 As West et al. (2007) and Bowles and Gintis (2011) note, if altruism is defined by reference to lifetime fitness, then Trivers' theory is not really about the evolution of altruism at all; for behaviours that evolve via reciprocation of benefits, as described by Trivers, are ultimately of direct benefit to the individuals performing them, so do not reduce lifetime fitness. Despite this consideration, the label ‘reciprocal altruism’ is well-entrenched in the literature, and the evolutionary mechanism that it describes is of some importance, whatever it is called. Where reciprocal altruism is referred to below, it should be remembered that the behaviours in question are only altruistic in the short-term. 