An evolutionary approach to the extraversion continuum

Heritable individual differences in personality have not been fully accounted for within the framework of evolutionary psychology. This paper argues that personality axes such as extraversion can usefully be seen as dimensions of trade-off of different fitness costs and benefits. It is hypothesized that increasing extraversion will be associated with increasing mating success, but at the cost of either increased physical risk or decreased parenting effort. In a sample of 545 British adults, extraversion was a strong predictor of lifetime number of sexual partners. Male extraverts were likely to have extra-pair matings, whilst female extraverts were likely to leave existing relationships for new ones. On the cost side, increasing extraversion increased the likelihood of hospitalization for accident or illness. There was no direct evidence of reduced parenting effort, but extravert women had an increased likelihood of exposing their children to stepparenting. The study demonstrates that extraversion has fitness costs as well as benefits. Population variation related in the trait is unlikely to be eliminated by selection due to its polygenic nature, likely spatiotemporal variability in the optimal value, and possible status- and frequency-dependent selection.