Definitions and the genetic bases of beneficent behavior

Abstract

I n a recent paper (Rothstein and Pierotti 1988), we reviewed the distinctions and similarities between reciprocal altruism (RA) and other forms of cooperative/beneficent behavior and developed models for the initial evolution of such phenomena. Symons (1989a) raised two issues concerning our paper. We believe that one of these issues is mistaken but that Symons is justified in raising it, given a lack of sufficient precision in one of our definitions. Symons suggests that we should consider a type of by-product beneficence (BB) not mentioned in our paper. We defined BB (p. 200) as a situation in which ” . . . one individual aids another as a result of its own selfish behavior. . .” Following this definition, we modeled two cases with different payoffs to determine whether BB can increase from an initial frequency near zero in an unstructured population. In case I, individuals whose actions cause BB (BBers) receive the same gross benefits (i.e., benefits before costs are subtracted) whether they associate with another BBer or with a no-BBer (an individual who lacks the BB trait). In case 2. a BBer receives more benefits if it associates with another BBer than if it associates with a no-BBer. In both cases, no-BBers receive more net benefits than BBers when the two associate because only the latter pay the costs of BB. We pointed out that the modeling could be made more elaborate by considering other cases, e.g., the possibility that the gross benefits received by a no-BBer exceed those received by a BBer.