Evolutionary speaking, we have to find pussies attractive. What if the first male monkeys who would later become humans decided to fuck the female monkeys in the ass because they didn't think the pussies of their female companions were very attractive... There wouldn't be any humans today.
So something, either hormones or our instinct (or both), tells us "yummy, pussy!!!!!". If this wasn't present our earlier ancestors wouldn't have fucked in the way they were supposed to (why do something you don't want to do if you're not yet evolved enough to think about the consequences?).
This isn't wrong in the classical sense of the word, as things like that happen a lot in real life. There are animals (& even humans) who, even though they were born & raised in the wild, cannot or will not take care of their children. Because of this, the genes causing this do not survive for another generation.
This doesn't mean that this behavior becomes extinct after a while., since genes have a tendency to mutate, thanks to multiple factors (sunrays are one of them, a slightly higher or lower temperature than normal could be another, toxins, specific food sources containing lots of proteins, etc.) & that's a good thing. We are what we are because of these mutations.
onder:
