Cerebellar Volume

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True   Likely   Speculative
Human Uniqueness Compared to "Great Apes": 
Relative Difference
Human Universality: 
Individual Universal (All Individuals Everywhere)
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The volume of the human cerebellum is smaller than expected for an ape of human size, but the cerebellum of non-human apes is much larger than expected in monkeys. It has previously been suggested that developmental programming constrains brain growth of individual neural components, such that size of individual components scales predictably with allometric trends. A principle components analysis of 131 mammalian species demonstrated that brain size did indeed account for over 95% of differences in size of neural components, and that the cerebellum size of humans and other primates followed the expected trend (Findlay and Darlington 1995). However, others suggested that the huge amount of variance that the allometric equation accommodated for in this study (up to 250% structure size difference in two species with the same brain weight) masked phylogenetic grade shifts of certain evolutionarily coordinated neural systems (Barton 2006). To examine this question in the cerebellum, one group measured overall brain volume and cerebellar volume through in vivo MR scans in 44 primates representing 11 haplorhine species (Rilling and Insel 1998). They found that cerebellar volume relative to brain volume was 45% larger than expected in non-human apes, while the relative cerebellar volume in humans was smaller than expected. These results suggest that the evolution of cerebrocerebellar circuit diverged in human and non-human apes, such that the cerebellum became more enlarged in non-human apes, while the cerebral cortex became more enlarged in humans (Rilling and Insel 1998).


Timing of appearance of the difference in the Hominin Lineage as a defined date or a lineage separation event. The point in time associated with lineage separation events may change in the future as the scientific community agrees upon better time estimates. Lineage separation events are defined in 2017 as:

  • the Last Common Ancestor (LCA) of humans and old world monkeys was 25,000 - 30,000 thousand (25 - 30 million) years ago
  • the Last Common Ancestor (LCA) of humans and chimpanzees was 6,000 - 8,000 thousand (6 - 8 million) years ago
  • the emergence of the genus Homo was 2,000 thousand (2 million) years ago
  • the Last Common Ancestor (LCA) of humans and neanderthals was 500 thousand years ago
  • the common ancestor of modern humans was 100 - 300 thousand years ago

Definite Appearance: 
6,000 thousand years ago
The Human Difference: 

 Human cerebellum is smaller than expected for an ape of human size.

Universality in Human Populations: 

 This is true for all human populations.

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Topic Certainty
Size of Dentate Nucleus True


  1. Sperm whales and killer whales with the largest brains of all toothed whales show extreme differences in cerebellum., Ridgway, Sam H., and Hanson Alicia C. , Brain Behav Evol, 2014, Volume 83, Issue 4, p.266-74, (2014)
  2. Primate brain evolution: Integrating comparative, neurophysiological, and ethological data, Barton, Robert A. , Evolutionary Anthropology: Issues, News, and Reviews, Volume 15, p.224–236, (2006)
  3. The primate neocortex in comparative perspective using magnetic resonance imaging., Rilling, J K., and Insel T R. , J Hum Evol, 08/1999, Volume 37, Issue 2, p.191-223, (1999)
  4. Linked regularities in the development and evolution of mammalian brains., Finlay, B L., and Darlington R B. , Science, 1995 Jun 16, Volume 268, Issue 5217, p.1578-84, (1995)