HEMISPHERIC SPECIALIZATION: EVOLUTION OR REVOLUTION

Some twenty years ago, I addressed the Montreal Neurological Institute on the topic of temporal lobe function. My data were obtained from experiments performed with monkeys. Wilder Penfield was in the audience and opened the discussion with the question as t o whether I believed that the difference between man and the nonhuman primates was quantitative or qualitative. My answer was that I believed the difference t o be quantitative but of such an extent that qualitative changes emerged. I used the then new computer technology as an example. Vast increases in the capacity of the memory in central processors had changed computational power not only quantitatively but qualitatively. Penfield argued the case for a more fundamental distinction that distinguished man and we agreed t o disagree. My interest in the topic of this conference-hemispheric specialization-thus fits a larger set of issues, which in my Arthur Lecture t o the Museum of Natural History I entitled, What Makes Man Human?’ At stake are such theoretical stances as “evolution,” “mind-brain dualism,” “the origin of language” (the subject of a fascinating conference held in this Academy last year) as well as some very practical concerns as t o the limits of applicability of animal research t o our understanding of the human condition, the cure and prevention of disease, and the improvement of life on earth and in space. How then are we t o obtain substantive answers t o the question posed by Penfield? I believe my reply of twenty years ago was correct in spirit if not accurate in expression. I did not then, nor would I today, hold that the only difference in brain structure and function between man and other animals is quantitative. Changes in organization, in chemical composition, in developmental sequence, and in time and duration of critical periods are only a few of the differences that might make the important distinction that we recognize as human. But whether such differences constitute a revolution or evolution i s an empirical not a theoretical issue. This was the point of my answer t o Penfield and from the contents of the program of this conference I believe that my view is shared by our hosts. For, if and when we fill any knowledge gap in comparative biology with sufficient relevant data-and can, to some considerable extent, specify the mechanisms that lead from one data point t o another-we arrive on the side of evolution, eschewing revolution or other form of discontinuity. The task of this conference is therefore t o chart the evidence for neural specialization, especially as it concerns lateralization of function, and to provide in each instance a possible or plausible mechanism that can stand the tests of scientific analysis. To the extent that we are successful, t o that extent an evolutionary approach t o the evidence is supported-despite the apparent revolutionary consequences that the evolutionary process has wrought.