Learn About the Origins of Green Eyes
What causes people to have green eyes?
Green eyes are especially rare. In humans, the pigmentation of an iris can range from very light amber yellow to a very dark brown, bordering on black. The darkness of the iris depends on its concentration of melanin. The amount of melanin in your eyes or skin determines it's color. The greater the concentration of melanin, the darker the eye color. Green eyes possess low to moderate amounts of melanin. However, green is actually not a pigmentation of the iris at all.
The main role of skin pigmentation seems to be to absorb ultraviolet radiation and this is true about the iris of the eyes too.
Rayleigh scattering is the dispersion of light off of air molecules, this helps determine eye color. This same scattering of light occurs in the sky which makes it appear blue, orange, pink, etc. and mountains in the distance appear purple or blue. In the eye, this effect occurs in the top layer (stroma) of the iris. The blue optical effect of the Rayleigh scattering combined with the light to medium melanin pigmentation combines to make the eye appear green.
Origins of Green Eyes
Light Melanin Pigmentation In Green Eyes
Genetics, Prevelance and Distribution of Green Eyes
Only 2% of the world's population have green eyes or about 140 million people. Why do so few people have this trait? The answer boils down to genetics.
Until 2007, it was believed that there was a hierarchy of eye color. Brown was dominant over green, which was dominant over blue. You received two genes for an eye color, one gene from each parent, and whichever was the dominant gene would express itself. Therefore two brown genes would obviously express itself as brown. A brown gene and a blue or green gene would express itself as brown. A green gene and a blue gene would express itself as green. And only a combination of two blue genes would express itself as blue.
The study disproving this Mendelian theory for eye color was published in the American Journal of Human Genetics, and was supported with grants from Australia's National Health and Medical Research Council and the United States of America's National Cancer Institute.
Now it is proven that eye color is controlled by more than one gene; in fact, up to 16 genes contribute to eye color. This means that there is a chance that a person can inherit virtually any eye color, no matter the eye color of the parents (although the chances for people of certain heritages having a particular eye color are different than for others).
Africa, Asia, Europe, the middle east and the America's have been home to those with green eyes for thousands of years. Iran, Pakistan, Afghanistan, Central Asia, Russia, Spain, and Brazil all have had populations with green eyes for a long time. All races, including Caucasian, African, Asian, Pacific Islanders, Arabic, Hispanic and the Indigenous Peoples of the Americas can also have green eyes. Green eyes most likely developed because of the migration of people over time, those from northern latitudes with light coloring traveled south and people of dark coloring traveling north intermixed, leading to a variation of melanin produced. Today the green eyes of their descendents can be found on every continent.
Notably, there have been records of people with green eyes originating around the Caucasus mountains, which links Europe and Asia. Several passes through the mountain range made it a strategic region or military and trade(silk road).
There is a village in north western China called Liqian in which two-thirds of the inhabitants have green eyes and blonde hair. DNA has linked these people to an ancestor(s) that was caucasian. Some believe that they are descendents of the legendary missing army of Marcus Crassus, a Roman general that disappeared in 36 bc. However Liqian is along the silk road trade route so many people passed through. Until more proof is found, no one is sure if Marcus Crassus and his army were ever in Liqian.
Is it possible there will be more green eyed people in the future due to mass migration and globalization? For now only time will tell.
Chameleon Eyes or Rayleigh Scattering
Factors That Can Slightly Alter Green Eye Color
Because of this, changes in the light being scattered by the iris of lighter colored eyes will change the apparent color of the eyes. This results in "chameleon eyes", or eyes that change color. They fall into the amber, hazel, green, grey, and blue range. Specific factors that can cause the eyes to appear to change colors are:
- Mood: Mood plays a role in the color of your eyes. Or rather the optical illusion of eye color. If you have bloodshot eyes, you may notice your eyes are bright green, this is because of the contrast red/pink is the opposite of green. Pupil dilation is also a factor and your pupils change size depending on the emotions you feel. Happiness and also anger cause your pupils to dilate, thus increasing the amount of light let in. This increases the rayleigh scattering and your eyes may appear more green. Smaller pupils let less light in, making them appear more grey. This is also a signal you are sad or not feeling well.
- Weather: The weather can change the ambient light. There is a big difference between the spectrum of colors in the light cast by a cloudy day, a sunny day, a moonlit night, and a sunset.
- Temperature: Temperature can seem correlated to eye color, but this is because the temperature may vary in various lighting situations—for example, the lighting in your office when it's cold and cloudy and the windows are drawn vs the lighting in your office when it is sunny and the windows are open.
- Colors you are wearing: Wearing certain colors such as blue, yellow, or green will provide more of that color for your eyes to scatter, enhancing that color. Green and gold eyeshadows act similarly. On the flip side, other eyeshadows that make green eyes stand out more are colors in the purple family (plum, lavender, lilac), coppers, and apricot because they contrast with the green, making it stand out even more.
- Colors around you: The colors in close proximity to you will act similarly to the colors you are wearing.
- Lighting: Artificial lighting can vary to an even greater degree than natural lighting, and the varying spectrums of light will impact your apparent eye color
Again, drastic eye color changes, especially in adults, could be a sign of an eye problem. If they occur, please see your eye doctor.
Medical Reasons for Eye Color Change
A color change in the iris can be caused by factors such as radiation, disease, and chemicals. For example, glaucoma medications report a side effect of permanently changing lighter colored eyes to brown. Glaucoma medication was discovered to also have the side effect of lengthening eyelashes and is marketed as an eyelash lengthener. These products are FDA approved under the supervision of a doctor.
Heterochromia is when one of the eyes is a different color from the other one. It can be genetic, from an injury or illness.
If, as an adult, one or both of your eyes changes colors drastically, see a doctor. It could be a symptom of diseases such as Fuch’s heterochromic iridocyclitis, Horner’s syndrome, or pigmentary glaucoma or something else.
Other health risks for people with lighter colored eyes can come from radiation. Melanin in the iris helps protect eyes from UV sunlight. People with lighter colored eyes, including green, are more at risk for sun-related eye problems including melanoma of the uvea, a type of cancer. People with lighter colored eyes should wear UV-protective sunglasses while outside for extended periods of time.
Personality associations with green eyes
A relatively small amount of people have green eyes, it is no wonder that some interesting associations have flourished around the eye color. These are not proven facts. Here is a list of some of the perceptions surrounding them:
- Green eyes are said to be magical.
- People with green eyes tend to have long lasting relationships.
- People with green eyes are the most passionate.
- Green-eyed people are jealous, as in the saying "green with envy".
- Green-eyed people may be more prone to have liver or other digestive problems.
- They are a powerful aphrodisiac.
- People with green eyes are very inventive.
- People with green eyes act spontaneously
- People with green eyes are perceived as less trustworthy than blue or brown eyes.
- Green eyed people can be more provacative.
- Green eyed people are strange!
Eyeshadow on Green Eye
Cosmetic Eye Surgery
While illegal in the United States, elsewhere in the world iris implants are available with surgery, resulting in light grey eyes. This procedure can sometimes be reversed.
While very few companies offer permanent eye color change for cosmetic reasons, researchers are studying ways to change eye color permanently without the use of implants.
Magical, Mysterious Green Eyes
Here is a bit of interesting trivia, take it with a grain of salt. The International Community for Alien Research conducted a study of potential alien contactees and found that green eyed people were the largest group to report contact!
"Green/Hazel eyes make up 48% of the 1400 contactees that took part in this study and make up 70% of the O Neg. group. Blue eyes making up 36% of the blood types and 23% of the O Neg. group. Brown eyes make up 16% of the study group and 7% of the O Neg. group."
What Color Eyes (natural) Do you have?
About the poll
I expect that the majority of the votes in the poll will be "green eyes" because many people that read this article will be curious about their own eye color, thus it will be biased. Keep this in mind.
Famous People and Celebrities with Green Eyes
Here is a list of celebrites with green eyes. Green eyes can occur within various ethnic backgrounds Notice how diverse the people are:
- Charlize Theron
- Kate Hudson
- Tyra Banks
- Scarlett Johanssen
- Kristen Stewart
- Hayden Panetierre
- Jennifer Connolly
- Aishwarya Rai
- Vanessa Williams
- Channing Tatum
- Lindsay Lohan
- Julianne Moore
- Ava Gardner
- Cyndi Lauper
- Dita Von Teese
- Jean Harlow
- Sophia Loren
Biological anthropology is a study of the biological and behavioral differences of humans, other non-human primates, and extinct ancestors of humans. The causes of present human diversity are very important to this science.
All eyes are windows to the soul. Every color eye is fascinating in its own right. Love your eye color and take good care of your eyes so you can see all the beauty in the world.
© 2010 Courtney Rhodes