Changes in brain size

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A note for Lesson no. 1, "You Have One Brain (Not Three)," in Seven and a Half Lessons About the Brain by Lisa Feldman Barrett.
Some context from page 22‌ is:

But the real question here is whether the human cerebral cortex has gotten bigger, proportionally speaking, relative to the rest of the brain.

It’s important to study:

  • changes in brain size relative to changes in body size
  • changes in the size of brain parts like the prefrontal cortex relative to changes in the size of the whole brain

This study is called allometry.[1] Positive allometry means that a brain has grown larger than expected, relative to the growth of the body, or that a brain region has grown relatively larger than expected given an increase in the size of the whole brain. Positive allometry suggests that the change was selected for during natural selection. The human cerebral cortex doesn’t have positive allometry, when compared to the cortices of other primates, because it’s the size you would expect for a primate with our brain size; scientists call this expected growth isometric.[2][3][4][5] Even studies that claim to have evidence that the human prefrontal cortex is exceptionally large actually show that this region of the cerebral cortex grows proportionally to the size of the human brain.[6] Our cerebral cortex might have new capacities because of its size and microwiring[7], but the fact of the size itself is not special in any way.


  1. Shingleton, Alexander W. 2010 “Allometry: The Study of Biological Scaling.” Nature Education Knowledge 3 (10): 2.
  2. Finlay, Barbara L. and Richard B. Darlington. 1995. "Linked Regularities in the Development and Evolution of Mammalian Brains." Science 268: 1578–1584.
  3. Charvet, Christine J. and Barbara L. Finlay. 2012. "Embracing Covariation in Brain Evolution: Large Brains, Extended Development, and Flexible Primate Social Systems." Progress in Brain Research 195: 71–87.
  4. Yopak, Kara E., Thomas J. Lisney, Richard B. Darlington, Shaun P. Collin, John C. Montgomery, and Barbara L. Finlay. 2010. “A Conserved Pattern of Brain Scaling from Sharks to Primates.” Proceedings of the National Academy of Sciences 107 (29): 12946–12951.
  5. Finlay, Barbara F. and Alan D. Workman. 2013. “Human Exceptionalism.” Trends in Cognitive Sciences 17 (5): 199–201.
  6. Donahue, Chad J., Matthew F. Glasser, Todd M. Preuss, James K. Rilling, and David van Essen. 2018. “Quantitative Assessment of Prefrontal Cortex in Humans Relative to Nonhuman Primates.” Proceedings of the National Academy of Sciences 115 (22): E5183–E5192.
  7. Barrett, Lisa Feldman. 2017. How Emotions are Made: The Secret Life of the Brain. New York: Houghton Mifflin Harcourt.