How did they evolve so fast?

This question really ruined the last two movies in the series for me. 20 years is not enough time for apes to evolve into what they were in that movie. It takes millions upon millions of years for species to evolve in the slightest bit, so how the hell did the earth get populated with all these advanced apes in less than one generation since Escape From Planet of the Apes? They just glazed over this obvious question in the movie, we are supposed to believe that taking in apes as pets opposed to dogs or cats will result in rapid evolution. Even under that flawed logic we'd have to assume cats and dogs would have evolved at some point.

I dunno, am I out of line here? I know the premise of the whole series is a little far fetched to begin with, but come on man. It was way cooler in the first one when we assume that apes just naturally evolved over the course of 2 thousand years in a nuclear wasteland; that's somewhat believable at least. Plus the idea that man destroyed himself, only to be replaced by apes whom share our own flaws is what makes POTA so thought provoking. But this movie ruined that all by making an "ape revolution".