Penguins being monogamous is an evolutionary trait. Noone needed to teach them because their genetics already taught them, or more correctly, the world/environment they live in taught them.

I don't think the corollary drawn from penguins, or bonobos, or any other animal is a strong one because of how different humans and the rest of the animal kingdom are. From what it looks like, human relations are still evolving and developing. It may very well be that polyamory is what is best for our species, and it also may very well be that monogamy is what is best for our species.

To complicate things even further, effective contraception is brand new in the grander scheme of things as is successful STI mitigation, so there's no telling how that changes things 1000's of years from now. I'm personally very uneasy about calling one thing right and another wrong.