Impartial Chimps?
A few years ago, I was skiing, and I saw a woman plow into another skier, and both went tumbling. A few people, including me, stopped to see if everyone was ok. A young man said, “Lisa… are you ok, honey?” She allowed as to how she was, and then said, “It was totally his fault.” There was a bit of a pregnant pause, and then this young man replied, “But… you were uphill of him, so, really, it was your responsibility to avoid him.” She shot him a look full of anger, apologized to the man she had plowed into, and skied off by herself. The young man, who was less likely to have as pleasant an après-ski as he had hoped, shrugged and followed her down the hill.
Humans don’t always take the side of their friends, allies, or relatives when conflicts arise. In other species, we would immediately notice this sort of oddity. If we saw a bear cub pick a fight with an unrelated bear cub, we would be astonished if both mothers sided against the one who started it. Instead, each mom will favor her own. Impartiality is, then, a perplexing feature of human psychology, and an issue that my former student Peter DeScioli and I, as well as Deb Lieberman, have been thinking about recently. (I put a couple of citations below.)
Partly for this reason, a recent paper caught my eye, entitled, “Impartial Third-Party Interventions in Captive Chimpanzees: A Reflection of Community Concern” by von Rohr et al., published in PLoS ONE. They were interested in trying to understand why chimpanzees intervene in others’ conflicts, particularly in cases in which they don’t appear to side with one disputant or the other.
To do this, the authors identified three candidate hypotheses (holding that a fourth one has already been roundly falsified). The first is that intervening in conflicts impartially is beneficial because it increases group stability, i.e., more benefits are possible through having more stable relationships in the group. The second hypothesis is that interventions help dominant males control other males’ potential ascent in the dominance hierarchy. The third possibility is that impartial interventions discourage female out-migrations, which has obvious potential benefits for the intervening male. (See Table 1, from the paper; click to get the larger image.)
Predictions derived from three hypotheses
To distinguish among the three candidate hypotheses, they investigated the circumstances of “impartial interventions,” which was was operationalized (per the Supplemental Material) as follows:
An individual breaks up a conflict without taking sides by e.g. attendance (the individual approaches the conflict and looks at the opponents without showing any affiliative or agonistic behaviours), interposition or running through the conflict.
Before getting to the data, it’s worth noting that “impartiality” in human affairs has a slightly different connotation. Baseball umpires are “impartial” by applying the rules equally to all players, rather than by breaking up a conflict (though they’re supposed to do that as well, except, it seems to me, in hockey, in which they seem to stand around while players fight, at least for a while).
And, at the risk of being repetitive, I note that the authors use behavioral data in the service of the goal of their work, which they articulate as follows: “The aim of this study is to test the predictions of the three hypotheses to identify the function of policing in chimpanzees.” In the animal behavior literature to which this piece contributes, there’s nothing unusual about testing the predictions of hypotheses about evolved function by using behavioral data. (And note that it’s all observational rather than experimental to boot.) As usual, there have been no squawks from the blogosphere, as far as I can detect, about how you need genetic data, a history of selection, or anything else, to test hypotheses about function. (Indeed, the twittersphere seems broadly happy with the work.) Because this is about impartiality in chimps, as opposed to impartiality in humans, testing functional claims with behavioral data isn’t given a second thought. (I recently quoted Dan Dennett on this issue.)
In any case, von Rohr et al. investigated impartial intervention in four different groups of chimpanzees. In one case, in Gossau, observations were collected by a member of the research team. In other cases, the authors used previously collected data to investigate these hypotheses. From Table 2 (again, click through to see the full sized image), one can see that policing is rare, with Gossau being an exception. Here is a passage from the Discussion section of the paper:
Table 2.
In the main study, we found that only adult, high-ranking males performed policing and they policed conflicts of all sex-dyad combinations. The primary predictor of policing was conflict complexity, in that polyadic conflicts were policed more often than dyadic ones. The occurrence of policing across all sex-dyad combinations does not support the assurance of dominance hypothesis or the assurance of sexual benefits hypotheses, but is consistent with the group stability hypothesis. Moreover, the high prevalence of policing coincided with social instability in the group, i.e. the introduction of three adult females and a rank reversal between the two top-ranking males. Thus, social relationships were unstable and easily disturbed. Policing as a group stabilizer may have prevented conflicts from escalating, thereby preventing further disruption of group stability.
It’s worth noting that the authors are cautious in their inference, suggesting only that it is “plausible” “that the main function of policing in chimpanzees is to stabilize group dynamics” (p. 6), and they note that observations in the wild that policing occurs during times of social instability lend some additional credence to their focal claim. They conclude with the notion that impartial intervention might reflect a “community concern.”
Perhaps. But would one chimp turn on his close ally if she bowled into another skier on the slopes?
References
DeScioli, P., & Kurzban, R. (2009). Mysteries of morality. Cognition, 112, 281-299.
Lieberman, D., & Linke, L. (2007). The effect of social category on third party punishment. Evolutionary Psychology, 5, 289-305.
von Rohr CR , Koski SE , Burkart JM , Caws C , Fraser ON , et al. 2012 Impartial Third-Party Interventions in Captive Chimpanzees: A Reflection of Community Concern. PLoS ONE 7(3): e32494. doi:10.1371/journal.pone.0032494
Pingback: Guest Post: To be fair…it is a bit puzzling | Evolutionary Psychology