While the evolution of cooperative behaviors has generated an intense debate among evolutionists and animal behaviorists, the proximate mechanisms underlying cooperative relationships have received much less attention. In recent years, it has become clear that an understanding of proximate causation of cooperation is needed in order to obtain a more balanced and complete picture of the phenomenon. The proximate cause of cooperation refers to the immediate situation that triggers behavior, and the role of learning, memory, physiology, and neural processes. Since from an evolutionary point of view cooperative relationships are maintained because of the subsequent benefits they bring, there has been the tendency to erroneously assume that they are also motivated by their future benefits. This assumption would imply that animals engage in social interactions in order to gain future benefits, or that they are able to remember the services given by another individual in order to offer a service in return at a later date. While this "rational" calculation offers a possible explanation, it is currently unclear whether or not some animal species have these cognitive capacities. Here I will argue that, while complex cognitive mechanisms may be present in some species, less cognitively demanding mechanisms, based on emotions, could be at the basis of the flexibility needed to form complex, enduring cooperative relationships in both human and non-human animals.