Why Do Some Adult Primates Play While Others Don’t? New Study Points to Social Structure

Adult play among primates is not just a human quirk—it occurs in about half of all primate species. However, a new analysis of 37 species has uncovered a surprising reason why some primates stop playing once they reach adulthood. The key factor lies in the nature of their societies: despotic, hierarchical groups rarely engage in adult play, while more egalitarian groups often do. This finding sheds light on the evolutionary role of play in maintaining social bonds and reducing tension.

What did the study find about adult play in primates?

An international team of researchers analyzed social play behavior across 37 primate species and discovered that adult play is strongly linked to the type of society the animals live in. In despotic or highly hierarchical societies—where dominance is rigid and enforced—adult play is rare or absent. In contrast, species with more egalitarian or relaxed social structures frequently engage in playful interactions as adults. The study suggests that play serves important functions such as building alliances, defusing conflicts, and reinforcing social bonds, which are less necessary in strict hierarchies where relationships are already clearly defined.

What exactly is a 'despotic' primate society?

A despotic primate society is one where power is concentrated in a single individual or a small elite, and social relationships are based on strict dominance hierarchies. In these groups, access to resources like food, mates, and grooming is determined by rank, and lower-ranking individuals must constantly defer to higher-ranking ones. Examples include many species of macaques, baboons, and some lemurs. Such societies are characterized by frequent aggression, submission signals, and a clear top-down structure. Because social positions are unchallenged, there is little need for the kind of negotiation or bond-testing that adult play provides, which may explain why play declines.

How many primate species were studied, and which ones were included?

The research team examined data from 37 different primate species, covering a wide range of social systems, body sizes, and habitats. The sample included both Old World and New World monkeys, as well as prosimians and apes. Species ranged from the highly despotic rhesus macaque (Macaca mulatta) to the more egalitarian bonobo (Pan paniscus). The researchers drew on long-term field observations and published literature to classify each species' social structure and record instances of adult play. By including such a diverse set, the study could statistically separate the effects of social organization from other factors like brain size or diet.

Why do some primates continue to play as adults while others stop?

The difference appears to stem from the social functions of play. In egalitarian societies, adult play helps maintain alliances, practice social skills, and reduce tension without the risk of escalating into real aggression. Playful interactions can also reinforce cooperative relationships, which are vital in groups where no single individual holds absolute power. In despotic societies, such behaviors could be misinterpreted as challenges to authority or as weakness, so they are suppressed. Instead, social interactions are highly ritualized. The study also notes that environmental factors like food availability may influence play, but social structure was the strongest predictor among the species analyzed.

Does adult play occur in any despotic primate species?

Adult play is not completely absent in despotic societies, but it is significantly rarer and usually limited to specific contexts. For example, in some highly hierarchical macaque species, adult play may occur between individuals of similar rank or among close kin, especially when tensions are low. However, the frequency and complexity of play are drastically reduced compared to egalitarian species. The researchers found that in despotic groups, when adult play does happen, it often involves lower-ranking individuals or occurs during times of relaxation, such as after feeding. In extreme cases, such as in the Papio baboons, adult play is virtually nonexistent.

How do researchers measure 'play' in primates?

Play in primates is typically identified by specific behaviors that differ from serious interactions. Common indicators include play faces (relaxed open-mouth expressions), exaggerated movements, role reversals, and self-handicapping (where a stronger individual holds back). Researchers also look for sequences that are not goal-directed, lack aggression, and are repeated. For adult play, the study focused on social play between two or more adults—not play with infants or juveniles. Observations were made in the wild and in captivity, and only species with sufficient data on both social structure and play were included. This rigorous methodology allowed the team to draw robust conclusions about the link between social organization and adult play.

What does this study tell us about the evolution of play?

Play is often seen as a juvenile activity that helps develop motor skills, social cognition, and stress management. This study suggests that in species where adults continue to play, it likely evolved to serve ongoing social functions—particularly in complex, flexible societies where alliances need constant maintenance. In despotic groups, where social roles are fixed, the evolutionary pressure to retain adult play may be weaker. The findings also imply that play is not just a byproduct of high intelligence or surplus energy but a social tool that adapts to the group's power dynamics. Understanding these patterns can help primatologists predict how social change, such as the loss of a dominant individual, might affect play behavior.

Are there implications for understanding human adult play?

Yes, the study has intriguing parallels with human behavior. Humans, like many primates, engage in adult play—from sports and games to teasing and humor. Our societies vary widely in how hierarchical they are, and this research suggests that the frequency and style of adult play may be influenced by social structure. In more authoritarian or rigidly stratified human societies, adult play might be suppressed or channeled into safe, ritualized forms. Conversely, egalitarian human groups may foster more spontaneous play. While humans have unique cultural factors, the primate findings offer a biological baseline. Understanding these roots can help psychologists and sociologists explore the role of play in human bonding, stress relief, and creativity across different social systems.