Original article:

Left-handedness and male-male competition: Insights from fighting and hormonal data

Evolutionary Psychology 9(3): 354-370 Charlotte Faurie, CNRS, Institute of Evolutionary Sciences, Université de Montpellier 2, Montpellier cedex 5, FranceViolaine Llaurens, CNRS, Institute of Evolutionary Sciences, Université de Montpellier 2, Montpellier cedex 5, France, violaine.llaurens@univ-montp2.frAlexandra Alvergne, Human Evolutionary Ecology Group, Department of Anthropology, University College London, London, United KingdomMarcel Goldberg, INSERM Unit 687 –IFR 69, Hôpital National de Saint-Maurice, Saint-Maurice cedex, FranceMarie Zins, INSERM Unit 687 –IFR 69, Hôpital National de Saint-Maurice, Saint-Maurice cedex, FranceMichel Raymond, CNRS, Institute of Evolutionary Sciences, Université de Montpellier 2, Montpellier cedex 5, France

Abstract

Male-male competition can shape some behavioral or morphological traits of males. Here we investigate if this competition could play a role in the persistence of the polymorphism of handedness in human populations. A negative frequency-dependent selection mechanism has been hypothesized, based on the fact that left-handed men may benefit from a “surprise” advantage during fighting interactions because they are rare in human populations. This advantage may thereby enhance the probability of survival of left- handed men and/or their reproductive success through an increase in social status. In this study, we first explored the association between hand preference and lifetime fighting behavior in a population of 1,161 French men. No effect of hand preference on the probability of fighting was detected, suggesting that the innate propensity to fight does not differ between left- and right-handers. However, among men who had been involved in at least one fight during their lifetime, left-handers reported significantly more fights than right-handers. To explore the biological basis of this behavior, we also investigated the testosterone concentration in saliva samples from 64 French university students. Consistent with frequencies of fights, we found a significantly higher average testosterone concentration in left-handers than in right-handers. We suggest that these behavioral and hormonal differences may be acquired throughout life due to previous experiences in a social context and may favor the persistence of left-handers in humans.

Keywords

lateralization, hand preference, warfare, aggressiveness, humans, testosterone

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Evolutionary Psychology - An open access peer-reviewed journal - ISSN 1474-7049 © Ian Pitchford and Robert M. Young; individual articles © the author(s)
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