Throughout history green eyes have been associated with jealousy. More than five hundred year ago, in 1603, in the play Othello, Shakespeare wrote, “O beware, my lord, of jealousy; It is the green-eyed monster which doth mock the meat it feeds on.” Shakespeare had previously used the idea in The Merchant of Venice in which Portia refers to “green-eyed jealousy.”
The association with green eyes and jealousy most likely originated in Greek mythology in the tale of Cupid and Psyche. In folktales around the world, witches, nymphs and water spirits often have green eyes.
One of the oldest myths in human genetics is that having blue eyes is determined by a single gene, with the allele for blue eyes recessive to the allele for non-blue eyes (green, brown, or hazel). Many people think that two blue-eyed parents cannot have a brown-eyed child; however, eye color is determined by at least 16 genes and a child of blue-eyed parents can have an unexpected eye color.
How is eye color determined?
A region on chromosome 15 plays a major role in eye color. Within this region on chromosome 15 there are two genes that are located close together—OCA2 and HERC2 and these two genes are responsible for the greatest portion of eye color variation.
Several other genes play smaller roles in determining eye color. Some of these genes are also involved in skin and hair coloring. The effects of these genes likely combine with those of OCA2 and HERC2 to produce a continuum of eye colors in different people.
The cells in the iris (melanocytes) make a pigment called melanin that is responsible for eye color. Melanin is a brown-colored pigment and if your eyes are brown then you have a lot of melanin in your iris.
Blue eyes do not have blue pigment, but just less of the brown melanin pigment so more light bounces back from the eye and makes it appear blue. This same physics of bounced back (reflected) light is why the sea and sky look blue.
Most and least common eye colors
Asian and African populations have a much higher percentage of brown eyes when compared to European populations. In these regions, higher levels of melanin in the irises help protect people’s eyes from the sun’s strong UV rays. In less sunny places, like Iceland and Scandinavia, most people have light-colored eyes.
More than half the people in the world have brown eyes that range from dark to light brown. The estimates for those with blue eyes range from 8 to 10% of the world’s population.
And those green eyes that have so many myths and superstitions around them—they only account for about 2% of all eyes worldwide, but in Ireland and Scotland about 9% of the population have green eyes.
Hazel and amber eyes are uncommon in the world population where only about 5% have those eye colors, but in the US about 18% of the population has a variation of hazel or amber eyes.
The most uncommon eye color of all is gray eyes. Close to 2% of the world’s population have gray eyes. People with gray eyes have little or no melanin in their irises, but they have more collagen in a part of the eye called the stroma. The light scatters off the collagen in a way that makes the eyes appear gray.
No matter your eye color, take care of your vision
No matter what your eye color, you need to take care of your eyes. Treat your eyes well, shield them from the sun, and visit your eye care professional for regular examinations.