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.
"In general, then, there is at least reasonable evidence for associations between both handedness and reduced left-hemispheric speech lateralization in stutterers compared to nonstutterers. Lateralization and Tourette syndrome. TS, as mentioned earlier in connection with immune system and specific language-disability relations, is associated with an elevated frequency of dyslexia and stuttering and as such, might be considered to be a disorder involving language mechanisms. Although Shapiro, Shapiro, and Wayne (1972) found a very high incidence of left-handedness (35%) in TS patients, a much larger study by Comings and Comings (1987) failed to confirm this. If we use the Comings and Comings data on writing hand and combine the data from the two studies, the incidence of left-handedness in 195 TS patients is 14.6%, while Comings and Comings report a figure of 14.5% for their 47 control subjects. To summarize, in general there is at least modest evidence for an association between handedness and some developmental disorders of language. Thus, left-handedness or ambiguous handedness appears to be more common in dyslexia, in autism, in articulatory disorders, and in stutterers and the normal anatomical asymmetries of the brain appear to be less common in developmental dyslexics, but there appears to be no elevation of non-right-handedness in Tourette's syndrome. To a large extent, the data reflect an increased incidence of poorly lateralized individuals, rather than an increase in the proportion of left-handedness. Such data may indicate a breakdown of the normal lateralizing mechanism rather than a true increase in left-handedness. Thus, while these data may be viewed as being at least moderately consistent with the GBG hypothesis, they can almost certainly be accommodated by other models. (e.g., Bishop, 1990a; Satz et al., 1985b) just as readily." (Bryden MP, McManus IC, Bulman-Fleming, MB (1994) Evaluating the Empirical Support for the Geschwind-Behan-Balaburda Model of Cerebral Lateralization. Brain and Cognition 26: pp. 146)