Eye color is one of many inherited characteristics that tie us to our parents. It’s something that fascinates parents and families of new babies as they try to guess what color the child’s eyes will be. Determining eye color is a complicated equation that can’t be answered until the child is born. And even then, in some instances, eye color can change based on age, and even emotion.
The ring of color in the human eye is known as the iris. The iris contains pigmentation that makes the eye appear to be one of several common colors, including brown, blue, green, hazel, and gray, or a combination of these colors. Most babies are born with blue eyes. This is because melanin, which is a brown pigment, is usually not present in the eye at birth. As the baby grows and melanin is produced, the iris gradually darkens to its final color, which may or may not match the color of the parents.
The Genetics of Eye Colors
It was once believed that brown eyes were dominant, blue eyes were “recessive” or least dominant, and green eyes were somewhere in the middle. Scientists now know that eye color is much more complicated than that. Three genes have been identified as contributing to eye color, and it’s likely that more genes will be found to participate as further study is done.
On a basic level, genes are bits of information that are inherited from the parents. Inside every cell in the human body, there are structures called chromosomes that carry genes which provide genetic information. You may have seen chromosomes illustrated as a spiral step-ladder. When a baby is conceived, half of the information for each chromosome is provided by the father and half is provided by the mother. So each chromosome has two matching parts that pair up to provide the complete information that determines all the characteristics of the new baby, including eye color.
Predicting Eye Colors
If eyes came in only two colors, blue or brown, it would be simple to determine the odds that a baby would have either color. Because there are multiple genes involved in determining eye color, there is no simple formula that can be used. Darker colors tend to be stronger than lighter colors, so in general, brown eyed parents are more likely to have children with brown eyes rather than blue eyes. Similarly, green eyed parents are more likely to have children with green eyes, while two blue eyed parents are very likely to have blue eyed children. But there is no guarantee that this will hold true, especially when the parents do not share the same eye color.
Changing Eye Colors
It is also possible that eye color can appear to change under different circumstances. The pupil, which is the black circle at the center of the iris, allows light to enter the eye so we can see. When the light is bright, the pupil contracts so less light enters the eye. In a darker place, the pupil opens to allow more light into the eye. These changes in the size of the pupil cause the pigment in the iris to spread apart or compress together, which can affect the color of the iris. Strong emotions can also affect the size of the pupil, which is why people sometimes say they see changes in the color of their eyes when they are angry or emotional.
It’s also possible for eye color to change as we age. As already noted, babies are often born with blue eyes that later change to green or brown. Among Caucasian people, who typically have lighter eye colors, about 10 to 15 percent of adults will see changes in their eye color as they age. Brown eyes may fade to hazel, and hazel eyes may get darker over time. It’s important to note that dramatic changes in eye color in an adult can be a symptom of a more serious eye condition. If one eye changes from brown to green or from blue to brown, see your eye doctor right away for a check-up.
Eye color, while fascinating, is ultimately only a cosmetic issue. The color of the eye has no affect on how well we can see or how the eye functions. Eye color may be a unifying trait in a family, or may vary dramatically within a close family group. If you don’t like the color of your eyes, colored contact lenses can change your appearance, even if you don’t need the lenses to correct your vision. But remember, all contact lenses should be prescribed from an eye care professional to be sure they fit correctly and will not cause damage than can affect your vision.
Sources:
All About Vision
Athro, Limited