Bipedalism and brain expansion explain human handedness | PLOS Biology
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Abstract<br>Humans exhibit a striking and near-universal population-level right-hand preference, an evolutionary singularity unmatched among primates. Despite its pervasiveness, the origins of this lateralization remain poorly understood. Here, we combine phylogenetic comparative methods with meta-analysis to investigate manual lateralization across 41 anthropoid species (n = 2,025), testing longstanding eco-evolutionary hypotheses for handedness direction (mean handedness index, MHI) and strength (mean absolute handedness index, MABSHI). Our models reveal significant phylogenetic signal for both traits and identify Homo sapiens as an evolutionary outlier, exhibiting exceptional rightward bias and strength relative to phylogenetic expectations. However, this outlier status disappears when brain size (endocranial volume) and intermembral index are included, suggesting these factors are central to the emergence of human handedness. We also show that high MABSHI evolved early in hominin evolution, while MHI increased to unparalleled levels with the appearance of the genus Homo. Our findings identify bipedalism and neuroanatomical expansion as likely key drivers of uniquely human lateralization, while also revealing broader ecological patterns shaping handedness across primates. This work provides a framework for disentangling human-specific adaptations from general primate trends in the evolution of behavioral asymmetries.
Citation: Püschel TA, Hurwitz RM, Venditti C (2026) Bipedalism and brain expansion explain human handedness. PLoS Biol 24(4):<br>e3003771.
https://doi.org/10.1371/journal.pbio.3003771<br>Academic Editor: Catherine Hobaiter, University of St Andrews, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND<br>Received: October 23, 2025; Accepted: April 8, 2026; Published: April 27, 2026<br>Copyright: © 2026 Püschel et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.<br>Data Availability: All relevant data are within the paper and its Supporting information files.<br>Funding: This work was funded by a Leverhulme Trust (https://www.leverhulme.ac.uk) Research Leadership Award to CV (RL-2019-012). The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.<br>Competing interests: The authors have declared that no competing interests exist.<br>Abbreviations:<br>ECV,<br>endocranial volume; IMI,<br>inembral index; MABSHI,<br>mean absolute handedness index; MHI,<br>mean handedness index
Introduction<br>In all human cultures across every corner of the globe about 90% of people favor their right hand [1–4]. Based on archeological evidence, some have argued that this has been true since the Neolithic [5], whilst others contend that it has been constant through the entire Homo lineage [6–11]. Furthermore, individual human's strong manual lateralization means that ambiguous hand preferences, or forms of ambidexterity, are extremely rare, which appears unusual when compared to other primate species [11–13]. Still, some level of directional manual lateralization is present in sub-populations of various primate species, but the level and consistency of handedness in humans is unmatched, and despite much interest, still represents an unexplained evolutionary singularity [4,11,12,14–16].
At a mechanistic level, the neurological basis of handedness is known to be rooted in specialized brain regions [17,18] showing associations with hemispheric specialization for some higher cognitive functions [19,20]. Genetic studies further indicate that handedness is a highly polygenic trait, influenced by several loci alongside complex epigenetic interactions, though the full complexity of genetics on handedness is still unclear [21]. At the ontogenetic level, hand preference appears to begin developing in utero, as suggested by early unilateral arm movements observed in embryos [22,23], although the interpretation of these early movements remains uncertain due to small sample sizes. Hand preference then continues to develop and consolidate throughout infancy and adolescence [24], potentially influenced by early life factors [25], and ultimately resulting in lasting changes in bone shape and density [26]. Still, at the evolutionary level, the origins and persistence of population-level handedness remain enigmatic [4,27–31]. Several hypotheses have been advanced to account for its emergence and maintenance across primates, often linking manual asymmetry to ecological, anatomical, or cognitive pressures (Fig 1; S1 Table). However, many of these explanations have only been posited in ambiguous and descriptive terms making them difficult to test and hampering...