Across cultures, women are much higher than men on fearful personality traits. Why? The sex difference in fear is mediated by that in physical strength.

Physical Strength Partly Explains Sex Differences in Trait Anxiety in Young Americans. Nicholas Kerry, Damian R. Murray. Psychological Science, April 2, 2021. https://doi.org/10.1177/0956797620971298

Abstract: Among the most consistent sex differences to emerge from personality research is that women score higher than men on the Big Five personality trait Neuroticism. However, there are few functionally coherent explanations for this sex difference. The current studies tested whether this sex difference is due, in part, to variation in physical capital. Two preregistered studies (total N = 878 U.S. students) found that sex differences in the anxiety facet of Neuroticism were mediated by variation in physical strength and self-perceived formidability. Study 1 (N = 374) did not find a predicted mediation effect for overall Neuroticism but found a mediation effect for anxiety (the facet of Neuroticism most strongly associated with grip strength). Study 2 (N = 504) predicted and replicated this mediation effect. Further, sex differences in anxiety were serially mediated by grip strength and self-perceived formidability. These findings add to a nascent literature suggesting that differences in physical attributes may partially explain sex differences in personality.

Keywords: anxiety, Neuroticism, personality, sex differences, physical strength, formidability, open data, open materials, preregistered

General Discussion

In two studies, grip strength negatively predicted anxiety, and sex differences in anxiety were serially mediated by grip strength and self-perceived formidability. These findings suggest that some sex-based variation in personality may be partly attributable to variation in physical attributes.

These results suggest the testable hypothesis that other psychological and behavioral sex differences could be partly explained by differences in physical attributes. For example, there is evidence that social dominance and aggression—both of which tend to be higher in men—also covary intrasexually with physical strength (Farrington, 1989; Gallup et al., 2007; Price et al., 2011). Future research might investigate whether these and other psychological sex differences can be partly explained by differences in strength or stature.

Important limitations of this work should be noted. First, within-sex associations between strength and anxiety were small and somewhat inconsistent, and sex still accounted for some variance in anxiety beyond that explained by physical strength. Imperfect measurement of the key variables may have contributed to the small effects observed (see the Supplemental Material). Another possible explanation for the small within-sex effects is that the measures of strength and formidability employed here acted as a proxy for another variable, such as health or attractiveness (which both covary with grip strength; see Gallup & Fink, 2018). Although we cannot rule out this explanation, analyses reported in the Supplemental Material found relationships to be robust when controlling for several potential confounds, including body mass index, age, and a measure of self-perceived attractiveness. Similarly, though, these effects could be explained by a common underlying physiological factor, such as developmental testosterone levels (testosterone levels correlate negatively with anxiety in both sexes; see McHenry et al., 2014). Finally, a key limitation relating to the causal interpretation of these findings is that the mediational models presented here use cross-sectional data and cannot alone demonstrate causality. Thus, although the data here are consistent with the hypothesis that lower physical strength leads to higher anxiety, we cannot rule out alternative causal explanations.

Further, several additional questions remain unanswered. Is the association between strength and anxiety best explained by developmental calibration (i.e., people adapting behaviors to their strengths and weaknesses), genetic pleiotropy (i.e., genes associated with physical formidability also being associated with lower dispositional anxiety; see Lukaszewski & Roney, 2011), or facultative epigenetic processes whereby methylation of genes associated with strength also has consequences for anxiety? And, importantly, will these relationships generalize to other cultures, and would effects be larger for cultures and populations in which formidability is a more functional part of social life? Although these and other questions must be addressed in future research, the studies presented here support the hypothesis that sex differences in anxiety can be partly explained by differences in physical strength and self-perceived formidability. These findings suggest that further work on sex differences in personality may benefit from an increased focus on the role of physical attributes.