Evolutionarily Speaking, Monogamy Isn't All That Romantic

We learned a lot about monogamy in mammals this week, specifically, that it evolved because it’s good for the health of the species, which is usually why things evolved. Exactly how that works, however, is still up for debate. Is it because there’s so much space on earth and males had to pick a lady to make sure they didn’t lose the chance to reproduce? Or is it because males wanted to make sure their kids wouldn’t die? Both are such beautiful and moving options.

One study, from Science Magazine, alleges the former: that monogamy occurred as a social construct in areas where there was originally a lot of animals living solitarily, which meant that male mammals of a species probably wouldn’t get the chance to meet a lot of ladies in their lifetime. Additionally:

Our results suggest that social monogamy evolved in mammals where feeding competition between females was intense, breeding females were intolerant of each other, and population density was low. Under these conditions, guarding individual females may represent the most efficient breeding strategy for males.

The researchers behind the Science Magazine data profoundly rejected the idea that monogamy developed as a way to prevent males from killing their own offspring, a finding touted by the Proceedings of the National Academy of Sciences. In their study, PNAS scientists found that the lengthy amount of time that mammals breastfeed for made it more likely that another male, who wanted to mate with a female, might feel threatened and kill the child its new partner had had with a previous one. According to PNAS, if a pair stays together, lactation time shortens and the chances of another dude coming in to kill the child they had lessens:

Of the traits we tested, high male infanticide alone consistently preceded the appearance of social monogamy across primates. Our analyses suggest that socially monogamous species are much more likely to have low male infanticide rates, presumably as social monogamy provides an effective counter-strategy. Social monogamy can reduce the incidence of infanticide because one or both pair-members can defend infants.

Both studies resoundingly contradict each other, and the scientists behind each are sticking with their own work (shocker), though neither were particularly willing to take what they learned about non-human mammals and make grandiose assumptions about how people came to be monogamous. According to the New York Times, one of the PNAS guys said that the researchers who published in Science Magazine “don’t use the latest methods, which is a bit of a pity” (insert upturned nose here). They’ve officially made this current battle far more interesting than the usual anything involving battles of the sexes.