![]() ![]() Whereas a significant expression of manual lateralization at population level is not exclusive to humans, the universal proportion of approximately 85–95% right-handers in our species appears to be an unmatched extreme among primates ( Meguerditchian et al., 2013). Pronounced right-handedness is a universal trait among extant human populations ( Coren and Porac, 1977 Raymond and Pontier, 2004 Faurie et al., 2005) and might be an ancient attribute of the genus Homo ( Toth, 1985 Lozano et al., 2017). This will be of interest to researchers studying the origins of human behaviour as well as the emergence of asymmetries in the brain. While the results cannot explain the cause of this behaviour, they do help to rule out some of the theories that aim to explain how this preference evolved. These findings confirm that humans do exhibit exceptional right-handedness, being unique among primates. However, ground-living primates tended to show weaker individual preferences for a specific hand than tree-living species, with humans being a notable exception to the trend. found that the presence of tool use as well as brain size were not associated with the degree of handedness in species. However, no species had an extreme preference for using one specific hand the way humans do. Similar to humans, some species of monkey only had small proportions of ambidextrous individuals. ![]() ![]() This dataset illustrates how approximately 1800 primates across 38 species retrieve mashed food from a tube (or pieces of paper in the case of humans). used existing data and new experimental observations to create a large dataset of hand preference. To fill this gap in our knowledge and understand how handedness may have evolved in monkeys and apes, Caspar et al. However, handedness had not been studied in a standardized manner across a wide range of primates. Many researchers have regarded the extreme population-wide preference for using the right hand as being uniquely human. Several hypotheses have been proposed to explain this extreme preference, including the use of tools, the larger size of the human brain, and the fact that humans live primarily on the ground. While it is known that handedness is caused by certain brain regions that are specialized in one of the two hemispheres, it is not clear how this evolved or why right-handedness dominates. Editor's evaluationĪbout 90% of humans are right-handed. Finally, our data show that human lateralization patterns do not align with trends found among other anthropoids, suggesting that unique selective pressures gave rise to the unusual hand preferences of our species. Furthermore, they point to a potential adaptive benefit of disparate lateralization strength in primates, a measure of hand preference that has often been overlooked in the past. These results challenge popular ideas on primate handedness evolution, including the postural origins hypothesis. In particular, terrestrial primates tend to display weaker hand preferences than arboreal species. In contrast, we recovered highly variable patterns of hand preference strength, which show signatures of both ecology and phylogeny. Species-level direction of manual lateralization was largely uniform among non-human primates and did not strongly correlate with any of the selected biological predictors, nor with phylogeny. We confirm that human right-handedness represents an unparalleled extreme among anthropoids and found taxa displaying population-level handedness to be rare. Based on that, we employ quantitative phylogenetic methods to test prevalent hypotheses on the roles of ecology, brain size, and tool use in primate handedness evolution. By combining original data with published literature reports, we assembled data on hand preferences for standardized object manipulation in 1786 individuals from 38 species of anthropoid primates, including monkeys, apes, and humans. Manual lateralization patterns in non-human primates have the potential to elucidate evolutionary determinants of human handedness, but restricted species samples and inconsistent methodologies have so far limited comparative phylogenetic studies. The evolution of human right-handedness has been intensively debated for decades.
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