Assessing the link among laterality, sex and competitiveness to verify the evolutionarily stable strategy of handedness

About 90% of humans are right-handers, and some evolutionary theories explain this asymmetry as an advantage at the population level, with right-handers having advantages in cooperative behaviours and left-handers (particularly males) having advantages in competitive behaviours. To test this hypothesis, in Experiment 1 we collected online self-report questionnaires from more than 1100 respondents, finding that stronger left-handedness was positively related to self-developmental competitive orientation and negatively related to anxiety-driven competition avoidance. Importantly, higher levels of hyper-competitive orientation emerged in left- compared to right-handers. The Laterality Quotient (LQ) was not related to personality traits, but sex differences emerged in neuroticism, depression, anxiety and in all measures of competitiveness. In Experiment 2, a subset of 48 left- and right-handers (half females) were invited to complete a pegboard task: the resulting dexterity index did not correlate with self-report LQ, nor with any of the measures collected in Experiment 1. We conclude that LQ and dexterity are distinct measures of laterality, with LQ (not dexterity) specifically related to competitiveness. These results add evidence supporting evolutionary explanations of population-level lateralization.