Humans have at least two characteristics to be proud of. Compared with other great apes, we are not only better collaborators but also more generous. On page 328 of this issue, Hamann et al. explore the connection between these two traits (K. Hamann et al. Nature 476, 328–331; 2011).


The age at which humans first show tendencies towards sharing has been investigated extensively. Three-to-five-year-olds seem to divide any windfall resources unfairly, keeping something they have obtained without effort mostly to themselves. After that, however, they become more inclined to share windfalls equally.

Hamann and colleagues wondered whether children would behave differently if the resource had been obtained through joint effort. They studied pairs of 2- and 3-year-old children when, in each case, one child had greater access to the resources (to three of four toys) and so could choose whether to share them with their partner. The toys could be obtained in three ways: through the collaborative efforts of both children; freely, with no effort by either; or through independent work.

The authors found that 3-year-olds, but not 2-year-olds, in the position of power opted to share more often (approximately 75% of the time) after a collaborative effort than after parallel work (about 25%). So, although the toddlers may not have acquired a sense of 'reward in return for work', they understood that resource distribution should depend on how the resource was obtained.

Is this link between collaboration and fairness uniquely human? If other primates don't appreciate the value of collaboration as much as we do, they would be expected to be indifferent to the idea of allocating resources depending on how they were acquired. Testing this hypothesis, Hamann et al. found that, when in a position of advantage, chimpanzees sometimes shared, but this was independent of whether a food resource was obtained through collaboration or luck.

An explanation for this behaviour in chimps may be that, unlike in humans, foraging does not depend on collaboration. In other words, humans appreciate the importance of collaboration for survival and so invest in being included in future collaborative efforts by sharing existing resources. Luckily, we seem to learn this quite early on.