Avoiding the wash: Extraversion provides a net fitness gain

As the fields of personality and evolutionary psychology merge, new conceptualizations of personality traits will arise. However, individual differences continue to present a recurrent problem for evolutionary psychologists. We contend that the heterogeneity of personality traits provides fitness benefits and fitness costs that relate to fitness outcomes. As these costs and benefits balance one another in the course of individuals' lives, only those traits that create a net positive balance will be correlated with improved fitness outcomes. In this study (N = 155), we showed how extraversion provides positive fitness outcomes to both sexes, suggesting that extraversion creates the best balance of positive and negative characteristics and habits of all of the Big Five. In contrast, other aspects of the Big Five were not related to number of lifetime sex partners, suggesting that the positive and negative aspects of those traits create a near-neutral balance. © 2011 Journal of Social, Evolutionary, and Cultural Psychology.