Vision-Centered Brain Selection Pressure Partly Responsible for Lower Neanderthal Intelligence

 by Independent Thinker Raceology December 27, 2019

A model of a Neanderthal

Pre-Article Summary:

Arguments made against Richard Lynn's cold winters theory, claiming that the case of Neanderthals having lower IQs than AMHs disprove his theory are fallacious since they fail to understand the different brain organization between AMHs, and Neanderthals.  Neanderthals evolved larger body sizes, and better visual systems and areas for visual processing in their brain than AMHs leaving them less cranial space for other functions like intelligence, whereas AMHs evolved social-centered brains increasing the sizes of their neocortex, and so intelligence.  When AMHs left Africa and diverged into colder environments they had more capacity to develop higher intelligence owing to their different brain organization, and proclivity to complex social structure, whereas the Neanderthals did not have this ability. Thus the evolutionary trajectories and constraints of Neanderthals and AMHs were quite different, and in so in no way is Lynn's theory disproven by this example.

Vision-Centered Brain Selection Pressure Partly Responsible for Lower Neanderthal Intelligence

It has frequently been asserted that Neanderthals had lower average intelligence than anatomically modern humans (AMHs).  This is supported through several lines of evidence, although more recently there has been some questioning of just how much lower the Neanderthal intelligence really was. Accepting the assumption that it was indeed significantly lower, it is well worth understanding why.

I have sometimes seen the argument being made against the cold-winters theory of Richard Lynn, for example, in a review in Psychology Today, by Scott A McGreal.  The theory goes along that those that lived in colder climates were selected for higher intelligence due to the demanding nature of that environment. McGreal stated:

"Lynn (2006) acknowledges that anatomically modern humans first appeared in Africa. Yet he does not explain why it is that the modern human race that evolved in tropical Africa developed greater intelligence and cognitive sophistication compared to their Neanderthal relatives who had been surviving in harsh Ice Age conditions for so many millennia."

  There are really several fallacies at play here one of these is assuming that a single factor is at play when it comes to the evolution of intelligence. The second, and in my opinion, obvious fallacy is to erroneously assume a 1:1 similarity between the brains and selection pressures of Neanderthals and humans. The two were in fact dissimilar.

It is really immaterial as to whether or not Neanderthals were a different species from Homo sapiens or simply a different subspecies. The important distinction is that on the average they had a significantly different morphology in terms of the body, and brain organization.

Research from Pearce, Stringer and Dunbar suggests a reason for why this may be the case is a paper that they published in 2013.  They suggest that despite having similar average brain sizes between Neanderthals and AMHs, and in addition to the fact that Neanderthals had larger body masses, and so less neural matter devoted to cognitive functioning, that it was the Neanderthals larger devotion of brain matter to their visual systems that doomed them to having lower average intelligence.

In their paper they start of mentioning that despite there being various similarities in the assumed brain organization of Neanderthals and AMHs, that they probably also have several important differences in their organization based on similar lines of evidence, for example, the temporal lobe is larger and more forward projecting in AMHs than Neanderthals and other hominids. Although a rough idea of brain region volume can be estimated simply from overall brain volume, this kind of simple comparison between brain volume does not allow for detailed assumption of brain regions.  For example, some primates have significantly larger or smaller areas of their brains than would be predicted by brain volume alone. Gorillas and orangutans have larger cerebellas and smaller neocortices than would be predicted by brain volume alone.  One method of gauging internal organization of the brain is to look at the size of the eye orbits, since the elements of the visual system scale with each other, larger orbits means larger eyes, which correlates with larger visual cortices in the brain.

Neanderthals lived in high latitudes which had lower light conditions than the AMHs in sub-Saharan Africa.  Even in recent humans those that see better in lower light conditions have larger eyes, and to achieve the same level of visual acuity those that live in higher latitudes require larger eyes than those that live in lower latitudes.  There would have been an evolutionary selection pressure for Neanderthals to develop better vision. The analysis by the team of researchers showed that from an older group of Neanderthals to a younger group in terms of fossil age, although the absolute brain size did increase over time the relative proportion of neural matter devoted to somatic functioning and visual processing did not change, whereas for AMHs, it was other proportions of the brain e.g. the frontal lobes that underwent an increase in size without a proportional increase in the visual or somatic systems.  What does this mean?  It means that AMHs had significantly more brain matter to devote to higher cognitive processing than Neanderthals, in spite of evolving the same average brain size. When adjusted for brain volume devoted to somatic functioning and visual processing Neanderthals had smaller brain volumes devoted to cognitive functioning than AMHs. 

Different Evolutionary Trajectories

Larger visual systems imply larger brains for recent humans (within the last 200, 000 years) so it may be expected that Neanderthals would have evolved larger brains than AMHs, however that didn't happen, implying the following, according to the authors of the paper: 1) Neanderthals and AMHs had different brain organization 2) Because more neural tissue was devoted to visual and somatic processes, less brain tissue was left with dealing with other functions in comparison to AMHs.

Starting with the common ancestor Homo hiedelbergensis Neanderthals evolved larger visual and somatic regions of their brains whereas AMHs achieved a larger volume by increasing other areas of the brain. Neanderthal visual areas of their brains seem to be more in line with what would be expected for a primate that size, with humans actually having smaller visual systems than expected adding more support to this argument. There are relationships between brain and bonded-group size in primates, as well as specific areas of the frontal lobe and personal active social network within macaques, and humans. There is a relationship between total network size and areas of the neocortex.  The most number of individuals that an individual can keep track of constrains the group size, and thus brain size and function placed a constraint on group size and group complexity. Using estimated neocortex size in AMHs and Neanderthals shows that Neanderthals likely had a smaller active social network, and although the archeological evidence is scant, it does indeed suggest that Neanderthals had smaller active social networks than AMHs did. Group size itself is a convenient index for the ability to have social complexity.

The Neanderthal smaller group sizes meant that they could cover less area as a group and have less trade of exotic goods.  Also, innovative ideas had less of a chance of being passed on to the next generation.  I'd also mention that additionally smaller group sizes would give less of a chance for the evolution of high intelligence (another factor in Richard Lynn's cold winters theory). They would have also been more vulnerable to demographic fluctuations and hence to extinction.

Neanderthals followed the evolutionary trajectory of developing enhanced vision and retaining the robustness of H. hiedelbergensis, while not developing superior social cognition. This was a good strategy at first, but the AMH evolutionary strategy of evolution in the warm climate and bright lights of Africa ultimately won out, with them developing larger relative areas of the frontal lobe, and likely the neocortex to develop a socially centered brain.  Also, it should be pointed out that generally speaking the more social species tend to be more intelligent than less social ones for example, dogs are more intelligent than cats.

Relation to Cold Winters Debate

Back to Lynn's cold winters debate, the relation is that it is incorrect to compare Neanderthals and AMH as they followed different evolutionary trajectories since their last common ancestor. Neanderthals evolved larger visual parts of their brains, and developed larger body size whereas AMHs developed social brains. The crucial part is that AMHs developed a different brain organization than Neanderthals, with superior average intelligence. Once this organization had already evolved it gave AMHs the capacity to evolve even higher intelligence by increasing the volumes of their neocortex through natural selection, whereas in Neanderthals this wasn't quite as possible. Also the generally larger group sizes of AMHs would have made it easier for alleles for higher IQ to develop. Thus after the social brain transformation of AMHs, once group migrations started to different parts of the world, and the groups were separated in different environments with different average winter temperatures those groups subjected to colder winters would have had more selection pressure for higher intelligence.  Their social abilities and proclivities due to their social-centered brains, along with more space in the brain available for things like the neocortex would have made it more likely that it would be this area of the brain that was more selected unlike Neanderthals who did not have much cranial capacity available for developing as high of an intelligence, since much was devoted to increased body size, and visual processing coupled with a weaker social cognition and proclivity.

Thus as was shown the argument against Lynn's cold winters theory is a fallacious one since it assumes that Neanderthals and AMHs had the same capacity to develop high IQ, whereas due to the different brain organization this was extremely difficult  for the Neanderthals due to their initial evolutionary trajectory toward a better visual system and larger bodies.
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PS: I realize that parts of this little article are redundant, but I really wanted to drive home the point since I realize quite a few people did not understand this argument when I presented it to them before (many still don't or won't unfortunately).

Also for another summary of this research for the layman you may see this article, it also had a brief few quotes from Dunbar to live science:

https://www.livescience.com/27850-social-brain-beat-neanderthal-vision.html