Wednesday, March 23, 2011

so much for genome-determinists!

"The dramatic expansion and increasing functional importance of dopamine systems in the human brain occurred over a long period of time, only partially paralleled by the changes in our physical appearance, and the dopamine rise continued long after our common genetic lineage. For those who believe that the great intelligence of humans relative to the rest of the primate world requires an exalted evolutionary progression, this theory is highly disappointing in that:

1. there is no positing of specific genetic mutations for language or other advanced intellectual functions;
2. no importance is ascribed to the changes in cranial size and shape; and
3. most of our intelligence is regarded as a by-product of physiological adaptation, diet and population pressures.

This theory is, however, consistent with a number of crucial facts, including:

1. the lack of a causal relationship between brain size and intelligence;
2. the tenuous relevance of the human genome to intelligence;
3. the importance of dopamine to our advanced intellect;
4. the specific expansion of the dopamine-rich striatum and cerebral cortex relative to the rest of the brain in humans as compared to chimpanzees (Rapoport, 1990);
5. the known effects of diet and physiology on dopamine function;
6. the sub-Saharan origins of humanity; and
7. the >100,000 year gap between the establishment of the modern human anatomy and genome and the appearance of a variety of cultural artifacts associated with a distinctly modern human intellect.

This theory merges genetic, epigenetic and cultural factors and blends the African gradualistic theory of McBrearty and Brooks (2000) with the general intellectual explosion posited by Mithen (1996), but with his European locus of the intellectual "Big Bang" now placed at an earlier juncture in Southern Africa. In addition, this theory clearly explains why cognitive abilities like language, religion, art, advanced tool-making, mining, long-distance exchange etc. did not emerge as separate genetic selections but rather depended on a more fundamental increase in cognitive potential as expressed in enhanced working memory, cognitive flexibility, spatial and temporal distance (off-line thinking), mental speed, and creativity that could only be found in a brain rich in dopamine (see also Wynn and Coolidge, 2004). Finally, this theory dispels the notion that the evolution of advanced human intelligence was critically dependent on the capacity for speech, since the latter was present at least 200,000 years ago in the first anatomically modern humans and probably another 100,000 or 200,000 years before that in archaic humans (Arensburg et al., 1990), without leading to any dramatic intellectual advances.

By highlighting the epigenetic inheritance of dopaminergic activity, this scenario shows why the emergence of the dopaminergic mind was not associated with a unique, immutable genetic process but rather one that continued to advance long past the establishment of our common genome and anatomy."

excerpted from "The Dopaminergic Mind in Human Evolution and History" by Fred Previc

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