>>213523408From what I've gathered, human breeding habits were more lax before farming became a thing. Farming solidified the concept of ownership. Daughters became cattle to trade away. The invention of rings served men mostly so they could mark their possession.
For the most part, if a marriage sucked, it sucked the hardest for women. Women could be absolutely miserable in marriage. The modern era has changed this a bit. Most divorces are initiated by women. Cheating is common (more common that you might think) by both men and women.
Even still, open relationships don't work or at least shouldn't work in the modern era. It might have to do with how hierarchial our society is and how people are judged by their individual merits. Some men win hard and they could get an endless harem of women. Some men lose hard. Their woman is getting passed around but they don't get anything in return. It's more balanced for women. Nevertheless, the problem is the huge amount of jealousity that people can experience in open relationships. It can turn violent, especially towards the kids. This is an evolutionary thing.
A big difficulty are also STDs. Since we're one global community, you can get any STD known to man from the opposite side of the Earth.
Parenting as a duo is way harder than having a tight-knit community to look after each other. Before it was seen by the bitterness of the great generation and boomer parents. Now it's seen by the unwillingness to have children and modern work life demanding everything from both parents. The result is less and less kids being born and the older generations surviving without young people to look after them.