The unique level of prosocial regard shown by humans has long been an evolutionary puzzle. A number of ultimate causes have been suggested to promote the selection of prosocial behaviours, amongst which; reliance on cooperative activities such as cooperative hunting (1) and breeding (2), the strength of social bonds (3), kin selection (4) and reciprocity (5). To investigate the evolutionary origins of prosociality, studies have mainly focused on primates. However, in order to test for the socio-ecological pressures that lead to the selection of other-regarding tendencies, a broader comparative approach is necessary. Canids make a good model for this investigation as many species cooperatively breed and hunt and individuals within a group form strong social bonds (6, 7, 8, 9). Furthermore, by comparing wolves and dogs in particular, the differential effects of wolf ancestry (canine cooperation hypothesis; (10)) and domestication on prosocial tendencies in dogs can be investigated. Firstly, using a bar-pulling paradigm, we found that pet dogs altruistically give food to conspecifics and the level of altruism is mediated by the familiarity of the receiver (familiar vs. stranger, glmm: z=-4.26; p<0.001). Furthermore, by using stringent control conditions we could rule out social facilitation or lack of task understanding as alternative explanations. Subsequently we tested identically raised and kept pack-living wolves and dogs on a series of tasks to examine the levels of prosocial tendencies exhibited by each species. Results indicate that dominance and affiliation, but not species, affect the likelihood of acting prosocially towards a conspecific partner suggesting that prosocial effects in dogs are not due to domestication effects.