Next to hair color, eye color is probably the most fascinating genetic trait to many people. Everyone wants to know how these traits will manifest in their child, or how they themselves ended up with hair and eyes that don’t match either parent.

We typically think of eyes as coming in one of about six different colors: blue, brown, hazel, grey, green or amber (and a very small portion of the population have red eyes due to albinism). But eye color can get really complicated, and no two people are exactly alike. Some people even have multi-colored eyes, a condition known as heterochromia.

Did you know your eye color is dynamic? It changes with time in most people. Here’s a basic rundown of how our eye color develops and evolves throughout our existence.

How is eye color inherited?

Eye color, like every other genetic trait, comes from our biological parents. You inherit two copies of every gene, one from Mom and another from Dad. As a general rule, the more dominant genes win out over the recessive ones, but sometimes there can be multiple genes all interacting with one another and things can get complicated.

Genotypes and phenotypes

For centuries we’ve known that a child’s final eye color may not match that of either parent, and for a long time, this baffled science. How can you pass on traits you don’t have? Today we know that people carry multiple genetic traits, even if they don’t manifest physically.

Your phenotype refers to the traits you can see, and your genotype refers to the traits you carry in your genetic code. Many things can affect phenotype, including the environment and the recession of certain genes to more dominant ones. Someone with brown eyes, for example, has brown eyes as their phenotype, whereas their genotype may include “other eye colors”.

Since the more in-depth study of the human genome began, we have been able to determine that upwards of a dozen different genes likely influence eye color, meaning determining this trait accurately is a little more complicated than simply comparing “dominant” and “recessive” eye colors. That said, an old-fashioned Punnett square will still give you a pretty good idea of a child’s most likely eye colors.

How long before eye color fully develops?

Because pigment levels play such an important role in eye color (and skin color!) many babies are born with significantly lighter eyes than they will later develop. In fact, a baby’s eyes have a lot of development to do even after they’re born. Not all babies are born with blue eyes, but many non-Hispanic caucasian babies are. Babies from Hispanic or Black families may start out with a lighter brown or grey that usually darkens with time. The more varied a child’s racial background, the more eye color options they have.

If a child’s eyes are going to darken, it will usually be noticeable by six months of age or so. If a two-year-old still has bright blue eyes, then they’re probably going to keep them!

Children are particularly vulnerable to eye damage from the sun and UV rays because they have less pigment to protect them. Be sure to shield your child’s eyes from the sun as much as possible using strategic hats and 100 percent UV-resistant sunglasses.

Eye color later in life

You might think that, as an adult, your eyes are set in their color, but the opposite is actually true. Close to 15 percent of the population see their eyes darken as they progress through adulthood. People with lighter skin are especially vulnerable to eye color changes later in life because their eyes are more likely to be a lighter color to begin with.

Eye color and emotions

Eyes are one of the most expressive parts of the human body. We rely on them for a lot of nonverbal communication and signaling. And it turns out that cartoon characters aren’t the only ones whose eyes change color to match their emotions. This happens in the real world, as well, albeit to a much lesser extent. When your pupil expands or contracts with various moods, it affects the dissemination of pigment in your iris. The more concentrated the pigment, the darker your eyes seem, and vice versa. 

These changes are more noticeable in some people than in others. The next time you feel a strong emotion, try glancing at your eyes in a well-lit mirror, you just might notice a slightly new color.

Show off your eye color!

Eyes are the window to the soul. If you wear prescription glasses, make sure they’re not dulling your vibrant irises! A pair of glasses coated with anti-glare technology will keep your lenses crystal clear. Prescription eyeglasses from 39DollarGlasses can be equipped with Blue495 Anti-Glare Coating, which not only keeps your eyes shining bright, but also protects them from the harmful effects of blue light.