Chimps lend a hand

Finding suggests nonhuman primates have theory of mind

A chimpanzee in need gets help indeed, on two conditions. Another chimp must both see his or her predicament and receive a blatant help request from the needy animal, a new study finds.

HELP WANTED Pal, a chimp at a Japanese primate facility, participated in a new study indicating that these apes understand others’ goals but don’t offer help without an obvious request and a clear view of the situation. Etsuko Nogami

Observations in the wild and in previous experiments indicate that chimps seldom help others (SN: 8/27/11, p. 10), but that’s not because the chimps don’t understand their peers’ motivations, as some researchers suspect, says primatologist Shinya Yamamoto of Kyoto University in Japan.

In a series of lab tests, chimps who saw one of their relatives unsuccessfully reach for a juice box and then request help picked out a useful tool and passed it to their kin, Yamamoto and colleagues report online February 6 in the Proceedings of the National Academy of Sciences.

“Chimpanzees can understand others’ goals from obvious cues and then provide help,” Yamamoto says.

This ability to grasp that another individual has a goal in mind based on his or her behavior represents one element of what psychologists call theory of mind — an ability to attribute beliefs, desires, pretending and other mental states to oneself and others.

Until now, scientists had studied chimps’ understanding of other chimps’ goals only in competitive situations, such as clashes over food and mates. That fueled suspicion that chimps discern others’ goals only in the heat of such struggles.

“The new study opens an important new avenue for investigating chimps’ theory-of-mind abilities in cooperative contexts,” remarks psychologist Josep Call, director of the Wolfgang Köhler Primate Research Center in Leipzig, Germany. Comparable forms of helping probably occur among chimp friends, not just kin, Call says.

Yamamoto’s team tested five chimps housed at a Japanese primate center. Each chimp and one of its relatives — either a mother or a grown son or daughter — occupied adjacent booths. Helpers could select an appropriate tool from a set of seven objects to hand through an opening to a partner unable to pull a juice box out of a small space in the compartment next door.

If chimps could see their partners’ predicament, helper chimps typically first gave pleading compatriots — who sought help by sticking their arms through a wall opening and clapping or waving their hands — a stick or a straw as needed to extract the treat.

When helpers couldn’t see the problem, chimps tried to help a partner upon request but usually forked over several useless items before happening upon the right tool. One plucky chimp peeked through the wall opening to check out his partner’s situation and then selected the correct item.

Yamamoto plans to study helping in pygmy chimps, a highly sociable species. Wild pygmy chimps frequently share food, but it’s not clear whether that’s because those with food realize that others want some or because they simply don’t like to eat alone, Yamamoto says.

Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.

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