The human eyeball. What a loser. Image: Sam Bald
Did you watch the second episode of Cosmos last night using your fancy eyeballs? The episode, entitled “These Are Some of the Things That Molecules Do,” had a fantastic segment on the evolution of eyes, complete with a “Creature's Eye View” side panel that powerfully illustrated the cumulative adaptations that led to the revolutionary power of sight.
The show is doing a magnificent job of resurrecting that special Sagan friendliness when it takes on controversial subjects. Based on the first two episodes, it's obvious that Ann Druyan, Neil deGrasse Tyson, and Seth MacFarlane want to challenge viewers who are still reticent about accepting evolution, the age of the universe, and the legitimacy of the scientific method in general. Let's just come out and say it: they are targeting the religious population—and not just the Christian right, but the whole spectrum of people who tend to side with mysticism over empiricism.
But Tyson, like Sagan, has a gentle demeanor when debunking religious propaganda, and he seems to gently invite the anti-science crowd into the show rather than slapping them on the wrist for their anachronistic beliefs. Last night's episode was packed to the brim with examples of this delicate balance, and the segment on the evolution of the eye was particularly brilliant.
Creationists often fall back on a woefully flawed argument that the eye is far too complex an organ to have evolved through natural selection—an argument that betrays a basic misunderstanding of how natural selection works in the first place. After all, if you believe our planet's age is not in the billions, but in the thousands, then there is indeed not enough time for something as complex as an eye to form.
Tyson has always emphasized the dumb side of natural selection, owing to its inability to start over from scratch. In his book Space Chronicles, he wrote: “Down there between our legs, it's like an entertainment complex in the middle of a sewage system. Who designed that?”
In Cosmos, he hits on this point again by showing how the human eye, impressive though it undeniably is, has been stunted by our evolutionary heritage in the oceans. Had we evolved entirely on land, our eyes would be much more useful to us. Watching the segment, I couldn't help but be reminded of Brother Cavil's frustrated rant about “these ridiculous gelatinous orbs” in Battlestar Galactica. Creationists, if human eyeballs are so great, why can't they see the vast majority of the electromagnetic spectrum? To quote Cavil, “I WANT TO SEE GAMMA RAYS!”
Indeed, Tyson didn't go far enough in his takedown of the human eye (not that I blame him, as the episode had a lot of material to cover). Before we go around trumpeting the awesomeness of our little soul-windows, we should take a look around at the animal kingdom, because that is a fast track to feeling totally ripped off by evolution's strict economy of adaptations.
Take the mantis shrimp, as an example. This crustacean has the world's best pair of peepers, with 16 different photoreceptor pigments (compared to our measly three). As the Oatmeal so eloquently put it, “the rainbow we see stems from just three colors, so try to imagine a mantis' rainbow created from sixteen colors. Where we see a rainbow, the mantis shrimp sees a thermonuclear bomb of light and beauty.” Feeling shortchanged yet? Because the list of visual superpowers in the animal kingdom goes on and on.
The mantis shrimp also happens to be BAMF. Via YouTube
Chameleons have a 360-degree field of vision. So do dragonflies—in fact, these insects have “compound eyes” that allow them to see the ultraviolet spectrum, and navigate using polarized light (for which humans require sunglasses).
The eyes of the helmet gecko are 350 times more light-sensitive than human eyes, allowing the species to distinguish between colors at night. The spookfish evolved mirrors in its optical cavities, and the Deinopis genus of net-casting spiders replaces its optical membrane every single day. Perhaps most relevantly to last night's episode, the surface-dwelling four-eyed fish has evolved two levels of sight: one for air vision, the other for water vision.
Far from disproving evolution, the huge variety of eyeballs in nature highlights how essential vision is for the survival of most species. But you are a Motherboard reader, so you knew all that already. The great thing about the Cosmos reboot is that it not only retreads familiar territory for science buffs, but that it aims to open new eyes to the wonder of the real, empirical universe.