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.
"Twenty-two individuals in the National Child Development Survey sample who (by the presence of nuclear symptoms) later developed schizophrenia, complete the test of hand skill at the age of 11 years (Crow et. al., 1996b). They differed from the rest of the population in being closer to the point of hemispheric indecision (ANOVA F 7.76, p<0.005). They were also more likely to be described by their mothers as ambidextrous at age 7. Predisposition to schizophrenia, it seems, is associated with inadequacy or delay in establishing dominance in one or other hemisphere. Parallel to this loss of functional asymmetry is evidence for loss or failure of development of the anatomical symmetries (e.g., of Sylvian fissure length or brain width) that are present in the brains of most individuals (Crow, 1990; Crow et al., 1989). Risk of schizophrenic symptoms, it appears, is associated with a brain that is less clearly lateralized in anatomy and physiology. ... According to the above considerations the genetic predisposition to psychosis is related to that for asymmetry. Two lines of evidence are consistent with the presence of a gene for aymmetry on the X and Y chromosomes: (1) Turner's syndrome (XO) individuals have right hemisphere impairments, whilst Klinefelter's (XXY) and XXX individuals have left hemisphere deficits. This suggests a gene for the relative growth of the two hemispheres is present on the X chromosome. But since normal males (XY) have only one X but lack the deficits seen in Turner's syndrome, there must be a balancing influence on the Y chromosome (Crow, 1993). (Crow TJ (1997) Aetiology of schizophrenia: and echo of the speciation event. International Review of Psychiatry 9: 326)