Why Are We Monogamous?

How did humans and some other primates learn to be monogamous when a vast majority of mammals are not? What is the reason they stick to one member of the opposite sex when they could have more than one? Today, humans can cite things such as love and bad economy for the reasons behind monogamy but our primate ancestors it seems had other reasons.

Social monogamy - when a male and female of the species stick together for the long term, although may mate with others - is rare in mammals generally. However, it occurs in over a quarter of primate species, including humans and gibbons.

A new study suggests that the threat of infants being killed by unrelated males is the key driver of monogamy in humans and other primates.

To investigate what originally drove us to establish such pair bonds, a team led by Kit Opie of University College London and Susanne Shultz from the University of Manchester, UK, gathered data on the mating behavior of 230 primate species. They selected behavioral traits associated with several possible evolutionary drivers of monogamy, including the risk of infanticide, the need for paternal care and the potential for guarding female mates.

Using data on the genetic relationships between the species, the team ran millions of computer simulations of the evolution of these traits to work out which came first. All three were linked to the evolution of monogamy but only behaviors associated with infanticide actually preceded it, suggesting that this was the driver.

The team also found that following the emergence of monogamy males are more likely to care for their offspring. Where fathers care for young, not only can they protect infants from other males, but they can also share the burden of childcare.