Though only questionably ubiquitious among humans, social monogamy across mammalian species may have developed in response to intense competition among jealous females — for food sources within overlapping territories.

As time passed in the ancestral world, females of the mammal class dispersed toward discrete territories, preferring a more solitary than sisterly subsistence on a higher quality diet. With this shift, even the most arduous of males found it hard to defend multiple female territories, and were forced to commit.

In a new study, researchers from Cambridge University analyzed phylogenetic information — mitochondrial and autosomal genes — from more than 2,500 mammalian species, using Bayesian probability to determine the likelihood of causation versus correlation.

"Monogamous societies of mammals have almost always evolved when female are intolerant of one another and widely distributed," researcher Tim Clutton-Brock told reporters on Monday, describing the analysis, which also included 230 species of primate. "Fifteen years ago, this approach would have been impossible."

Clutton-Brock and his colleague Dieter Lukas, lead author of a paper published in the journal Science, say the genetic analysis shows an evolution among some mammalian species toward monogamy for a couple of secondary reasons, as well, including a greater chance of survival for offspring born to cooperating parents. Aside from paternal food sources, the male provided protection to the female and their offspring from infanticidal males, who hoped to maximize their own genetic probability. However, the presence of a paternal influence in the family brood occurred after the shift to monogamy, perhaps helping to maintain that behavior.

The investigatory pair compiled information on thousands of some 5,400 living mammalian species, classifying each as solitary, socially monogamous, or group-living — taking care to include species recently found to be socially monogamous.

"It took about two years, on and off, to collect the data on the social systems," Lukas said. "We searched for information for every known mammal, consulting multiple sources, and we discussed our classification with researchers who are conducting field studies."

To be sure, social monogamy — or pair-living, with occasional bouts of sexual infidelity — is prevalent among only three percent of mammalian species, a behavioral phenomenon much more common in birds, at 90 percent or so.

"These findings indicate that in mammals, social monogamy is the consequence of resource defense," Lukas said. "Female behaviors influenced by the distribution of food and male behaviors influenced by the distribution of females."

The development of social monogamy among some species of mammal also promoted a lower infanticide rate, as both parents invested in protecting their offspring.

Source: Opiea C, Atkinson QD, Dunbarc R, Shultzd S. Male Infanticide Leads To Social Monogamy In Primates. PNAS. 2013.

A male dik-dik antelope closely follows the female as she searches for food in her territory, guarding her against other males. [Image courtesy of Peter Brotherton]