Study Uncovers How Mammals Became Monogamous – Not As Romantic as Expected

Scientists have been scratching their heads for years as to the origins monogamy among mammals. Two new studies released Monday revealed different conclusions, and neither of them is romantic in the least.

The first study published in the journal Science, argued that monogamy evolved as a practical solution for males because females lived far apart from one another. Another study in Proceedings of the National Academy of Sciences (PNAS), argues that males embraced monogamy to protect their offspring from rival males, who might see the youngsters as obstacles to mating with females.

"This is the first time that the theories for the evolution of monogamy have been systematically tested, conclusively showing that infanticide is the driver of monogamy," said anthropologist Christopher Opie of University College London, lead author of the PNAS paper, which analyzed 230 species of primate. "This brings to a close the long-running debate about the origin of monogamy in primates."

Meanwhile, both studies addressed the same mystery: since male mammals can produce many more offspring per breeding season than females, it would seem that mating with only one female would be less adaptive for a male than spreading his seed widely.

The PNAS paper, which analyzed 230 species of primates, concludes that protecting the kids is the greatest benefit of male monogamy. By sticking close to his mate a male reduces the risk of infanticide. Although the study examined only non-human primates, that reasoning has resonance in people. It will also move towards helping scientists to understand the evolution of human mating behavior

Although humans aren't completely monogamous, "the emergence of pair-bonding in humans was a major evolutionary transition, which dramatically altered the evolutionary trajectory of our species," says Sergey Gavrilets, an evolutionary biologist at the University of Tennessee, Knoxville.

Many researchers think that we could not have evolved our large brains without joint parental care during the extended period of helplessness required for infant brains to grow to their full size. "Understanding the forces that drove that transition can help us better understand the causes of human uniqueness," Gavrilets adds.