Two things have been known for some time now: Human brains get bigger as you go north, and the volume of the primate eye and the primate brain are correlated.
This COULD mean, and this may not be true, that as you go north in human populations you’ll get larger brains (for thermoregulatory reasons) and you’ll therefore get larger eyes (because eyeball and brain size is somehow correlated). But a new paper suggests a different model: Large eyes evolve at high latitudes because there is more dark, and the larger eye demands a larger brain.
Maybe, but I doubt it. the largeness of high latitude brains is way higher in magnitude than could be explained by even a two digit increase in the volume of optical processing of data. But maybe. On the other and, the relationship between orbit size and brain size demonstrated some years ago by John Kappleman (but at first ignored for reasons that I’ve never understood) is cross species an may not apply within species (many such relationships don’t). So, it is all rather mysterious for the present.
In any event, the new research could be of interest.
The farther that human populations live from the equator, the bigger their brains, according to a new study by Oxford University. But it turns out that this is not because they are smarter, but because they need bigger vision areas in the brain to cope with the low light levels experienced at high latitudes.
Scientists have found that people living in countries with dull, grey, cloudy skies and long winters have evolved bigger eyes and brains so they can visually process what they see, reports the journal Biology Letters.
The researchers measured the eye socket and brain volumes of 55 skulls, dating from the 1800s, from museum collections. The skulls represented 12 different populations from across the globe. The volume 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, 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.’
Co-author Professor Robin Dunbar, Director of the Institute of Cognitive and Evolutionary, 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.’
That the explanation is the need to compensate for low light levels at high latitudes is indicated by the fact that actual visual sharpness measured under natural daylight conditions is constant across latitudes, suggesting that the visual processing system has adapted to ambient light conditions as human populations have moved across the globe.