you have to ask why human beings are monogamous in many cultures? There are some theories that speak of feminine instinct of survival for herself and her children ... other socioculural purely on that fact. Well, I think the real reason is much simpler than all this: jealousy. We
monogamous because we need someone to do something for us and only us. Attach a position of supremacy to someone, you elevate to a position highlighted above all others to make it clear that it is for that person for whom we strive, through whom we do special things, whom we will support and pamper more than anyone. And besides, we need someone to lift us to that pedestal we do not get along very well ... someone "our level" need more attention than us. And if you do not believe me, compliments in a peer group to one of the members and see their faces ... reckon expressions "and why not me" and know what I mean. To sow discord just have to break the balance of care in a group and apparently, for it is much more effective to have a detail with a member not have it with any ...