Hey there, curious minds! Have you ever heard the saying that eyes are the “window to the soul”? Well, it turns out they’re more like windows that focus light onto a special part of the eye called the retina. Our eyes are unique, just like our fingerprints, and they’re full of amazing patterns and colors. Let’s dive into the science behind what makes our eyes so special!
What color are your eyes? People around the world have different eye colors, and scientists use a special scale to classify them. The colorful part of your eye is called the “iris,” named after the Greek goddess of the rainbow. But here’s a fun fact: all those beautiful eye colors are actually made from just one color! The iris contains a pigment called melanin, and there’s no blue melanin—only shades of brown.
If you have blue eyes, you might wonder how they can look blue when there’s no blue pigment in them. This is where the Tyndall effect comes in. Imagine shining a light through water with a little milk in it. The light beam looks bluish because tiny particles scatter the blue light. Similarly, in blue eyes, tiny pigment particles scatter blue light, making the eyes appear blue.
Most people have brown eyes, but lighter eye colors like blue and green are found in some parts of the world. The mutation that led to blue eyes is ancient, possibly originating over 10,000 years ago. But how is eye color inherited? It’s not as simple as you might think. Eye color is influenced by multiple genes, not just one. These genes interact in complex ways, creating a spectrum of eye colors from brown to blue and everything in between.
In the past, we thought one gene determined eye color, with brown being dominant over blue. But now we know that at least 10 different genes play a role in determining eye color. It’s like a genetic symphony, with many genes working together to create the unique color of your eyes.
Your eye color is one of the most beautiful and unique things about you. So, how would you describe your eyes? Share your thoughts and stay curious about the amazing world around you!
For more fascinating content, check out the PBS Digital Studios series “Say It Loud,” which celebrates Black history and culture. Hosted by Evelyn from the Internets and Azie Dungey, the series offers a fun take on identity and pop culture. I even joined them for an episode about DNA ancestry tests. Stay curious and keep exploring!
Use colored pencils or markers to create a color wheel that represents the spectrum of eye colors. Label each section with the corresponding eye color and include a brief description of how melanin affects each color. This will help you visualize the range of eye colors and understand the role of melanin.
Conduct a simple experiment to observe the Tyndall effect. Fill a glass with water and add a few drops of milk. Shine a flashlight through the glass and observe how the light scatters. Write a short paragraph explaining how this experiment relates to the appearance of blue eyes.
Create a chart of your family members’ eye colors. Research and write a short explanation of how genetics might have influenced the eye colors in your family. Consider the role of multiple genes and how they interact to determine eye color.
Interview a family member or friend about their eye color and what they know about it. Share your findings with the class, highlighting any interesting stories or facts about eye color inheritance in their family.
Create an infographic that explains the science behind eye colors, including the role of melanin, the Tyndall effect, and genetics. Use images and diagrams to make your infographic engaging and informative. Share it with your classmates to spread awareness about the fascinating science of eye colors.
Sure! Here’s a sanitized version of the transcript:
—
Hey smart pupils, Joe here. William Shakespeare called the eyes the “window to the soul.” But it turns out they’re actually just a window that focuses photons onto a light-sensing tissue called the retina. And these are mine. They’re brownish with a sort of hazel ring going on. I’m honestly not even really sure what hazel is, but let’s go with it. And these are the eyes of some really cool and popular YouTubers who kindly let me use my macro lens when we were hanging out. Can you tell who these belong to? If not, don’t feel bad; I mean, when was the last time you just stared at someone’s eyeball from six inches away? It’s kind of unusual. In fact, looking at eyes looking back at me is starting to creep me out… Much better.
Our eyes are just as unique as our fingerprints, like tiny galaxies, full of shapes, patterns, and colors. Where do these eye colors come from? Don’t blink, here comes the science.
What color are your eyes? Anthropologists use an official scale to classify people’s eye colors from around the world. Tag yourself… I’m a 10. That little colored part on the front is called the “iris.” It’s named for the Greek goddess of the rainbow, but this entire kaleidoscope of colors is actually made from just one color. The blues, the greens, the browns… are all a trick of physics. If you could look at the pigment molecules inside your irises, you’d find they would all be brown! The iris contains cells that have a pigment called melanin, and there’s no blue melanin—only earthy tones. In every color of eye, the back layer of the iris is densely packed with dark melanin, but that’s covered by a meshy front layer, and that’s where things vary from person to person.
If you have brown eyes, the cells in the meshy front of your iris are full of pigment. If you have blue or blue-grey eyes, there’s not much pigment in that meshy layer at all. The other eye colors fall somewhere in the middle. So how can you have blue eyes when there’s nothing blue inside them? Let me show you a quick experiment. If I shine a light through plain water, the beam is almost invisible. But when we add some milk, the beam becomes visible and has a bluish tint. It’s called the Tyndall effect. There are tiny particles of milk suspended in the water, just like there are tiny packets of pigment spread out inside blue eyes. Even though those particles aren’t blue, they scatter shorter blue wavelengths of light away, while redder wavelengths pass through.
It’s also why smoke looks blue and why the sky is blue. In the case of the sky, light is scattering off air molecules and not dust particles. So how’s this happening inside the eye? In people with blue eyes, those scattered pigment particles bounce blue light back out of the iris due to the Tyndall effect, while the iris absorbs the red light. So the eye appears blue even though there’s nothing blue in it. The denser those little pigment specks, the more brown it looks. Light-colored eyes like green, blue, and grey aren’t truly those colors; they’re just less and less brown.
For most of the human population, brown eyes dominate, but we find pockets of lighter-eyed people throughout the world. The mutation that originally caused blue eyes in European populations is at least 6,000 years old, but it could be even older—maybe originating in Africa more than 10,000 years ago. Speaking of which, how is eye color inherited? Traits come, in part, from genes: little bits of DNA passed down from parents. In grade school, maybe you heard that one gene determines eye color, and the brown-eyed trait always dominates over the blue-eyed trait. Or that blue-eyed parents can’t have brown-eyed kids? Well, that’s not accurate.
Eye color genetics is nowhere near as simple as we’ve been taught. Maybe you’ve heard of the monk, Gregor Mendel, who studied inheritance in the 1800s? Most of our old explanations about eye color genetics came from his ideas, but more recently we’ve discovered that most traits don’t fit neatly into Mendel’s squares because they involve several genes interacting together. For example, we have this gene. How strongly it’s turned on determines how much pigment cells in our eyes make. What version of this gene you have is responsible for around 75 percent of having blue vs. brown eyes. However, another gene that lives close by can interfere with or even switch that gene off. So even if you have a “brown” trait, you can end up with lighter eyes. And that’s just two genes!
In total, we’ve identified at least 10 genes that influence eye color, and there are probably many more. Like height or intelligence, it’s more like a genetic symphony, all playing together. No one’s eyes can really be described by a single word; they fall on a continuous spectrum from brown to blue, and a lot in between. Turns out, your eye color is one of the most beautiful and unique things about you. What’s an interesting way to describe YOUR eyes? I’ll be looking for answers in the comments.
Stay tuned for more content, but first, I want to tell you about the new PBS Digital Studios series “Say It Loud,” a celebration of Black history and culture, and its impact on how we live today. It’s hosted by Evelyn from the Internets and Azie Dungey, who provide a humorous take on identity and pop culture. I recently joined them for an episode about DNA ancestry tests. Check out “Say It Loud” at the link in the description below.
And finally, you know what they say about eye puns… Stay curious!
—
Let me know if you need any further modifications!
Eyes – Organs that detect light and allow us to see. – The human eyes are capable of distinguishing millions of different colors.
Color – A property of an object that depends on the light it reflects and how it is perceived by the eyes. – In science class, we learned how the color of an object can change under different lighting conditions.
Iris – The colored part of the eye that controls the size of the pupil and the amount of light that enters the eye. – The iris adjusts to let more or less light into the eye, helping us see better in different lighting.
Pigment – A substance that gives color to tissues or materials by absorbing certain wavelengths of light. – The pigment in the iris determines the color of a person’s eyes.
Melanin – A natural pigment found in most organisms, responsible for the color of skin, hair, and eyes. – People with more melanin in their irises tend to have brown eyes.
Blue – A color that is often associated with the sky and the sea, and can also describe a type of eye color. – Blue eyes are less common than brown eyes because they have less melanin.
Genes – Units of heredity that are made up of DNA and determine specific traits in an organism. – The genes you inherit from your parents can influence your eye color.
Inherited – Received genetic traits from one’s parents or ancestors. – Eye color is an inherited trait that can be passed down through generations.
Unique – Being the only one of its kind; unlike anything else. – Each person’s eye color pattern is unique, like a fingerprint.
Science – The study of the natural world through observation and experiment. – In science class, we conducted experiments to understand how light affects vision.
