You may have learned in biology class that your eye color is determined by the genes you inherited. (Genes are essentially “sets of recipes” that are provided in our DNA.) Along with that, you were probably taught about dominant and recessive genes. For eyes, the dominant gene for the color brown always won over the recessive gene for blue eyes. Unfortunately, that information isn’t right. In the past decade, scientists have discovered the influence of genes on eye color is a little more complicated.
A number of different factors define a person’s eye color, the most important of which is eight different color-related genes. The genes control how much melanin, or color pigment, exists in the iris of your eyes. For instance, a gene called OCA2 controls almost 75 percent of the blue-brown color spectrum. Other genes can overrule OCA2, but that rarely happens. This can explain why green eyes are a rarity throughout the world.
What defines human eye color is the amount of light that reflects off the iris, which is a muscular structure that controls how much light enters the eye. So, a person with a high level of melanin pigment in their iris will have brown eyes. Those with a moderate level of iris melanin will have green or hazel eyes, while someone with a low amount will have blue eyes.
There’s a wide range of eye color among people, and many of them don’t fall neatly into the categories of brown, hazel, blue, and green eyes. That is the result of the many ways in which the eight eye color genes can affect one another. Individuals with eye colors other than brown have a European descent, and those who have brown eyes are typically from African and Asian populations. Interestingly, a group of researchers found in 2008 that the gene associated with blue eyes only appeared in the last 6,000 to 10,000 years in Europeans.