Research has shown that everyone in the world who has blue eyes shares one single common ancestor, who lived between 6,000 and 10,000 years ago, and that the blue eyes were caused by a genetic mutation in this one ancestor.
A research team at the University of Copenhagen found the genetic mutation, which they called "the cause of the eye colour of all blue-eyed humans alive on the planet today". The team, who have worked on the research for over 10 years, examined and compared the eye colour of blue-eyed people in a number of countries from Denmark and Turkey.
We had to dust off our CGP Biology GCSE textbooks to understand the science behind it, but the way lead researcher Professor Eiberg from the Department of Cellular and Molecular Medicine at the university explains it, we all had brown eyes originally.
"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," explains Professor Eiberg in a statement.
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The statement goes on to explain: "The OCA2 gene codes for the so-called P protein, which is involved in the production of melanin, the pigment that gives colour to our hair, eyes and skin. The 'switch', which is located in the gene adjacent to OCA2 does not, however, turn off the gene entirely, but rather limits its action to reducing the production of melanin in the iris - effectively 'diluting' brown eyes to blue."
The OCA2 gene was not totally turned off or destroyed though, otherwise we wouldn't have any melanin in our hair, eyes or skin, which is known as albinism.
The way the researchers figured out that all blue-eyed people share one common ancestor was to look at the fact that variations in eye colour from brown to green are due to the degree of melanin in the iris, but those with blue eyes only have a small variation in the amount of melanin in their eyes.
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"From this we can conclude that all blue-eyed individuals are linked to the same ancestor," says Professor Eiberg. "They have all inherited the same switch at exactly the same spot in their DNA."
It's also interesting to hear that the mutation from brown eyes to blue was not a "positive nor a negative" thing - instead, it's as simple as being bald, having freckles or having beauty spots. Just a mutation that "neither increases nor reduces a human's chance of survival", according to the research team.
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