The Primate Diaries

i-26c193e6b37238fb46d7bc7869d0cd1c-Chimpanzee Model.jpg     New research finds chimpanzees follow
 prestigious models when learning new tasks.
        Monika Thorpe / Creative Commons

This post was chosen as an Editor's Selection for ResearchBlogging.orgIf one were to play psychiatrist to the natural world, most human beings would be committed for our certifiable obsession with other peoples’ behavior. We compulsively examine, study, appraise, size up, and scope out what those around us are doing and then gossip with others about what we’ve seen or heard. New ideas or behaviors are especially compelling and will often have cultural critics discussing them at length, whether they’re tribal elders or the United States Congress.

Given this equal opportunity scrutiny, why is it then that only some individuals and not others become cultural innovators, serving as models for our own behavior? For example, when Benjamin Franklin adorned his rustic fur cap in France or when Tupac Shakur wore his baggy jeans on stage, they inspired widespread cultural trends that made their mark on history (by contrast, notice how few people copied Henry David Thoreau’s fetching neckbeard or the, let’s call it unique, style of Vanilla Ice). In societies around the globe certain influential figures, to use the concept of anthropologist and philosopher Pierre Bourdieu, benefit from “cultural capital” because of their social prestige in a given society. This results in others being more likely to adopt any unique cultural traits that they invent. After all, if someone who is widely admired and successful adopts a new way of doing things, perhaps following their lead could make you admired and successful too?

Now, a new study in PLoS ONE by Victoria Horner, Darby Proctor, Kristin E. Bonnie, Andrew Whiten, and Frans de Waal suggests that prestige is an important factor in other primates as well. By employing a simple behavioral experiment these researchers demonstrated that chimpanzees, when given a choice between two nearly identical tasks, will choose the one they previously witnessed a high-ranking member of the troop perform.

It has long been assumed that humans are the only species in which prestige has an influence on the behavior of others in a social group. To cite just one example, anthropologist Francisco Gil-White and economist Joe Henrich wrote in their 2001 paper “The Evolution of Prestige” (pdf) that:

Humans appear to be the only species with prestige status. The reason why, we argue, is culture.

This argument, of course, breaks down once it’s granted that nonhuman primates also possess culture. As I wrote earlier in my post Cultural Transmission in Chimpanzees (also see here for bonobos) not only is culture a common feature in our evolutionary cousins, the number of cultural traits are more frequent in some societies than others. Johan Lind and Patrik Lindenfors found that female chimps were the primary carriers of cultural innovations and those groups that had a higher number of females were more likely to have a higher number of unique cultural traits. But how did these traits get started in the first place?

To explore this question Horner and colleagues conducted a series of trials at the Yerkes National Primate Research Center’s Field Station near Atlanta, Georgia. The experiment involved two separate groups of female chimpanzees as the models (n = 4) while the rest of the troop was divided between the groups as test participants (n = 10). The models were selected to have very different social ranks, such that Model A in both groups was older, held a position of high status in the troop, and had previously been observed introducing novel behaviors. In contrast, Model B was younger, held the lowest rank in the troop, and had no previous experience introducing novel behaviors. Based on these criteria, Model A held the characteristics of prestige in chimpanzee society while Model B did not.

i-05e6dcdfca5c82d7b2b0e467459d2093-journal.pone.0010625.g002.png
(A) trained models retrieve a token from an experimenter standing between the receptacles outside
the enclosure fence; (B) models deposit their token into their respective receptacles; (C) a food
reward is thrown to the model by a second experimenter standing on an observation tower.

Model A and Model B were then trained to perform identical behaviors with a single variation (see figure above). In Group 1, Model A was taught to collect plastic tokens and place them in a spotted container in order to receive a food reward. In the same group, Model B was taught to deposit identical tokens into a striped container located 10 meters from the first and would also receive a food reward. In Group 2 this was reversed so that Model A used the striped container and Model B used the spotted one. The question was, would the rest of the troop follow the example of high-ranking Model A, low-ranking Model B, or would it be evenly divided since both received identical rewards?

In three experimental trials on separate days Model A and Model B each collected and deposited their token only once while the rest of the troop watched. Each participant was then allowed to copy one of the two models until all chimpanzees had accomplished the task. Group 1 and Group 2 were separate from each other and did not see either the models or the participants from the other group perform their task. The results clearly demonstrated that, in both groups, participants preferred to follow the example of the high-ranking Model A by a significant majority. These results remained consistent both between groups (p < 0.0001) as well as between individuals within groups (p < 0.05). When given the choice between two similar tasks, chimpanzees overwhelmingly chose to follow the example of the most prestigious model.

i-247a39de641ed6aa0bc39b3543a51373-journal.pone.0010625.g003.png
In both Group 1 and Group 2 participants were significantly more likely to follow the behavior
of high-ranking Model A to low-ranking Model B.

What this study suggests, apart from debunking yet another myth about human uniqueness, is that chimpanzees carefully observe the behavior of other members of their social group and preferentially follow the behaviors of those deemed successful within their society. Like in humans, they confer cultural capital onto certain high-ranking members and use these individuals as models for their own behavior. It’s also important to emphasize that there was no evidence of coercion or threats by the high-ranking chimpanzees who modeled the behavior and there was no significant difference in the distance between participants and the behaviors of Model A or Model B. Participants merely chose to follow the cultural innovation of the more prestigious chimp.

The evolutionary benefits of such a strategy in the wild should be relatively straightforward. Those individuals that rose to positions of high social rank, whether influenced by successful gene variants or because of fortunate decisions, would have demonstrated that they had what it takes to make it in a difficult environment. Other members of the social group that followed their example would therefore have had greater potential fitness than those who weren’t paying attention (or who followed the behavior of less successful individuals). Discriminating between those with obvious prestige and those of more modest ability would therefore be under strong selection pressure. In the evolution of humans, as in the evolution of chimpanzees, paying attention to the behavior of influential members of the community and hopping on board cultural trends would have been in our reproductive interests.

This doesn’t mean, of course, that the individuals who invented “The Macarena” or who somehow inspired a generation to wear bell-bottoms have better genes than the rest of us. All it means is that we’re predisposed to follow cultural trends set by prestigious members of society. For our ancestors this may well have been a life or death decision. Today, in our mass media landscape, these largely unconscious desires can be easily manipulated by corporations and celebrities who have nothing to offer but the cultural equivalent of junk DNA. While both chimpanzees and humans may have evolved to follow the example of prestigious innovators, such an adaptation doesn’t hold the same significance when removed from the natural world. As our hypothetical evolutionary psychiatrist might well advise, being open to inspired innovations is all well and good. But in the artificial environment most of us are now committed to, it’s probably not in our interest to obsessively follow the example of every lunatic who claims to be running the asylum.

Reference:

Horner, V., Proctor, D., Bonnie, K., Whiten, A., & de Waal, F. (2010). Prestige Affects Cultural Learning in Chimpanzees PLoS ONE, 5 (5) DOI: 10.1371/journal.pone.0010625