Left-handedness and time pressure in elite interactive ball games

1. Background

Frequency-dependent selection can ensure the maintenance of polymorphisms in animal and non-animal species [1,2]. In humans, the fighting hypothesis proposes that negative frequency-dependent selection may account for the stable maintenance of an unbalanced handedness polymorphism over thousands of years [3,4]. Assuming that handedness is a partly heritable trait, health-related fitness costs potentially associated with left-handedness might be outweighed by fitness benefits associated with its relative rarity, thereby ensuring reproductive success [5]. Fitness benefits are predicted for duel-like situations where unfamiliarity with left-handers may directly affect performance. Sport data support this notion in that left-handed athletes are found overrepresented in the high echelons of interactive (e.g. cricket, baseball) but not non-interactive (e.g. darts, snooker) professional sports [4,6]. The factors strengthening or attenuating the benefits of performing left-handed in interactive contests, however, have yet to be specified.

Athletes develop task-specific perceptual–cognitive and motor skills to counter the spatio-temporal constraints induced by small distances between competitors, fast movements and/or high ball speeds in interactive sports [7]. Similar to processes of adaptation in the wild [1], predominant exposure to right-handers can result in the acquisition of skills optimal for competition against right- but not left-handers [8]. This is expressed, for example, by better anticipation of right- than left-handers' action intentions [8,9], decision-making preferences [10] or deficiency in responding to unfamiliar left-handed deliveries like in cricket batting [11].

These issues can promote an advantage of relatively rarer left-handers [6], presumably particularly in competition under severe time pressure. If time pressure is relatively low, inaccuracy in anticipation and related motor control processes, for instance, might still be corrected successfully in time based on an online integration of sensory feedback (e.g. vision) and action [12,13]. In highly time-constrained situations, however, corrections are harder to make timely, despite the athletes’ perceptual–motor system being attuned to uncertainty under time pressure [14]. Therefore, here it was hypothesized that the occurrence and extent of a left-hander's advantage in interactive sports are linked to the contests’ underlying time pressure. Specifically, the advantage should be higher (lower) in more (less) time-constrained sports.

The recently reported higher proportion of left-handers among the top-100 players in table tennis (a fast sport) compared with tennis, badminton and squash might be interpreted as providing some tentative initial indication for such a relationship [15]. However, that finding was based on a single retrieval date, it did not include measures of time pressure and it was restricted to four sports from men's competition. Here, to test the above hypothesis more comprehensively, the time constraints acting upon athletes in elite competition of baseball, cricket and the above four racket sports were determined and then correlated with the frequencies of left-handed players observed in the respective sport's elite rankings. The latter measure served as proxy for a left-hander’s advantage [3,11,16,17]. The sports were selected owing to similarity in composition, performance demands and game strategy. Specifically, in all the sports, a ball is hit or thrown, a bat or racket is used for interception and players try to force their opponent into not reaching the ball or making a return error. This ensured the determination of a comparable measure of time pressure across sports and precluded consideration of interactive sports that do not share the former features (e.g. boxing). Analyses included data on males and females (racket sports only; table 1 for details), but focus was on male competition as left-handedness was found particularly relevant in male–male contests [3,17].

2. Material and methods

3. Results

In male competition, binomial tests (one-tailed) revealed a left-hander overrepresentation in baseball (p < 0.001), cricket (p < 0.001) and table tennis (p < 0.001), but not in tennis (p = 0.066), badminton (p = 0.185) and squash (p = 0.784) relative to a normal population estimate of 10.3% [3]. Across sports, left-hander frequency and the mean time interval between interacting players' actions were related negatively (Spearman's ρ = −0.886, p = 0.019; figure 1a), suggesting that left-handedness decreased from high (i.e. small time interval) to low time-constrained sports. The robustness of the correlation is supported by additional analysis, where a cases bootstrap (100 000 replications; see [18] for the same analytic approach) revealed a 95% confidence interval on estimates of Spearman's ρ ranging from −1 to −0.2 (figure 1b; electronic supplementary material S2 for details). When grouped, left-handedness was 2.6 times more likely among ‘high’ (baseball, cricket, table tennis) compared with ‘low’ (badminton, squash, tennis) time pressure contests (table 2). Restriction to racket sports did not alter the effect: left-handedness was more likely in table tennis than in the other racket sports combined and when compared with each sport separately. No notable differences were found between badminton, tennis and squash. Left-handedness was slightly more likely in baseball pitchers than cricket bowlers (table 2).

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In female competition, left-handers were again overrepresented in table tennis (p < 0.001), but not in badminton (p = 0.499), tennis (p = 0.548) or squash (p = 0.507) relative to a normal population estimate of 7.7% [3]. Left-handedness was 2.76 times more likely in table tennis compared with the other racket sports combined and when compared with each sport separately (table 2). No meaningful differences in left-hander frequency were found between badminton, tennis and squash. Overall, left-handedness was more prevalent in male (15.44%) than female (10.70%) racket sport competition, p = 0.004, odds ratio = 1.52, 95% CI (1.12, 2.07).

4. Discussion

A left-hander’s advantage does not emerge to a similar extent across structurally similar interactive sports. Left-handed male and female players were more prevalent at the elite level of highly time-constrained sports (baseball, cricket, table tennis) as opposed to sports where players have more time available between actions (e.g. tennis, squash). Only in the former type of sports was a clear left-hander overrepresentation relative to the normal population found. This suggests that left-handers' relative rarity and the interactive nature of a contest may not be sufficient to provoke a measurable fitness benefit. Rather, its occurrence appears linked to the time pressure underlying interactions, being more likely in high compared to relatively lower time-constrained contests.

The present findings refine the fighting hypothesis as to the conditions likely required to elicit a left-handers’ performance advantage. An excess of left-handedness in high but not low time pressure sports, combined with no meaningful frequency differences between badminton, tennis and squash, suggest that left-dominance may be reliably identified only below a yet unknown time pressure threshold. In the latter contests, achievement may depend to a larger extent on basic physiological and psychological aspects (e.g. agility, concentration, emotion regulation) irrespective of an opponent's laterality (see also the discussion by Malagoli Lanzoni et al. [15]). Team-strategic considerations might additionally explain part of the excess of left-handedness in baseball and cricket. This, however, neither applies to racket sports [17] nor contradicts the hypothesis of time pressure being one, but possibly not the only, factor moderating left-dominance [6]. The relevance of time constraints and the existence of a hypothesized threshold for eliciting left-dominance need next be tested experimentally.

Humans in close-distance fights are especially under severe time pressure and these fights' outcomes are assumed to have contributed to the maintenance of left-handedness in humans [3]. Consequently, the data at hand could provide additional tentative support for the fighting hypothesis. However, direct experimental evidence has recently been claimed to put that hypothesis to real test [18]. The present results indicate that researchers then need to ensure that the experimental task is performed under adequate time pressure. Otherwise, proper verification of negative frequency-dependent selection may fail, for example, because an initially suboptimal behavioural strategy against a left-handed opponent, resulting from adaptation to common right-handed opponents in the course of an experiment [8–10], could still be corrected in time without measurable performance impairment. The current findings illustrate that research should take a closer look at the interplay between specific performance demands and frequency-dependent selection in interactive contests.

Data accessibility

The datasets supporting this article have been uploaded as part of the electronic supplementary material.

Competing interests

I declare I have no competing interests.

Funding

This research was supported by an internal grant of the University of Kassel (Zentrale Forschungsförderung) awarded to F.L. It was also closely connected with the project ‘Laterality in sports’ funded by the German Research Foundation (DFG; HA 4361/5-2 and STR 490/11-2).