Like any other close relative at the family table, chimpanzees may throw vengeful fits, but they also lend a helping hand.
From This Story
A recent spate of experiments out of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, has revealed that chimpanzees exhibit some of the same traits—altruism and vengeance—displayed in human society. Spiteful motivations and sophisticated social learning skills, however, appear uniquely human.
The new studies give insight into how and when such traits evolved. Most importantly they help answer the age-old question: What makes us lucky bipeds human?
"The most important way to ask these really hard questions—is human altruism unique, is human spite unique, is human fairness unique—is to ask non-human animals," says Laurie Santos, director of the Comparative Cognition Laboratory at Yale University. This behavioral process of elimination defines humans as it progresses.
Since chimpanzees can't speak our language, researchers design experimental scenarios to detect the presence or absence of such traits. Recently, Felix Warneken, a developmental and comparative psychologist at Max Planck, and his colleagues conducted a series of tests to see whether chimpanzees were helpful—or, as they put it, "spontaneously altruistic."
To do this they compared the behavior of children with that of chimpanzees, one of the two closest relatives to humans (the other being bonobos). If chimpanzees engaged in helpful behavior, it would suggest that the trait went as far back as a common ancestor to chimpanzees and humans, some five to seven million years ago.
"If any animal or human passes this task, we have to assume that this organism possesses certain skills," Warneken says. "We're not just trying to attribute something to them."
In the first test, an adult human stretched for a baton that was out of its grasp but within the reach of the chimpanzee, or an 18-month-old infant. If the test subject passed the baton to the adult, the researchers considered it an act of "spontaneous altruism." In the end, chimpanzees and human infants were equally helpful, the researchers report in the July PLoS Biology. When the scientists made it a bit harder for the subjects to help, by erecting some obstacles, the results remained the same.
In the final experiment, chimpanzees were given the opportunity to help out one another—and sure enough, they obliged. More often than not, the chimpanzees opened a door that allowed a fellow chimp access to some food. The results represented a breakthrough, as previous lab experiments had found the opposite.
"It looks like, in certain situations, chimps are very helpful and as helpful as young children," says Brian Hare, a Max Planck psychologist involved in the study. "So probably whatever makes us human in terms of our helping and cooperative behavior … it didn't spring out of nowhere during human evolution."