https://medium.com/inside-of-elle-beau/yes-our-ancient-ancestors-were-egalitarian-b32df87bed57

Patriarchy overran the peaceful egalitarian settlements that preceeded it, and spread in large part because it was so destabilizing. Patriarchy brought with it not just gender inequality but social stratification and a class system that had not been there in the past. America was founded in that kind of social stratification, so it's not likely to go away any time soon.

“In a demographic simulation that Omkar Deshpande, Marcus Feldman and I conducted at Stanford University, California, we found that, rather than imparting advantages to the group, unequal access to resources is inherently destabilising and greatly raises the chance of group extinction in stable environments. This was true whether we modelled inequality as a multi-tiered class society, or as what economists call a Pareto wealth distribution (see “Inequality: The physics of our finances“) — in which, as with the 1 percent, the rich get the lion’s share.

Counterintuitively, the fact that inequality was so destabilising caused these societies to spread by creating an incentive to migrate in search of further resources. In other words, inequality did not spread from group to group because it is an inherently better system for survival, but because it creates demographic instability, which drives migration and conflict and leads to the cultural — or physical — extinction of egalitarian societies.”