The Modification of the Hominin Brain | Evan Kiely

The Hominin brain evolved from a primate precursor and, previously, from that of ancient vertebrates via phylogenetic layering in relation to the shift from an arboreal niche to a terrestrial, omnivorous, extractive, and social niche, which allowed for higher level cognition. A way to explore this is, not only by observing the increasing complexity of stone tools, emotions, and embodied cognition in parallel to that of the brain, but also by using those things as metaphors for neurological development over time via the lens of phylogenetic layering.

When faced with a concept as broad as the one outlined above, it helps to view component pieces of a whole and then reintegrate them after elucidating their core principles. By doing so one is allowed to gain an intimate understanding, not just of the constituents of the whole, but of the whole itself, thanks to an in depth knowledge of the way those constituents interact, in tandem with comprehension of their standalone properties. To begin with, it is important to clarify what a couple of the above terms, phylogenetic layering and embodied cognition, mean in the given context.

Phylogenetic layering has its basis in the word phylogeny which is, at its most basic, a way of understanding an organism’s history related to where it has progressed from evolutionarily. Thus phylogenetics is a way of doing this with the method of exploration originating from genetics (i.e. by creating phylogenetic trees via sequences of known genes). Phylogenetic layering, however, introduces an interesting new concept of building upon previous advances within a given species, rather than across the evolutionary timeline of the origin of that species (i.e. modification of a species that remains that species vs. how a species came to be from a series of common ancestors). This process of striation over time is seen most literally in the brain of anatomically modern humans. For example, the modern human brain can easily be split temporally into three distinct groupings (from least to most recent): primitive brain, midbrain, and cortex, each of which, very literally, builds upon the previous (Dunbar, 1996, 61-62). With increasing physical complexity and size comes increased synaptic and cognitive complexity as well, eventually allowing for a very interesting understanding of embodied cognition.

Embodied cognition is another case of a vastly multifaceted concept attempting to masquerade as something far simpler via seemingly straight forward terminology. At its most basic, it is the way in which cognition is influenced, not simply by the brain, but by the body as well. Beyond that, Andy Clark, in Supersizing the Mind, ends up breaking embodied cognition into a hierarchy of three levels which seem to mirror, in some ways, the hierarchy of the brain previously outlined. They are as follows (again, from least to most complex): mere embodiment, basic embodiment, and profound embodiment (Clark, 2008, 42).

Though the assertion of neural hierarchy mirroring the hierarchy of embodied cognition laid out by Clark does not fit with Clark’s definitions of embodiment (all biological systems seek to make the most of their physical manifestations and place in space, along with advantageous opportunity seeking, meaning all biological systems are profoundly embodied), the self-reflexivity of feeling/emotional control that is associated with higher order cognition (as presented by Antonio Damasio) in many ways parallels the phylogenetic layering present in the modern human brain. That is to say, only with the cortex does an organism achieve control over feelings/emotions, only with the midbrain does an organism achieve higher level emotion (what Damasio refers to as “emotions-proper”), and only with a primitive brain does an organism achieve emotion at all (in the way it is colloquially understood, though Damasio does a good job of arguing tangentially to that with his paramecium example) (Clark, 2008, 42 & Damasio, 2003, 40-43). This self-reflexive control, in many ways, is an example of self- reflexive control of embodied cognition (one can evoke certain feelings/emotions which alter the state of the body). What this culminates in is a hierarchy of both embodied cognition and neurological complexity that seem to have evolved in tandem and, likely, in response to the shift from an arboreal to a terrestrial, omnivorous, extractive, and highly social niche. Furthermore, with Damasio’s nesting principle, various levels of organismal regulation are inherently nested within one another, to at least a certain extent, as the previous level is required for the formation of the following, which, again, shows striking similarities to the ways in which phylogenetic layering have shaped the human brain (Damasio, 2003, 30-42 & 96-102). The creation and usage of stone tools seems to follow a fairly similar pattern and likely, once more, in tandem with the aforementioned processes.

Naama Goren-Inbar and Dietrich Stout, et al. have both explored the transition from Oldwan to Early and then Late Acheulean style stone tools. Both researchers show phylogenetic layering of a sort, exemplified by typical stone tools of the period, that seem to follow the above described framework of neurological layering. That is to say, Oldwan tools are relatively simplistic and form the basis for the, eventual, evolution of more complex biface tools (i.e. Early and Late Acheulean tools), much in the same way the primitive brain is relatively simplistic and forms the basis for the, eventual,evolution of the midbrain and cortex. Additionally, both authors lend credence to the idea that the complexity of tool type evolved in parallel with the complexity of the brain (i.e. phylogenetic layering in the neurological realm allowed for externalizations of said layering via a stone medium) (Goren-Inbar, 2011, 1044 & Stout, et al., 2008, 1939-1940 — quotes from Stout). The ability for emotional control that comes along with high levels of embodied cognition would be very import in the tool making process as it is complex and social, potentially evolving in tandem with language, “More skill-intensive, bimanual toolmaking methods … overlap functionally and anatomically with important elements of the human faculty for language” (Stout, et al., 2008, 1941 & 1947). This pattern seems to have evolved at least partially in relation to embodied cognition as well; the ways in which humans interact with their environments, via processes of niche construction, are uniquely complex.

Much in the same way the previously explored pieces have no clear delineations of interaction (they interact so complexly that to attempt to summarize the ways in which they do would be highly reductionist), so too do the ways in which they have evolved relative to the changing niche. However, with that in mind, it is, in many cases, easier to see how certain arrangements arise when taking a semi-reduced point of view. That is to say, all of the above most likely evolved slowly, over a very long period of time, and in tandem with one another, as well as the niche. There were also processes of layering required across the modifications as well; higher level cortical processing not only gave rise to higher level embodied cognition but also, as a result, increased sociality which seems to have evolved in coordination with tool creation (Stout, et al., 2008, 1944 & 1947). Thus, by using the lenses offered to examine, and as metaphors for, the way in which the brain has been modified, it is very easy to understand the basic layering processes that are present in each of them, as well as the ways in which those layering processes were required for one another. This creates a sort of interactive phylogenetic nesting as a result of the need to adapt to a changing niche, which, in turn, leads to higher level cognition. There is a degree of reflexivity in human-niche interaction (as described by niche construction theory), that is exemplified by this: niche encouraged larger brains for adaptive fit, but those larger brains also encouraged high levels of modification of niche, thus allowing for larger brains. With that perspective it is extremely difficult to determine exactly the ways in which niche has modified the human brain as it is a kind of chicken-egg scenario, however, it can be said with certainty that it is the distinct human niche that caused these changes, as we are the only animals to display them.



Clark, Andy
2008 Supersizing The Mind: Embodiment, Action, and Cognitive Extension. Oxford: Oxford University Press.

Damasio, Antonio R.
2003 Looking For Spinoza: Joy, Sorrow, and the Feeling Brain. Orlando, FL: Harcourt.

Dunbar, R. I. M.
1996 Grooming, Gossip, And the Evolution of Language. Cambridge, MA: Harvard University Press.

Goren-Inbar, Naama
2011 Culture And Cognition in the Acheulian Industry: a Case Study from Gesher Benot Ya’Aqov. Philosophical Transactions Of the Royal Society B: Biological Sciences 366(1567): 1038–1049.

Stout, Dietrich, Nicholas Toth, Kathy Schick, and Thierry Chaminade
2008 Neural Correlates of Early Stone Age Toolmaking: Technology, Language and Cognition in Human Evolution. Philosophical Transactions Of the Royal Society B: Biological Sciences 363(1499): 1939–1949.


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