hmmm…. that’s only true in certain agrarian circumstances, and esp where the w

hmmm…. that’s only true in certain agrarian circumstances, and esp where the women do the farming work. And usually the most impoverished. For the simple reason most men can’t afford them. In fact most societies both past and even present allow polygamy, but (a) few men can afford it, (b) and where men die a lot in war, so surplus women are economically safer.

Natural form is serial monogamy, with lots of cheating. 😉
The reason is simple: access to mate is the principle reason men kill. So serial monogamy with lots of (or at least frequent) cheating is the natural equilibrium.