Unconditional generosity towards unknown others in a community is an important determinant of its social capital. We develop a two-player double-index utility model that explains individual choices to display unconditional generosity to unknown others. Our model incorporates the influence of individuals’ selfish and ‘other-regarding’ motives, their community embeddedness, group identities, and social norms, to predict choices. We tested the model through field experiments in a First Nation of Canada using modified Dictator Games. The experiments included a retrospective elicitation of motives and provision to dictators of no, or partial information about the identities of second players. Results revealed strong relationships among expressed motives, social norms, group identities, and allocations. First Nation’s culture was manifested by a pattern of more generous giving to elders and women. Provision of partial information about second players’ identities was found to increase average giving and shift self-regarding to other-regarding preferences.