Monday, February 26, 2024

Blue eyes share a common ancestor

AI-generated picture of a woman with blue eyes.

It is likely that all individuals with blue eyes share a common ancestor. Approximately 6,000 to 10,000 years ago, the prevailing eye color among Homo sapiens was brown, considered an evolutionary advantage due to the protection provided by melanin against UV radiation. However, a mutation in the OCA2 gene during the Neolithic expansion in Europe led to the birth of an individual with blue eyes, deviating from the typical brown. Scientists propose that all blue-eyed individuals, constituting about 10% of the global population, are descendants of this original ancestor with the blue-eye mutation.

Interestingly, the mutation causing blue eyes doesn't actually impart a blue color to the eyes. Blue eyes are not genuinely blue. The iris of the eye consists mainly of two layers: the stroma and the epithelium. Unlike brown eyes, which have a brown-black melanin pigment in both layers, blue eyes lack melanin pigment in the stroma. Blue eyes, devoid of any pigment, exhibit a reflection of white light through the Tyndall effect. This optical phenomenon occurs as the shorter blue wavelengths are reflected more by the fibers in the eyes, absorbing longer red-orange wavelengths. Although the perception is that people have "blue" eyes, from a pigment standpoint, they essentially lack any color.

Source: Interesting Facts

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