Did humans evolve bigger brains to see at dim latitudes?

Humans living farther from the equator evolved bigger brains. But it doesn’t mean that they’re smarter – they need bigger brains in order to see in low light.

The farther that human populations live from the equator, the bigger their brains, according to a study by Oxford University researchers, who measured skulls from 12 populations around the world.

But it doesn’t mean that people in higher latitudes are smarter – over time, humans living closer to the poles evolved bigger brains in order to see in low light. A paper on the link between bigger eyes and bigger brains in people from countries with cloudy skies and long winters appears in the July 27, 2011 online issue of Biology Letters.

The primary visual cortex (blue) showing pathways responsible for the guidance of actions and recognizing where objects are in space (green) and object recognition and form representation (purple). Via Wikimedia

The researchers studied skulls from museum collections, measuring the eye sockets and brain volumes of 55 skulls, dating from the 1800s. The volumes of the eye sockets and brain cavities were then plotted against the latitude of the central point of each individual’s country of origin. The researchers found that the size of both the brain and the eyes could be directly linked to the latitude of the country from which the individual came.

Lead author Eiluned Pearce, Institute of Cognitive and Evolutionary 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.

Sami child. Via Wikimedia

Co-author Robin Dunbar, Director of the Institute of Cognitive and Evolutionary Anthropology, 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 study takes into account a number of potentially confounding effects, including the effect of phylogeny (the evolutionary links between different lineages of modern humans), the fact that humans living in the higher latitudes are physically bigger overall, and the possibility that eye socket volume was linked to cold weather (and the need to have more fat around the eyeball by way of insulation).

The study skulls were from the indigenous populations of England, Australia, Canary Islands, China, France, India, Kenya, Micronesia, Scandinavia, Somalia, Uganda and the United States. By measuring the brain cavity, the researchers found that the biggest brains came from Scandinavia, while the smallest came from Micronesia.

This study adds weight to similar research exploring links between eye size and light levels. Other studies have already shown that birds with relatively bigger eyes are the first to sing at dawn in low light. The eyeball size of primates is linked to when they choose to eat and forage: Species having the largest eyes are those active at night.

Sami nomads from the late 1800’s. A research study of museum skulls showed bigger brain size in the ones from Scandinavia. Via Wikimedia

Bottom line: Researchers at the University of Oxford measured the brain cavity and eye sockets of museum skulls representing populations from various latitudes and determined a link between bigger brain and bigger eye socket size and higher latitude regions. Their paper appears in the July 27, 2011 online issue of Biology Letters.

Read more at University of Oxford

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