Nicolakakis et al. (2003) reported a higher rate of species diversification
in avian parvorders that are larger-brained and
have a higher rate of innovation. Sol et al. (2005) showed that
larger-brained species of Holarctic Passeriformes have more
subspecies. In a study of 116 primate species, Reader and
Laland (2002) provided empirical support for one of the key
assumptions of behavioural drive, positive correlations between
the taxonomic distribution of innovation rate, relative
neocortex size and rate of social learning.