Never underestimate the power of a strong friendship.
In a new study, researchers have found that certain female monkeys that have female friends live longer than those who don’t have close relationships.
Scientists studied female white-faced capuchin monkeys in Costa Rica to determine how hanging with fellow females affected their life span.
Until relatively recently, scientists believed that only humans had cultural practices and rituals, study senior author, UCLA anthropology professor and field primatologist Susan Perry, tells Treehugger. But animal behavior researchers have started studying these practices in many species.
“We are particularly interested in the social rituals because this form of social tradition is most rare in nonhumans, yet we think of these types of rituals as being an extremely important part of human cultural practices,” Perry says.
“Understanding how rituals have evolved to serve as ‘social glue’ for testing and cementing social relationships, both at the level of the dyad (pair) and the society more generally, is an important unsolved research question.”
For more than three decades, Perry has directed the Lomas Barbudal Monkey Project in Guanacaste, Costa Rica. There, researchers observe hundreds of large-brained monkeys, documenting their daily life and social dynamics.
A typical day involves heading into the forest for 13 hours to watch white-faced capuchins (Cebus capucinus) as a model to better understand human traits and behaviors.
Perry says she originally became fascinated with the species because she wanted to know what was going on in their enormous brains.
“Capuchins’ relationships are extremely important to them, and unlike most species, they have evolved a rich repertoire of species-typical signals for coalition formation, such as the ‘overlord’ posture in which they stack on top of each other and bare their teeth towards a common enemy,” Perry says.
“They also have more quirky ways of testing their social bonds with one another, which are culturally derived by particular pairs of monkeys, and seem to convey information about how committed they are to particular friends and allies. These culturally derived rituals are rare in the animal kingdom, and may provide special insight into the evolutionary origins of some types of human ritual practices.”
Tracking Social Behavior
For the recent study, researchers focused on the connection between female capuchin relationships and their survival. They analyzed 18 years of data to follow 11 social groups of monkeys. They used models to estimate how likely each female is to groom another female in her group, forage for food nearby, or become part of a conflict.
“To study social relationships in capuchins we spent thousands of hours watching and carefully documenting who spends time with whom and what they do together in capuchin social groups,” lead author Kotrina Kajokaite tells Treehugger. She earned her bachelor’s, master’s, and doctorate at UCLA while working on the monkey project with Perry.
Interactions and behaviors aren’t always easy to document. For example, it’s easy to miss grooming because animals are usually quiet when they do it. In order to effectively track these more subtle behaviors, researchers followed one monkey for 10-minute intervals, making sure to document everything the animal did with any group members.
Conflicts were easier to note because monkeys usually scream and chase each other. In these situations, researchers recorded what happened when they saw a fight start. But even those incidents are hard to record because animals can move so quickly and a lot happens at once.
After analyzing all these social interactions, researchers found that those females who were more involved in the social network with other adult females lived longer.
“Females who more frequently engaged in affiliative interactions with other females, and who were more frequently tolerated by the other females in a feeding context, survived better a given calendar year than those who engaged in these two behaviors less frequently,” Kajokaite says.
On the other hand, how much a female interacted with adult males did little to predict her life span.
The findings were published in the journal Behavioral Ecology.
Social Relationships Key to Survival
Researchers are particularly intrigued by white-faced capuchin monkeys because they are neonatal primates that diverged from Old World primates (where humans belong) about 40 million years ago. They’re very different from humans as far as behavior, diet, and social organization, but they’ve still developed some human-like characteristics like large brains, long life spans, social learning, and long-term social relationships.
“We find it fascinating that despite numerous differences in the factors that shape human and animal social environments, the relationship between social integration and natural life span appears to be similar in humans and nonhuman primates,” Kajokaite says. “This study reinforces the general finding that social relationships are critical for survivorship and, perhaps, for lifetime reproductive success.”
Capuchins live in social groups that are usually made of adult females and several adult males, plus their offspring. Males change groups many times as adults, usually in the company of male brothers and cousins so they always have allies.
“Humans are well known for the richness and variety of their social structures, relationship types, and variety of social rituals,” Perry says.
“We know little about these topics in other species, but in order to explain the evolutionary history of such behaviors in humans, we need to know the extent to which such behaviors exist in other species, and the possible characteristics of those species that promote the use of flexible, learned social rituals to promote, test, and maintain the friendships and alliances that are so essential to lengthening life span and increasing reproductive success.”
