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Some eye colors are more common than others. Which one is the rarest?

There are many ways to feel special. Maybe you’re a stellar athlete. Maybe you excel at your job. Or maybe you have a unique physical trait like a rare eye color.

Ever wondered if the latter is the case?

There are four main eye colors in the human population. These are brown, blue, hazel and green. We talked to Dr. Purnima Patel, spokesperson for the American Academy of Ophthalmology and ophthalmologist at ORA Vision in Atlanta, to find out how common each eye color is – and which one is the rarest of them all.

What is the rarest eye color?

The rarest eye color is green, according to the American Academy of Ophthalmology. Only two percent of the global population has green eyes.

Green is also the rarest eye color in America. A 2014 survey by the Academy found that 45 percent of Americans had brown eyes, 27 percent had blue eyes, 18 percent had hazel eyes and nine percent had green eyes. The survey also found that 1 percent had eyes that were a color not listed.

Some colors that are not included in the main four may be due to uncertainties or conditions. Gray eyes have traditionally been labeled a shade of blue. Although some studies are considering it its own color. Some people who have albinism may appear to have pink or pale red-colored eyes, but this is because you can see the blood vessels in their eyes. Some people have two different colored eyes. This is a condition called heterochromia.

Why are green eyes so rare?

To understand why some colors are rarer than others, it’s helpful to know what causes eye color in the first place. Every iris contains a pigment called melanin, but the amount of melanin varies from person to person. No person has the exact same amount of melanin in their irises.

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The amount of melanin in your iris determines your eye color. “It’s all about the internal reflection of light proportional to the amount of melanin,” says Patel. “It’s not really that the iris is … green, its actually that the amount of melanin that that iris has is reflecting a color and it happens to be green in color.”

Brown eyes have the most melanin, and blue eyes have the least amount of melanin. The amount of melanin in green irises is somewhere between blue eyes and brown eyes. This amount is the least common you can have. Experts don’t have a reason for why exactly that’s the case, says Patel.

Why are brown eyes the most common?

They do have a theory as to why darker eye colors are more common than lighter eye colors though. Melanin acts as a protective agent for the eye against harmful UV light, which means that in sunny areas brown eyes would be an adaptive trait. When humans lived primarily near the equator, they would have all had brown eyes. Perhaps, as our human ancestors moved away from the equator, a large amount of melanin was no longer necessary to protect the eyes, says Patel. This would allow for genetic mutations that caused lighter eye colors like blue and green to survive in the gene pool and be passed on to later generations.

Key takeaway – if you have green eyes, you’re special! But don’t fret brown-eyed people. At least your melanin has an adaptive advantage.

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This article originally appeared on Cincinnati Enquirer: What is the rarest eye color?