Faithful monkeys, it turns out, are rewarded with more babies—and a better chance of their genes carrying on into the future—than unfaithful ones. When owl monkeys break up, researchers found, the mate that takes up with “the other partner” produces fewer offspring than monkeys that stick with their original animal spouse.
In the animal kingdom, monogamy, especially for males, does not make much sense. Why not just hook up with as many partners as possible, to spread your genes far and wide? This example, however, shows how faithfulness can give certain individuals the edge.
Since 1997, the monkey-loving research team intently watched nocturnal owl monkeys in Argentina, totaling about 154 individuals from 18 groups. In 2008, the researchers noticed so-called “floater” individuals—loner monkeys—stirring up trouble between normally monogamous couples. The floaters would swoop in, attack the same-sex partner in a couple and then steal the newly single male or female for themselves. The love fights were intense and sometimes the loser would die.
Pairs that underwent such a transition, the researchers found, produced 25 percent fewer offspring per decade than those that remained true from the beginning.
The researchers don’t know what causes this discrepancy, but they plan to further investigate the owl monkeys’ relationship dynamics. In the process, they also hope to turn up insight about the evolution of pair bonds in humans.
“There’s some consensus among anthropologists that pairs-bonds must have played an important role in the origin of human societies,” they said in a statement. “Call it love, call it friendship, call it marriage, there is something in our biology that leads to this enduring, emotional bond between two individuals that is widespread among human societies.”
More from Smithsonian.com: