Research Article

Evolutionary Biology

, Volume 39, Issue 4, pp 600-612

First online:

On the Possible Shapes of the Brain

  • Roberto ToroAffiliated withHuman Genetics and Cognitive Functions, Institut PasteurCNRS URA 2182 “Genes, synapses and cognition”, Institut PasteurHuman Genetics and Cognitive Functions, Université Paris Diderot Email author 

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The human brain is unique among primates in its complexity and variability. Here I argue that this variability is, however, strongly constrained by developmental processes common to all mammals. Comparative analyses of grey and white matter volume, cortical surface area and cortical folding show that the rostro–caudal axis of the central nervous system is a main direction along which mammalian neuroanatomical diversity is organised. Phylogenetically, rostral structures are often disproportionately larger and more differentiated in large mammals compared with small ones. Ontogenetically, caudal structures differentiate earlier but show less variation among species than rostral structures, which differentiate later and for a longer period. Theoretical considerations suggest that growth oriented along the rostro–caudal axis should produce non-linear differences in white matter volume and cortical folding. Growth appears then as a fundamental parameter to understand mammalian neuroanatomical variability, whose effects should be common to all species. This seems to be indeed the case for humans: the volume of different brain structures as well as changes in the extension and folding of the cerebral cortex resemble the trends observed across mammals. A strong global pattern of coordinated variability emerges, where differences in total brain volume are non-linearly related to local neuroanatomical changes. Finally, I review evidence suggesting that the changes related to this global pattern of variability may have an influence on the organisation of behaviour, modulating the development of certain cognitive traits or even affecting the susceptibility to psychiatric disorders.


Brain development Brain evolution Cortical folding Mathematical modelling Neuroanatomy