Pigment determines eye color, and a number of genes influence pigment. Brown is the most common eye color worldwide by a large majority.
What is eye color?
The iris is the name of the colored part of the eye.
The iris surrounds the pupil, which is the small black hole in the middle of the eye that helps control how much light enters it.
What determines eye color?
Scientists used to think that eye color linked to just one gene and that brown eyes were dominant over blue eyes.
They now know that what determines eye color is more complex.
As many as 16 genes influence eye color by determining the amount of melanin inside the specialized cells of the iris. Most of these genes play a role in the production, transportation, or storage of melanin. Melanin is the pigment responsible for eye color.
Melanin is a brown pigment that determines the color not only of someone’s eyes but also of their hair and skin.
Eyes that are not brown do not have different color pigments. Instead, they absorb less light because they have less melanin. As a result, they scatter more light, reflecting it along the spectrum of light color.
An iris with the least melanin will appear blue. Those with a little more melanin will appear green or hazel, for example.
Eye color around the world
Globally, brown is the most common eye color. Scientists believe that it was the only eye color up until about 10,000 years ago.
The second most common color is blue, but people can also have green, gray, amber, or red eyes.
People with red or violet eyes have little or no melanin in their irises.
Some people have eyes that are different colors than each other (Heterochromia).
Medically reviewed by Ann Marie Griff, O.D. — Written by Amanda Barrell on November 25, 2020
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