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The Human Eye: Perfect Design or Marvel of Evolution?

February 15, 2009

I’ve heard it said both ways.  Well, no, not really.  I’ve never actually heard someone come out and say that the eye was the pinnacle of evolutionary genius.  But I have heard the claim from creationists: that the eye is perfectly designed, and that since partial eyesight is not helpful there is no way that eyes could have evolved over time.

Well, first I’d like to thank the creationist who said that for remembering how evolution works.  Many of them can’t get past the “lightning hit a mud puddle and life happened” model, which is a huge strawman of the actual theory of evolution.  Indeed, according to the best scientific evidence, evolution happens when an animal develops a small trait that makes it superior to its ancestors, and its descendants continue to make improvements on that trait over a lengthy period of time.  Applied to the eye, this implies that life-forms spent a large portion of time with only a small amount of eyesight as rudimentary eyes rapidly grew in complexity.  So is it true that an eye that only enables you to see a little bit is no improvement over no eyes at all:

There’s a swift and obvious answer to this: No.  Just no.  Normally I’d show off the evidence and then let you decide for yourselves, but come on, this one is obvious.

Picture this: You’re a little cluster of cells floating about in the ocean; a rudimentary worm, if you will.  You probably already have a small patch of cells somewhere on your body that are sensitive to the chemicals in the water around you, enabling you to smell.  This neat feature has been in the family for a few generations; the sensitivity it lends you to the environment has enabled you to locate food and avoid predators better than your non-smelling relatives, so you’ve survived and reproduced very nicely.

But there’s one feature that separates you even from these advanced relatives.  Another patch of cells, not too far from the first one, has become sensitive to light.  It’s not much, just a tiny nodule that tells you whether or not it’s dark in your area; at this point you can’t even see the way most people are familiar with.  You may have noticed that it gets light and dark in succession — the day and night cycle.  But you’ve probably noticed something else, too – sometimes, when it grows dark very suddenly, you can pick up the scent of a predator.  You’ve come to realize that darkness can mean danger.  Other times, darkness can mean safety, as you dart into the safe recesses of a tiny cave.

The ability to distinguish between light and dark might not seem that useful compared to your rudimentary sense of smell, but it becomes useful later.  When you flee a predator in a panicked state, it may take you a while to analyze a smell and figure out what it means, but light and darkness are recognized almost immediately.

This model may not be entirely accurate; for example, plants have rudimentary light-sensing abilities and no sense of smell, so it’s possible that sight came first – in which case the creatures that could see would have a huge advantage over their nonsighted relatives.  As demonstrated above, even the ability to distinguish between light and darkness aids the rudimentary worm as it learns to associate darkness with different things.  At night, when there’s not enough light to distinguish between high and low levels, you’re back on the same footing as your sightless family, but during the day that simple ability enables you to avoid certain threats and find safety.

Still not convinced?

Take a look at plants.  Plants require sunlight to survive.  In order to help them to locate that sunlight, their cells have light-detecting abilities – the basis of sight – to enable them to locate and move toward the best supply.  The movement of plants is somewhat ineffectual compared to ours, in that they must grow to reach wherever they’re going, but the ability to find and put themselves in the best sources of light enables them to get the energy they need to survive.

Then there are arthropods – more commonly known as insects, arachnids, and crustaceans.  Most arthropods come equipped with two kinds of eyes: the well-known compound eyes, which serve to make out complex shapes, and the lesser-known ocelli, very simple eyes that specialize in detecting light levels.  In other words, either type of eye performs only partial vision.  And here’s a shocker: after some experimentation, it was discovered that an arthropod can get on quite well with only one of these types of eyes.

I hope that whoever made this rather outrageous claim to begin with wasn’t legally blind, because there are also significant numbers of humans with only partial eyesight who still benefit.  Although they may not be able to see much – men may resemble trees, for a Biblical example – the ability to make out basic shapes is enough to prevent them from walking into lampposts, cars, or other people.  It would also enable them, in the wild, to detect the swift motion of an oncoming predator and escape before they are killed.  An individual who was completely blind may be able to hear the oncoming predator, but would have a difficult time finding a place to hide with no eyesight.

This is all lovely evidence that the eye is not irreducably complex, but it still doesn’t prove that complex eyes arose from simple ones.  But really, if you’re a die-hard creationist, nothing is going to prove that.  I could provide all the transitional fossils that have been found between simple eyes and more complex eyes, just as people have provided what seem to be transitional forms between apes and humans, and you still probably wouldn’t believe it.  And since the idea of a Creator God is non-falsifiable, there’s no way I can prove that one wasn’t involved in the creation of Earth.  What I can provide – the only thing I can provide – is the evidence which suggests that his Creation is not nearly as perfect as we first thought.

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