Unifying the theories of inclusive fitness and reciprocal altruism
Dept. of Zoology, University of British Columbia
Systems Science Ph.D. Program, Portland State University
Last modified: April 25, 2006
Inclusive fitness and reciprocal altruism are considered distinct explanations for how altruism evolves. Here we show that they rely on the same underlying mechanism. We demonstrate this commonality by applying Hamiltonís rule, normally associated with inclusive fitness, to two simple models of reciprocal altruism: one, an iterated prisonerís dilemma model with conditional behavior; the other, a mutualistic symbiosis model where two interacting species differ in conditional behaviors, fitness benefits, and costs. Previous attempts to unify inclusive fitness and reciprocal altruism theories have had difficulty because traditional versions of Hamiltonís inclusive fitness rule do not apply when genotype and phenotype frequencies differ or when fitness effects are non-additiveóboth of which are true in classic models of reciprocal altruism. Here we demonstrate how Quellerís generalization of Hamiltonís rule accommodates both of these complexities. Quellerís equation is more general in that it applies to all situations covered by earlier versions of Hamiltonís rule, but also handles non-additivity, conditional behavior, and lack of genetic similarity between altruists and recipients. Despite being twenty years old, this generalization of Hamiltonís rule is not sufficiently appreciatedóespecially its implications for the unification of the theories of inclusive fitness and reciprocal altruism.