World Eyesight Day | Revealing Evolution Of Human And Animal Eyes
When we're young, we often take our eyes for granted. I remember back in fifth grade when I got to experience the magic of Camp Waskowitz for a week. We ventured into the forest, explored the Snoqualmie river, and learned about community living. Still etched in my memory is the cabin I stayed in: B1. During one of our excursions, a friend's name tag slipped off in the forest. The ground was a carpet of pine needles, making finding that tiny silver pin like looking for a needle in a haystack of pine needles. But guess what? I stopped, peered down where she stood, and incredibly found that pin amidst the pine needles. Even the camp counselor, who was quite the seasoned adult, was impressed by my vision. Oh, how I wish I still had that kind of eagle-eyed sight today!
Every second Thursday of October, we celebrate World Sight Day. It's a time to think about those who can't see and those who gradually lose their sight. Being without sight is a real challenge. Check out these eye-opening facts:
Nearly 90% of individuals with visual impairments live in developing countries.
About 65% of folks with visual impairments are 50 or older.
Shockingly, around 19 million children grapple with significant visual impairments, many of which could've been prevented.
And hold on to your hats, an astonishing 1.4 million children have to navigate life with lifelong vision loss.
As organisms adapted to their surroundings, their eyes underwent changes to maximize survival and reproductive success. Human eyes, characterized by a high-resolution and color vision, evolved to suit our diurnal lifestyle, enabling us to identify fine details and a broad spectrum of colors in various lighting conditions. In contrast, animals developed eyes tailored to their specific ecological niches. For instance, the eyes of nocturnal creatures like cats evolved to excel in low light, emphasizing motion detection for effective hunting. The eyes of prey animals such as deer prioritize wide-angle views to spot predators, while underwater creatures like octopuses possess camera-style eyes adapted to the depths of the ocean. Thus, the diverse evolutionary paths of human and animal eyes reflect the remarkable adaptability of life to its environment.We need our eyes to perceive the world, work and survive which makes this topic incredibly important to all humanity.
Now, here's something to ponder: the NGSS science standards 4-PS4-1 and 4-PS4-2 delve into constructing arguments about animals' internal and external structures that support survival, growth, behavior, and reproduction. World Sight Day serves as the perfect occasion to educate your students about vision and encourage them to craft models that illustrate how eyes function.
If this sounds good to you, click on this link to purchase EVOLUTION OF HUMAN AND ANIMAL EYES. This is a great product written at three different reading levels that will teach your students that the eye did NOT form itself. All eyes are the product of environmental pressures.
Imagine the journey of light as it enters your eye. It starts with the cornea, which acts like a clear windshield, bending light to help your eye focus. Then, light sneaks through the pupil, adjusting like a camera aperture to control the light flow. The iris, the colorful part of your eye, takes charge of this light regulation. Next up is the lens, an inner component fine-tuning the focus. It teams up with the cornea to ensure the light lands accurately on the retina – a light-sensitive tissue layer at the back of your eye.
Now comes the enchanting moment – when light meets the retina. Special cells known as photoreceptors work their magic, transforming light into electrical signals. But the journey isn't over yet. These signals hitch a ride on the optic nerve, headed straight to the brain. And in your brain, the real enchantment unfolds. The brain translates these signals into the images you perceive, completing the remarkable spectacle of sight.
And speaking of adaptation, let's dive into how different animals view the world due to their distinct eye evolution.
Cat: These creatures are crepuscular, meaning they're most active during dawn and dusk. Their eyes are tailored for low-light conditions. With retinas packed with rod cells specialized for detecting movement and light, they're adept at seeing in dim settings. Their pupils dilate widely, and a reflective layer called the tapetum lucidum boosts their night vision. That's why a cat's eyes might gleam in the dark. They prioritize motion over color, making them exceptional nocturnal hunters.
Snake: Snakes have a unique visual system. Active during the day, they don't move their eyes much. Instead, they sense heat through special pit organs around their mouths. Their eyes have fixed lenses and no eyelids. Their vision isn't top-notch; they detect movement and shapes, relying more on heat detection for hunting.
Deer: Being prey animals, deer need a wide field of view to spot potential threats. Their eyes are positioned on the sides of their heads, giving them nearly 310-degree vision without turning their heads. But this wide view sacrifices depth perception. They excel at detecting motion, helping them identify predators from a distance. Adapted to low-light conditions, their eyes are their allies during the dawn and dusk hours.
Bear: Bears possess eyes well-suited for their mixed lifestyle. They're omnivores, active both day and night. Their eyesight, similar to humans, offers color vision and depth perception. Though not as specialized as others, their sharp sense of smell compensates for their visual limitations. Equipped with a tapetum lucidum, they're better equipped for night vision. Yet, their sense of smell reigns supreme for hunting and navigating.
Each of these creatures showcases the marvels of visual adaptation across the animal kingdom. Their eyes have evolved to serve their unique needs, whether it's hunting in the dark, detecting heat, spotting danger, or a mix of these tasks.
EVOLUTION OF THE EYE
While anthropology primarily studies humans, examining the evolved eyes of other animals can teach us a lot about our own visual system. It's a reminder that eyes are finely tuned to their environments, emphasizing the fact that different needs yield different eyes.
While scientists can easily learn about how bones changed over time from fossils, it's much harder to find out about soft parts like eyes. Even when soft parts do fossilize, they don't show enough detail to tell us exactly how they evolved. But scientists have been making progress in understanding how eyes developed. They've looked at how eyes form in developing animals and compared the eyes of different animals to figure out when important changes happened. What they found tells us that the kind of eyes we have, which many animals share, evolved in less than 100 million years. They started as simple light sensors about 600 million years ago and turned into complex organs around 500 million years ago. This discovery supports Charles Darwin's ideas and shows that the "flaws" in our eyes are actually signs of their long journey of development.
To learn about where our eyes came from, we need to go way back in time. Humans have a family tree that goes back about four billion years to the start of life on Earth. Around a billion years ago, simple creatures started to change. Some became radially symmetrical, meaning they had a top and bottom but no front or back. Others became bilaterally symmetrical, like us, with a head end and left-right sides. Later, about 600 million years ago, those bilaterally symmetrical creatures split into two groups: invertebrates (creatures without backbones) and vertebrates (creatures with backbones, like us). This big change set the stage for the "Cambrian explosion," around 540 to 490 million years ago. During this time, many different animal body plans evolved quickly. This burst of changes helped create the complex eyes we have today.
The Journey of Eye Sensors
As we explored the development of the retina's three layers, a fascinating question arose about the evolution of photoreceptor cells—these are the special cells that detect light. There are two main types: rhabdomeric and ciliary. It was previously believed that invertebrates had rhabdomeric cells, while vertebrates had ciliary cells. However, it's more intricate than that. Ciliary cells are found in many animals and are used for tasks not related to vision, like managing daily rhythms. Rhabdomeric cells, on the other hand, are all about vision. Insects' compound eyes and mollusks' camera-like eyes, such as those of octopuses, use rhabdomeric cells. But for vertebrate eyes, like ours, ciliary cells take care of vision.
In 2003, Detlev Arendt discovered that our eyes still carry changed versions of those rhabdomeric cells, which now act as messengers sending information to our brain. This finding indicates that our retinas have both ciliary and rhabdomeric descendants. Nature often adapts existing structures for new jobs, and this adaptation is how evolution works. The fact that these cells perform different roles in our eyes compared to invertebrate eyes provides more proof that our eyes developed naturally. But why did ciliary cells become more important for vertebrate vision, and why did rhabdomeric cells change into messengers? To answer this, I examined the features of their light-detecting pigments, called rhodopsins. These pigments contain a protein called opsin. In 2004, Yoshinori Shichida and his team discovered that early vertebrate pigments changed to be stronger and more active when exposed to light.
Our Visually Impaired Students
We have some students who find it really hard to read because they might have problems with their eyes or because of some other issue, such as autism, down syndrome or developmental delay. For our kids who are autistic, their eyes and ears work well, but sometimes they need a little help to see and pay attention to things on the computer.
There's a special tool you can find on Amazon that can make reading and learning easier. It's called the "Hands-Free Magnifying Glass with Neck Wear." This tool is like a big magnifying glass that you wear around your neck. It has 36 super bright lights that can be made brighter or dimmer to help you see things better.
For kids with autism, these bright lights can help them focus on what they're reading. And for any student who has trouble seeing, whether it's because of their eyes or something else, this tool can make reading books or looking at the computer screen much easier.
It's not hard to use at all. You just put it around your neck, and you can use it hands-free. It's the same kind of thing that doctors and dentists use to look closely at things, but it's also great for the classroom. So, if you know someone who needs a little extra help with reading, this tool might be just what they need. There are reading tools that are on a stand, like the one featured below, and there are reading tools with straps that fit around the neck. To purchase, follow these links as I have listed more than one example. LED Reader 1. Led Reader 2. Led Reader 3
So, as we celebrate World Sight Day, let's not only appreciate the gift of vision for ourselves, but also for the insights it provides into the world around us. Visual anthropology reminds us that cultures hold hidden depths beyond the surface, waiting to be discovered, learned from, and celebrated. 🌎👁️🗨️✨
