Left-handedness is associated with greater fighting success in humans

Abstract

14Left-handedness is a costly, sexually dimorphic trait found in all human populations. How the 15 handedness polymorphism is maintained is unclear. The fighting hypothesis argues that left-16 handed men have a negative frequency-dependent advantage in fighting giving them a selective 17 advantage. In support of this, many studies have found that left-handed men are overrepresented 18 in combat sports, but studies typically find no difference in fighting success between left and right-19 handed fighters. We studied over 9800 professional boxers and mixed martial arts fighters of 20 varying abilities in three of the largest samples to test this hypothesis to date, finding robust 21 evidence that left-handed fighters have greater fighting success. This held for both male and 22 female fighters and when considering percentage of fights won, and objective measures of fighting 23 ability. We replicated previous results showing the left-handed fighters are strongly 24 overrepresented in professional combat sports, but left-handed fighters did not show greater 25 variance in fighting ability, a hypothesis suggested in previous studies. Overall we find strong 26 evidence consistent with the fighting hypothesis. 27 30 population is left-handed [6] and though exact numbers vary with culture, [7] left-handers are 31 always a minority. Since left-handedness is under direct negative selection, its persistence in 32 humans is an evolutionary puzzle. 34One explanation for the persistence of left-handedness is the fighting hypothesis [8]. This argues 35 that the polymorphism in human handedness is maintained due to a negative frequency-dependent 36 advantage that left-handedness confers to males in combat (see [9] for theoretical support, and [10] 37 for a review of empirical evidence as well as alternatives). According to this theory right-handed 38 males often lack experience fighting rare left-handed males, while left-handed males accumulate 39 plenty of experience fighting right-handed males, putting them at a selective advantage. Combined 40 with the intrinsic fitness costs of left-handedness, this would explain the universal pattern of low but 41 stable levels of left-handers in all studied populations. There is mounting evidence that intrasexual 42 contest competition such as fighting has been a key component of sexual selection on human 43 males [11]. Modern males may possess adaptations to assist them in fighting and assessing 44 opponents' fighting ability [12]. Handedness could therefore be considered a sexually selected trait 45 in males, and may be expressed in females a by-product [9].48 overrepresented in combat sports. Sports are particularly relevant systems for testing theories 49 based on intrasexual competition, as they are thought to have evolved culturally as a display for 50 males to advertise fighting and competitive ability [13]. Overrepresentation of left-handers has 51 been seen in boxing (where is it referred to among coaches and fans as 'Southpaw Advantage': 52 [14-16], mixed martial arts or MMA ...

Facial width‐to‐height ratio predicts fighting success: A direct replication and extension of Zilioli et al. (2014)

“…These studies laid the foundation for conducting research on human fighting ability from an evolutionary perspective (e.g., Aung et al, 2021; Lane & Briffa, 2020; Richardson & Gilman, 2019; Třebický et al, 2019). These studies were also the first to draw attention to the use of data from MMA fighters competing in the UFC©.…”

“…It should be noted that fight data has been criticised (e.g., Richardson, 2020), as the winner of a single fight can be suddenly and unexpectedly determined which might make dichotomous fight outcome measures (i.e., win/lose) less than preferable. Indeed, much of human contest competition research has used fighter data (Aung et al, 2021; Richardson & Gilman, 2019; Richardson, 2020; Třebický et al, 2013, 2015, 2019). In Study 3, we sought to expand Zilioli et al (2014) by examining the associations between fWHR and contest data among individual fighters.…”

“…These studies were also the first to draw attention to the use of data from MMA fighters competing in the UFC©. This data proved to be paramount to this emerging sub‐field because contest competition research requires large sample sizes (Kasumovic et al, 2017; Richardson & Gilman, 2019) that might not be feasible when using ordinary sampling methods (e.g., simple random sampling). For example, Zilioli et al (2014) comprised 241 UFC fighters who fought, on average, 21 professional fights.…”

Cognitive and Neurophysiological Models of Brain Asymmetry

“…A classical monogenic explanation for a balanced polymorphism is heterozygote advantage with the best known example being sickle cell anaemia, where affected homozygotes have a high mortality, but heterozygotes, carrying just one copy of the gene, are protected against malaria, which means the gene continues to survive in the population [137]. An alternative mechanism is frequency-dependent selection, where rarer phenotypes have an advantage precisely because of their scarcity, a mechanism found in the lateralisation of scale-eating cichlid fish [392], and often invoked for left-handers being better at fighting or sport [393,394], although there is controversy over the strength of the effects [394][395][396]. The only other major method of polymorphisms being maintained in the population is by mutation, and it is clear that new mutations are responsible for maintaining the relatively rare disease, haemophilia [397].…”

No association between adult sex steroids and hand preference in humans

“…Furthermore, recent studies have found that left-and mixed-handers report being more aggressive and engaging in more fights than right-handers (van der Feen et al, 2020;Zickert et al, 2018). The 'Fighting Hypothesis' of left-handedness proposes that left-handedness has been maintained in humans by natural selection due to left-handers having an advantage in ritual fighting and war (Raymond et al, 1996;Richardson & Gilman, 2019). Left-handers' increased fighting success is thought to be due to their rarity giving them a negative frequency dependent advantage.…”