Human evolution theory utilizing concepts of neoteny & female sexual selection
An etiology of neuropsychological disorders such as autism and dyslexia, and the origin of left handedness.

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Paul Maclean

The Triune Brain in Evolution: Bibliographical Excerpts

"This situation is to be contrasted with what is required when enunciating words with precise meanings. Since the tongue is a midline organ, there must be snychronized action of both sides if there is not to be slurring of speech. Since the cerebral hemispheres are mirror images of one another, and since delay is involved in relaying information from one side to the other, it is unlikely that both could cerebrate exactly alike and "speak as one voice." Each side of the tongue might receive impulses for the same word at slightly different times, or, worse, receive the neural command for two different words. The result would be stammering or stuttering. Penfield and Welch have pointed out that upon stimulation of the motor cortex in human beings, the responsive movement is always on the contralateral side except for such structures as the tongue and pharynx that straddle the midline." (MacLean (1990) The Triune Brain in Evolution. Plenum Press: New York p. 543)



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