For Great Apes, Addressing Inequality is Child’s Play

by Eric Michael Johnson

Ed note: I’m pleased to bring you this guest post from Eric Michael Johnson as part of his Primate Diaries in Exile blog tour. You can follow other stops on Eric’s tour through his RSS feed or at the #PDEx hashtag on Twitter. You can also follow Eric himself at Twitter. — David Dobbs

New research shows that gorillas understand inequality through their play behavior.
Image: William Burrard-Lucas / Flickr

This post was chosen as an Editor's Selection for ResearchBlogging.orgIt was already stifling at 9 o’clock in the morning as I frantically took notes on what I was witnessing through my field glasses. Without warning a black, hairy arm reached out to smack an unsuspecting victim, immediately giving way to a frantic chase that roused the entire troop. With teeth bared, the large, muscular ape bared down on his assailant amidst high-pitched screams of excitement before a resounding smack reverberated beneath the canopy and signaled the end of hostilities. Having reciprocated the attack, the young bonobo I had come to know as Aaron then calmly moved away, leaving Jumanji to rub his shoulder and stare at the ground in a way that, should he have been human, would probably be interpreted as nursing a bruised ego. However, as expected, not fifteen minutes would pass before Jumanji was at it again, sneaking up on his older and stronger playmate to tag him and begin the chase anew.

What I had witnessed during my bonobo field research is a common pattern among great apes as a whole. In a behavior seemingly identical to the children’s game of tag, one individual smacks another and then runs away only to reverse the chase once they have been “tagged” themselves. Earlier research had suggested that this kind of play behavior was a way to prepare juveniles for the kind of social interactions they would face as adults. Now, research with gorillas has confirmed this hypothesis and proposes that these great apes are utilizing this game as a way to both challenge inequality and learn important social lessons.

Video of one chase bout taken by Marina Ross at Zoo Zürich in Switzerland.

Writing in the Royal Society journal Biology Letters, researchers Edwin Van Leeuwen, Elke Zimmermann, and Marina Davila Ross have shown that gorillas demonstrate an understanding of inequality that they use to modify their behavior under changing social conditions. Rather than my few isolated examples witnessed in a single troop, Van Leeuwen and colleagues have surveyed 86 bouts taking place among six different social groups of gorillas. Furthermore, in their analysis of the data there were several remarkable consistencies that popped up over and over again.

In more than 85% of the play bouts it was the tagger who made the first move to run as well as the one who ran away. This suggests that there was an implicit understanding that the act of tagging resulted in an unequal relationship and that a response from the individual tagged would therefore be expected. In this way, play teaches important social lessons about inequality and how to respond in a social group. “Play allows gorillas to improve their physical and social skills and to learn about their social partners,” Dr. Ross said.

Hitters were significantly more likely to move first and to run away (p = 0.026; 0.004).
Figure from Van Leeuwen et al. (2010).

It may also be that an understanding of inequality is what motivates the tagger in the first place. Not only were gorillas who were lower in the social hierarchy the usual taggers, but they were twice as likely to tag again than were those who were more dominant. This suggests that the game served as a way to challenge inequality and push the envelope as they developed their social behavior within the group as a whole. Furthermore, by learning these lessons through play it serves to avoid the kind of costly aggression that such direct challenges have in adults.

Previous work with great apes has shown that they have the cognitive capacity for this kind of understanding about inequality. Research published earlier this year by Sarah Brosnan showed that chimpanzees will refuse to accept a food reward if the treats were distributed unfairly, even among those who stood to benefit. This refusal to cooperate when faced with an unequal distribution of resources may have its social parallel in these games of tag. By challenging hierarchical boundaries these juveniles are learning the skills that will serve them as adults, behavior that would ultimately be fitness enhancing.

The games our children play often prepare them for the complex social skills they will need as adults, and it would seem we are not alone among the apes in this regard. Considering the attention and effort that children put into determining fairness in their social play, it should not be surprising if the moral lessons gained from these actions were also being learned in our ape cousins.


Van Leeuwen, E., Zimmermann, E., & Ross, M. (2010). Responding to inequities: gorillas try to maintain their competitive advantage during play fights Biology Letters DOI: 10.1098/rsbl.2010.0482


Related at Neuron Culture:

Chimpanzee hunting tactics – an aerial view

The Science of Gossip, in Scientific American

Williams Syndrome, or why are we so social? Plus why the big brain?

and my related article at the Times on Williams syndrome, “The Gregarious Brain“

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