[Boripiomi]

Yes, obviously in past there was mixture of mono and poly. Certainly it was much easier for rich man to have few wives or many women on side.
For the rest of ordinary man it was a huge task to support even one female with many kids.
It pretty much boils down to economy. Mind that in past there was no birth control (at least sure and popular ones). You had sex and most likely made a child. One woman, lets say on average, can have around 10 kids through life time. Also keep in mind that food was a very limited resource back then, and still is in poor countries today. Mostly hunger was responsible for only 2-3 kids surviving till adulthood. Why would a man from past (90% of population) want to have more wives than one? In reality it was a grueling every day work of two adults to feed 3 growing kids, and they were always hungry.
Just for this economic reason most of today's population, regardless of the law and religion, go monogamist.
Social justice of “one for one” comes strong too in second place.


If we go even farther back to small hunter's group. The sharing aspect becomes one of the most important. So either they all could have sex with anyone, or one man pairs with one woman. Any bigger inequality in small groups destroys them, so both ways are just and right, makes them survive and live peacefully, unless I’m missing something.

Interesting thing develops now in China and India. Thanks to traditions and modern technology, fetuses of unwanted girls are killed, in favor on proffered boys. I think the ratio of mail to female is 100 to 90, respectively. 10% of men won't find a woman to live with. In case of India that's 50 million strong population of lonely man! If someone could organize these young horny man into an army, ...wow, scary to think...they'll will come and take your woman away,...or even start a regime of Lonely Horny Men Party, lol.
The only escape for Indian government against new revolution is to buy 50 million of Japanese pump dolls, or even robotic wives, and give it to these men. And hurry up, before someone organizes them….
Cheers