Northern people have bigger eyes

It’s dim up north – so people living at higher latitudes have bigger eyes and brains, research has shown.

Northerners evolved more developed visual processing to help them cope with long winters and grey skies, a study suggests.

Scientists measured the eye sockets and brain capacity of 55 human skulls representing 12 different populations from across the world.

They found that the further north of the equator people lived, the bigger their eyes and visual brain regions were.

Both are adaptations to low light that have only appeared since humans moved into northern Europe and Asia, a very short length of time in evolutionary terms.

Lead researcher Eiluned Pearce, from Oxford University’s 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.”

People’s actual ability to see in natural daylight is roughly the same whether they live in Nairobi or Newcastle.

This indicates that humans adapted themselves to their ambient surroundings as they migrated out of Africa around the world, say the scientists.

The study, published in the Royal Society journal Biology Letters, took account of a number of factors that could have swayed the results.

These included overall body size, genetic links between populations, and the fact that cold weather might lead to enlarged eye sockets lined with a thick layer of insulating fat.

The skulls, housed in museum collections, came from England, Australia, the Canary Islands, France, India, Kenya, Micronesia – an island region in the Western Pacific Scandinavia, Somalia, Uganda and the US.

Measurements of the brain cavities showed that Scandinavians had the biggest brains and Micronesians the smallest.

Eye socket volume increased from around 22 millilitres close to the equator to around 26 millilitres at latitudes of 45 to 60 degrees, the band which covers the UK.

Previous studies have shown that birds with bigger eyes are the first to sing at dawn in low light.

Eyeball size across all non-human primates is also associated with when they choose to eat and forage. Species with the largest eyes are those most active at night.

Co-author Robin Dunbar, professor and director of the Institute of Cognitive and Evolutionary Anthropology at Oxford University, 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 cloudy skies, dull weather and long winters we experience at these latitudes.”