Phylogenetic and neuroanatomical determinants of primate behaviour
(1) Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany,
(2) Center for Research and Interdisciplinarity, Université de Paris, Paris, France,
Brain volume and cortical surface area vary widely among primates, with larger brains showing intricate and strongly conserved folding patterns. These are related to the cytoarchitectonic, connective and functional organisation of the brain, which are thought to result from genetic and activity-dependent processes. We have previously observed, however, that primate species with similar brain volume tend to show remarkably similar folding patterns, independent of phylogenetic similarity. This suggests that mechanical morphogenetic processes resulting from the physics of growth could be responsible for the establishment of folding patterns, and could play a causal role in brain development and evolution. Here, we investigated whether behaviour was also more similar among primates with similar brain anatomy, or if behavioural similarity was more strongly linked to genetic similarity. We reconstructed 3D surfaces for more than 60 primate species, spanning a 1500- fold difference in cerebral volume. We measured cerebral volume, cortical surface area, degree of folding, number of folds, folding length, average fold width and depth.
We collected behavioural and physiological data from the literature across the primate phylogeny. We computed distance matrices and used Mantel tests to determine whether neuroanatomical, physiological, behavioural and genetic distances were correlated. We observed strong, statistically significant correlations between neuroanatomical, physiological and behavioural distance matrices. Behavioural and genetic distances, however, were not correlated or the correlation was much weaker. Principal component analyses and hierarchical clustering confirmed this observation. Species such as the Tufted capuchin were closer to neuroanatomically-similar macaques, instead of closer to phylogenetically more similar cebidae, such as marmosets or night monkeys, with much smaller brains. Our results suggest that mechanical morphogenetic processes that constrain development and evolution of primate brain organisation, on a structural and functional level, may also shape cognitive function, giving rise to the emergence of similar behavioural traits across far branches of the tree.