Exactly why so many humans choose monogamous pair bonds over juggling multiple partners has long been a mystery to scientists. After all, having several partners at the same time should lead to more offspring — an outcome you’d think evolution would favor. Now a new study has linked the phenomenon to sexually transmitted diseases, arguing that monogamy could have evolved because it offered protection against the threat of infection.
Monogamy is, of course, the norm in Western societies. But there are many cultures where a husband can have more than one wife (polygyny) or, less commonly, a wife can have more than one husband (polyandry). This diversity of human mating systems is also hard to explain. What we do know, however, is that many hunter-gatherer societies, living in small groups, were most often polygynous (and many remaining groups still are). But with the rise of agriculture, societies tended to become more complex — and less polygynous. In the most strictly monogamous societies, there was often a social punishment for polygynists, either informally or, as in many modern societies, through a legal system.
Many explanations for this evolution have been put forward, including changes to the way that women chose their partners, such as being faithful to men who invested in provisioning for them. Another possibility is that groups of monogamists may have performed better than groups of polygynists. But the new research adds a further option: could an increased risk of infection from sexually transmitted infections associated with polygyny have contributed to – or even driven – the overall move from polygyny to monogamy?
