Instrumental helping and short-term reciprocity in chimpanzees and human children

Chimpanzees (Pan troglodytes) and humans cooperate in reciprocal patterns, but it is unclear whether these interactions are based on the same psychological foundations. While there is evidence suggesting that both species engage in long-term forms of reciprocity, there is very little work exploring their short-term behavioural contingencies with suitable methods. Here, we present a direct comparative study on short-term reciprocity in chimpanzees and human children using a novel, low-cost instrumental helping task. We investigated whether participants help a conspecific partner to obtain a tool for accessing a reward, and whether the level of helping depends on the partner's previous helpful or unhelpful behaviour. In line with prior research, both chimpanzees and children demonstrated helping behaviour towards their partner. However, the extent to which the two species showed short-term reciprocity differed considerably. After receiving help, tested children always helped in return. They helped substantially less when interacting with an unhelpful partner. Chimpanzees showed a higher tendency to help when interacting with a helpful compared to an unhelpful partner only in the first half the experiment. With increasing trial number, chimpanzees stopped discriminating between helpful and unhelpful partners. This study provides evidence for short-term reciprocity in human children and, to a lesser extent, in our closest living relatives. Our findings demonstrate that helping paradigms provide a useful context to investigate reciprocal motives in humans and chimpanzees alike.