In my last post, I looked at the Zulu greeting “Sawubona” and its translation, “I see you.” It got me thinking about the verb “to see,” and the depth of meaning that it has. “I see what you mean.” “Can I see that?” “See, the way to solve a quadratic equation is to complete the square.” “Seeing is believing!”
The word “see” conveys far more than just the action of looking at something, and it’s frequently used to communicate a sense of understanding — even by those who aren’t able to see physically. Vision is a pretty big deal for us humans.
So I did a little research about eyes.
Proponents of creationism and intelligent design frequently use the eye as an example of an organ that is “irreducibly complex” — in other words, they hold that eyesight is too complex a system to have developed through natural selection. On the flip side, those who support the theory of evolution argue that complexity, even in something as complicated as an eye, can easily arise through natural selection if you wait long enough. (And 3.8 billion years is a really, really long time.)
I’m entirely on the side of evolution, and so the rest of this post will take that as a given. (If that’s going to piss you off, you may want to stop reading now and move on to another post.) Other people have done a great job of hypothesizing the process by which natural selection might go about shaping an eye (National Geographic’s description is one of my favorites), so I’m not going to go into it here. Instead, I’d like to highlight some of the things I find fascinating about eyes.
First off, there is such an astonishing variety of eyes out there. There are compound eyes, which are drastically different from human eyes; rather than the usual eyeball + lens + retina + rods/cones + optic nerve setup, compoundedly eyed insects have thousands (or tends of thousands) of ommatidia “eyeballs.”
There are the mantis shrimp, which have the most complex eyes ever discovered — 12 types of color receptors (as compared to 3 in people); the ability to see ultraviolet, infrared, and polarized light; independently moving eyes; and three sections per eye (giving them “trinocular” vision, even if they were to lose one eye). Someday, their eyes may even help us detect cancer. In short, mantis shrimp eyes are amazing.
And why did mantis shrimp get this nifty vision, and not, say, us? Well, the short answer is that they got these interesting mutations in the first place primarily due to luck (well, and exposure to mutagens, but mostly just luck). And they got to keep said mutations because they make the shrimp better at finding mates (and living long enough to reproduce in the first place) — natural selection and all that. (For instance, male mantis shrimp may “chat up” female mantis visually.)
Lizards are cool, too. You know how most of us have two eyes? Turns out that most lizards (and frogs, lampreys, and some fish) have a third “eye,” called the parietal eye. This eye isn’t very complicated and is primarily just used to figure out how bright it is outside, although some lizards can also use it to differentiate between blue and green light. Scientists believe that these features of the parietal eye help lizards figure out where and when to bask in the sunlight.
What’s even more fascinating than just the fact of this parietal eye is that it may help explain both the process through which our own eyes evolved to see color, as well as shedding light (pun intended) on mammals’ transition from ectotherm to endotherm.
At the end of the day, though, the really interesting things are the people and animals behind these eyes. Most people are extremely good at telling what someone’s feeling just by looking into their eyes. And if you’ve ever wondered if your pet dog, horse, or jackdaw is trying to tell you something when they look into your eyes — well, you may be right.
It’s not for nothing that we call eyes “windows into the soul.”
See you next time.