Association Cortex Size

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True   Likely   Speculative
Human Uniqueness Compared to "Great Apes": 
Absolute Difference
MOCA Domain: 
MOCA Topic Authors: 

The classical association cortical regions are larger in absolute terms in humans than in other primates,

and also larger relative to primary sensorimotor regions. In humans and in apes, the lower-order sensorimotor areas of the cortex are about the same absolute size (in surface area and volume). Human brains are much larger than those of apes, and the difference reflects the much greater absolute and relative size of the "association" cortex, including the classical prefrontal, posterior parietal, and temporal association regions.


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

Possible Appearance: 
6,000 thousand years ago
Definite Appearance: 
2,000 thousand years ago
Background Information: 

 Data come primarily from the work of Brodmann (1912) and Blinkov and Glezer (1968).  See the recent summary in Preuss (2011).

The Human Difference: 

 Humans have much more association cortex, both in absolute amount and relative to the amount of primary sensory and motor cortex, than do apes or monkeys.

Implications for Understanding Modern Humans: 

 The association cortices provide the main neural substrate of the extreme cognitive and behavioral specializations of the human species.

Related MOCA Topics


  1. The human brain: rewired and running hot., Preuss, TM , Ann N Y Acad Sci, May, Volume 1225 Suppl, p.E182-91, (2011)
  2. The Human Brain in Figures and Tables, Blinkov, Samuil M., and Glezer Ilʹya I. , New York, (1968)