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Old 02-27-2017, 04:30 PM
md2000 md2000 is offline
Join Date: Feb 2009
Posts: 13,052
Several people have described the evolution of light-sensitivity to functional eye. Some creatures have eyes on aim-able stalks IIRC; one can see the evolutionary advantage of shrinking the stalk to make it less vulnerable until it retracts into the body (sumo style) so only the lens is exposed, but still retaining some aim capability.

Another point is that a lot of the intermediate products (half-way there eyeballs?) disappear as the creatures that had them lose the evolutionary battle to the better model.

Even a pit with a few dozen light-sensors gives the creature an idea whether it has ventured out from under a rock, for example, and should reverse course and duck under cover again. Evolution advantage...

* * *

The key to any evolution change is - does the advantage allow the person to have more children than others and allow those children to survive into adulthood? The latter is critical because humans have a notoriously longer childhood than many species, before they can fend for themselves. In fact, modern human society is directly countering many evolutionary tendencies - welfare generally means that even the least capable persons survive to reproduce; modern medicine and vaccines reduce the risk of childhood mortality, and that child welfare systems ensures those children survive to adulthood even if the parents don't. Birth control reduces the tendency of differential reproduction rates; you may have a great mutation, but if you choose to use protection, you will not pass it on to more children than your rivals. One study I read suggested that regardless of abortion, or available birth control, most women in western society tend to have as many children as they want and no more. Regardless, biological "fitness" is less of a criteria for how many children one raises to adulthood. Indeed, it's possible that irresponsibility and immunity to the effects of birth control hormones may be the major factors being selected for.

(We had a long thread earlier about the issue of whether modern medicine is causing the reverse, genetic dilution with traits that would be detrimental to survival outside the modern support system; do eyeglasses and insulin and antibiotics and IVF result in generations that contain a more tech-dependent population).

Last edited by md2000; 02-27-2017 at 04:32 PM.