed 27 July 2011