What’s the most common eye color? What’s the most uncommon?
Our skin, hair, and eye color are determined by melanin, a natural skin pigment. Specialized cells that make melanin are called melanocytes.
Everyone has the same number of melanocytes, but in some people those melanocytes produce more melanin.
When melanin production is very light then skin, hair, and eyes will also be light. Melanin is an aggregate of smaller component molecules and there are many different types of melanin with different proportions and bonding patterns.
Color by percentages
The rarest eye color is gray and only about 2% of the world’s population have gray eyes. People with gray eyes have very little to no melanin in their irises, but they have more collagen in the layer of the iris called the stroma and light scatters off that collagen in a way that makes the eyes appear gray.
Green eyes are also uncommon and worldwide only about 2% of people have green eyes, but in some parts of the world green eyes are quite common. In Ireland and Scotland about 9% of the population has green eyes.
About 5% of the world’s population have hazel (or amber) eyes, but in the US about 18% of the population has hazel eyes.
Blue eyes are the second most common eye color. About 8 to 10% of the world’s population has blue eyes, but in the U.S. the percentage is higher and about 25% of people have blue eyes.
Brown eyes are the world’s most common eye color and about 70% of the world’s population have brown eyes.
Less than 1% of people have two different eye colors. Some people are born with two different eye colors or it can be caused by an eye injury or a medical condition.
The iris is the part of the eye that has color. There are two layers of the iris—the front pigmented fibrovascular layer known as the stroma and beneath the stroma is the pigmented epithelial cells. Eye color is determined by the amount of melanin in the front layer of the iris.
The muscles in the iris also control how open or closed the pupil of your eye is. When your pupil is wider (dilated), more light gets into your eye, and when it is narrower (contracted) less light gets in. This is how your eyes accommodate for the amount of available light.
The iris is filled with a fluid called aqueous humor that your eye constantly produces and drains. The aqueous humor maintains the eyes’ shape, size and pressure.
How do we inherit eye color?
In the past it was believed that one gene determined color and that the color of the eyes followed a simple inheritance pattern, for example, it was believed that parents with blue eyes would not have a child with brown eyes. We know differently now.
Eye color inheritance is complex and is determined by multiple genes. At least 16 genes play a role in determining eye color.
Generally, a child’s eye color can be predicted by looking at the color of the parents’ eyes, but because eye color is determined by so many genes a child may also have an unexpected eye color.