kdpierre:
My current feeling is that monogamy is not natural. Possible, yes, but not natural.
That depends on whether you're a man or a women. Evolution takes a long time to work, our minds have not changed much since paleolithic times. The urge for reproduction tends to drive us.
In a primitive hunter/gatherer society a woman had certain requirements in order to reproduce. During the latter stages of pregnancy doing things such as climbing trees for fruit, hunting, gathering food, etc. were difficult. After the baby was born she had to keep it with her and nurse it for several years. After the baby was weaned other women in the tribe could care for the child her freeing her for other activities. So her best shot at having children was to find a man who was willing to stay with her and provide for her and the child for at least the length of time for her to get pregnant and finally wean the child, about two and half to four years. By the way, that is the most likely time for most marriages around the world to break up, after two and a half to four years.
For a man his best shot at reproduction was to impregnate as many women as possible. In primitive societies the infant mortality rate is fifty per cent and would be even higher if the man takes off and doesn't help the woman. However if he manages to impregnate ten women in a few years and only two or three of those children reach adulthood that means he is two or three times more successful at reproduction than if he stayed with one women for that length of time to make sure her one child survives.
An example of how women favor monogamy and men favor polygamy is to look what happens when the other sex isn't involved as in the gay community. In the US the first state to allow gay marriage was Massachusetts. In the first few months quite a few gay couples rushed to get married, ninety percent of them were women. Gay women tend to be more monogamous and gay men are notoriously polygamous. Think of "glory holes" as an example of that.