Abstract
There is controversy around the mechanisms that guided the change in brain shape during the evolution of modern humans. It has long been held that different cortical areas evolved independently from each other to develop their unique functional specializations. However, some recent studies suggest that high integration between different cortical areas could facilitate the emergence of equally extreme, highly specialized brain functions. Here, we analyse the evolution of brain shape in primates using three-dimensional geometric morphometrics of endocasts. We aim to determine, firstly, whether modern humans present unique developmental patterns of covariation between brain cortical areas; and secondly, whether hominins experienced unusually high rates of evolution in brain covariation as compared to other primates. On the basis of analyses including modern humans and other extant great apes at different developmental stages, we first demonstrate that, unlike our closest living relatives, Homo sapiens retain high levels of covariation between cortical areas into adulthood. Among the other great apes, high levels of covariation are only found in immature individuals. Secondly, at the macro-evolutionary level, our analysis of 400 endocasts, representing 148 extant primate species and 6 fossil hominins, shows that strong covariation between different areas of the brain in H. sapiens and Homo neanderthalensis evolved under distinctly higher evolutionary rates than in any other primate, suggesting that natural selection favoured a greatly integrated brain in both species. These results hold when extinct species are excluded and allometric effects are accounted for. Our findings demonstrate that high covariation in the brain may have played a critical role in the evolution of unique cognitive capacities and complex behaviours in both modern humans and Neanderthals.
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From fossils to mind
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Data availability
All data required to replicate this study are available at https://doi.org/10.6084/m9.figshare.21202775. Source data are provided with this paper.
Code availability
The code required to replicate this study is available at https://doi.org/10.6084/m9.figshare.21202775.
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Acknowledgements
We are grateful to M. White, P. Piras and C. Fruciano for their useful comments during manuscript preparation.
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The study was conceived by G.S., A.P., S.W. and P.R. D.R.M., S.L., A.P., J.L., M.M. and K.A. processed the endocasts. S.L. and G.S. digitized the landmarks. G.S., P.R., A.P., C.S., S.C., M.M. and A.M. analysed the data. G.S., P.R., A.P. and S.W. wrote the manuscript with substantial contributions from all the other authors.
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Extended data
Extended Data Fig. 1 Endocast local integration assessment.
The set of each semilandmark (a) and its 9 closest semilandmarks define the N-Core (b). The remaining semilandmarks define the C-Core (c). The N-Core and R-Core are subjected to two independent GPAs and the covariation between the two blocks is calculated by PLS (d). With CR the GPA is computed the entire set (e). The values from PLS and CR analyses are used to create a colour map of integration (f) and modularity (g).
Extended Data Fig. 2 Evolutionary rates of CR values within the Cercopithecinae clade.
Evolutionary rates of CR values within the Cercopithecinae clade.
Extended Data Fig. 3 Evolutionary rates of CR values within the Strepsirrhini.
Evolutionary rates of CR values within the Strepsirrhini.
Extended Data Fig. 4 Evolutionary rates of CR values within the family Cebidae.
Evolutionary rates of CR values within the family Cebidae.
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Supplementary Figs. 1–4, Tables 1–3, specimens institutional codes and tree in Newick format.
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Sansalone, G., Profico, A., Wroe, S. et al. Homo sapiens and Neanderthals share high cerebral cortex integration into adulthood. Nat Ecol Evol 7, 42–50 (2023). https://doi.org/10.1038/s41559-022-01933-6
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DOI: https://doi.org/10.1038/s41559-022-01933-6
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