Humans actively share resources with one another to a much greater degree than do other great apes, and much human sharing is governed by social norms of fairness and equity. When in receipt of a windfall of resources, human children begin showing tendencies towards equitable distribution with others at five to seven years of age. Arguably, however, the primordial situation for human sharing of resources is that which follows cooperative activities such as collaborative foraging, when several individuals must share the spoils of their joint efforts. Here we show that children of around three years of age share with others much more equitably in collaborative activities than they do in either windfall or parallel-work situations. By contrast, one of humans' two nearest primate relatives, chimpanzees (Pan troglodytes), 'share' (make food available to another individual) just as often whether they have collaborated with them or not. This species difference raises the possibility that humans' tendency to distribute resources equitably may have its evolutionary roots in the sharing of spoils after collaborative efforts.

This study investigated young children's commitment to a joint goal by assessing whether peers in collaborative activities continue to collaborate until all received their rewards. Forty-eight 2.5- and 3.5-year-old children worked on an apparatus dyadically. One child got access to her reward early. For the partner to benefit as well, this child had to continue to collaborate even though there was no further reward available to her. The study found that 3.5-year-olds, but not 2.5-year-olds, eagerly assisted their unlucky partner. They did this less readily in a noncollaborative control condition. A second study confirmed that 2.5-year-old children understood the task structure. These results suggest that children begin to appreciate the normative dimensions of collaborative activities during the 3rd year of life.

The present study investigated young preschoolers' proportional allocation of rewards in 2 different work contexts. We presented 32 pairs of 3.5-year-old peers with a collaborative task to obtain rewards by pulling ropes. In order to establish differences in work input, 1 child's rope was not immediately accessible but had to be retrieved from the apparatus by means of a specific tool, while the other child had no such additional work to do. The result of the game was that 1 individual received 1 toy and the other received 3 toys. In the Deserving condition, the working child received the 3 toys (thus work and reward matched), whereas in the Undeserving condition, the other child received the 3 toys (he or she was overpaid, and the working child was underpaid). Another 32 dyads participated in a noncollaborative, parallel work task, again in a Deserving condition and an Undeserving condition. On average, children with 3 toys shared with their partner more in the Undeserving condition than in the Deserving condition after collaboration but not in a parallel work setup. These results suggest that young children take merit into account in distributing resources at a much younger age than previously believed and that peer collaboration is an especially facilitative context for children's attention to norms of fairness.

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