Approximately every tenth person on the planet has eyes whose shade can be compared to the color of a summer sky, a tropical ocean, or even pale aquamarine. In some European groups this percentage can rise to three out of four people.

Why this eye shade continues to attract attention, especially when compared to the more earthy tones of others, has long been the subject of research. According to anthropologists in the UK, blue eyes may have an advantage in low-light conditions.

Their study, pre-published on the peer-review server bioRxiv, suggests that blue eyes may provide some advantageous visibility in low light.

In their study, Kyoko Yamaguchi and Faith Erin Kane from the University of Liverpool examined this hypothesis by having 39 adult volunteers undergo a simple vision test in gradually dimming light over 30 seconds.

Eye color was determined and confirmed as blue or brown using the new classification manual, resulting in 25 people with blue eyes and 14 with brown eyes.

The results showed that people with blue eyes had better readability of wall codes in low light, averaging 0.7 lux, compared to brown-eyed people, who had an average light level of 0.82 lux.

Despite the preliminary nature of the study and its small sample size, the results support the theory that loss of iris pigmentation could be an adaptation to low-light conditions.

Like many other adaptations, the reasons for the persistence of this mutation can be varied. It could provide a survival advantage or be associated with beauty. It may also have required fewer of the body’s resources to function in dark conditions, where the melanin in the iris was no longer as necessary.