Total number of food rewards provided by focal rats to specific partners in relation to the number of food rewards previously received from them. Food donations exchanged between the focal individuals and their partners were positively correlated. For the statistical analysis, only the data from “cooperators” were considered. Numbers beside points denote the number of overlapping data points. Focal individuals donated more food to partners that had provided more food to them during the experience phase than to those that had been less generous.