Even very young babies can tell the difference between someone who's helpful and someone who's mean — and lab studies show that babies consistently prefer the helpers.
But one of humans' closest relatives — the bonobo — makes a different choice, preferring to cozy up to the meanies.
That's according to experiments described Thursday in the journal Current Biology, by scientists who wanted to explore the evolutionary origins of humans' unusually cooperative behavior.
"In the animal kingdom, there are all kinds of acts of cooperation. But we don't see things like building skyscrapers or the establishment of institutions," says comparative psychologist Christopher Krupenye, who did the studies while at Duke University. "Humans are much more cooperative, and we do elaborate kinds of cooperation in ways that we don't see in our closest relatives."
This bias toward helpfulness seems almost hardwired in humans. Back in 2007, for example, researchers reported that 6- and 10-month-old infants could evaluate social interactions that they saw in puppet shows. These babies couldn't even talk, but they showed a definite preference for interacting with characters that had been helpful to others. What's more, they would avoid those who had meanly thwarted another's efforts to reach a goal.
One test involved three strangers putting on a little skit in front of the apes. One actor played with a stuffed animal, laughing and throwing it in the air. The toy then fell out of reach, and a "helpful" actor picked it up and tried to return it to its owner. But before that could happen, however, a "mean" actor snatched it away and placed it in a bucket behind him. Then everyone stood up and approached the bonobo, who had been watching through the bars of a cage. The "helper" and "meanie" both offered a piece of food.
"The bonobos weren't very interested in the helper," says Krupenye. Instead, they consistently chose to take food from the jerk.
Humans might not want to interact with someone who is not nice, but it looks like bonobos interpret the meanie's behavior as a sign of dominance. "Dominance is really important for apes because it determines access to resources, access to food and mating opportunities and things like that," says Krupenye. "They're attracted to an individual who might be a powerful friend or ally, as opposed to someone who is just generally helpful or pleasant."
The researchers did this experiment in bonobos because these apes are known for being particularly friendly and social. Now they want to know how chimps react in these experiments, because bonobos, chimps and humans share a common ancestor that existed about 6 million years ago. "In order to get at the full evolutionary picture, chimpanzees are a really important next step," says Krupenye.
"In some ways, it's really surprising that bonobos don't show the human-like pattern — finding this result in human infants one might assume that a preference for nice individuals might be a universal pattern for all social species," says Laurie Santos, a comparative psychologist at Yale University who studies the origins of human cognition. "This new bonobo study suggests that looking to a species' ecology can help us to better interpret their social preferences, and that humans may be unique in more of these preferences than we suspect."
Kiley Hamlin, a researcher in developmental psychology at the University of British Columbia who did the original studies in human infants, points out that hierarchies are ubiquitous in both human and primate societies, so the bonobos' sensitivity to dominance is not surprising.
"Even human infants are sensitive to dominance relationships," she writes in an article being published alongside this new research. But she says evidence suggests that toddlers prefer those whom others appear to respect, while they dislike bullies who dominate through force.
"Interestingly, bonobos do not appear to share this aversion," Hamlin writes, noting that many questions remain about what mechanisms support pro-social behavior in both humans and other species.