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The Co-evolution of Manual Dexterity and Language Grammar

August 23rd, 2012 by Robert DePaolo | Posted in Psychology | No Comments » | 250 views | Print this Article

By Robert DePaolo


This article discusses the advent of human language grammar as a concomitant of the fine motor planning and executive skills that also facilitated advanced tool making. Neither skill is viewed as antecedent. Instead the point is made that they were essentially concurrent and interdependent in human evolution; that the brain’s capacity to orchestrate manual behaviors toward a pre-planned outcome as seen in tool making extended to oral-motor cortical regions (and vice versa), enabling early humans to develop simultaneously a manual and linguistic grammar.

The idea that human language derives from tool making has been supported by a number of researchers and theoreticians, for example Sample (2010) and Stout (2011).That is in part due to the anatomical, functional and neurological interrelationship between oral and fine motor expression.
Around 75,000 years ago the human brain reached its current volume of roughly 1200 centimeters. Its expansion featured an outward growth of the outer layer – known as the cerebral cortex. Not only did this brain section expand substantially, it also folded up in development so as to maximize its size and experiential influence without overriding the size of the human skull case. The cause of cortical expansion – to the extent that one can insert determinism into the evolutionary process – is uncertain.

There are several possibilities. One is that the primate brain has always had a higher probability of encephalization due to its need to adapt to the sensory-motor demands of an arboreal existence. Implicit in this idea is that Darwin’s concept of chance mutations is inaccurate; that the genetic history of any given organism skews its mutative drift. At the risk of invoking the Aristotelian notion of inside-out teleological development, it would seem lions are more likely to develop changes in coat color and canines than to develop gill slits. Thus “predisposition theory” (which holds that mutations are skewed in terms of a prior ontogenetic template) might provide one answer.

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