Jan

25

 I asked the doctor, "how did evolution create vision?" His quick reply was that because of predators, individuals must be able to detect them for their survival, and thus vision developed.

Well that's quite a story. But what is behind the intelligence that creates the marvelous, intricate organ like the eyeball which coordinates perception with neurons in the brain? It is really startling to think about my vision.

David Wren-Hardin comments:

Vision almost certainly didn't arise from an attempt to spot predators, but rather as the development of a phototaxic behavior. Remember, light = energy, and if you're the sort of organism that can convert energy to light, or if you eat the plants and algae that do, then you need a way to find the light. The arms-race in vision probably began when predators on these organisms used their photoreceptors to find areas that were likely to contain their prey. Now there is pressure on the preyed-upon to evolve ways of using their photoreceptors to spot predators first.

Once you have one photoreceptor, building an eye is a snap. Nature loves adding extra features to organisms, whether it's extra segments, limbs or other peripherals. Pick up a bunch of random cats, for example, and you are assured of finding a few with non-standard numbers of digits. Once an animal has a grid of photoreceptors, it can now map visual space, and build all sorts of cool edge and looming detectors very easily.

Uncomfortably for the Intelligent Design crowd, the mammalian eye is a lousy design. The wires that carry the signal from the photoreceptors run across the surface of the eye, and leave it in a cable that forms a blind-spot in the receptive field. This would be like an engineer at Sony who decided the best way to build an LCD TV is to have each wire for each pixel run across the front of the TV. In addition, the retina is composed of many layers of cells, and the actual receptors are buried under these layers; the light has to go through them to get to the rods and cones. The octopus, however, did it differently, with its photoreceptors in front, and the outputs running out the back. So either there were a couple of intelligent designers running around, or there were trial versions, and we got the short end of the stick.


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