"No one has ever given a systematic battery [of tests] like this one to both apes and humans," study co-author Esther Herrmann, an evolutionary anthropologist at the Max Planck Institute in Leipzig, Germany, said at a press conference in Berlin. "What we found is that at the same age when children have similar cognitive skills dealing with problems of the physical world [as apes do] children already have more sophisticated cognitive abilities for dealing with the social world."
She said the finding, published this week in Science, contradicts the "general intelligence hypothesis" (that humans are different from apes because their brains are three times bigger, allowing for greater cognitive skills) and supports the alternative "cultural intelligence hypothesis," which states that these heightened social skills are unique to humans, who needed them exchange information within groups and cultures.
Over the past three years, the research team, which also included scientists from Duke University in Durham, N.C., and Complutensian University in Madrid, gave 106 chimpanzees, 32 orangutans and 105 toddlers two sets of tasks to perform. The apes ranged in age from three to 21 years old; the toddlers between two and three years old. One group of tasks was designed to test the subjects' views of the physical world, probing their ability to judge space, quantity and causality (which involved determining what was responsible for producing a sound or understanding the functional worth of a tool). The second series of tests measured social intelligence. Among them: the ability to solve problems by imitating others' actions, communicate nonverbally and interpret one another's intentions solely based upon behavior. Study co-author Joseph Call, a senior scientist at Planck's Wolfgang Köhler Primate Research Center, noted at the press conference that the chores were crafted to mimic the types of problems apes might routinely encounter.
All of the species on average showed a similar facility with the physical tasks, but the human tots were more than twice as competent when it came to dealing with social challenges. In one task, for instance, the subjects were asked to retrieve a piece of food from inside a tube. The youngsters swiftly removed the morsel by following the lead of the experimenter but the apes bit, scratched and pummeled the container in a number of mostly futile attempts to reach the scrap.
"One of the keys to this research is the comparative method," Call said. "This allows us to pinpoint where are the similarities and where are the differences [between species]. We can [then] make inferences about when certain skills may have evolved." He said the group plans to compare the social skills of apes with other ape species as well as with those of nonprimates like dogs.
David Premack, an emeritus professor of psychology at the University of Pennsylvania and author of the 1976 book Intelligence in Ape and Man, criticized the new study for failing to take account of 20 years of research proving "the uncanny knowledge that infants have on both the physical and psychological world."
"The difference between humans and animals is that whenever an animal has an ability, it's extremely narrow, it's tied to one goal," he says. "All our abilities are extremely broad; they can be applied to many different goals."