Vol.7 Blue eyes and brown eyes

What colors do your eyes see? Different people use different colors around their pupils. In addition, people worldwide have various eye colors. Why do people have different eye colors?
Eye color = iris color

Inside our eyes, there is a part called the “iris” that regulates the amount of light entering the eye. The color of the iris is generally referred to as “eye color. The pupil at the center of the eye was black.

 

Why the color difference?

Two possible reasons may explain the color difference.

First, genetic differences play a role between the groups. Many genes influence iris color, but two main genes have the most significant impact.

Chromosome number Gene name Dominant and recessive genes
Chromosome 15 EYCL3 Dominant = brown, recessive = blue
Chromosome 19 EYCL1 Dominant = green, recessive = blue

The combination of these genes determines eye color; however, since multiple genes determine eye color and their combinations vary, eye color varies from person to person.

The next difference is the amount of melanin.

Melanin is an important pigment that protects the skin from harmful ultraviolet rays. It is found not only in the eyes but also on the skin, hair, and other parts of the body. Generally,　a high amount of melanin pigment in the iris produces a brown color, whereas a low amount produces a blue color. In countries with high rates of sunlight exposure, large amounts of melanin accumulate in the iris to protect it from ultraviolet radiation, resulting in black or brown eyes. Conversely, in countries with low sunlight exposure, the amount of melanin pigment in the iris is low, resulting in light-colored eyes. The same person can also change their eye color if they produce less melanin or if they live in a country with different sunlight exposure rates. Therefore, the amount of melanin produced depends on environmental conditions.

Blue eyes were born 10,000 years ago

According to a recent study, blue eyes did not appear more than 10,000 years ago. Focusing on the gene that produces melanin, it is believed that blue eyes may have been caused by a gene that partially stopped functioning 10,000 years ago.

We do not know the reason for the emergence of blue eyes; however, one theory suggests that environmental changes may be responsible. As humans’ habitats expanded, they may have had less need to protect their eyes from ultraviolet rays in areas with less sunlight. These genes may have partially stopped functioning, leading to the emergence of blue eyes.

“Blue eyes born 10,000 years ago” are based on this hypothesis.

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