It's no secret that we humans are smarter than our primate relatives. But exactly how are we smarter? Experiments with chimpanzees, orangutans, and more than 100 German toddlers suggest that our social intelligence is what sets us apart from other apes, allowing us to build on our inborn intelligence. As intuitive as this might sound, the conclusion is controversial.
Ph.D. student Esther Herrmann of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, along with her adviser, psychologist Michael Tomasello, and their colleagues, compared 106 juvenile and adult chimpanzees living in sanctuaries in Uganda and in the Republic of the Congo, 32 orangutans at a care center in Indonesia, and 105 2.5-year-olds from Germany. The participants were asked to perform an involved series of tests lasting 3 to 5 hours. Six tasks were social, meaning that one of the scientists took part and the children, chimps, or orangutans needed to discern social cues. The other 10 were physical, such as tracking down a reward (food for the apes and toys for the children) after it had been hidden.
On the physical tasks, children performed no better than the chimps or orangutans. The chimps even outperformed the children on three tasks. For example, when the researchers placed three raisins under one cup and two under another, the children and chimps both picked the cup with more raisins. But when the researchers showed their subjects a third cup with two raisins in it and then added those raisins to the cup that already contained two raisins, the chimps recognized the difference and went for the bigger bounty. The children often did not.
When it came to social cognition, however, the toddlers were well ahead of the game. Showed by a researcher how to extract a toy from a plastic tube, the child immediately copied the action and retrieved the prize. But "if you demonstrate to a chimpanzee or orangutan, ... they try to get it out by their own means" without copying, says Herrmann. Other social tasks included following the gaze of a researcher or picking the cup hiding a reward after a researcher pointed toward it or stared at it. Among the social tasks, the children succeeded about 74% of the time; the chimps and orangutans, about a third of the time, the researchers report in tomorrow's issue of Science. "Human children are not overall more intelligent than other primates but have specialized skills of social cognition," concludes Herrmann.
Others aren't so sure. One question, according to primatologist Marc Hauser of Harvard University, is whether the children, who are accustomed to people, were more likely to respond to the researchers. Herrmann disputes this, noting that the chimps and orangutans were more interested than the children were in approaching a human they had not met before.
Another concern is whether the children outperformed on the social tasks not because the tasks were social but because they were inherently more difficult and abstract than the physical challenges, says Daniel Povinelli, director of the Cognitive Evolution Group at the University of Louisiana, Lafayette. If so, he says, that might have stumped the chimps and given the children an unfair advantage.