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New discoveries about altruism in chimpanzees

Ayumu, one of the chimps taking part in this test, is also a rocket scientist when it comes to memory tests.

There’s more and more evidence that chimps have what scientists call a “theory of mind” – the ability to understand the minds of others. (It was once thought that only humans had this ability.)

The latest example of theory of mind has just been demonstrated at Kyoto University.

Researchers presented five chimpanzees with seven tools on a tray: a stick, a straw, a hose, a chain, a rope, a brush and a belt. The apes observed other chimps struggling with tasks where they could receive a reward of juice, and could potentially help them by handing them a tool – like a stick to reach a juice bottle, or a straw to drink juice through a hole. The test was described in Scientific American:

The first chimpanzee was given a task to accomplish in order to receive a juice reward. The task required the use of one of two types of tools: a stick or a straw. The stick and the straw, however, as well as five other items were found not in the first chimpanzee’s booth, but in the second chimp’s booth. There was a small opening between the two booths where the second chimp could pass the necessary tool to the first. By itself, this could test whether or not the second chimp was willing to help the first chimp.

Cartoon by Scientific American

But to see whether the ability to understand the goal of another individual modulates the potential to help, the researchers created two further conditions: half the time, the barrier separating the two booths was a transparent window, and half the time it was a completely opaque wall. If chimpanzees modulate their responses to a help request based on whether or not they can see the goal of another individual, then they should give the appropriate tool more often when in the transparent window condition.

During the transparent window condition, the chimpanzees were more likely to offer up the appropriate tool (e.g. a stick during the stick condition, or a straw during the straw condition) than any of the other tools. This result itself shows that the chimpanzees were able to understand which tool their partner would need in order to solve a given task. Importantly, ninety percent of tool offers occurred only after a request was given by the first chimpanzee, suggesting that while chimpanzees may not spontaneously engage in helping behaviors, direct requests are effective in soliciting assistance.

“Chimpanzees as well as humans help others without any direct benefit for themselves, and their helping fits the others’ needs,” primatologist Shinya Yamamoto told LiveScience.

The potential helpers offered either a stick or a straw for the juice tasks about 80 percent to 100 percent of the time. This suggested they understood the needs of the potential recipients …

Amusingly, “in our experiments, helper chimpanzees just helped, and the recipient monopolized the juice — they never share the juice,” Yamamoto said. “When the helper chimpanzee reached out his or her arm toward the juice in the recipient’s hand, the juice owner drank up the juice and handed the empty bottle to his or her benefactor. It was somewhat embarrassing for me. But finally I realized that these are chimpanzees, and that they live in line with their own rules, not with human rules.”

Yamamoto and his colleagues Tatyana Humle and Masayuki Tanaka detailed their findings February 6 in the Proceedings of the National Academy of Sciences.

There’s more about what we’ve been learning of chimps demonstrating theory of mind in the wild here.