Monogamy is probably the stupidest thing humans could've done when we still were hunters and gatherers.
Nowadays, it really doesn't matter.
Well Monogamous and Polygamous relationships have been in observed in nature. If you argument is that people should be knocking each other up left and right during that time period, that would be a really dumb statement. You have remember when lived in a time where there were very few sustainable resources. Fruits, edible grains, edible plants were scarce during winters, and most animals were big and strong, you also had large animals which required many people to carry. Larger populations tend to consume more resources, more people means more food. If run out of plant resources while hunting and scavenging, then you have to eat and fish, and you are consuming those at a rate where they can't be replenished fast enough, then you are screwed. Look at the East Islanders, too many people, fragile environment, limited food, over fishing and over hunting of resources. There might have been exchanges between passing by groups, but who knows how often this occurred.
Another issue too is genetic diversity, you have to remember that tribes in that period were large families, of people that. It wouldn't do you much good to randomly knock up your whole tribe because that would just lead to more inbreeding. Another thing too is that other tribes might have been considered strangers or too far away to make contact with, or they might not have stayed in one place for too long,
I tend to associate polygamy with those hippy people that preach free love, peace, and marijuana and those crazy branch Davidians. Commune types.
