The Human Neocortex


I finally picked up How To Create A Mind by Ray Kurzweil, and so far it has been a thoroughly enjoyable read.  Kurzweil gives an eloquent overview of why the human neocortex is important, and how it enables us to build cumulative culture:

“Only Homo sapiens have a knowledge base that itself grows exponentially, and is passed down from one generation to another.”

— Ray Kurzweil

Animal behaviourists know that some other species exhibit behaviours that can be interpreted to be cultural.  However, it seems that no other species possess what evolutionary scientists call “cultural ratcheting” or “cumulative culture”.  This is the phenomenon where by knowledge and technology improve and increase in complexity over time (Dean et al., 2012).  Primatologist Victoria Horner has suggested: “if cumulative culture does exist in other species, it is extremely rare.”  In my opinion, cumulative culture of some kind probably does exist in other species, although this process would be impossible to empirically test.  During the start of any exponential process, complexity increases undetectably over small timescales.  It is only noticeable in retrospect (e.g., exponential improvement of hominid tool technology).  Either way, it is clear that we are the only species that has ever existed on Earth that exhibits an indisputable form of cumulative culture.

This is all very interesting, but why has our neocortex enabled this type of progress, when other species also possess a neocortex?  In fact, the neocortex is a defining characteristic of all mammals, and recent research (e.g., Dugas-Ford et al., 2012) has also revealed that different neocortical architecture exists in birds and reptiles.  Presumably, it is this brain architecture that allows animals like crows, parrots, and octopi to exhibit behaviour that many scientists consider to be “cultural”.  So what is it about our neocortex that is special?  Kurzweil argues that the organization of the neocortex is more important than whether it is present or absent.  The mammalian neocortex is organized hierarchically in six-layers.  In contrast, the bird neocortex is organized into nuclei and the reptile neocortex is organized into cortical areas.  According to Kurzweil the organization of bird and reptile neocortices prevents them from creating technology that has its own evolutionary course of development (Kurzweil, 2012), and that this is only possible with a six-layered mammalian neocortex that can leverage “the innately hierarchical nature of reality” (Kurzweil, 2012).

I slightly disagree with this assessment.  Since we know of only one species that has developed technology with its own evolutionary course of development, who is to say that the organization of our neocortex is what enables cumulative culture?  Perhaps the avian neocortex could also enable cumulative culture given enough time and the right evolutionary pressures.  After all, convergent evolution is very powerful.  Eyes have evolved independently between 50-100 times and have utilized different organizational frameworks to accomplish the same task (Land & Nilsson, 2002).  Considering how important the neocortex is for the evolution of intelligence, evolution could develop different organizational structures that would enable cumulative culture.  Perhaps it is the proportion of the neocortex, relative to the cerebral cortex, that is important, as opposed to the organizational structure.  As stated above, all mammals have a six-layered neocortex, but only humans are known to possess cumulative culture.  If it is the proportion, and not the structure that is important, then the expansion of the human neocortex is one of the most important evolutionary developments in the history of life on Earth.  Although scientists still know relatively little about the origin of the neocortex itself (Dugas-Ford et al., 2012), evolutionary anthropologist Robin Dunbar does have a working hypothesis for the emergence of the human neocortex.

 Dunbar (2001) claims that the human neocortex coevolved with increased primate group size.  This hypothesis was formulated after the realization that primates that lived in large groups had a proportionally large neocortex region.  Further analysis revealed that the larger the neocortex, the larger the group that can be maintained as a coherent entity (Dunbar, 2001).  This correlation also applies to hominid evolution.  Data suggests that Australopithecine group size was not that much larger than the group size of living chimpanzees, however group size spikes significantly with the appearance of Homo habilis, before stabilizing again.  This is spike in group size is correlated with an increase in overall brain size from 350-400 cm3 to 600 cm3.  Throughout the Homo erectusperiod there is also steady rise in brain size from 800 cm3 to 1500 cm3 that correlates with an equally steady increase in group size.  Although it is difficult to conclude definitively that neocortex expansion itself is correlated with these increases in group size, it appears to be consistent with both primatological observations and the available fossil record.  This line of reasoning is further validated by the fact that the primate neocortex is specifically used for rational thought and language.  Under this framework, the evolution of a proportionally large neocortex enabled our ancestors to use language as a social glue to increase group size.
Regardless, even though I have a slight disagreement with Kurzweil about the evolution of the neocortex, I think his fundamental point that the human neocortex allows for a unique type of thought, is well-grounded in current evidence and theory.  Perhaps it is best summed up by Kurzweil: “[Our neocortex allows us to] understand a structure composed of diverse elements arranged in a pattern, representing that arrangement with a symbol, and then using that symbol as an element in a yet more elaborate configuration.”  All evidence suggests that this occurs in our vastly expanded mammalian neocortex.  As a result of this structure we are capable of building ideas that are ever more complex.  In the long-term we may be able to expand and improve upon this structure, enabling yet another giant leap in our capabilities.  As a consequence, there may be no upper boundary to what we can eventually understand, control, and achieve.  If you want to learn about how this could happen in your lifetime, I definitely recommend picking up How To Create A Mind: The Secret of Human Thought Revealed.


Dean, L.G., Kendal, R.L., Schapiro, S.J., Thierry, B., & Laland, K.N.  2012.  Identification of the social and cognitive processes underlying human cumulative culture.  Science, 335: 1114-1118.

Dunbar, R.  2001.  Brains on two legs: group size and the evolution of intelligence.  In Tree of Origin: What Primate Behavior Can Tell Us About Human Social Evolution (173-191).  London: Harvard University Press.

Dugas-Ford, J., Rowell, J.J., & Ragsdale, C.W.  2012.  Cell-type homologies and the origins of the neocortex.  Proceedings of the National Academy of Sciences.  109: 16974-16979.

Kurzweil, R.  2012.  How To Create A Mind: The Secret of Human Thought Revealed.  New York: Penguin Group.

Land, M.F. & Nilsson, D.E.  2002.  Animal Eyes.  Oxford: Oxford University Press.


About Cadell Last
Hello. I'm probably drinking coffee and reading.

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