A scientist has said that many people with blue eyes can be linked back to a single ancient ancestor.
Dr. Melissa Ilardo discussed the topic during an appearance on Andrew Huberman’s podcast, where she explained the striking theory behind the origin of blue eyes.
Eye colour is one of the clearest visible signs of genetics. Brown is by far the most widespread shade, outnumbering all other eye colours combined.
The colour itself comes from pigmentation in the iris, the coloured ring of tissue that surrounds the pupil. Eye colour usually falls somewhere on a spectrum from very light blue to dark brown, with green, hazel and grey also appearing naturally.
In rare instances, people can also have heterochromia, a condition where each eye appears a different colour. That can mean subtle variation between similar shades or a much more noticeable contrast, such as one blue eye and one brown eye.
Although eye colour is influenced by several genes, researchers say a major part of blue-eye inheritance is tied to the OCA2-HERC2 region on chromosome 15. Variants in this area can reduce the amount of melanin in the iris, producing lighter eyes.
Describing it as one of her ‘favourite genetic facts’, she said:
“Everyone with blue eyes descends from the same person.”
She continued:
“At one point in human history, one person had a change in their eye colour. And it’s just amazing to imagine this person who had blue eyes for the first time.”
Dr Ilardo said the characteristic spread ‘through many generations’, adding that this was ‘probably because that was a more attractive and interesting feature in that individual’.
The discussion also touched on the ‘F1’ of blue eyes. In this case, the term does not relate to motorsport, but instead refers to the first known individual to display a specific trait.
Researchers have explored this theory before, including a University of Copenhagen study that examined DNA from blue-eyed individuals from several parts of the world, including Turkey, Jordan and Denmark.
Professor Hans Eiberg, from the Department of Cellular and Molecular Medicine, said:
“Originally, we all had brown eyes. But a genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a ‘switch’, which literally ‘turned off’ the ability to produce brown eyes.”
He added:
“They have all inherited the same switch at exactly the same spot in their DNA.”
This change is thought to have happened thousands of years ago, so there is no reason for modern blue-eyed couples to worry about sharing a recent ancestor.
Scientists believe the best-known blue-eye mutation may have arisen roughly 6,000 to 10,000 years ago, probably in the region around the Black Sea. But eye colour is more complex than the old school idea of a single blue-eye gene, and different genetic combinations can produce blue, green, hazel and brown eyes.
That means the headline claim is broadly right in spirit, but simplified: many blue-eyed people likely descend from one ancient founder carrying a key mutation, while eye colour itself is still controlled by a network of genes rather than one switch alone.