From an evolutionary standpoint, yes. From my standpoint, yes. To others, no. It's all a matter of persepective and finding what works for you.
I've mentioned before that I'm in a polyamorous relationship. It works for us, and feels natural, although we know by most standards it's not. The way I feel, how can one person fulfull all of another's emotional needs? There's so many different kinds of people, and so many different kinds of love, it just seems impossible.
From the take of evolution, the general idea is to propogate our genes. Women are supposed to be hardwired to want one partner, while men are supposed to do the propogating. When you think about it, with the bulk of species in nature, the females care for the young, and the men bolt. Humans are animals, on the base level, like it or not.