A new study on primates from researchers at the University of California, Los Angeles (UCLA) found that female monkeys with a tight-knit group of female friends tend to live longer.

The team studied the relationships between female white-faced capuchins of all sexes and ages to see if friendship among them is linked to their survival, MailOnline reported. They tracked their behavior, such s grooming and foraging habits, and observed how they support one another. They found a positive correlation between same-sex friendships and survival in heterosexual friendships.

Female Monkeys With Female Friends Live Longer: New Study Shows the Evolutionary Benefit of Friendship Among Same Sex
(Photo: Pixabay/blende12)
Female Monkeys With Female Friends Live Longer: New Study Shows the Evolutionary Benefit of Friendship Among Same Sex


Female to Female Friendships are Beneficial to Survival

The findings of the study, titled "Social Integration Predicts Survival in Female White-Faced Capuchin Monkeys," published in Behavioral Ecology, are based on the friendship between female capuchins associated with their survival. The authors tracked the primates for 18 years and observed the interaction of female monkeys with other females, males, and companions of any age.

Professor Susan Perry, who has been directing the Lomas Barbudal Capuchin Monkey Project in Costa Rica for three decades, said that their study aims to understand why humans invest so much in relationships and whether it leads to a longer life and more reproductive success. She also noted that measuring this in humans requires a lot more effort than in monkeys.

With lead author Kotrina Kajokaite, who earned her bachelor's, master's, and doctorate at UCLA under the supervision of Professor Perry, the team has been documenting the daily lives of hundreds of monkeys. Their key finding is that adult female capuchins are better integrated into social networks with other female monkeys and tend to survive longer.

Female-to-female friendships include giving and receiving grooming, participating in coalition conflicts, foraging nearby, helping one another during fights or conflicts, and chasing or making aggressive sounds and facial expressions.

On the other hand, interactions with adult males only had the same effect if females provided more grooming. There is also no evidence that heterosexual relationships provide survival-related benefits to females.

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Findings Could Explain Some Evolutionary Precursors to Human Rituals

In a separate study, titled "Capuchin Monkey Rituals: An Interdisciplinary Study of Form and Function," published in Philosophical Transactions of the Royal Society B, the team discovered that the monkeys perform intended rituals to test their friendship.

Science Daily reported that these rituals include inserting a finger into their friends' mouth, eye, nostrils, or ear, prying each other's mouths, passing an object back and forth using their mouths, and clasping each other's hands. Other rituals also observed were cupping the hand over their friend's face, sucking an appendage of their friend, and using their friend's belly as a drum.

Researchers hypothesize that these rituals were used to test the quality of friendships and alliances prevalent in pairs of monkeys uncertain of their status as friends. They are usually performed in pairs and are most often used with a history of friendly interactions.

Although these seem to have some elements of the definition of rituals in anthropology and psychology, they differ from human rituals in the sense that all group members do not perform them. Perry said that the bond-testing may have been beneficial in the evolution of non-human primates.

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