Melanin is the pigment responsible for eye color – as well as hair and skin color – and a series of genes determine the amount of melanin in the cells of the iris. Brown is the most widespread eye color worldwide, while green is one of the rarest.
Having light or dark eyes not only influences your physical appearance, but can also determine your visual ability depending on the greater or lesser brightness of the environment. At least that is the conclusion reached by a new study carried out by researchers at Liverpool John Moores University (LJMU) who have found that people who have blue eyes could have better vision in low light conditions compared to those with brown eyes.
This theory could explain the greater prevalence of the color blue in certain populations, such as in northern Europe, where the skies tend to be darker. This is a study that has been described as “preliminary” by Dr. Kyoko Yamaguchi, who works in the School of Environmental and Biological Sciences and specializes in the genetic basis of skin, hair and eye color and is one of the authors.
The findings of the work have been published in BioRxiv (a repository where studies that have not yet been peer-reviewed for inclusion in a scientific journal are published), and must be confirmed in a larger study. The study was based on a hypothesis that Dr. Kyoto formulated when she moved to Europe from Japan.
Prevalence of blue eyes in the population of northern Europe
Specifically, the researcher was struck by how dim the lighting was in the buildings, which she often found too dark to read. This led her to wonder if there was a biological basis for this weaker lighting, rather than just a cultural reason. To investigate further, she and her student Faith Erin Cain examined the vision of 40 people of European descent with blue or brown eyes.
After the volunteers remained in the dark for 30 seconds, the researchers gradually increased the brightness of the light until they could read a sequence of letters on a wall three meters away. Those with blue eyes needed a light level of 0.7 lux on average, compared to 0.82 lux for those with brown eyes.
According to a report in New Scientist, other experts believe that the idea that having blue eyes helps in low light conditions makes sense, but the number of volunteers in this study was too small to draw definitive conclusions. “The concept is plausible,” says Cassie Ludwig of Stanford University in California. Pirro Hysi of King’s College London comments: “It is possible, [pero] “It is not proven because the analyzes were based on a small sample.”
The current theory is that blue eyes were a side effect of selection for lighter skin and blonde hair, with the goal of getting enough vitamin D.
If the finding is confirmed, it could help explain why blue eyes evolved in some northern European populations, Dr. Yamaguchi says. The current theory is that blue eyes were a side effect of selection for lighter skin and blonde hair, which would be promoted by the need to get enough vitamin D. Our bodies use ultraviolet rays to produce vitamin D in the skin. , so darker skin can contribute to a vitamin D deficiency in regions with little sunlight.
However, blue eyes can be a disadvantage when the light in the environment is bright. Some studies suggest that blue irises scatter more light than brown ones, degrading image quality. Dr. Yamaguchi hopes to get funding for a larger study that would also include people with a broader range of eye colors, but Mackey notes this could be difficult. “Although eye color is very interesting to the general public, it is really difficult to get funding for research in this area,” she concludes.
