I'm talking about polygyny and hypergamy respectively.

While I do believe that it's in a man's nature to want multiple different women and a woman's nature to want the best possible man, these instincts are not indomitable. As incredibly cheesy as the quote is, love really can conquer all. A man in love will only desire the object of his love; even if has the opportunity to cheat, he simply won't feel the need. Similarly, a woman in love will only desire the object of her love- even if a better man comes along, she won't care. Hell, she won't even see him as such.

I've seen many people swear off relationships because "he's going to cheat anyway; it's just male nature" or "she's just gonna branch swing; she's a woman after all". Yes- many people do indeed cheat and branch-swing in relationships but there's only one real reason for that: they weren't in love. If you love your partner, you simply won't be capable of doing those things- nature or not.