In laboratory experiments with antibiodics and bacteria, it isn't really evolution though. The bacteria are killed off that aren't resistant, but aren't the resistant bacteria usually much weaker than the bacteria that weren't resistant?
Someone explained it to me like this. Its sort of a weird way of looking at it, but just follow along. Say a new dictator (the antibiodic) comes to power. He orders everyone's left hand to be chopped off. So as hes chopping off everyone's left hand, he comes across 2 people who were born without a left hand. While everyone else bleeds to death, the 2 people without left hands survive and reproduce having more people without left hands. These people are naturally weaker though because they only have one hand.
Thats sort of like how an antibiodic works. It will attack something in the bacteria, but because some bacteria don't have what the antibiodic is attacking, they survive. because these surviving bacteria never had this thing the antibiodic was attacking, they are naturally much weaker compared to the rest of the bacteria without the antibiodic present.
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