Science Proved Everyone's Eyes Are Actually Brown — And Here's Why

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Science is a weird and fascinating world. If it isn’t contributing to amazing inventions, radical new technologies, or trying to solve the medical mysteries of the world, it can also reveal facts we don't necessarily like all the time.

If it’s not proving that the dinosaurs all sort of looked like giant chickens and didn’t roar, or taking Pluto’s planetary status away, science gets personal to prove that people with “unique” colored eyes really just have brown eyes beneath it all. 

That's right — everyone started out with brown eyes.

RELATED: What Your Eye Color Reveals About Your Personality

What causes brown eyes?

Blue eyes? Green eyes? Hazel eyes? Gray eyes? Science says your eyes are actually brown.

Dr. Gary Heiting is a licensed optometrist and the senior editor of an eye care website called All About Vision. According to Heiting, “Everyone has melanin in the iris of their eyes, and the amount that they have determines their eye color. There’s really only (this) one type of pigment.”

Melanin is the pigment that’s in your hair and skin as well as your eyes, and the color is — you can probably guess it — actually dark brown. Melanin absorbs light, so when there is a lot of it present, it can take in more and appears darker. Hence, why darker hair, skin color, and yes, even eyes, have larger amounts of melanin present.

Heiting adds, "It's an interaction between the amount of melanin and the architecture of the iris itself. It's a very complex architecture."

When it’s in an eye, higher melanin levels actually make the iris (the colored part of the eye) appear brown, because it’s absorbing a lot of light, and less light gets reflected out. Conversely, if you don’t have a lot of melanin in your eyes, they will appear lighter because they’re reflecting more light back.

The color brown is a result of a high concentration of melanin in the iris, causing more light to be absorbed and less light to be reflected.

People with brown eyes make up between 55 and 79 percent of the world and are the most common eye color. Green is the rarest eye color.

Does eye color change in babies?

Blue eyes are said to have the least amount of pigment of all the eye colors. So, although a baby's eyes may appear blue when they're born, they will probably develop more melanin later on, causing their eyes to become darker in color.

Heiting says, "As a baby develops, more melanin accumulates in the iris."

The actual process is called “scattering,” and the light that your eye is reflecting back happens to bounce back on shorter wavelengths that appear on the blue side of the spectrum of light color.

What is the difference between brown eyes and hazel eyes?

Brown eyes and hazel eyes are normally roped into the same category, when, in fact, they are quite different. The melanin levels of brown and hazel eye colors are very unique compared to other eye colors like bue. 

Both hazel and brown eyes have a normal level of melanin presence at their back layer. But at the front layer, brown eyes have a heavy melanin presence of brown, while hazel eyes have a higher presence of green.

Therefore, people with hazel eyes have two dominant pigments (eumelanin and pheomelanin) fighting each other, which causes the color to constantly change.

What is special about brown eyes?

Apparently, brown-eyed people have great health benefits all because of their eye color.

For example, people with brown eyes are less likely to develop macular degeneration due to age when compared to people with light eyes. People with brown eyes also have a lower risk of having type 1 diabetes or melanoma of the eye in comparison to lighter-eyed individuals.

However, people with dark eyes are more likely to get cataracts. A study from the early 1990s conducted research into the risk factor of brown-eyed people getting cataracts. Researchers found that brown-eyed people are more than twice as likely to develop cataracts in old ages than those with light eyes. 

The study was published in the American Journal of Ophthalmology, where researcher Robert Cumming, Ph.D., explained, "According to our research, those with darker eyes are at greater risk, whether they're sun worshipers or not."

RELATED: People With This Color Eyes Are More Prone To Alcoholism

Are brown eyes attractive?

1-800-Contacts conducted a survey in September of 2019 to determine the most attractive eye color in the U.S. They surveyed 1,000 people of different genders, ages, and sexualities in order to figure out people's perceptions of eye color.

The study found that gray eyes were both the rarest and the statistically most attractive eye color. Hazel and green were close seconds. Brown eyes, however, were found to be the most common yet the least attractive to the survey's participants.

But don't let that get you down. Apparently, due to the way brown eyes are made through flecks of color, no set of brown eyes is the same as another person's. Therefore, brown eyes are unique in their own way.

Why do I have dark brown eyes? 

According to The American Academy of Ophthalmology, "The iris is made up of two layers of muscle and other kinds of cells. In most people, the back layer has at least some brown pigment in it, even if their eyes don't look brown. In people with brown eyes, the iris’s front layer also has some brown pigment in its cells. The more melanin there is in the iris, the darker brown it will be."

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The color of a person's eyes can also be determined by their location. Dark brown eyes are most common in Africa, East Asia, and Southeast Asia; light brown eyes are found in West Asia, the Americas, and Europe. This is due to the high melanin levels meant to protect the hair and skin from the sun in these hotter regions.

One theory is that eye color evolution may also be traced back to earlier times. People used to need more melanin in their bodies to protect them from hotter climates, but as people moved to less sunny locations, that need has changed. 

Another theory suggests that it may be the cause of a common mutation. "It's believed that's how blue eyes came about, but it may just be the de-emphasis on the need for all the melanin," Heiting says.

There 16 genes that determine eye color, but two are truly essential.

Many once believed that eye color was solely determined by one gene which, yes, genes do play a role in eye color. However, there are several genes that come into play when determining eye color. "Several genes have an influence on eye color. It's not something you can predict with ease," Heiting adds.

There's a total of 16 genes that determine eye color, but it is mostly attributed to two adjacent genes on chromosome 15, protein 2 (HERC2) and ocular albinism (that is, oculocutaneous albinism II [OCA2]). 

There's the substance that OCA2 produces, which helps determine eye color: P protein, which works to mature melanosomes. Melanosomes are a type of cellular structure that work to store and produce melanin. Since brown eyes have a lot of melanin, they have higher levels of P protein.

HERC2 has a region referred to as intron 86. Within this region is a DNA segment that controls OCA2 gene activity. Basically, HERC2 turns the OCA2 gene off or on when it's necessary. With higher OCA2 activity, your eyes will be darker.

To debunk a myth about brown-eyed parents only having brown-eyed kids, since so many genes are at play, parents can actually have children with an eye color neither of them has! That's genetics for you.

So, yes, the reason that your eyes look green, brown, gray, or any other color is probably because you’re actually lacking melanin in your irises.

RELATED: What Are Sanpaku Eyes? How To Tell If You Have Them — And Can They Predict Your Future?

Merethe Najjar is a professional writer, editor, and fiction author. Visit her website, Merethe Walther, or follow her on Twitter.

Editor's Note: This article was originally posted in January 2017 and was updated with the latest information.