The sources of skill in seriating cups in children, monkeys and apes

Is a concept of either reversibility or of hierarchical forms of combination necessary for skilled seriation? We examined this question by presenting seriating cups to adult capuchin monkeys and chimpanzees and to 11-, 16- and 21-month-old children. Capuchins and chimpanzees consistently created seriated sets with five cups, and placed a sixth cup into a previously seriated set. Children of all three ages created seriated five-cup sets less consistently than the capuchins and chimpanzees, and were rarely able to place a sixth cup into a seriated set, Twenty-one-month-olds produced more structures containing three or more cups than did the younger age groups, and these children also achieved seriated sets more frequently. Within all participant groups, success at seriating five cups was associated with the frequency of combining three or more cups, regardless of form. The ability to integrate multiple elements in persistent combinatorial activity is sufficient for the emergence of seriation in young children, monkeys and apes. Reliance on particular methods of combination and a concept of reversibility are later refinements that can enhance skilled seriation.