Parent—offspring conflict: the full–sib—half–sib fallacy

Abstract

R. L. Trivers used Hamilton's rule regarding the evolution of altruistic behaviour to demonstrate the occurrence of parent–offspring conflict and concluded that this would be more severe when future offspring were half siblings rather than full siblings of the offspring currently receiving investment. Here we show that Trivers' formulation applies in a limited range of circumstances and offer an alternative formulation that is universally applicable. Under this formulation the optimal investment from the offspring's point of view in species with uniparental care and, hence, the extent of parent–offspring conflict depends on the cost of the caring parent's investment to the future fitness of the non-caring parent.