The origin of blue eyes: a common ancestor
Recent research shows that people with blue eyes have a single common ancestor. A team from the University of Copenhagen has managed to trace a genetic mutation that makes Logar had 6,000 to 10,000 years and that is causing the color of all blue-eyed people in today's world.
"Originally, we all had brown eyes," says Professor Eiberg from the Department of Cellular and Molecular Medicine. "But a genetic mutation affecting the OCA2 gene in our chromosomes proved to be a switch which literally turned off the ability to produce brown eyes." The OCA2 gene codes for the protein called P, which is involved in the production of melanin, the pigment that gives color to hair, skin and eyes. The "switch" which is located in a gene adjacent to OCA2 does not turn off the gene entirely but limits its action to reduce the production of melanin in the iris with the effect of diluting the color brown eyes blue. Therefore, the effect on OCA2 is very specific. If the OCA2 gene had been completely destroyed or turned off, human beings have no melanin in their hair, eyes or skin. This condition is known as albinism.
The other eye colors
Variation in eye color from brown to green can be explained by the amount of melanin in the iris, but blue-eyed people only have a small degree of variation in the melanin in their eyes. "From this we can conclude that all people with blue eyes are linked to the same ancestor," says Professor Eiberg "We all have inherited the same change in the exact same spot in their DNA.". Brown-eyed people, by contrast, have considerable individual variation in the area of DNA that controls melanin production.
The mutation from brown to blue eyes is neither positive nor negative. It is one of several mutations such as hair color, baldness, moles or beauty spots, it does not increase or reduce the ability of survival of man. As Professor Eiberg says, "simply shows that nature is constantly mixing the human genome, creating a genetic cocktail of human chromosomes and trying different changes as it does."