Why Do Most People Have Brown Eyes?
You may have noticed that brown eyes are more common than green, blue or hazel eyes, but did you know that originally all humans had brown eyes? The brown pigment is melanin, which also colors hair and skin cells brown. The less melanin in the iris or colored part of the eye, the lighter the eye color.
How did blue and other lighter-colored eyes come into the picture? Scientists trace the historic change back to a single common ancestor. That person had a change in a gene that controls melanin production. This change, or mutation, is believed to have reduced the production of melanin in the iris.
Interestingly, parents with the same eye color can have children with entirely different eye colors. This is because eye color is not determined by a single gene, but might be affected by as many as 16 different genes.
Very young infants sometimes have blue eyes while their melanin is still developing. By the time a baby is 12 months old, cells begin to produce melanin, and as more melanin builds up in the iris, eye color may darken.
Large amounts of melanin in the eyes and skin are protection against the sun’s damaging rays, which explains why people (or ancestors) who live near the equator have darker eyes and skin. On the other hand, in Iceland, most people have blue eyes.
Eye color has been linked to certain eye diseases. People with brown eyes have a lower incidence of eye cancer, macular degeneration and diabetic retinopathy. However, brown-eyed people have a higher risk of cataracts. Since many serious eye diseases have no symptoms, an annual eye exam can help monitor your eye health for these potential risks.
May 10, 2017