In the span of a few thousand years human beings have achieved some remarkable feats, innovating and crafting a rich web of traditions and beliefs that we pass from one generation to the next. The young learn from the old, and not only master traditional techniques but reshape them, creating a dynamic culture in which creativity and inventiveness yield increasingly complex solutions. But beyond intelligence and opposable thumbs, how did humans develop culture in such myriad, complex ways, when other brainy, dexterous species did not? Tests comparing young children, chimpanzees and monkeys suggest that collaboration, rather than competition, may be the key to human culture.
Some behavioral scientists suggest that although cultural traditions exist in many species, only humans possess a culture that accumulates. Put simply, if culture is evidenced when an innovator's idea, behavior or tool spreads across a population and persists over generations, then many animals possess culture. Dolphins, for example, appear to pass from mother to offspring clever foraging uses for conches and sponges. But in cumulative culture, individuals transform and improve on a cultural idea, increasing its complexity and sophistication. Psychologist Robert Kurzban of the University of Pennsylvania has compared an example of consistently simple tool use in chimps, such as stick tools to fish for termites, with the evolving advancements in human technology, such as the transition from an abacus to a calculator.
"In cumulative culture, you end up with something that's way more complex than anything anybody could have devised for themselves," says Kevin Laland, a biologist at the University of Saint Andrews in Scotland.
Last week Laland and his colleagues at Saint Andrews, The University of Texas M. D. Anderson Cancer Center, the University of Strasbourg in France and Durham University in England published a study that they believe reveals why humans alone possess a capacity for cumulative culture. Using a learning test, they examined the performance of children three to four years old and compared it with that of chimpanzees and capuchin monkeys. Given that all three species have evidenced some degree of culture, the researchers hoped to glimpse the evolutionary variation in different parts of the primate family tree.
Each species was studied in small, mixed age and gender groups and presented with a special puzzle box. The box had three increasingly difficult levels. When done in order, each level could be solved in part by using a trick learned at the previous level and adding on a solution. For example, the first level involved sliding a panel, whereas the second involved sliding a panel and pushing a button. The model therefore tested for cumulative learning, a foundation for cumulative culture.
Opening each level of the box led to a reward: fruits and vegetables for the nonhuman primates and stickers for the children. The rewards scaled up in quality and quantity with each level, meaning bigger, more sparkly stickers for the kids and more coveted snacks, like grapes, for the chimps and monkeys.
While the subjects worked on the puzzle box, the scientists observed each group to evaluate various behaviors—such as vocalizing, watching one another, imitation and sharing or stealing rewards. They also attended to the social rank, sex and age of subjects to assess their influence on how subjects learned. Overall, the children outperformed other primates at more difficult puzzle levels. Although all groups performed well at the first level, most chimps and capuchins were stymied by the second and third. In short, only the children demonstrated cumulative learning.
So what did the kids do differently? During the task they actively talked to, instructed and imitated one another. They were cooperative and even shared their rewards. These behaviors, which were not observed in either of the other two species, were therefore strongly correlated to success in solving the puzzle box. The researchers concluded that these so-called pro-social behaviors indicate the importance of social cognition in developing cumulative learning and culture. "There was so much more going on in the children," Laland says.