Christopher Ryan and Cacilda Jethá have a new book on the evolution of sexuality. They argue - duh - that monogamy is unnatural:

Biologists distinguish sexual monogamy from social monogamy. As DNA testing has grown cheaper in recent years, we’ve learned that most species formerly classified as “monogamous” (primarily birds) are socially monogamous, but not sexually so. In other words, they form pairs that cooperatively care for that season’s brood of young, but the male may well not be the biological father. Applied to humans, we argue that a more flexible approach to sexual fidelity can increase marital stability and thus lead to greater social and family stability.

In a Q&A with the authors the open relationships of some gay couples are discussed:

First of all, they’re both men, so they both know what it’s like to be a man. They both know from experience that love and sex are two very different things, and it seems that for women the experience of sexuality is much more embedded in narrative, in emotion, in emotional intimacy. But also it’s really hard to judge what women would be like if they hadn’t been persecuted for the last five or six thousand or ten thousand years for any hint of infidelity.

Gay men in the United States have also by definition gone through a process of self-examination. The whole process of coming out is a process of integrating sexuality into your life in a way that takes courage, and it’s not something that happens naturally. I think gay people have an advantage because they’ve already gone through a process of saying: "Look, my sexuality is what it is. I’m not ashamed of it. I’m going to live openly and in accord with it." That puts them on a different level than most heterosexual people who are able to pass along and pretend that they fit into the normal parameters.