I don't think you can equate things such as the UN or EU to natural systems. Sure, the UN and the EU are a result of humanity, but the point I'm trying to get across is that natural selection doesn't select what is "best" (which at the end of the day is a variable opinion) but selects what is stable. And it seems, from our history, that it was stable to maintain a relationship between two individuals, with a slight amount of infidelity. I don't think we can say "know the future by knowing the past" because that implies a certain amount of choice in the past. We can only know the future by knowing the past if we know the choices we made in the past and avoid them in the future. However, I am talking of a time before ancient humans had a choice, and were subject to their biology.