The very existence of left-handedness seems to defy Darwin. According to the theory of evolution by natural selection (in very simplified terms), a species should retain the characteristics necessary for survival and reproduction and discard those that are not very useful. And yet around 10 percent of people continue to develop greater dexterity in their left hand, a rate that has remained stable throughout history. Why do humans continue to retain this peculiar ability?
A study conducted by researchers at the University of Chieti-Pescara in Italy set out to confirm a hypothesis indicating that, while right-handed people have advantages in cooperative behaviors, left-handed people—particularly males, the study notes—have advantages in competitive behaviors, especially in one-on-one situations. This hypothesis is based on evolutionarily stable strategy (ESS), a concept from game theory applied to evolution.
This is how ESS explains why the proportion of left-handed people remains low but constant. If almost everyone in a population is right-handed, being left-handed offers a frequency-dependent advantage: Being in the minority, left-handers are less predictable in competitive interactions (e.g., a boxing match), which may translate into small advantages (left hook!). But if left-handedness became very common, that advantage would disappear because others would adapt to encountering left-handers with the same frequency. In evolutionary terms, a “stable equilibrium” is reached when the majority are right-handed and a minority are left-handed, because neither “strategy” can completely eliminate the other since their advantages change depending on how frequent each is in the population.
How can a study support this hypothesis? The Italian researchers conducted two experiments to see whether a dominant hand is linked to any specific personality type. The results were recently published in the academic journal Scientific Reports.
Righty vs. Lefty
In the first experiment, about 1,100 participants completed questionnaires designed to measure their handedness (their level of dexterity between one hand and the other) and various facets of competitiveness, such as their inclination to achieve personal goals or their aversion to anxiety-driven competition. The results showed that people who identified with greater left-handed laterality tended to show higher levels of personal development-oriented competitiveness and lower levels of anxious avoidance. That is, left-handers tended to be more inclined to engage in competitive situations than right-handers.
In addition, when strongly lateralized groups were compared (just pure southpaws, no ambidextrousness), left-handers scored higher on “hypercompetitiveness,” a trait that implies an intense desire to win, even at the expense of others.
In the second experiment, a subgroup of 48 participants (half right-handed and half left-handed, with equal proportions of men and women) took a pegboard test, a classic laboratory test that measures manual dexterity. Interestingly, no significant differences were observed here either between left-handers and right-handers or between laterality measures and competitiveness scores. This suggests that hand preference and competitiveness are not directly related to motor skills.
Give Them a Hand
According to the authors of the study, left-handedness is not simply a biological accident, but a characteristic that may offer advantages in competitive contexts and is therefore worth preserving. This supports, at least in part, the idea that the unequal distribution between right-handers and left-handers could be maintained by an evolutionary balance. While the right-handed majority favors social cooperation, the left-handed minority benefits in competitive contexts, where surprise plays a role.
But what about other personality types? Are left-handed people more extroverted or more emotionally unstable? The study cited here found no significant differences between left-handed and right-handed people in the Big Five personality traits (openness, conscientiousness, extraversion, agreeableness, and neuroticism). Nor was there any relationship between handedness and levels of depression or anxiety in this sample of people without a psychiatric diagnosis. This suggests that the advantage associated with left-handedness is more linked to competitiveness than to general differences in personality or mental health.
The study also examined differences by sex. Men, in general, scored higher on hyper-competitiveness and development-oriented competitiveness, while women showed a greater tendency to avoid competition due to anxiety. This suggests that the interaction between hand preference, competitive profile, and gender is complex and likely influenced by multiple biological and environmental factors that warrant further investigation.
This story originally appeared on WIRED en Español and has been translated from Spanish.