Nature played with one of our ancestors, and it caused the blue eye color to appear; and now, women are in love with the blue eyes of Brad Pitt and men with those of Kristanna Loken. And that ancestor lived 6,000-10,000 years ago, as found by a research carried out at the University of Copenhagen.
"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 ", said Professor Eiberg from the Department of Cellular and Molecular Medicine.
The OCA2 gene encodes the P protein, which controls the synthesis of
melanin, the pigment protein that gives the color of our hair, eyes and skin. The mutation is found in the gene adjacent to OCA2 that controls the activity of OCA2 and does not turn off completely the OCA2. It just decreases its action of spurring melanin synthesis in the iris, so that the low amount of melanin in the iris appears as blue, and not brown.
If the OCA2 gene had been silenced completely, the result would have been a total lack of melanin in hair, eyes or skin, a disease called albinism. In this case, the eyes would have been red, due to the blood vessels of the iris.
Eye color variation from brown to green is caused by the variable amount of iris melanin, but blue eyes are correlated with a very low level of variation in the melanin levels of the eyes, strictly linked to one genetic variation.
"From this we can conclude that all blue-eyed individuals are linked to the same ancestor. They have all inherited the same switch at exactly the same spot in their DNA," said Eiberg.
Oppositely, brown eyes can be the result of a large variation in the DNA sector controlling the melanin synthesis. The team investigated mitochondrial DNA (coming always from the maternal line) from blue-eyed individuals coming from countries far from one another, such as Jordan, Denmark and Turkey.
In 1996, the same team had detected that OCA2 was involved in the eye color. The mutation from brown eyes to blue eyes is another example of neuter mutation; like hair color or baldness, it does not impact the individual's survival ability.
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