What, If Anything, Is Biological Altruism?

The study of biological altruism is a cornerstone of modern evolutionary biology. Associated with foundational issues about natural selection, it is often supposed that explaining altruism is key to understanding social behaviour more generally. Typically, ‘biological’ altruism is defined in purely effects-based, behavioural terms—as an interaction in which one organism contributes fitness to another, at its own expense. Crucially, such a definition isn’t meant to rest on psychological or intentional assumptions. We show that appearances and official definitions notwithstanding, the notion of biological altruism carries a vestige of the psychological, intentional concept familiar to us from the human domain. In particular, definitions of altruism from Hamilton onwards presuppose an actor-recipient distinction—a distinction, so we argue, that has questionable biological grounding. We arrive at this conclusion step-by-step, first looking at several simple, ‘austere’ definitions and their problems, and then critiquing the actor-recipient distinction directly. If successful, our arguments suggest that the category of biological altruism requires a significant rethink.