Everyone With Blue Eyes May Descend From a Single Human Ancestor
9th October 2023
Every eye color links directly to the volume of melanin in the iris. Green eyes, even more rare than blue, marks a reduced level of melanin, thought not as reduced as blue eyes. It only takes a miniscule change to shift from brown to blue. “From this we can conclude that all blue-eyed individuals are linked to the same ancestor,” Eiberg says. “They have all inherited the same switch at exactly the same spot in their DNA.”
He refers to that that switch as a specific genetic mutation event, and believes that it only produced the first-ever blue-eyed human thanks to the mutation of the regulating HERC2 gene. The combination is the only known way eyes can turn blue (in contrast, red hair can happen for one of nearly a dozen reasons). That mutation remained in place for the next generation, meaning the reduced production of melanin in the iris allowed for the continued dilution of brown to blue.