How Did Monogamy Happen to Certain Mammals?
This summer sure hasn’t helped clarify the question of monogamy — and I’m not just talking about your escapades, you player, you. In July, two papers digging into the roots of monogamy hit the news simultaneously, one in the Proceedings of the National Academy of Sciences (PNAS), and the other in Science — but instead of bringing the issue closer to rest, the papers offered somewhat contradictory conclusions.
The PNAS paper, Male infanticide leads to social monogamy in primates, reports that monogamy evolved in primate species as a result of infanticide by rival adult males. Researchers looked at 230 primate species — a quarter of which live in pairs — sorting out characteristics using Bayesian statistics.
“It is only the presence of infanticide that reliably increases the probability of a shift to social monogamy, whereas monogamy allows the secondary adoption of paternal care and is associated with a shift to discrete ranges,” writes lead researcher Christopher Opie.
Killing her infant can bring about fertility sooner in a female primate, so roving males do seem to benefit from infanticide. As a result, it makes sense that monogamy would have developed as a way for males to defend their offspring and their partners. They argue that females started living in discrete territories after social monogamy came about.
The paper that appeared in Science, Evolution of social monogamy in mammals, meanwhile, says that it’s these discrete territories — the increased distance between females — that resulted in the development of monogamy. Their research looked at 2,500 species of mammal — less than 10 percent of which are monogamous.
“The evolution of social monogamy does not appear to have been associated with a high risk of male infanticide, and paternal care is a consequence rather than a cause of social monogamy,” write Dieter Lukas and Tim Clutton-Brock. “Social monogamy has evolved in nonhuman mammals where breeding females are intolerant of each other and female density is low, suggesting that it represents a mating strategy that has developed where males are unable to defend access to multiple females.”
According to their research, when females live far from one another, males have a better chance of producing more offspring if they stick around at home as opposed to venturing to far-off lands in search of more mating opportunities.
“Female behavior is influenced by the distribution of food, and male behavior is influenced by the distribution of females,” Lukas told NPR.
Lukas isn’t convinced that humans have developed monogamy, given the number of cultures that practice polygyny; he told Science News that his research had little bearing on humans. Opie, meanwhile, did include humans in his analysis as a monogamous species.
The teams are sharing data and trying to sort out the details. It’s likely that the first step will involve defining “monogamous” in a manner that satisfies both groups.
(Keep in mind that when I talk about monogamy in this context, I am referring to social monogamy — animals living in a breeding pair — and not addressing fidelity.)
Header image by epSos.de.
