>> Why do you think evolution isn't universal -
>> ie it picks some specias and grows legs on them
>> and yanks them up out of the water in a matter of
>> a few million years but others just don't quite get it
I posted this on SNG's thread the other day, it seems appropriate for your question, so I'll repeat it here:
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A frog with an extra leg sticking out of his side, for instance. That creature will not survive as well as his peers, and his mutated genes will die with him. But sometimes just at random a change takes place that's a good thing. Maybe the frog's tendons attach a little higher or lower on his legs, giving him a better jumping ability to escape predators. Because he can escape when others can't, he'll survive longer. He'll have more offspring that also carry his better jumping genes. If there's any sort of pressure in his environment (lots of predators) he and his children will be the ones that survive, pretty soon taking over the population. Now they ALL have better legs, and the not-so-good legged ones have to either die off, or find a less predator-rich environment to live in. (Let's assume they moved)
(Note here that mutations occur at random, but the "good" ones are selected as keepers by virute of the fact that they are being carried by the creature most likely to survive and reproduce. Mutation is random, selection is not.)
That explains how a frog might become a better frog, but how could a frog ever become something else, something not a frog?
The trick is to realize that tiny changes add up. A frog with better legs can hop clear out of the water. While he's out, he can snap up food on the sides of the pond that other frogs can't reach. Once all the frogs can do that, the ones that can see better can be even more successful. And the ones that manage to get the ability to detect sounds will do better still. A frog that can ultimately live completely out of the water might be able to survive better still. And since he's out of the water, being covered with a fuzz would prevent him from getting sunburned. If that fuzz was thicker, he'd even survive better when it gets cold. And if the coloration on his fur made him attractive to females, he'd reproduce more.
Go back to the weaker frogs that moved away from the predators. They live in the water, they don't see well, they can't hear (for purposes of this illustration), they are furless. Compare them with the frog that has stronger hind legs, better eyes, hearing, and a fur-like coat. Is he a frog anymore? If so, how much more do we need to change before he isn't a frog?
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The point is that both sets of frogs are well evolved for their environments. It's a big balancing act. Faster lions eat more gazelles, faster gazelles don't get eaten as much. The pressure is on both groups to be faster, but that has practical limits. Still, any slight edge starts to tip the balance, causing pressure, inviting a welcome mutation to set things right again.
Or not, in which case the gazelles all get eaten and it's over for the gazelle. Extinction happens.
Dave
