Supplementary Material for: Genetics of Cerebellar and Neocortical Expansion in Anthropoid Primates: A Comparative Approach

What adaptive changes in brain structure and function underpin the
evolution of increased cognitive performance in humans and our close
relatives? Identifying the genetic basis of brain evolution has become a
major tool in answering this question. Numerous cases of positive
selection, altered gene expression or gene duplication have been
identified that may contribute to the evolution of the neocortex, which
is widely assumed to play a predominant role in cognitive evolution.
However, the components of the neocortex co-evolve with other
functionally interdependent regions of the brain, most notably in the
cerebellum. The cerebellum is linked to a range of cognitive tasks and
expanded rapidly during hominoid evolution. Here we present data that
suggest that, across anthropoid primates, protein-coding genes with
known roles in cerebellum development were just as likely to be targeted
by selection as genes linked to cortical development. Indeed, based on
currently available gene ontology data, protein-coding genes with known
roles in cerebellum development are more likely to have evolved
adaptively during hominoid evolution. This is consistent with phenotypic
data suggesting an accelerated rate of cerebellar expansion in apes
that is beyond that predicted from scaling with the neocortex in other
primates. Finally, we present evidence that the strength of selection on
specific genes is associated with variation in the volume of either the
neocortex or the cerebellum, but not both. This result provides
preliminary evidence that co-variation between these brain components
during anthropoid evolution may be at least partly regulated by
selection on independent loci, a conclusion that is consistent with
recent intraspecific genetic analyses and a mosaic model of brain
evolution that predicts adaptive evolution of brain structure.