Brown is the color of eye prevalent worldwide by a huge margin. It is, in fact, green is considered to be one of the rarest eye colors around the globe. The color of the eye depends entirely upon the amount of melanin present in them.
Melanin is a brown pigment, so it is included in the coloring of skin as well as the eyes. As many as 16 genes have been described to regulate the amount of melanin inside the specialized cells of the iris.
We also consider the distribution of the world population by the share of people with each eye color.
What determines eye color?
The colored part of the eye is known as the iris, which contains pigments that determine a person’s eye color.
Eye color is largely genetic.
As many as 16 genes dictate what a person’s eye color will be. Most of these genes play a role in the production, transportation, or storage of melanin. Melanin is a brown pigment that determines the color not only of someone’s eyes, but also their hair and skin.
The more melanin in the eyes, the browner they are.
Eyes that are not brown do not have different color pigments. Instead, they have less melanin. An iris with the least melanin will appear blue, while those with a little more melanin may appear green or hazel.
Scientists used to think that just one gene determined eye color, and that brown eyes were dominant over blue eyes. They now know that what determines eye color is more complex.
Eye color percentages around the world
The vast majority of people in the world have brown eyes. The second most common color is blue, but people can also have hazel, green, or gray eyes.
Brown eyes
According to a 2020 studyTrusted Source, 79% people worldwide have brown eyes, making brown the most common eye color.
It may also be one of the oldest eye colors in humans.
Around 10,000 years ago, everyone on Earth had brown eyes. The melanin helps protect the eyes from the sun, which is why brown eyes are most common in countries in Africa and Asia.
People with brown eyes may be less likely to develop eye cancer, macular degeneration, and diabetic retinopathy than those with lighter eyes.
However, brown-eyed people may be more at risk of cataracts as they get older. The reasons for this are unclear.
Blue Eyes
There is no such thing as blue pigment in blue irises
The color of our eyes depends on how much melanin is present in the iris. Blue eyes get their color the same way water and the sky get their blue color — they scatter light so that more blue light reflects back out.
The iris has two layers. Even people with blue eyes, the back layer, which is called the pigment epithelium, contains pigment in all but a few cases.
The front layer of the iris, called the stroma, is comprised of overlapping fibers and cells. For people with brown-colored eyes, some of the cells also have brown pigment in them. If there is no pigment at all in that front layer, then the fibers scatter and absorb some of the longer wavelengths which are incoming. More blue light gets back out and the eyes appear to be blue.
Blue Eyes are More Susceptible to Light
Melanin in the iris of the eye appears to protect the light-sensitive back portion of the eye from damage by the destructive ultraviolet and high-energy visible “blue” light present within sunlight and artificial sources of these rays.
Since blue eyes contain less melanin than green, hazel, or brown eyes, photophobia is more pronounced in blue eyes than in darker coloured eyes. For these reasons, therefore, having lesser melanin in your irises means you must protect your eyes much more from the UV rays of the sun. It is thus advised to those with blue eyes that they stay away from the sun for an extended period and try to don their protective eyewear whenever they venture outdoors.
All Blue-Eyed People May Have A Common Ancestor
We all originally had brown eyes, but the researchers from the University of Copenhagen believe that a genetic mutation in one of these individuals in Europe, thousands of years ago, caused the birth of blue eyes. Knowing this, we might then tend to assume that such a genetic mutation must be responsible for the eye color of all the blue-eyed people in the world today.
Genetic mutation
A genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a “switch”, which “turned off” the ability to produce brown eyes. The OCA2 gene codes for the ‘P protein’, which is involved in the production of melanin (the pigment that determines the colour of our eyes, skin and hair). The “switch”, does not, however, turn off the gene entirely, but rather limits its action to reducing the production of melanin in the iris – effectively “diluting” brown eyes to blue.
According to Hans Eiberg, associate professor in the Department of Cellular and Molecular Medicine from the University of Copenhagen,
Hazel
What causes hazel eyes?
The pigmented structure inside the eye that surrounds the pupil and gives eyes their colour is called the iris. The pigment responsible for eye colour is called melanin, which also affects skin colour.
The reason many white, non-Hispanic babies are born with blue eyes is that they don’t have the full amount of melanin present in their irises at birth. In the first few years of life, more melanin may accumulate in the iris, causing blue eyes to turn green, hazel or brown.
Babies whose eyes turn from blue to brown develop significant amounts of melanin. Those who end up with green eyes or hazel eyes develop a little less.
Babies of African American, Hispanic and Asian ethnicities usually are born with dark eyes that stay brown throughout life. This is because these individuals naturally have more melanin in their eyes and skin, compared with non-Hispanic whites.
Light absorption and scattering
There are no blue, green or hazel pigments in the eye. Eyes merely have different amounts of melanin, which is a dark brown pigment.
So how can a dark brown pigment create blue, green or hazel eyes?
Two effects are responsible for this:
Melanin in the iris absorbs various wavelengths of light entering the eye.
Light is diffused and reflected by the iris, and some wavelengths-scatter more easily than others.
Eyes intensely laden with melanin absorb more light entering the eye; consequently, less is scattered and reflected back from the iris. The result is a brown eye color.
In eyes with lower concentrations of melanin, fewer photons are absorbed and more light is scattered and reflected by the iris. Light rays, which have shorter wavelengths-scatter more easily than light rays with longer wavelengths (red light), will appear green or hazel when a person has fewer light-absorbing melanin and blue in an individual with very low concentrations of melanin.
Melanin can diffuse heterogeneously, and it’s just this that, with different distribution patterns in different parts of the iris, can make hazel eyes light brown near the pupil but appear green in the periphery.
Green
Green eyes are not the result of pigmentation, but a lack of it.
The color of the eye is, by a pigment called melanin in the outer layer of the iris. In green eyes, the melanin levels are lesser as opposed to a case of brown or hazel eyes.
Finally, the amount of melanin decides that these eyes seem green or blue. More melanin makes them hazel, and brown eyes contain the most melanin.
Eye Color It is found out by genetics. Of course, many people still believed and thought that eye color was based on one gene alone.
Recent genetic studies finally proved that there are 16 genes responsible for color. These genetic differences in color often contribute to the reason why some parents can give birth to a child who has different eye colors.
Since your baby has blue eyes when he or she was born, there is a possibility that his eyes change once they completely develop their color. Between the first few months or a couple of years, your baby will start to produce more melanin, which may make their blue eyes turn green, hazel, or brown.
How Common Are Green Eyes?
Green eyes are the rarest eye color in human beings. According to the World Atlas, only 2 percent of people in the world have green eyes. This rarity makes it a sought-after color.
People with green eyes are generally found in northern, central, and western Europe.
Advantages of Green Eyes
A 2014 study from the University of Pittsburgh found that women with green or blue eyes may be able to handle pain better than women with brown or hazel eyes. Further studies are needed to draw strong conclusions on the association between eye color and pain tolerance.
People with green eyes are often considered creative and imaginative. This eye color is associated with jealousy and passion. Since it is rare, it is often deemed very attractive.
Disadvantages of Green Eyes
Green eyes, like blue and gray eyes, may have an increased risk for certain eye cancers.
People with lighter eye colors may be more likely to develop cancer of the eye called uveal melanoma. The uvea is the middle layer of the eye.
Melanoma of the uvea is an extremely rare disease. It affects about six in every 1 million adults in the United States annually.
People with green eyes are also often fair-skinned, so they may be at greater risk for various forms of skin cancer as well.
An additional disadvantage of green eyes may be light sensitivity. If you have green eyes, you have less pigment in the iris. Due to this, it may be harder to block out sunlight or bright fluorescent light. As a result, your eyes may feel more sensitive to light.
Gray
Like any other color of the eyes, grey eyes can vary in shades, lighter or darker. Grey eyes may have gold or green flecks. And, like hazel eyes, there is also a possibility that you may notice color on different parts of the irises. Blue-grey, green-grey and even hazel-grey are just some of the possible combinations.
What Causes Grey Eyes?
Like blue eyes, grey eyes have very little melanin in the front layer of the iris, named the stroma. But some research claims that grey eyes contain more collagen in their stroma than blue eyes, which somehow contributes to their difference in color.
Melanin in Grey Eyes
Melanin is found in everybody, a brown pigment that exists in skin, eyes, and hair. All irises have a layer on the back of their structure that contains brown pigment. It is the pigmentation of the front layer of the iris that varies from one individual to another.
The melanin in the eye affects how much light is getting into and bouncing back out and, consequently, the color of your iris. An iris with more melanin tends to appear darker; one containing less melanin has a lighter-colored iris. And, again, low melanin levels result in grey-colored eyes.
Collagen in Grey Eyes
Collagen is a type of protein found in the iris, and it affects how light is scattered in the eye. Because grey eyes have higher amounts of collagen present, light scatters differently than it does in other eye colors.
