  From a theoretical point of view, the most satisfactory resolution of this ambiguity is to use lifetime fitness as the relevant parameter (cf. West et al. 2007) Thus an action only counts as altruistic if it reduces an organism's lifetime fitness. This stipulation makes sense, since it preserves the key idea that the evolution of altruism requires statistical association between donor and recipient; this would not be true if short-term fitness were used to define altruism, for behaviours which reduce short-term fitness but boost lifetime fitness can evolve with no component of kin selection, or donor-recipient correlation. However, the stipulation has two disadvantages: (i) it makes it harder to tell whether a given behaviour is altruistic, since lifetime fitness is notoriously difficult to estimate; (ii) it has the consequence that most models of ‘reciprocal altruism’ are mis-named.