More specifically, it takes 1:1 relationships. Since humanity is naturally a bit of a tournament species culture and religion have historically provided stability through artificially enforced pair bonding species behavior. When that isn't an unofficially enforced cultural norm a small number of men end up getting the majority of the sexual access (as with any tournament species), while an ever increasing number get little to none. Increasing numbers of sexually frustrated men cause large problems for society. I don't have a solution for this problem. What we need is a way to enforce monogamy that isn't oppressive to women and isn't based on religious fictions. That's a hard problem.