Female white-faced capuchin monkeys living in the dry tropical forests of northwestern Costa Rica may have discovered the secret to a longer life: having females as friends.
“As humans, we assume that social interactions have certain benefits, but it’s really hard to measure the success of our behavioral strategies,” said Susan Perry, a UCLA anthropology professor and field primatologist. “Why do we invest so much in our relationships with others? Does this lead to a longer lifespan? Does this lead to better breeding success? It takes a colossal effort to measure this in humans and other animals.”
Perry would know. Since 1990, she has been leading the Lomas Barbudal Capuchin Monkey Challenge in Guanacaste, Costa Rica, where her team of researchers documents the daily lives of hundreds of big-brained monkeys. While chimpanzees and orangutans are more closely related to humans, the white-faced capuchin monkey has very sophisticated social constructs that influence behavior and are passed on to others.
Throughout the year, Perry’s team of graduate students, postdoctoral students, international volunteers and local researchers trek through the forest for hours of observation to try to draw conclusions that can help us understand our own relationships, culture and other behaviors.
Relationships women-women matter
The latest findings, recently published in Behavioral Ecology, have focused on the relationship between social integration and survival of female nasturtiums. The authors tracked female monkeys’ interactions with other females, males, and mates of all genders and ages, based on 18 years of data. Lead author Kotrina Kajokaite earned her BA, MA, and Ph.D. at UCLA while working with Monkey Project data under Perry’s supervision.
Their key finding: adult female nasturtiums that are better integrated into social networks with other adult females survive longer.
Interactions counted in the study included giving and receiving care, seek nearby food, and participate in coalition conflict – intervene to help each other in conflict by fighting, chasing, or making aggressive sounds and facial expressions.
There was no evidence that heterosexual relationships provided survival benefits for women, less regarding the forms of behaviors measured in this study. But this does not exclude the possibility that some adult women may benefit from social interactions with one or a few male partners who cohabit with them for long periods of time.
Although it There is also evidence that women who were more socially integrated in their global group survived longer, the overwhelming conclusion of the research is that female-to-female relationships had the greatest impact on survival.
Testing friendship through rituals
In another study published in a special journal of the Royal Society, the Perry’s team observed white capuchin monkeys engaging in socially learned human fate rituals. Among the interactions: inserting a finger into the mouth, eye, nostril or ear of a social partner opening each other’s mouth or most importantly for a detailed inspection of its contents passing a object from mouth to mouth in a gentle tug of war and shaking hands.
Other rituals observed included cutting the most important part of the face of the partner, sucking on an appendage belonging to the partner, and using the partner’s back or stomach as a drum to create loud, rhythmic noises. Some of these rituals lasted up to 18 minutes, although some include uncomfortable elements that could annoy a partner.
How do these behaviors work in the lives of these animals and what – if anything – can they tell us about the evolution of ritual behaviors in humans?
Rituals are used to test the quality of friendships and alliances and are especially common among uncertain monkey couples of their current relationship status, Perry said. They are most often performed by pairs who rarely interact the rituals are also most often used by monkeys with a history of mostly friendly interactions.
Although the Capuchin rituals have almost all the elements present in the definitions of rituals of anthropologists and psychologists, they differ from humans in that they are not performed simultaneously by all members of a group. Perry said the psychology behind the examination of non-human primate bonding may have been an evolutionary precursor to the more group-oriented form of humans’ ritual practices.