During contest competition, the amount of resource an individual is able to acquire depends not only on its own resource holding potential (RHP), but also on that of its rival. If RHP traits are heritable, genetic variance for contest behaviour, and resource dependent traits that depend on contest outcome (e.g. growth, survival, reproduction) may arise through both direct (DGE) and indirect genetic effects (IGE). The latter, which occur when focal phenotype depends on rival genotype have important implications for the evolution of traits both causal and consequent to contest outcome. Using experimental studies of swordtails and data from several other animal populations, we show that i) personality traits such as aggressiveness are a larger component of RHP than has previously been recognized, ii) that heritable variation in personality is a source of IGE, and iii) that IGE on resource dependent traits act to constrain adaptive evolution of life histories.