As I understand evolution, it is a process whereby random genetic changes in an organism get a chance to demonstrate whether or not they (those changes) offer an advantage to the organism.
If, for example, squirrels were once ground dwellers only, and by some genetic quirk, one of them had the ability to climb a tree, then it is possible that that ability figured in his survival to the point that he lived longer and was able to father--or mother--more offspring, many of whom had that same ability, and after a couple of hundred years, we find that the ground dwellers have all died out and the tree climbers are still doing well.
Now, if that is true, can't we see evolution in action whenever a weed killer becomes ineffective? Or when a medicine becomes less effective to control an infection? Certainly we all know that microbes develop immunities to the chemicals that once controled them very nicely. Don't they develop this immunity because those few who were unaffected by the chemical in the first place were the only "breeding stock" left to propagate their kind?
Isn't this a form of evolution?