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Every single person on Earth with blue eyes is descended from a single ancestor who lived 6,000 to 10,000 years ago.
Originally, 100% of human beings had brown eyes due to high concentrations of melanin protecting the iris.
A single individual near the Black Sea region experienced a genetic mutation on the HERC2 gene, which acted like a "dimmer switch," turning down the melanin output in the iris.
Because this exact genetic "switch" is identical in every blue-eyed person alive today, scientists confirmed that all blue-eyed individuals share the exact same family line.
© Human Genetics & Evolutionary Digest