However, variation on Cloninger’s scales seems very likely to relate to fitness. For example, it is hard to imagine that individuals’ propensity to avoid harm (Harm Avoidance) would be unrelated to their survival and reproductive prospects. Very low levels of Harm Avoidance would lead to greater chance of injury or death, but very high levels would lead to excessive timidity that would likely impair survival and mate acquisition, especially in animals or in human hunter gatherer societies. Thus the ‘optimal adaptive design’ would be an intermediate level of Harm Avoidance, and the same could be argued for Novelty Seeking, Reward Dependence, and Persistence. In this scenario (stabilising selection), a mutation-selection balance explanation would involve high mutation loads disrupting the optimal design and being associated with maladaptive high and low extremes of each Cloninger personality scale. Purported indicators of mutation load such as fluctuating asymmetry and low intelligence (Gangestad & Yeo, 2006; Keller & Miller, 2006; Prokosch, Yeo, & Miller, 2005) would be expected to show a curvilinear (U-shaped) relationship with the scales. The offspring of relatives, being homozygous at more
