Throughout your life, you've most likely seen different people having various eye colors ranging from dark brown to light blue. What is the science behind these different eye colors and how is yours determined? Continue reading to find out!
Eyes can be a variety of colors: brown, blue, green, grey, amber, hazel, red, and more! They do not have any known effect to our vision, so why do they exist?
A part of our eye, called the iris, is where color is given off. The iris is the section surrounding our pupil, which is the black circle in the middle of our eyes, and the iris's color is determined by something called melanin pigmentation. Melanin is a pigment that gives our eyes their color, and the color varies based on the amount of pigment that is present, since pigments are what give things color. People with lighter eye colors have less melanin, while more of that pigment is present in darker eyes.
Interestingly, up until 10,000 years ago, everyone had brown eyes, and the lighter eye colors only became present due to a mutation that caused pigmentation in the iris to turn off. A mutation is a change in a DNA sequence which can be caused by a mistake made during the DNA replication process, or environmental factors like exposure to UV light and cigarette smoke.
Environmental factors also explain why people from different demographic backgrounds have different eye colors. For example, most ethnically African and Asian people have brown eyes because the climate is notably hotter and sunnier in those geographic areas. Melanin serves as protection from damage due to UV light exposure, which is also why these racial groups have darker hair and skin compared to other ethnic groups, for example, in Europe. This also explains why people with darker eyes are less sensitive to sunlight than those with less melanin present in their eyes.
The eye color we inherit is due to our genes which we receive from our biological parents. For example, a child is more likely to have blue eyes if both of their parents also have blue eyes. However, it is still possible for two blue-eyed parents to have a child with brown eyes, as eye color is determined by 16 genes rather than just one, allowing many possible phenotypes, or different physical traits, for offspring.
Here are some fun facts about eye colors!
- Over 55% of the population have brown eyes, making it the most common eye color.
- A study shows that lighter-eyed individuals are frequently more competitive than their darker-eyed counterparts.
- Amber eyes are hypothesized to be due to a greater amount of pheomelanin, another pigment.
- All babies' eyes appear blue, or almost colorless, and darken as they grow older. Therefore, it is stated that babies' eye colors may change up until they're 12 months old.
- Since the job of our irises are to control pupil size to allow us to see in different amounts of light, eye color may slightly change due to the pigment being compressed closely together or spread apart.
- A condition called Heterochromia Iridium causes individuals to have a different color for each eye, while Heterochromia Iridius is a different condition that causes individuals to have multiple colors in each eye.
- People with albinism, which causes low levels of pigment, have eyes that can appear to be red or violet.
Hopefully you've learned something new and interesting in this article. Thank you for reading, and stay safe!
Written by: Janice Le
References:
“How Does Melanin Affect the Eyes?” WebMD, 6 July 2020, www.webmd.com/eye-health/qa/how-does-melanin-affect-the-eyes.
Puiu, Tibi. “Why Eyes Have Different Colors: A Science-Based Look.” ZME Science, 15 Feb. 2019, www.zmescience.com/science/why-eyes-colored-04322.
“What Is a Mutation?” Yourgenome, 25 Jan. 2016, www.yourgenome.org/facts/what-is-a-mutation.
“Why Are Brown Eyes Most Common?” American Academy of Ophthalmology, 26 June 2017, www.aao.org/eye-health/tips-prevention/why-are-brown-eyes-most-common.
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