EVOLUTION OF THE CEREBELLUM IN PRIMATES - DIFFERENCES IN RELATIVE VOLUME AMONG MONKEYS, APES AND HUMANS

According to the 'developmental constraint hypothesis' of comparative mammalian neuroanatomy, brain structures enlarge predictably as the en tire brain grows both ontogenetically and phylogenetically. In this st udy, brain and cerebellum volumes are measured from in vivo magnetic r esonance scans of 44 primates from 11 haplorhine species. After contro lling for overall brain volume, the cerebellum in both pongid and hylo batid apes is, on average, 45% larger than in monkeys. These results d emonstrate that all primate brains are not similarly organized and tha t developmental constraints are not tight enough to preclude selection for increased cerebellar volume independent of selection on overall b rain size.