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Originally Posted by Mercedes Benzene
One of the largest challenges to Darwin's theory of evolution is the eyeball....Some have suggested that eyes evolved from light sensitive "spots", but this itself poses some questions.-Why would a light sensitive spot have been necessary??.
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The answer to this vexing problem has been spelled out in fascinating and precise detail by the likes of Richard Dawkins, in his book "
Climbing Mount Improbable" and Daniel Dennett (who is a philosopher) in his book "
Darwin's Dangerous Idea". Both books are fun to read.
Let's take your two questions, which are really just one: Why would a light sensitive spot have been necessary? The answer is: they would NOT have been necessary.
That's right, they weren't necessary. Single cell critters lived and died like crazy without those spots. Seeing as how they were the very first critters on Earth, and the whole DNA/reproduction thing was nowhere near as "exact" and "self-correcting" as it eventually became, reproduction was not "exact". Critters were constantly bumping into new chemicals, being poisoned, eating them, absorbing them, incorporating them, creating them, excreting them. And this led to zillions of cells that were different in one way or another.
Do you know how many chemicals are sensitive to light? Lots. The entire porphyrin family are ALL light sensitive to one extent or another. A molecule gets hit with a photon of the right energy, and the molecule twitches. Or pops off an electron. Nothing fancy or complicated at all.
There would be single cell critters that could "benefit" from knowing if it was day or night. Knowing that could make them more efficient, because sunlight affects the environment drastically: temperature, tides, deep water currents raising nutrients to the surface.
All it would take would be one critter with a flummoxed RNA strand that caused it to create a single porphyrin molecule--a molecule that when "energized" by light kicked off electrons that activate the critter; and when not--the critter became dormant. (or vice versa, either). Bingo, you have a critter that "knows something" its neighbors do not. If this gives it any survival advantage at all (
THE CORE OF EVOLUTION THEORY) then its descendents will tend to outnumber those critters who can't do this trick.
There really is NOTHING very hard or complicated about this. In the first billion years, Life would have been sloppy, unstable and hit-or-miss in its reproductive process, as you would expect. That means random variations out the wazoo. Mutations for a simple single cell critter do not carry the same "death penalty" as they do for large complex animals. So, trillions of these random variations would have been "experiments": does THIS increase my survivability? does THIS increase my survivability? does THIS increase my survivability?...
