People with blue eyes can read better in darker conditions than those with brown eyes, a small study has found. This suggests having blue eyes is an advantage in low-light conditions, and might help explain why the trait evolved in northern Europe. But the finding needs to be confirmed in a larger study.
鈥淚t鈥檚 preliminary,鈥� says at Liverpool John Moores University in the UK, who studies the genetic basis of skin, hair and eye colour.
Yamaguchi says when she moved to Europe from Japan, she was struck by how much dimmer the lighting was in buildings, often finding it too dark to read by.
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This made her wonder whether there was a biological basis for this weaker lighting, rather than just a cultural one. To learn more, she and her student Faith Erin Cain tested the vision of 40 people of European descent who had either blue or brown eyes.
After the volunteers sat in darkness for 30 seconds, the researchers gradually increased the brightness of the lighting until the participants were able to read a sequence of letters on a wall 3 metres away. Those with blue eyes needed a light level of 0.7 lux on average, compared with 0.82 lux for those with brown eyes.
Other experts say the idea that having blue eyes helps in dim conditions makes sense, but the number of volunteers in this study was too small to draw firm conclusions. 鈥淭he concept is plausible,鈥� says at Stanford University in California. at King鈥檚 College London says: 鈥淭his is possible, [but] not proven because the analyses were based on a small sample.鈥�
If the finding is confirmed, it might help explain why blue eyes evolved in some populations in northern Europe, says Yamaguchi.
The current thinking is blue eyes were a side effect of selection for lighter skin and blonde hair, and the driving force behind this was a need to get sufficient vitamin D. Our bodies use ultraviolet rays to make vitamin D in the skin, so darker skin can result in vitamin D deficiency in regions with little sunlight.
Another idea is that blue-eyed people had more children because the trait was seen as attractive, says at the Lions Eye Institute in Australia. 鈥淥r it may have a specific biological advantage, which is what this research is looking at,鈥� he says. 鈥淪eeing better at night in the northern winter would have some advantages.鈥�
However, blue eyes may be a disadvantage in bright light. Some studies suggest , degrading image quality.
Yamaguchi hopes to secure funding for a larger study that would also include people with a wider range of eye colours, but Mackey says this may be a struggle. 鈥淎lthough eye colour is very interesting to the general public, it is really hard to get funding to do research in the area,鈥� he says.
bioRxiv
