Blue Eyes: Is Everyone With
Blue Eyes Related?
Among human beings, blue eyes are less common than brown eyes. This is one reason that blue color contact lenses are popular.
Here are a few facts about blue eye color you might not know:
1. All Blue-Eyed People May Have A Common Ancestor
It appears that a genetic mutation in a single individual in Europe 6,000 to 10,000 years ago led to the development of blue eyes, according to researchers at the University of Copenhagen.
"Originally, we all had brown eyes," said Hans Eiberg, associate professor in the Department of Cellular and Molecular Medicine at the university and lead author of the study. "But a genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a 'switch,' which literally turned off the ability to produce brown eyes."
Eye color depends on the amount of a single type of pigment (called melanin) in the iris of the eye. This genetic switch, located in the gene next to the OCA2 gene, limits the production of melanin in the iris effectively "diluting" brown eyes to blue.
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In addition to having significantly less melanin in their iris than people with brown eyes, hazel eyes or green eyes, blue-eyed individuals have only a small degree of variation in their genetic coding for melanin production. Brown-eyed individuals, on the other hand, have considerable individual variation in the area of their DNA that controls melanin production.
"From this we can conclude that all blue-eyed individuals are linked to the same ancestor," said Eiberg. "They have all inherited the same switch at exactly the same spot in their DNA."
So if blue eyes are the result of a genetic mutation in a single individual, how did the trait spread from just one person to being present in 20 to 40 percent of the populations of some European countries today?
One theory is that blue eyes were immediately considered an attractive feature, causing people to seek mates with blue eyes to have children with, enabling the genetic mutation to multiply.
2. Blue Eyes Occur Without Blue Pigment
As mentioned above, blue eye color is determined by something called melanin. Melanin is a brown pigment that controls the color of our skin, eyes and hair.
The color of our eyes depends on how much melanin is present in the iris. There's only brown pigment in the eye there is no hazel pigment or green pigment or blue pigment. Brown eyes have the highest amount of melanin in the iris, and blue eyes have the least.
3. You Can't Predict The Color Of Your Child's Eyes
At one time, it was believed that eye color including blue eyes was a simple genetic trait, and therefore you could predict a child's eye color if you knew the color of the parents' eyes and perhaps the color of the grandparents' eyes.
But geneticists now know that eye color is influenced by as many as 16 different genes to some degree not just one or two genes as once thought. Also, the anatomic structure of the iris can affect eye color to some degree.
So it's impossible to know for sure if your children will have blue eyes. Even if you and your mate both have blue eyes, that's no guarantee your child's eyes will also be blue.
(Here's a royal example of the unpredictability of eye color: Princess Charlotte, the young daughter of blue-eyed Prince William and green-eyed Kate Middleton, has blue eyes. But her brother, Prince George, has very brown eyes.)
4. Blue Eyes At Birth Doesn't Mean Blue Eyes For Life
The human eye does not have its full adult amount of pigment at birth. Because of this, many babies have blue eyes, but their eye color changes as the eye develops during early childhood and more melanin is produced in the iris.
So don't be concerned if your child begins to lose that "baby blue" eye color and her eyes become green or hazel or brown as she gets a little older.
5. Risks Associated With Blue Eyes
Melanin in the iris of the eye appears to help protect the back of the eye from damage caused by UV radiation and high-energy visible ("blue") light from sunlight and artificial sources of these rays.
Because blue eyes contain less melanin than green, hazel or brown eyes, they may be more susceptible to damage from UV and blue light. Research has shown that blue eye color is associated with a greater risk of age-related macular degeneration (AMD) and a rare but potentially deadly form of eye cancer called uveal melanoma.
For these reasons, people with blue eyes should be extra cautious regarding their exposure to sunlight. And because eye damage from UV and blue light appears to be related to your lifetime exposure to these rays, wearing sunglasses that block 100 percent UV and most blue light should begin as soon as possible in childhood.
Also, if you spend several hours a day using a computer, smartphone or other digital devices, it's a good idea to wear eyeglasses that shield your eyes from high-energy blue light when using these devices.
It may take many years before we know the risks associated with cumulative exposure to blue light from computers and smart phones. But many eye care professionals believe it's prudent to use caution when it comes to protecting your eyes from these devices especially if you have blue eyes.
Also, intriguing research suggests that having blue eyes may increase your risk of alcohol dependency if you are a drinker. A study published in American Journal of Medical Genetics, Part B: Neuropsychiatric Genetics found that European Americans with blue eyes had up to 83 percent higher odds of becoming dependent on alcohol, compared with matched controls who had darker eye colors.
Iris color and associated pathological ocular complications: a review of epidemiologic studies. International Journal of Ophthalmology. October 2014.
Blue eye color in humans may be caused by a perfectly associated founder mutation in a regulatory element located within the HERC2 gene inhibiting OCA2 expression. Human Genetics. March 2008.
Three genome-wide association studies and a linkage analysis identify HERC2 as a human iris color gene. American Journal of Human Genetics. February 2008.
Blue-eyed humans have a single, common ancestor. University of Copenhagen. Press release issued January 2008.
[Page updated September 22, 2016]