Why do white people have blue eyes

The gaze-locking color of blue eyes can be striking. About half as many Americans have blue eyes as brown eyes. Worldwide, fewer than one in every 10 people sport a blue eye color. Between 6, and 10, years ago, a baby was born in Europe with a harmless genetic mutation. As far as researchers can tell, this was the first person with blue eyes, and everyone who has blue eyes today is a very distant relative of this ancient human. Eye color depends on how much of a pigment called melanin lives in the iris of the eye.

Melanin is also responsible for the color of our skin, eyes and hair. This genetic switch limits how much melanin is produced in the iris — effectively "diluting" brown eyes to a shade of blue. In addition to having significantly less melanin in their iris than people with brown eyes, hazel eyes or green eyes , blue-eyed individuals don't have very much variation in the part of their DNA responsible for melanin production.

The color of our eyes depends on how much melanin is present in the iris. Brown eyes have the highest amount of melanin in the iris, and blue eyes have the least. Brown melanin is the only pigment that exists in the eye; there is no pigment for hazel or green — or blue. Eyes only appear to be these colors because of the way light strikes the layers of the iris and reflects back toward the viewer. The blue tint is caused by thin or transparent scleral collagen found within the eye.

In osteogenesis imperfecta, the body fails to produce type I collagen, a component that helps form bone, connective tissues, teeth and the white part of the eye or sclera, says the American Academy of Orthopaedic Surgeons.

Other symptoms of the disease include multiple fractures, short stature, breathing problems, hearing loss, brittle teeth and bone deformities. While there are many types of osteogenesis imperfecta, some of them deadly, more than 60 percent of all cases are of the mild type. Brown-eyed individuals have considerable individual variation in the area of their DNA that controls melanin production.

But they found that blue-eyed individuals only have a small degree of variation in the amount of melanin in their eyes. It makes them have more kids. Jeanna is the editor-in-chief of Live Science.

Previously, she was an assistant editor at Scholastic's Science World magazine. Jeanna has an English degree from Salisbury University, a master's degree in biogeochemistry and environmental sciences from the University of Maryland, and a graduate science journalism degree from New York University. She has worked as a biologist in Florida, where she monitored wetlands and did field surveys for endangered species. She also received an ocean sciences journalism fellowship from Woods Hole Oceanographic Institution.

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