Female monkeys help explain why friendship helps us live longer

LOS ANGELES — Why do we feel so much pressure to earn the affection of our peers? Moreover, why is the “fear of missing out” (FOMO) a thing? A new primate study suggests there is an evolutionary benefit to maintaining friendships, especially among those of your own sex.

The findings reveal that having female friends helps white-faced female capuchin monkeys live longer. Understanding the strength of female friendships among monkeys may help to answer some of the most puzzling questions about our own behavior.

“As humans, we assume there is some benefit to social interactions, but it is really hard to measure the success of our behavioral strategies,” explains field primatologist Susan Perry, an anthropology professor at UCLA, in a university release. “Why do we invest so much in our relationships with others? Does it lead to a longer lifespan? Does it lead to more reproductive success? It requires a colossal effort to measure this in humans and other animals.”

Perry and her team have been documenting the daily lives of multiple primates in the forests of Costa Rica since the 1990s. While chimpanzees and orangutans are the closest human relatives, after several 13-hour days of observing primates, Perry noticed the white-faced capuchin monkey has similar social behaviors to humans. This includes a complex hierarchy that influences relationships and behavior.

What do female monkeys do with their friends?

The study authors collected 18 years’ worth of data involving the social interactions between female white-faced capuchin monkeys, their behavior towards males, and monkeys of any sex and age. Their biggest discovery was that adult female capuchin monkeys who were social butterflies with other adult females tended to live longer.

Frequent social behavior exhibited by females included grooming, foraging nearby, and intervening in conflicts, whether by fighting, chasing, or making aggressive postures and sounds to deter pests or unwanted suitors.

While the researchers did not find any benefit in maintaining a heterosexual relationship, the researchers predict there may have been some advantages for some females to maintain friendships with males.

While some evidence suggests that being sociable in general helped female monkeys live longer, it was ultimately the friendships between females that had the greatest survival benefit.

Monkeys give each other a ‘friendship test’

A separate study by the team also found that white-faced capuchin monkeys engage in socially learned human-like rituals. Among these included monkeys cupping their hand over a social partner’s face, prying open a friend’s hand, and clasping each other’s hands. Some rituals lasted for half an hour, even if they seemed uncomfortable — like inserting a finger into another monkey’s mouth or eye.

Study authors believe these bizarre rituals may help test the quality of a friendship or alliance. They were mostly done in pairs that rarely interact, suggesting these actions also confirmed the status of a friendship. Perry says bond-testing in primates may have been the evolutionary precursor to humans developing group-oriented practices such as hanging out at the bar after work.

The study is published in the journal Behavioral Ecology.

About the Author

Jocelyn Solis-Moreira

Jocelyn is a New York-based science journalist whose work has appeared in Discover Magazine, Health, and Live Science, among other publications. She holds a Master’s of Science in Psychology with a concentration in behavioral neuroscience and a Bachelor’s of Science in integrative neuroscience from Binghamton University. Jocelyn has reported on several medical and science topics ranging from coronavirus news to the latest findings in women’s health.

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