[GoNatural]

Forms of Polygamy, be it polyandry or polygyny have been around as long as written language has, at the least. It is natural if you judge it by how long it has been a part of human culture, and by how many cultures include forms of polygamy (which is about 80% of cultures).

Now, I must say that according to one of the leading anthropologist, Helen Fisher, polygamy is actually a "plan B" in the mating game, so to speak. It most likely arose in cultures as economic systems have arose and land ownership. In countries that have great disparities between the rich and the poor, or the haves and have nots, polygamy is more prevelent or accepted. It is all about the resources or availability of finding a healthy mate in a given environment.

What is most natural is for humans to form a pair bond, and pick a fovorite mate in which to nest with, or spend more/most of their life energies with. So social monogamy is natural, while sexual monogamy is not. Sexual monogamy is a construct of culture.

I believe that an open relationship arrangement would "feel" the most natural to the highest percentage of people. They would still form a pair bond with one mate, yet have secondary lovers on the side. Certainly, this would be a form of polyamory if emotional and romantic bonds were formed with the secondary lover/lovers.

I recommend the books written by Helen fisher, as well as a book titled The Myth of Monogamy: Fidelity and Infidelity in Animals and People.