Chimps, Cultivated Fruits, and Sex

PLoS One recently published a research paper called Chimpanzees Share Forbidden Fruit. The paper reports on studies of crop raiding behavior (and the aftermath) in Bossou, Guinea. The research covered one year and consists of observations on 786 crop raiding events were observed. On 58 (or 7%) occasions the raided items were shared.

Meat sharing has been reported frequently in other chimp communities, as does sharing of other types of items. For example, in Chimpanzee Politics by Frans de Waal, we find:

Holding a branch for another group member seems to be something people find more convincing as a proof of calculated assistance than the formation of a coalition. This same applies to sharing out leaves and meat. We see this as an act of generosity, more readily than the relinquishment of sexual privileges or the offer of protection. And yet both forms of giving are related. Chimpanzee males are surprisingly generous when it comes to material things; they even allow certain females to take objects from them. But they also demonstrate this characteristic in their social behavior (except, that is, with respect to rivals). Their control rests on giving. They give protection to anyone who is threatened and receive respect and support in return.

The leaves being referred to come from oak trees that had been protected with electrified fencing. The chimps had come up with a way to get the leaves anyway, but the endeavor was a stress filled ordeal.
Similarly, Jane Goodall describes a food sharing scene, not meat, in In The Shadow Of Man:

Late that morning David walked up to my tent and helped himself to the fruit [bananas – afarensis]. As he walked back toward the bushes I suddenly saw that a second chimpanzee was standing there, half hidden in the vegetation. It was Goliath. As David sat down to eat, Goliath went close to him, peering into his face. Then as David rolled a banana skin wad around in his lower lip, squeezing on the last juices, occasionally pushing it forward and looking down over his nose, Goliath reached out one hand to his friend’s mouth, begging for the wad. Presently David responded by spitting out the well-chewed mass into Goliath’s hand, and then Goliath sucked on it in turn.

Goliath was, according to Goodall, nervous around her at this point and would not enter her tent like David Graybeard would and was somewhat stressed when David Graybeard did. As the PLoS article points out meat is used as a social tool by chimps, they share it to cement alliances and relationships.
At Bossou hunting was practiced only infrequently owning to the paucity of prey items and the authors of the paper make the argument that crop raiding has the same function that hunting does elsewhere. To buttress this argument, the authors site the prevalence of rough self scratching among crop raiders (an indicator of stress and hence an indirect indicator that raided food had higher value), the fact that males were much more likely to raid village locations (interestingly enough, there was little food sharing among the raiders), the fact that wild foods were almost never shared whereas cultivated food was, and finally that the food was overwhelmingly shared with females of reproductive age. This latter leads them to suggest a “food for sex” hypothesis wherein male chimps were provisioning females in return for reproductive access and grooming, etc. To back this up they point out that food sharing with females occurred 25 times. Although I find the idea interesting and worth exploring, I am not convinced by the evidence presented. Sharing only occurred in 58 of 786 occasions, which amounts to 7% of the time which seems kind of low if the authors of the paper are correct. Rather, I think it was a case of the generosity mentioned above by Frans de Waal.

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