Presented by Alexis Harrison, Emily Kay, and Emily Jacobs-Palmer

The subject of promiscuity is rampant in the news. It appears in a social context – an affair can take down the campaign of a presidential candidate – and in a scientific one, as when theoreticians speculate on the evolutionary underpinnings of our relationship choices. As humans, we are the “monkey in the middle,” promiscuity-wise: our closest living relatives, chimpanzees, are highly promiscuous, but our slightly more distant cousins, gorillas, demonstrate female monogamy. And it goes without saying that the vast majority of us have given some serious thought to the choice between promiscuity and monogamy, whatever our conclusions. But is this choice a haphazard one? At least at the species level, the answer is an emphatic “no.” Promiscuity and monogamy each have a distinct set of causes – from resource abundance to the rate of development in offspring – and they also have a fascinating array of biological consequences, from the peacock’s tail to cooperative sperm in rodents (!). But even though there is an astonishing diversity of mating systems and strategies across the animal kingdom, each has one thing in common – it rises and falls at the whim of natural selection – fidelity and philandering will only survive to the extent that they help individuals pass on their genes to a copious quantity of offspring.