Cooperation Within Chimpanzees

Chimpanzees negotiate towards cooperation

Cooperation in animals is nothing new. Darwin mentioned it frequently. We know honeybees cooperate with kin to protect the colony, lions cooperate to take down a gazelle on the African savannah, chimpanzee males go on group border patrols in the African jungle, and humans often help move a disabled car off to the side of a busy highway. Cooperation, then, is quite common across the animal kingdom. New research, however, is beginning to show that, in its most complex forms, some animals may actually have more than just a simple understanding of how cooperation works.

In a study that dates back more than 70 years, chimpanzees learned to pull in a heavy box together to get the food that was placed on top of the box. More recent studies with capuchin monkeys that used a similar apparatus showed that capuchin monkeys will wait for the arrival of a partner before pulling, seemingly realizing that the drawer isn't going to move without a friend's help. A more recent study led by Japanese scientist Hirata used a novel task that required two chimpanzees to simultaneously pull two ends of the same rope to get food (see the picture below - a single rope is fed through a tube and two platforms, so that BOTH ends of the rope must be pulled together for the entire apparatus to move). Here too the chimpanzees learned to wait for a friend to arrive at the other end of the rope, pick it up, and pull before pulling the rope themselves. Clearly, these chimpanzees realized that they needed a partner to complete the task (i.e., obtain the food rewards).



A study by Melis, Hare and Tomasello looked even further into a chimpanzees' understanding of cooperation. Chimpanzees not only learned to coordinate their pulls to pull in a platform, but learned to PICK partners that were better pullers; in other words, chimpanzees chose to "play the cooperation game" with better collaborators (in these experiments, the chimps could pull a door pin to allow one of two chimpanzees into the room with them). In this cooperation task, chimpanzees demonstrated not only that they understood they needed a partner, but seemingly that some partners were better than others......

Now there is a new study by the same team in which two of the same type of rope-pull drawers were provided to two chimpanzees (the same chimpanzees from the previous studies who already understand how the task worked). Individuals compete for unequal resources, and sometimes need to negotiate over these resources so that both parties can successfully claim a reward. This study attempted to demonstrate how such negotiations lead to cooperation.

One drawer had equal amounts of food on both ends, while the other had unequal amounts (such that one plate was full of food, while the other had even less than the other drawer). Only ONE drawer could be chosen in each trial, and thus, the chimpanzees had to decide which drawer they would pull in together. Predictably, the first individual into the testing room, the dominant chimp, chose to sit in front of the biggest plate. But often, when the subordinate chimp entered the room, he refused to sit in front of the smallest food plate, instead opting to wait patiently in front of the "equal" drawer. Such behavior demonstrates that the chimpanzees seem to have realized that by simply agreeing to the dominant chimpanzee’s initial offer, the ultimate reward would be significantly less than if they “negotiated” for an equal reward.

In many of these tests, the chimps successfully pulled in the drawer. How? Well, although sometimes the dominant chimpanzee was quite stubborn and refused to give up his large reward, often, the dominant individual realized that unless he sat in front of the "equal" drawer and pulled with the other chimpanzee, he wouldn't get any reward at all. In this way, the chimpanzees learned to "negotiate" for cooperation. The only non-primate species to be tested in this type of cooperation task, rooks of the corvid family, succeeded in pulling in a drawer together but failed to wait for partners if released into the testing room individually. Are primates, then, the only group of animals able to understand cooperation on a more complex level? Only further research on a wide-range of species will provide an answer.

--Josh Plotnik

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