All blue eyes on Earth were caused by one genetic mutation less than 10,000 years ago, according to Danish scientists. That single change in the gene code created a “switch” that diminishes pigment production in some brown eyes, turning them blue.
How this works: The OCA2 gene code affects the P protein, which determines production of melanin — the pigment in our hair, skin, and eyes. The so-called switch we’re talking about — the one that affects the OCA2 gene code (and P protein, and melanin production) — is located not on the OCA2 gene code but right next to it on another gene code. So this switch doesn’t bring melanin production to a total halt — that would produce albinism, or pink skin and all-white hair — but it does reduce melanin production in the iris, the part of the eye that surrounds the pupil.
Brown, hazel, and green eye colors are all caused by wide variations in melanin. But the color differences between blue-eyed people are so tiny that scientists are sure all blue eyes derive from one common ancestor … one common mutant ancestor.
“They have all inherited the same switch at exactly the same spot in their DNA,”
explains Professor Hans Eiberg of the University of Copenhagen, where he was central to this study.
As time passes, DNA and the traits it causes get mixed around and less obvious. But the blue-eyed trait is still so strikingly consistent that scientists are sure it happened recently — between 6,000 and 10,000 years ago. Eiberg and his team examined DNA and eye color in 800 people — not just in Denmark but also in Jordan and Turkey.
So why did the change happen? Says Eiberg: “Nature is constantly shuffling the human genome, creating a genetic cocktail of human chromosomes and trying out different changes as it does so.” That’s evolution at work.
If you have blue eyes, look around. You’re distantly related to every other blue-eyed person in the room. Unless it’s your sister or brother. Or your mom or dad. Then there’s nothing distant about it.