In a long-running discussion about same-sex marriage, one of the participants asked a simple question. It was (paraphrasing): What’s so great about monogamy, anyway? The answer, in part, is that:
…imposing monogamous marriage reduces male reproductive competition and suppresses intra-sexual competition, which shrinks the size of the pool of low-status, risk-oriented, unmarried men. These effects result in (i) lower rates of crime, personal abuse, intra-household conflict and fertility, and (ii) greater parental investment (especially male), economic productivity (gross domestic product (GDP) per capita) and female equality.
Another interesting thought–not fully developed in the article–is that the prevalence of polygynous cultures combined with their relatively dismal track record implies that monogamy is a social innovation that doesn’t emerge directly from human nature. In other words, men by nature want lots of sexual partners and so most societies try that out. Those societies that actually try monogamy, however, found that although it runs counter to the biological aspirations of men it’s actually a better arrangement for everyone.