A remarkable feature of human handedness at the population level is specialization of the hands, the right hand performing usually better than the left. This specialization might have an evolutionary advantage, because it provides the individual and population with a wider range of skill. We therefore investigated the relationships between hand skill asymmetry and potential markers of Darwinian fitness that have been hypothesized to explain the bias in hand preference: creativity, aggression and developmental and health problems. Over twenty thousand participants (56% left-handers) completed an online survey, including a finger-tapping task to measure hand skill asymmetry. Left-skilled individuals were overall more aggressive than right-skilled individuals and rated themselves as more artistically creative. However, when assessed with a questionnaire, they were less creative on problem solving and equally artistically creative compared to right-skilled individuals, who reported more health problems. Conclusion: we found some evidence for current selection on the direction of lateralization of hand skill although the effect sizes were rather low. Strength of lateralization of hand skill showed only a few associations with fitness proxies. We suggest that Darwinian selection on hand preference (Zickert, Feen, van der, Geuze, & Groothuis, 2018 Zickert, N. , Feen, F. , van der, Geuze, R. H. , & Groothuis, A. G. G. (2018). Fitness costs and benefits associated with hand preference in humans: A large internet study in a Dutch sample. Evolution and Human Behavior, 39, 235–248. doi: 10.1016/j.evolhumbehav.2018.01.001 [Crossref], [Web of Science ®] , [Google Scholar] . Fitness costs and benefits associated with hand preference in humans: A large internet study in a Dutch sample. Evolution and Human Behavior, 39, 235–248) and hand skill asymmetry (present study) may be attenuated in modern society.

Brain lateralization is a fundamental aspect of the organization of brain and behavior in the animal kingdom, begging the question about its Darwinian function. We tested the possibility that lateralization enhances cognitive performance in single- and dual-tasks. Previous studies reported mixed results on this topic and only a handful of studies have measured functional brain lateralization and performance independently and simultaneously. We therefore examined a possible positive effect of the strength and direction of lateralization on two demanding cognitive tasks: A visuospatial task (mental rotation MR), and a language task (word generation WG), executed either as a singletask or as dual-task. Participants (n = 72) performed these tasks while their single-task brain lateralization was assessed with functional Transcranial Doppler for both tasks. From these measurements we determined strength and direction of lateralization for both tasks and the individual pattern of lateralization (contralateral or ipsilateral) was derived. These factors, along with sex, were used in a GLM analysis to determine if they predicted the respective performance measure of the tasks. We found that for MR there was a significant medium effect of direction of lateralization on performance with better performance in left-lateralized (atypical) participants (partial eta squared 0.061; p = .039). After correction for outliers, there was a significant effect for strength (p = .049). For the dual-task, there was a significant positive medium effect of strength of lateralization on performance (partial eta squared 0.062; p = .038, respectively) No other association between direction or strength in either tests were found. We conclude that there is no evidence for hemispheric crowding, and that strength of lateralization may be a factor that contributes to the evolutionary selection of functional brain lateralization. Pattern of lateralization does not, explaining the large inter-individual variation in these traits.

Lateral preference is a widespread organizational principle in human and nonhuman animals. In humans, the most apparent lateralized trait ( handedness) is unique in the animal kingdom because of a very pronounced bias towards right-handedness on a population level. In this study, based on previous experiments, we test the hypothesis that this bias wasdamong other factorsdshaped by evolution through the facilitation of social learning. We exposed 134 subjects to footage of right- or left-handed knot making and analyzed whether concordant handedness between instructor and student facilitated quicker and more successful imitation. We used a set of nautical knots of different difficulty levels in order to test whether the potential effect of concordance became stronger with increasing knot difficulty. For all three performance measures (time until correct completion, number of attempts needed and correct imitation), we found hand congruency and difficulty level to be significant predictors but not the interaction of the two. We conclude that concordance of handedness between teacher and student of a motor skill enhances the speed and accuracy of imitation, which may have been a beneficial trait for selection to act upon, thereby shaping the human population bias in handedness. (C) 2021 The Authors. Published by Elsevier Ltd.