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Bipedalism and brain expansion explain human handedness.

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Paper

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The authors' code

R · 64 lines · 2.1 KB · no license

  1. # Running intercept-only models for MHI and MABSHI using the maximum clade credibility (MCC) phylogeny.
  2. # These models can be adapted based on the specifications outlined in Supplementary Table 1
  3. # to reproduce all analyses described in the main text.
  6. # Load packages
  7. library(ape)
  8. library(brms)
  9. library(ggplot2)
  11. # Load pre-processed data and tree
  12. load("phylo_meta_analysis_input.RData")
  14. # Fit MHI intercept-only model
  15. model_intercept_mhi <- brm(
  16. mean_mhi | se(st_err_mhi) ~ 1 +
  17. (1 | gr(phylo, cov = Acov)) +
  18. (1 | species) +
  19. (1 | obs),
  20. data = data,
  21. family = gaussian(),
  22. data2 = list(Acov = mcc_vcv),
  23. prior = c(
  24. prior(normal(0, 1), class = "Intercept"),
  25. prior(cauchy(0, 0.05), class = "sd", group = "phylo", lb = 0),
  26. prior(cauchy(0, 0.05), class = "sd", group = "species", lb = 0),
  27. prior(cauchy(0, 0.05), class = "sd", group = "obs", lb = 0)
  28. ),
  29. chains = 4, cores = 4,
  30. warmup = 4000, iter = 12000,
  31. control = list(adapt_delta = 0.99, max_treedepth = 11)
  32. )
  34. # Summaries and checks
  35. summary(model_intercept_mhi)
  36. pp_check(model_intercept_mhi, ndraws = 100) + ggtitle("Posterior Predictive Check: MHI Intercept Model")
  37. plot(model_intercept_mhi, ask = FALSE)
  39. # Fit MABSHI intercept-only model
  40. model_intercept_mabshi <- brm(
  41. mean_mabshi | se(st_err_mabshi) ~ 1 +
  42. (1 | gr(phylo, cov = Acov)) +
  43. (1 | species) +
  44. (1 | obs),
  45. data = data,
  46. family = gaussian(),
  47. data2 = list(Acov = mcc_vcv),
  48. prior = c(
  49. prior(normal(0, 1), class = "Intercept"),
  50. prior(cauchy(0, 0.05), class = "sd", group = "phylo", lb = 0),
  51. prior(cauchy(0, 0.05), class = "sd", group = "species", lb = 0),
  52. prior(cauchy(0, 0.05), class = "sd", group = "obs", lb = 0)
  53. ),
  54. chains = 4, cores = 4,
  55. warmup = 4000, iter = 12000,
  56. control = list(adapt_delta = 0.99, max_treedepth = 11)
  57. )
  59. # Summaries and checks
  60. summary(model_intercept_mabshi)
  61. posterior_summary(model_intercept_mabshi)
  62. pp_check(model_intercept_mabshi) + ggtitle("Posterior Predictive Check: MABSHI Intercept Model")
  63. plot(model_intercept_mabshi, ask = FALSE)

pbio.3003771.s008.R, no license · at the source

Overview

Authors: Thomas A. Püschel1, Rachel M. Hurwitz1, Chris Venditti2
ORCID iDs: Rachel M. Hurwitz, Chris Venditti
  1. Institute of Human Sciences, School of Anthropology and Museum Ethnography, University of Oxford, Oxford, United Kingdom
  2. School of Biological Sciences, University of Reading, Reading, United Kingdom
Institutions: University of Oxford (United Kingdom); University of Reading (United Kingdom)
Journal: PLoS biology, volume 24, issue 4, article e3003771
Dates: received 23 October 2025; accepted 8 April 2026; published online 27 April 2026
Type: Research article · Language: English
License: CC BY
Identifiers: DOI 10.1371/journal.pbio.3003771 · PMID 42044164 · PMCID PMC13138751 · OpenAlex W7155976712
Open access: gold, a free copy (OpenAlex)
Status: code verified
Categories: human (organism)
Methods: Machine learning, Statistics
MeSH: Brain*, Functional Laterality*, Animals, Biological Evolution, Hominidae, Humans, Phylogeny, Primates (* major topic)
Journal subjects: Biology and Life Sciences, Evolutionary Biology, Evolutionary Systematics, Phylogenetics, Animal Phylogenetics, Taxonomy, Computer and Information Sciences, Data Management, Zoology, Organisms, Eukaryota, Animals, Vertebrates, Amniotes, Mammals, Primates, Organismal Evolution, Hominid Evolution, Hominin Evolution, Human Evolution, Research and Analysis Methods, Mathematical and Statistical Techniques, Statistical Methods, Metaanalysis, Physical Sciences, Mathematics, Statistics, Paleontology, Paleoanthropology, Archaic Humans, Hominids, Hominins, Earth Sciences, Social Sciences, Anthropology, Physical Anthropology, Physiology, Biological Locomotion, Phylogenetic Analysis
Topic: Hemispheric Asymmetry in Neuroscience (Cognitive Neuroscience, Neuroscience), according to OpenAlex
Funding: Leverhulme Trust (RL-2019-012)
Citations: cited by 1 paper (Europe PMC); 81 references in the paper

Abstract

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.

Reproduced under the paper's license (CC BY), from the paper cited above.

Repositories

Its files are read in the Code ↔ Paper reader above.

supp:PMC13138751/pbio.3003771.s008.R

License: none: the authors keep all their rights
State: the link answers, verified on 30 September 2026
Evidence: files inventoried
Languages: R (1)
Size: 1 file, 1 script
Software Heritage: not checked
Found in: the supplementary material
Not found: README, license file, CITATION.cff, environment file, tests, continuous integration, documentation
Tools: brms (1 file), ggplot2 (1 file)
Availability: 1 check, the latest on 30 September 2026: the link answers (HTTP 200)
  • 30 September 2026: the link answers (HTTP 200)
1 file
At the source: pmc-oa-opendata.s3.amazonaws.com/PMC13138751.1/pbio.3003771.s008.R

supp:PMC13138751/pbio.3003771.s009.R

License: none: the authors keep all their rights
State: the link answers, verified on 30 September 2026
Evidence: files inventoried
Languages: R (1)
Size: 1 file, 1 script
Software Heritage: not checked
Found in: the supplementary material
Not found: README, license file, CITATION.cff, environment file, tests, continuous integration, documentation
Availability: 1 check, the latest on 30 September 2026: the link answers (HTTP 200)
  • 30 September 2026: the link answers (HTTP 200)
1 file
At the source: pmc-oa-opendata.s3.amazonaws.com/PMC13138751.1/pbio.3003771.s009.R

Tracing map

Proposed by the machine: these links were found in the paper and verified at the source, without human review. The map will receive a Zenodo DOI once one of the paper's authors has validated it with their ORCID.

What the map holds:

  • 2 repositories of the authors' code, each at its verified commit, with its license and how the link was found in the paper;
  • 2 scripts, each with its path and the digest of its content;
  • no match between paragraphs and code yet;
  • neither the text of the paper nor the code itself.

Its JSON (tracing-map.json) is deposited on Zenodo with its DOI once the map is validated.

Data

No dataset and no data link were found in the paper.

Data Availability

All relevant data are within the paper and its Supporting information files.

Reproduced under the paper's license (CC BY), from the paper cited above.

Versions

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Version 1, 30 September 2026: the first record

Recorded: type, language, journal, volume, issue, pages, dates, 3 authors, 8 MeSH terms, 1 funder, 75 references.

Cite

This paper

Püschel, T. A., Hurwitz, R. M., & Venditti, C. (2026). Bipedalism and brain expansion explain human handedness. PLoS biology, 24(4), e3003771. https://doi.org/10.1371/journal.pbio.3003771

BibTeX

@article{puschel2026bipedalism,
author = {Püschel, Thomas A. and Hurwitz, Rachel M. and Venditti, Chris},
title = {{Bipedalism and brain expansion explain human handedness}},
journal = {PLoS biology},
year = {2026},
month = apr,
volume = {24},
number = {4},
pages = {e3003771},
publisher = {PLOS},
issn = {1544-9173},
doi = {10.1371/journal.pbio.3003771},
url = {https://doi.org/10.1371/journal.pbio.3003771},
pmid = {42044164},
pmcid = {PMC13138751}
}

RIS

TY - JOUR
AU - Püschel, Thomas A.
AU - Hurwitz, Rachel M.
AU - Venditti, Chris
TI - Bipedalism and brain expansion explain human handedness
T2 - PLoS biology
J2 - PLoS Biol
PY - 2026
DA - 2026/04/27
VL - 24
IS - 4
SP - e3003771
SN - 1544-9173
PB - PLOS
DO - 10.1371/journal.pbio.3003771
UR - https://doi.org/10.1371/journal.pbio.3003771
LA - en
ER -

CSL-JSON

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"page": "e3003771",
"DOI": "10.1371/journal.pbio.3003771",
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