Mind & Brain / Animal Intelligence

Nearly four years ago, a visitor to Brookfield Zoo, outside Chicago, captured an extraordinary event on video. A 3-year-old boy fell into a gorilla enclosure and was knocked unconscious. Within moments, Binti Jua, a female gorilla, approached, picked up the unconscious boy, and cradled him in her arms. Then she walked over and gently put the boy down in front of the caretaker's door. The event captured the nation's heart as newspaper headlines blared: "Gorilla Saves Boy." 

Most reports suggested that Binti saved the boy because she felt empathy for him. Although there is no ambiguity about what the gorilla did, there are a lot of questions about why. Did she realize the boy was unconscious? Was she concerned about his well-being? Would she have acted in the same way toward a conscious boy, a cat, a teddy bear, or a bag of potato chips?

Despite what the headlines implied about Binti’s moral fiber, the answer is by no means clear. Studies by developmental psychologists Susan Carey and Frank Keil, for example, have shown that children don’t fully grasp the distinction between when a being is dead or alive until they are almost 10 years old. And to date, no study of ape intelligence comes close to showing that orangutans, gorillas, or chimpanzees have the mental sophistication of a 10-year-old human. We can only guess why Binti did what she did. And one incident is not enough to warrant conclusions.

But Binti’s actions do raise the public and scientific interest in the broad question of what mental traits cause us to behave morally and to what extent other animals possess those tools. As a psychologist, I’m interested in the techniques we use to get at these questions: Can other creatures share, cooperate, punish cheaters, show empathy, and act altruistically?

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In a 1988 study, University of Zurich ethologist Eduard Stammbach set up an experiment with long-tailed macaque monkeys he hoped might identify their ability to rein in aggressive behavior and act cooperatively. First each monkey was trained to press a lever on a machine to receive a popcorn treat. Once each animal knew what to do and when, subgroups were created, and a low-ranking member in each subgroup was trained to press a set of levers in a specific sequence that caused the machine to deliver enough popcorn for three individuals.

At first, high-ranking individuals threatened low-ranking individuals to keep them away from the dispenser altogether. Then the high-ranking individuals learned that the low-ranking individuals had a unique skill, so they followed them to the machine and waited to grab all the popcorn. Before long the low-ranking specialists stopped operating the machine. But their strike didn’t last long. Some higher-ranking individuals changed. Rather than chase specialists away or eat all their popcorn, they began to inhibit their aggression. They approached peacefully and allowed the lower-ranking specialists to eat a portion of the popcorn. Further, some high-ranking individuals started grooming specialists more often, even during periods when the machine was inoperative. Although this attitude change enabled low-ranking specialists to access food that would normally be unobtainable, it had no impact on their dominance rank within the group. Specialists kept their low rank but were allowed a moment at the high table when their skills were of use to the royalty.

Possession is nine-tenths of the law: Monkeys who held their food tubes close weren’t robbed; those who dragged them were

Other experiments have found that monkeys even have a rudimentary sense of ownership and respect for property. Although these might seem to be srictly human concerns, territorial animals such as sunfish, lizards, sparrows, and gibbons are invested in these issues. The space that a territory owner defends is like his property, and an intruder’s respect reveals his acknowledgement of ownership and property rights.

 In a 1991 study, for example, University of Zurich ethologists Hans Kummer and Marina Cords tested macaques that had something other macaques wanted--a see-through tube filled with raisins. The tube was either fixed to a wall or freestanding. If it was freestanding, it was attached to a long or a short piece of rope, or no rope at all. A subordinate animal was allowed first crack at the tube in all the various conditions. Then researchers observed how the more dominant individuals reacted. Although dominants often take resources away from subordinates, the experiments revealed rules underlying their responses. Consistently, dominants took ownership of fixed tubes more often than free tubes, and took over free tubes when the subordinates failed to carry them. Staying close to the tube and looking at it were not sufficient cues of ownership from the dominant’s perspective. A dominant macaque would appear to inhibit its impulse to grab the tube if a subordinate held it close to its body. Here, then, is an intriguing example of how inhibition plays a crucial role in maintaining conventions among monkeys.

Some monkeys in established communities abide by this rule: Attack members that don’t share food they find.

But in any social situation with conventions, individuals often find that it pays to break the rules. Would such rule-breakers be punished? To explore this possibility, I conducted experiments on the island of Cayo Santiago, a research station near Puerto Rico that is home to some 800 rhesus monkeys. This particular species has an interesting convention: Unlike long-tailed macaques, which don’t share food, rhesus monkeys tend to call out when they find food. In the study, my colleagues and I located lone individuals and presented them with a small stash of food. Their first response was to look around, presumably to decide if there were enemies near. A few individuals waited and waited and then, as if in an infantry combat crouch, moved cautiously toward the food. Only half the discoverers called out. When they were detected by other group members, some were aggressively attacked. Our initial suspicion was that those who were being attacked were lower-ranking than those who were not. This hunch turned out to be false. Surprisingly, both high- and low-ranking individuals were attacked. Whether or not they were attacked seemed to depend on their vocal behavior. Silent discoverers who were caught with food were attacked more often and more severely than those who cried out. It was as if individuals were being punished for being inappropriately silent, for deceptively withholding information about a rich food source.