More info about this fact

Estimates suggest that roughly 10% of the people around the world have blue eyes. While the ratio of blue eyes is higher in European countries (particularly in Scandinavia), people with blue eyes exist around the globe in people of different ethnic backgrounds, although this is rare. Brown eyes on the other hand are the most common eye color for humans, and our ancient ancestors all had them. However, sometime between 6,000 and 10,000 years ago a mutation occurred that paved the way for all blue-eyed humans on earth.

The color of our eyes depends on the amount of the brown pigment melanin in the iris (the colored part of the eye). Darker eyes have more melanin, while lighter eyes have less. The amount of melanin in the eyes is controlled by a several genes. One of these genes, OCA2, determines how much melanin is in the eye, and therefore how brown it is. Imagine that the OCA2 gene is a dimmer light switch. There is another gene close to OCA2, this one is called HERC2. It turns out that a specific mutation in HERC2 is able to slide the dimmer switch all the way down to almost off, resulting in very little, or no brown pigment in the iris of blue-eyed people.

What is most amazing is that this one specific mutation in HERC2 is present in all people with blue eyes (with the exception of those with blue eyes as a result of ocular albinism or Waardenburg syndrome). The current theory, first reached by Danish researchers, is that all blue-eyed humans are related to one single ancestor, a female who was alive thousands of years ago. While this study had a small sample size, it is a compelling theory.

To read more about this study, click here.