The evolution and biological correlates of hand preferences in anthropoid primates

The evolution of human right-handedness has been intensively debated for decades. Manual lateralization patterns in non-human primates have the potential to elucidate evolutionary determinants of human handedness. However, restricted species samples and inconsistent methodologies have so far limited comparative phylogenetic studies. By combining original data with published literature reports, we assembled data on hand preferences for standardized object manipulation in 1,786 individuals from 38 species of anthropoid primates, including monkeys, apes, and humans. 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. We confirm that human right-handedness represents an unparalleled extreme among anthropoids and found taxa displaying population-level handedness to be rare. 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. In contrast, we recovered highly variable patterns of hand preference strength, which show signatures of both ecology and phylogeny. In particular, terrestrial primates tend to display weaker hand preferences than arboreal species. These results challenge popular ideas on primate handedness evolution, especially the postural origins hypothesis. 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. 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.

数十年来，人类右利手（right-handedness）的演化历程一直是学界热议的核心议题。非人灵长类的手部偏侧化（manual lateralization）模式，有望阐明人类利手性（handedness）的演化决定因素。然而，此前受限于有限的物种样本与不一致的研究方法，比较系统发育（phylogenetic）研究的开展受到诸多制约。我们将原始数据与已发表的文献报告相结合，整合了来自38种类人猿灵长类（anthropoid primates，包括猴类、猿类与人类）共1786个个体的标准化物体操作手部偏好数据。基于该数据集，我们采用定量系统发育方法，检验了关于生态学因素、脑容量与工具使用在灵长类利手性演化中作用的主流假说。我们证实，人类的右利手在类人猿灵长类中属于前所未有的极端类型，同时发现表现出种群水平利手性的类群十分罕见。非人灵长类的手部偏侧化方向在物种层面整体较为统一，且未与所选的任一生物学预测因子或系统发育关系呈现显著相关性。与之相对，我们观测到手部偏好强度呈现出高度多样化的模式，这些模式同时带有生态学与系统发育的特征印记。具体而言，陆生灵长类的手部偏好强度往往弱于树栖物种。上述结果对学界关于灵长类利手性演化的主流观点提出了挑战，尤其是姿势起源假说（postural origins hypothesis）。此外，本研究揭示了灵长类肢体偏侧化强度差异可能存在的适应性优势——这一手部偏好衡量指标在过往研究中常被忽视。最后，我们的数据显示，人类的偏侧化模式与其他类人猿灵长类的演化趋势并不相符，这表明独特的选择压力塑造了人类这一物种非同寻常的手部偏好特征。