Date: Sun Dec 05 1993 11:09:10 To: Jim Maroon Subj: Blind Watchmaker EVOLUTION

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Date: Sun Dec 05 1993 11:09:10 From: Karl Lembke To: Jim Maroon Subj: Blind Watchmaker EVOLUTION ------------------------------- JM>Hello. I am currently debating a fella name of John Barry on a local >echo here in central CA. His position is that since the human body is >so perfect, it must have been designed and created by an intelligent >designer. I am slightly acquainted with what Dawkins says in The Blind >Watchmaker, but if any of you have some suggestions, or better, actual >replies to John that I can forward to him, I would greatly appreciate it. How about the human eye? We have this exquisitely designed focusing apparatus (cornea and lens), a light regulator (the iris), and a photoreceptor (the retina). The retina is composed of millions of light sensitive cells which are connected by cables (nerve fibers) to the retina. To cut down on scattered light, which would contribute only fog to the image, the retina is backed up by a layer of black tissue which absorbs light. BUT.... These cables that run from the light sensitive cells are strung IN FRONT OF the retina, -=BETWEEN THE LIGHT SOURCE AND THE CELLS THAT ARE SUPPOSED TO RECEIVE THAT LIGHT=-! And since these nerve fibers have to go back through the eye at some point, they must either all pass through the retina individually at some location away from the cell they're carrying the signal from, or must pass through at some common point, which will mean no light sensitive cells can be placed at that spot. We refer to this spot in our eye as the "blind spot". Now, personally, if I hired an engineer to set up my VCR and he strung the cables in front of the TV screen and said "There, that's good enough", I'd not only fire him, but I'd have serious misgivings about ever hiring him to do anything else. I suppose, however, someone might argue that there is some arcane reason why the nerves have to be run between the pupil and the retina in humans, but.... The eye of the octopus appears very similar to the human eye. It has the pupil, the iris, the lens, the retina, etc etc etc. But in the case of the octopus, the nerve fibers emerge from the end of the visual receptors -=AWAY=- from the pupil, and come together to form the optic nerve well back of the retina. Thus, no blind spot. Now, it occurs to me to wonder if the octopod eye was fashioned after the human (and in fact, mammalian) eye, after God had had some experience in putting the thing together. And in fact, why did God not go back and rewire the mammalian eye, once he'd come across the wiring design for the octopod eye? Or could it be that the human eye developed through trial and error in small stages, with each solution to the next problem being "just good enough to pass muster"? And of course, speculative fiction writers like redesigning the human body. Arthur C. Clarke, in his stories that eventually led up to "2001", pointed out that, in particular, our mouths, throats and lungs are not very well designed. Air, food and water share common passages in their trip to where they're supposed to go. And they'd better get it right. Air in the gut isn't fatal, at least in small quantities, but it can be uncomfortable. Food or water in the lungs can have serious consequences. Now in most air breathing mammals, when food or water is swallowed, a flap of tissue closes over the trachea, preventing the swallowed material from entering the airway. Usually. Actually, in virtually all mammals except humans, it works pretty darn well. But humans have a throat which has been modified to allow for speech. This modification makes it a lot more flexible, and allows the production of a greater variety of sounds. There are trade-offs in all modifications, and in this one, we have traded enhanced speech for a slightly greater chance of choking to death over dinner. Surely an intelligent designer could have uncoupled the breathing and eating mechanisms? We don't need to pass food and water through our vocal apparatus, do we? In fact, rather than being a perfect design, I submit that the human pharynx is just good enough to pass muster.


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