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Human brain contralaterallization

March 18, 2006

Jul 20, 2005   Dov, in biologicalEvolution forum.

A note I e-mailed July 18, 2005 to C Walsh, Harvard, re his  "Asymmetry in Human Left/Right Cerebral Cortex", Science, Vol 308, Issue 5729, 1794-1798, 17 June 2005.

A) You write: "The human left and right cerebral hemispheres are anatomically and functionally asymmetric. To test whether human cortical asymmetry has a molecular basis, we studied gene expression levels between the left and right embryonic hemispheres using serial analysis of gene expression (SAGE). We identified and verified 27 differentially expressed genes, which suggests that human cortical asymmetry is accompanied by early, marked transcriptional asymmetries.

B) The expression "asymmetry has a molecular basis" sounds strange. The aspects of the asymmetry include, of course, ALSO genes' expressions, the total asymmetry being the product of specific evolution of the human cerebral cortex.

C) In July 1997 I wrote the following "conjectural picture":

" Humans' uniqueness on Earth was initiated by a stimulus in a zone in the brain of some of them when challenged by needs for new manipulations, and for new capabilities of analysis and assessments of wider vistas open to them when changing posture to erect due to change of environment from forests to plains. The new demands employed existing brain cells in one half of their brain, overtaxed its capabilities and led to compensation by overworking the symmetrically located cells in the second half of the split brain and this in turn led again to compensation in the first half thus causing contralaterallization that is still evolving now".

D) I suggest that the probability of a similar asymmetry might be sought in ocean mammals, having undergone a radical intensive change of living circumstance and mode, like our ancestral primates.


Dov Henis

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