Biologists tend to split monogamy into social monogamy (a pair living together to mate, share resources and care for young) and genetic monogamy (a couple exclusively having sex and reproducing with each other).
While we may prize monogamy in many human cultures, it’s pretty unusual among mammals, with just 3 to 5 per cent of species being socially monogamous. These include a few bats, grey wolves, some primates, prairie voles and Eurasian beavers, among others. In birds, monogamy is far more common with some 90 per cent of species exhibiting social monogamy. It is rare in fish, reptiles and amphibians.
Crucially, the definition of ‘social monogamy’ does not mean that the two animals in a pairing will be faithful to each other. In fact, many will have flings on the side when no one is watching.
It is thought that monogamy evolved to maximise the chances of offspring survival, with two parents available to help with care, feeding and protection.
- This article first appeared in issue 371 of BBC Science Focus Magazine – find out how to subscribe here