Gender and cultural differences in the development of reciprocity in young children.

A foundational mechanism underlying human cooperation is reciprocity. In the context of repeated interactions with others, it is not always clear the degree to which in-kind responses reflect responsiveness to partners' prior behaviors ("reactive" responses), an interest unrelated to the partner ("nonreactive" responses), or any combination of the two. To disentangle these two types of responses, we presented children with sequential, one-shot, and costly interactions between themselves and either egalitarian or selfish peers. Study 1 tested direct, generalized, and normative reciprocal scenarios (