Monogamy Is Modern, Right?

There's this idea in society that, like, we can't learn from cavemen. Most babies were born to boyfriends and girlfriends who were in a relationship at least for a few years. But on the other hand, our prehistoric ancestors did not have lifelong formal marriage. There's a large number of ancestral societies that are polygamous. It might be better to be the fourth wife of a rich man than the first wife of the number 50.