Did you know that the human eye can provide an image quality equivalent to a 576 mega pixel camera? (For frame of reference, an Iphone 12 only has 12 megapixels!)
But that’s not all. They can focus on 50 different objects every second, they can distinguish approximately 10 million different colors, and they are the most complex organs on the human body (aside from the brain of course!).
It is of no doubt that our eyes are incredible works of evolutionary art, but do you actually know how they came to be?
Within the rhetoric surrounding the evolution of the eye, the question of whether or not such a complicated organ could even arise spontaneously is often asked. It is a legitimate question, after all. The human eye certainly is complicated, but it is not impossibly complicated.
In fact, they are not unlike cameras, the kind we use every day. The cornea focuses the light into the pupil (a “hole” into the eye, essentially), the amount of which is regulated by an aperture-like structure called the iris. The light then enters the eye and comes in contact with the lens, which then focuses it onto the retina. The lens, much like the lens of a camera, is focused by the musculature that surrounds it, and the retina, much like color-sensitive film or the sensor of a digital camera, absorbs the light, sending that information to your brain along the optic nerves.
Composed of little more than that, the human eye really doesn’t get any more complicated; but the question remains, how did this seemingly perfect structure arise organically?
To understand the evolution of the human eye, researchers took a page from the book of Darwin himself and analyzed the eyes of less complicated organisms.
Darwin acknowledged the age-old argument that the eye is far too complex to have arrived spontaneously, however he proposed that if a collection of organisms could be found that could outline the progression of the eye from simple to complicated, that the mystery would be solved.
Thankfully, we have found many organisms that have differing levels of eye complexity, both extinct and extant, from the micro to the macro. Algae flagellates and hydras, for example, utilize the most rudimentary version of the eye known as the eyespot, a photosensitive collection of proteins that, instead of providing a detailed image, simply tells the organism where light is coming from. The nautilus has an eye similar to the pinhole camera and cubozoans have both rudimentary and complex eyes (with a lens, iris, cornea, and retina!)
The theory surrounding the evolutionary progression of the eye is that as the eyespot evolved, its structure became progressively more and more functional. Grooves could have developed around the eyespot, producing a pit to allow more light in. This pit would have gradually narrowed to create a pin-hole camera-like environment for the eyespot, which would then develop into the retina. The lens would follow, but likely as a protective layer over the retina at first. Over time it would evolve to permit and focus light through (an upgrade that improved image fidelity from 1 percent to 100 percent), and voila, you have your first functional eye.
This may seem unlikely, but in the natural world, given enough time, the unlikely becomes likely. The earliest organisms we’ve discovered with eyes were alive as far back as 550 million years ago, a significant amount of time greater than what was proposed to be necessary for evolution.
Researcher’s estimate that if the primitive eyespot were to improve upon itself by a mere 0.005% each generation, it would only take 364,000 years for it to form into the complex human eyes we all see with today.
So, it would seem that the unlikely eye isn’t so unlikely anymore, is it?