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Original photo by Pressmaster/ Shutterstock
Look Here! 6 Fun Facts About Eyes
Read Time: 4m
Article image
Original photo by Pressmaster/ Shutterstock

They've been described as the windows to the soul by William Shakespeare and the jewel of the body by Henry David Thoreau, and featured in song titles by musicians ranging from Van Morrison and The Who to Billy Idol and Billie Eilish. Needless to say, eyes hold a prominent place in our lives, both for our dependence on their functionality as well as the aesthetic qualities that have inspired so many artists. Here are six eye-opening facts about these amazing organs.

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The First Eyes Appeared at Least 540 Million Years Ago

A fossilized trilobite found in the Green River Formation in Wyoming.
Credit: Layne Kennedy/ Corbis Documentary via Getty Images

The first known organism to demonstrate the leap from light-sensitive receptors to complex eyes was the trilobite, which left records of its evolutionary impact from approximately 540 million years ago. The orbs of these early arthropods more closely resembled the compound eyes of modern insects, with multiple lenses, as opposed to the single lens-to-retina camera-style eye built into humans. Because they offered trilobites a clear advantage in hunting prey (and thus encouraged their predators to evolve in response), the emergence of working eyes in these and subsequent life forms may have helped drive the so-called "Cambrian Explosion," which gave rise to most of the creatures that now populate the animal kingdom.

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The Human Eye Can See Objects Millions of Miles Away

Blue eyed woman's face.
Credit: IoanaB/ Shutterstock

While the majority of us wouldn't consider our vision to be extraordinary, the human eye can see much farther than most of us realize. That's because our ability to perceive an object is based not only on its size and proximity, but also on the brightness of the source. Practically speaking, our sight is hindered by factors such as the Earth's curvature, which creates the dropoff point of the horizon just 3 miles away, and atmospheric conditions. However, a trip outside on a clear night reveals the true power of our vision, as most of us are able to make out the faint haze of the Andromeda Galaxy some 2.6 million light-years into space.

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Some People Can Distinguish Between 100 Million Colors

 Eyeglasses laying on colored papers with different colors visible thru the eyeglasses.
Credit: kmatija/ iStock

Most people are trichromatic, meaning they possess three types of cone cells in their retinas to detect variations of red, green, and blue light. Dichromatic or colorblind people are those with missing or defective cone cells; normally this means they have trouble differentiating between two colors, with red and green being the most common combination. On the extreme ends of the spectrum, those suffering from achromatopsia lack the ability to see any colors, while those born with an extra set of cone cells, tetrachromats, are said to be extraordinarily sensitive to light wavelengths and capable of distinguishing between 100 million colors.

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Woman with her eyes shut.
Credit: PhotoTalk/ iStock

There are a few established reasons for why we blink: This rapid closure triggers secretions that flush away foreign particles, while also providing a lubrication that keeps our precious eyes functioning smoothly. However, this action, which can be voluntary or involuntary, is also affected by a raft of psychological reasons. We blink less when concentrating, for example, and more when we're nervous. Recent studies also indicate that blinking may be a way of providing the brain a brief moment of rest. Regardless of the reasons, we all blink a lot. Most people average at least 15 per minute, which translates to 14,400 for each waking 16-hour period, and a whopping 7.8 million blinks per year.

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The Colossal Squid Boasts the Largest Animal Eyes

Huge squid with an eye popping out
Credit: sunara/ iStock

The human eye measures about two-thirds of an inch across at birth, before growing to its full size of 1 inch by adulthood. By comparison, the eye of the 45-foot-long colossal squid has been measured at 11 inches in diameter, making it the largest such organ in the animal kingdom and possibly the largest in the history of recorded life. Among land-dwelling creatures, the ostrich tops the pack with an eye that measures around 2 inches from the cornea to the retina — dimensions that also happen to be bigger than its walnut-sized brain.

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All Humans Had Brown Eyes at One Point

Close-up of an eye showing the details in the iris and sclera.
Credit: Peter Finch/ Stone via Getty Images

Eye color (along with skin and hair color) is determined by the amount of melanin our bodies produce; those with blue or green eyes simply possess a lower density of this pigmentation in the iris than those with dark brown peepers. According to research published by a University of Copenhagen team in 2012, all humans had brown eyes until sometime between 6,000 and 10,000 years ago, when a genetic mutation created the first blue-eyed individual. Nowadays, 70% to 79% of the world's population has brown eyes, with 8% to 10% sporting baby blues, approximately 5% featuring hazel or amber, and just 2% showing green. Less than 1% of people possess two completely different colored eyes — a condition known as heterochromia.