Skeleton model

The blue eye colour is a recessive trait in humans and is quite a unique thing in the world. In the US, only 1 out of 6 (some people think 1 out of 10!) have blue irises. In some other countries, especially those in Africa and Asia, the blue eye colour is almost non prevalent.
 

A blue eye colour gives rise when the eye produces only a very little amount of melanin. Melanin is the pigment you also find in your hair. A lot of melanin causes a darker, brownish colour. People with brown eyes produce a lot of melanin.

When we look at the entire world population, the blue-eyed-people are quite rare. Of course, not every country has only a small amoutn of those blue eyes. In fact, blue irises are quite common in Europe. Especially the nordic countries (Sweden, Norway, Denmark, Finland, Iceland, Netherlands, Estonia) has a lot of them walking around.

Blue-eyed Scandinavia

In Finland, almost 95% of all inhabitants have blue (or green) eyes. Estonia may have an even higher percentage. The Scandinavian countries are also very high in blue eyes, around 85%. The Netherlands follows with 70-80% light (blue) eyes. Germany, Ireland, Scotland, Poland, Latvia and Lithuania also have a lot of people with blue eyes (50+%).

Blue eyes as an infant

A lot of people in the US and Europe had blue eyes when they where an infant. The melanin production in the iris did not worked optimal so the eyes looked blue (low amount of melanin). Also, a lot of infants have very light blond hair. Hair and eye colour stay light when a person has the genes responsible for those light traits. 

Scientist believe that intelligence and blue eyes go well together. They found some significant effect between blue eyes and strategical thinking. Blue eyed participants seemed to be better on that dimension. Also people with green and grey eyes (light eyes) scored higher. Of course, the results can be biased.

Melanin and blue eyes

The level op melanin in the eyes is for every eye colour different. Brown eyes have a lot of melanin (pigmentation), other eye colours like green and blue have only a little bit. According to some researchers, blue eyed people have almost always the same level of melanin inside their irises whereas brown-eyed people show a lot of variation.


Read More: The blue eyed humans