auntblabby wrote:
To get back to the original question.
There probably is some grain of truth to this notion. Indeed it coincides with my own ideas while majoring in anthropology.
My guess is that humans are weakly monogomous by instinct. The natural tendency for humans is to settle into monogomous couples ( in contrast to the harems that gorillas have, and the sexual free for all that bonobos have, and other mating strategies of other apes).
But the question is if we are instinctively monogomous why would we need all kinds artificial, religous, and civil, legal, cultural, institutions to buttress monogomy?
The reason is that humans are not designed to constantly interact with large numbers of strangers as we do today.
For most of human history (which was actually prehistory) we lived in stone age hunter-gather groups. You would live in a band of about 60 people. That band would be part of a larger tribe of about 500 people of the same language. It took 20 square miles of land to support each person (by hunting and gathering wild food from nature) so your whole 'nation' would be 500 people spread out over 10k square miles.
Most of the time you were in contact with relatives or inlaws. Adults strangers of reproductive age all lived over the hill in the nieghboring tribe- the same people you fought wars with. So fidelity was a non issue.
With the advent of the plow, and agriculture, and of Bronze Age civilizations, you had the huge rise in population densities. Even in rural areas there would be hundreds of people per square mile. Cities would have thousands per square mile. So adult humans of reproductive age would be in frequent contact with other adult humans of reproductive age- in an unnatural way. So ancient societies invented repressive rules (like having to wear clothes) and both secular and religous strictures. Basically its all about population density.