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If you have blue eyes, then you share a common ancestor with other blonde humans.

"Originally, we all had brown eyes," said Hans Eiberg, one of the researchers, in a news release. "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."

The OCA2 gene codes for the so-called P protein producing melanin, which is a pigment giving the distinctive color to human hair, eyes and skin.

The switch takes place in the gene just adjacent to OCA2. It does not totally turn off the gene but just brings down the production of melanin in the iris, which makes brown eyes blue.

If OCA2 is totally destroyed or switched off, it could lead to albinism.

If the eyes turn from brown to green, the melanin in the iris can explain it. However, as blue-eyed individuals show just a small variation of melanin in their eyes, scientists conclude that blue-eyed people all share the same ancestor.

Scientists probed mitochondrial DNA and looked at the eye color of blue-eyed people in countries as diverse as Jordan, Denmark and Turkey, proving that the OCA2 gene tends to indicate eye color.

"They have all inherited the same switch at exactly the same spot in their DNA," said Eiberg.

On the other hand, brown eyed individuals show a lot of individual variation in the DNA regions that controls melanin production.

The study reveals a lot about not only blue eyes but also the genetics of humans in general.

The findings are published in the journal Human Genetics.