| Eyesight is just photon-sensing. There are primitive animals with primitive light/dark sensing. Hearing is just vibration- and motion-sensing. It evolved from the lateral line in fish, which is not limited to "hearing" per se, but detects motion—current and transient pressure waves that might indicate predator or prey swimming nearby. Smell is just chemical sensing. Catfish have chemoreceptors across their bodies. A lot of intermediate forms are impossible to present to you as evidence because all we have is the fossil record which generally doesn't include soft tissue, which is where most of the interesting stuff happens. One mutation that enables the slightest bit better sensing, provides an advantage, and offspring of that species in that area will gradually end up with that adaptation. Then it repeats. The "must have" is not dictated by some agent, but by environmental selective pressure, relative to pre-mutation versions of the same organism. It's induction, but for biology rather than math/cs. It's quite possible that other types of photon and vibration and chemical sensing could have evolved, and would be superior, but we started down a path that locally descended to where we are now. And the existing tree of life would predate or out-compete pretty much any new multi-cellular life that tried to "experiment" and "evolve" novel sensing organs. You want to talk about just-so stories? Cephalopod eyes attach to the optic nerve on the opposite (back) side of the retina, so they have no blind spot. Did a designer goof up on vertebrate eyes and not fix it, but instead implement a very complicated neurological fix involving saccades and "blinding" our brains to the instantaneous hole in our vision? |