Has human culture "shaped" the shape bias: Comparisons with other apes

Children show a bias toward information about shape when categorizing unfamiliar objects or learning new labels for objects. We presented two adult zoo-housed chimpanzees (Pan troglodytes) and 3- to 5-year old children with a relational matching task in which samples and comparison stimuli matched on either shape or color. Whereas children at all ages performed above chance on the task, chimpanzees performed at close to chance levels overall. However, closer examination of their performance revealed that, whereas children performed better on shape (86%) versus color trials (78.5%), chimpanzees showed the opposite pattern, performing at chance on shape trials (49%) and above chance on color trials (72%). I propose that the shape bias arises because of cultural effects, whereas color may be a more salient natural cue that differentiates, for instance, between ripe and non-ripe fruit. Interestingly, earlier work with orangutans and one gorilla, however, showed that the apes initially performed best on shape trials, but learned quickly to match more effectively by color. In a second order relational task, preferences were less clear. Further work is needed to determine the evolutionary history of the shape bias in human children.