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The Color of Your Eyes Could Actually Affect Your Reading Ability : ScienceAlert

About one in ten people worldwide have an eye color that, in poetic terms, can be compared to the hue of a summer sky, the hue of a tropical ocean, or even the pale hue of an impeccably cut aquamarine.

In some European populations, that fraction can skyrocket to three out of every four individuals.

Why this color persists in competition with the earthier tones of a darkly pigmented iris has long been a matter of speculation. Now, anthropologists in the United Kingdom propose that blue eyes might have a slight advantage in low-light conditions.

In their preliminary experiment, Kyoko Yamaguchi and her student Faith Erin Cain at Liverpool John Moores University explored the possibility with 39 adult volunteers undergoing a simple 30-second eye test under decreasing light intensities.

Eye colors were self-reported and then verified as blue or brown categories using a recently developed classification guide, providing the researchers with 25 people with some degree of blue eyes and 14 with light or dark brown eyes.

Once the numbers were calculated, those with bright blue eyes could read the codes depicted on a wall in significantly less light (a minimum of just 0.7 lux on average) than their brown-eyed peers, who averaged a minimum of 0.82 lux.

Considering that the study is preliminary with a relatively small sample size and has not yet been peer-reviewed, the findings of the experiment support the theory that loss of pigmentation in the iris was a trait selected in some populations to maximize the vision in low light environments.

Whether hazel with mossy flecks, storm gray with steely edges, or green with amber streaks, all irises consist of a pair of “canvases” dotted with varying amounts of proteins like melanin.

Generous doses of proteins in the overlaid canvas darken the eyes. As pigmentation is depleted, the scattering of light through the transparent layers of the eye gives the iris a bluer hue, not unlike how light scattered through the atmosphere takes on its familiar sky hues.

Of course, it’s fair to assume that evolution has given us pigmented irises for a good reason. Since people with darker eyes have a lower incidence of diseases such as cancer and macular degeneration, an iris full of melanin is likely to provide some degree of protection.

Around the time humans were starting to settle and figure out this whole farming thing, a mutation occurred in a single individual’s copy of a “switch” of a gene associated with albinism, giving his body the ability to dilute the level of melanin in a very Specific location: your eyes.

If this genetic change had also occurred at other times in history, it has long been lost in evolutionary dead ends. This event, however, was passed down to lineages everywhere over the centuries, and today is found in hundreds of millions of people around the world.

Like so many adaptations, the explanation for why this mutation persisted when it did is likely complex.

It may have been associated with prestige or beauty, conferred protection against bad moods in dark winter seasons, or simply consumed fewer body resources to build in hostile conditions where dark eyes were no longer necessary. Maybe all of the above.

If this study is anything to go by, seeing a little better in a cold, twilight world might have tipped the scales, increasing the spectrum of diversity that is the modern human body.

This research is available on the peer review server bioRxiv.



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