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.
"...primary hypogonadism, a condition resulting from the lack of increased production of androgen (testosterone) hormones in the interstitial Leydig cells in the testes at puberty. Because of this condition, emasculated singers may have been blessed with voices sweeter than a woman's, but burdened by an infantile penis, an underdeveloped prostate, "eunuchoid" (disproportionately long) arms and legs, beardlessness, pubic hair distributed in the female opposed to the male pattern, and fat deposits on the hips, buttocks, and breast area." (Margulis, L & Sagan, D. (1991) Mystery Dance, On the Evolution of Human Sexuality: Summit Books, New York pp. 67)
The heterochronic changes just outlined do not have to affect the entire organism (in fact they usually do not). The length of an organ such as horn may grow at a faster rate in the descendant (i.e., be accelerated) while shoulder height might not. This is an example of dissociated heterochrony, whereby different organs (or growth fields) can undergo heterochronies (or remain uneffected) independent of what is going on elsewhere.This process had long been known as "mosaic evolution"... (McKinney, M.L. & McNamara, K.J (1990) Heterochrony: The Evolution of Ontegeny: Plenum Press, New York p. 12)
"The evolution of smaller- or larger-sized traits may vary dimorphically and result in a reduction in competition for resources between sexes. Dissociation of head growth from body growth has been recorded in species of North American garter snakes, such as Thamnophis sirtalis parietalis (Shine and Crews, 1988). Because of the action of testicular androgens early in development, inhibition in growth of the head occurs in males, resulting in smaller heads (shorter jaws) than in females. Body sizes are similar in males and females. Androgen administration occurs early in ontogeny and initiates different growth rates between males and females." (McKinney, M.L. & McNamara, K.J (1990) Heterochrony: The Evolution of Ontegeny: Plenum Press, New York p. 267)