Evolution favors non-modular solutions

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Chapter 8 endnote 34, from How Emotions are Made: The Secret Life of the Brain by Lisa Feldman Barrett.
Some context is:

As Steven Pinker so nicely writes, “It is now simply misguided to ask whether humans are flexible or programmed, whether behavior is universal or varies across cultures, whether acts are learned or innate.”[1] The devil is in the details, and the details give us the theory of constructed emotion.

From the standpoint of natural selection, there is no intrinsic virtue in innate, mental organs. In the words of evolutionary biologist Ernst Mayr:

"I conclude that highly specific brain structures are not needed for the perception and understanding of our world. On the whole, it would seem that the evolutionary improvement of the central nervous system does not necessarily lead to highly specific neural structures but rather to a continuously improved general structure of the brain."[2]

When it comes to brains, evolution must optimize the following:

  • Low wiring costs
  • High computational power
  • Metabolically efficient information flow
  • High neural complexity
  • Degeneracy

A general solution, such as core networks (also called multipurpose neurons), will be favored when it "can do a good enough job at a low enough cost,"[3] and a prolonged period of brain development, which offsets some of the costs of development to epigenetic, cultural influences, is biologically efficient.[4][5] And in fact, biological systems normally do not evolve to produce separate units that perform different, independent functions (an arrangement called "modularity"). Even systems that begin as modular rapidly evolve into a non-modular solution,[6] a description that fits the theory of constructed emotion.

This arrangement makes sense from a functional standpoint: the ability to hold information in mind successfully (called working memory) requires the brain to reconfigure its networks to increase their connectivity (and reduce structural modularity),[7] whereas errors are linked to reduced connectivity and greater modularity.[8]

Modularity decreases, and integration increases, with age into early adulthood[9] and beyond.[10]


Notes on the Notes

  1. Pinker, Steven. 2002. The Blank Slate: The Modern Denial of Human Nature. New York: Penguin.
  2. Mayr, Ernst. 1998. This is Biology: The Science of the Living World. Harvard University Press, p. 76.  
  3. Laland, Kevin N., and Gillian R. Brown. 2002. Sense and Nonsense: Evolutionary Perspectives on Human Behaviour. Oxford University Press, p. 183.
  4. Boyd, Robert, Peter J. Richerson, and Joseph Henrich. 2011. "The cultural niche: Why social learning is essential for human adaptation." Proceedings of the National Academy of Sciences 108 (supplement 2): 10918-10925.
  5. Finlay, Barb. In press. "The timing of brain and body maturation, early experience and the human social niche." In Evolution of Nervous Systems, edited by Jon H. Kaas, Elsevier: Oxford University Press
  6. Kashtan, Nadav, and Uri Alon. 2005. "Spontaneous evolution of modularity and network motifs." Proceedings of the National Academy of Sciences of the United States of America 102 (39): 13773-13778.
  7. Kitzbichler, Manfred G., Richard NA Henson, Marie L. Smith, Pradeep J. Nathan, and Edward T. Bullmore. 2011. "Cognitive effort drives workspace configuration of human brain functional networks." Journal of Neuroscience 31 (22): 8259-8270.
  8. Ekman et al., 2012 [full reference to be provided]
  9. Hagmann et al., 2010. [full reference to be provided]
  10. Chan, Micaela Y., Denise C. Park, Neil K. Savalia, Steven E. Petersen, and Gagan S. Wig. 2014. "Decreased segregation of brain systems across the healthy adult lifespan." Proceedings of the National Academy of Sciences 111 (46): E4997-E5006.