Monogamy is not natural — hardly any species practice it, except for b

Monogamy is not natural — hardly any species practice it, except for birds. Social monogamy wherein two creatures mate and work together to meet their needs is especially uncommon among nonavian warm-bloods; only about 5% of the 4,000 mammal species are monogamous. Since mating with one female at a time lowers a male’s chances of producing as many offspring as possible, what good, evolutionarily speaking, can come of monogamy? Why would mammals be monogamous?

One reason, according to a report in the Proceedings of the National Academy of Sciences (PNAS), suggests that males stayed with one female to ensure their young were not killed by another male, but survived to reproduce to carry on their genetic lineage. Based on breeding and parenting behaviors of 230 primate species over several generations, the researchers determined that males balanced the need to spread their gene pool against the need to protect their young from being killed. The attacking males needed to kill the young so they could breed with its mother, who would delay conception of another offspring if she were nursing. So the father hung around to protect his genetic line and help raise the young so the mother could reproduce again sooner. “This is the first time that theories for evolution of monogamy have been systematically tested, conclusively showing that infanticide is the driver of monogamy,” trumpeted Christopher Opie, a researcher in anthropology. “This brings to a close the long-running debate about the origin of monogamy in primates.”

Well, not so fast! Another study, published in the journal Science, used a similar analysis, but across a wider sample — about 2,500 mammal species. Those authors, Dieter Lukas and Tim Clutton-Brock, found no correlation between infanticide and monogamy. They suggested that monogamy is about location and supply. “Monogamy develops where females live at low density,” says Lukas. Males cannot fend off rival suitors from more than one female at a time because they’re too spread out. To ensure their young are the ones the female is carrying, they stick with one female. “It’s a consequence of resource defense.” This study notes that in monogamous mammalian species, the females tend to be solitary and intolerant of other females. Unlike those of ungulates, who are rarely monogamous, these mammals’ nutritional needs are greater, and they therefore shoo off competitors for food resources.

As for human monogamy, the PNAS study is more comfortable extrapolating its results. Because humans have big brains, their infants take longer to nurture and are vulnerable for longer. Therefore, human males needed to protect their child-rearing female until breeding was done. So how important were kids in man’s move towards monogamy? It’s a fascinating fight, but ultimately, whether monogamy is natural is less relevant than whether it’s desirable. Human monogamy seems to be both an acquired taste and a social necessity. The question remains whether it’s worth the cost of learning it.