Letís start with variability. Remember that we had a few bugs that were resistant and many that were not:
That variability gave evolution something to work with. In fact, variability is sometimes called the "raw material" of evolution. If there was no variability, then the only bugs that survived would be those that hid under leaves. So we could kill off most of the bugs, then wait until the ones that had been hiding came out, and get them too. After 3 applications, most of the bugs would be dead.
Of course, a very few hoppers might survive by hiding repeatedly under leaves. How is this different from evolution? Well, just because a hopper happened to be under a leaf when you came along with your spray bottle doesnít make it a survival strategy. It just got lucky. Furthermore, that luckiness is not something it can pass on to its offspring in any way. That would be like saying that because my parents won the lotto jackpot, I should go into a gambling career. Luck doesnít get passed down in genes or anywhere else. Which brings us to the second tenet of natural selection: heritability.
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