Blue eyes

Image by GrashAlex/iStock

It seems everyone finds a particular eye color to be the most attractive. Some find the earthiness of brown eyes soothing, some like playful green eyes, and some like getting lost in a pair of deep blue eyes. Sadly, if you prefer the latter, you may be out of luck…in a few hundred years or so. The genes that control the color of your eyes favor most other colors over blue, so blue eyes are becoming rarer and rarer as generations go on.

The science behind eye color

The color of a person’s eyes is determined by two factors: the pigmentation of their irises and the frequency-dependent scattering of light in the stroma around their irises. These factors are in turn controlled by multiple genes in an individual’s genetic makeup.

Human irises can vary in pigmentation from light brown to black, a fairly narrow color scheme on its own. However, the scattering of light in the stroma (a layer of filaments around the edge of the iris) can result in blue, green, and hazel eyes. This scattering of light is why a person who has these lighter colors of eyes seems to have an eye color that changes a little dependent upon the lighting; it actually does!

Rare eye colors, such as amber, grey, red, and violet are caused by infrequent conditions that affect some part of the iris or stroma. Amber eyes are caused by an unusually high concentration of a yellow pigment, lipochrome, in the iris. Gray eyes are believed to be the result of more collagen than normal in the person’s stroma, resulting in the light being scattered in a unique way. Red and violet eyes only occur in albinos and are the result of a lack of the pigment melanin in the irises.

Recessive blueness

Unfortunately, the genes that cause a person to have blue eyes are recessive genes. “Recessive” genes are those whose effects are overridden by “dominant” genes. This means, in simple terms, that in order for a child to be born with blue eyes, both parents must have the recessive gene for blue eyes as well. If even one of them has the dominant brown eye gene, that parent’s genes will result in the child not being able to have blue eyes.

The result of this dominant versus recessive pattern is that people with blue eyes are slowly becoming less numerous. Because only couples who both have blue eyes can produce children with blue eyes, every time a person with blue eyes has children with someone with brown, green or any other color of eyes, it thins the numbers of blue-eyed people in the next generation.

How fast are blue eyes disappearing? Well, no-one knows for absolute certainty, but some studies show it happening relatively quickly. One study looked at the number of people in the US one hundred years ago and compared it to know. What the scientists found was that a century ago, nearly half the population of the US had blue eyes; now the US population only has 1 out of every 6 people with blue eyes.

Hope for the future

Will blue eyes ever die out completely? Not likely, scientists say. Even though they will become rarer and rarer, the genes that cause blue eyes will never disappear from the human genome, but will simply be covered up, waiting to come out of hiding, waiting for the right two people to meet, or a genetic mutation to occur and allow the blue eyes to shine again.

Aside from genetics, there is another hope for the future of blue eyes, but on an individual basis. A laser procedure pioneered a few years ago can remove some of the brown pigments in a person’s eyes and turn brown eyes into blue. While this wouldn’t affect the person’s genes in any way, and they would still have brown-eyed children, this means that for as long as people find blue eyes attractive, there will be people who have blue eyes.