The Imperfect Eye
June 30th, 2008 Posted in Biology, CreationismI was just watching a debate between disgraced Young-Earth Creationist Kent Hovind and founder of The Skeptics Society, Michael Shermer, which took place a few years back before Hovind’s incarceration for tax evasion. Here’s a great example of my first and second rules, from yesterday’s post, and how they relate to Creationist brainwashing. For those of you who don’t know, the human eye (in fact, the eye of all vertebrates, as far as I know) is a pretty strange design, with the light detector cells plugged in backwards so that light has to travel through all the nerve cells and blood vessels before it gets detected. There have been some very sophisticated (but ultimately confused and incorrect) attempts to explain this, such as those by the Creationist Michael Denton. But Hovind came up with an explanation based around the fact that humans live in the air, so our eyes need protection against ultraviolet rays, and the peculiar backwards design facilitates this. Invertebrates such as the octopus, whose eyes are plugged in “the right way round”, live in the water.
Well, there’s three obvious flaws, as far as I can see it, with that argument. The first is an obvious one – it’s nonsense. Plugging in the cells backwards doesn’t protect them against UV radiation at all. For a start, it actually places the most heat-sensitive part of the eye (the photoreceptor) right up against the biggest heat source, the choroid. But that’s not all. Of course, the human eye is a similar design to that in all invertebrates. Such as the fish. A creature which, unless I am very much mistaken, lives in water… And finally, the reverse is also true – not all land animals have vertebrate eyes. Gastropods, for example, such as the snail, have eyes that are plugged in “the right way round”. A design which, according to Hovind, is thoroughly terrible for any land-dwelling creature. So yeah, I think that one’s a bit out of touch with reality. Better luck in about eight to ten years, Kent!
