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.
"As noted below for the human case, discussions of behavioral features in terms of neoteny and paedomorphosis are often problematic. Nevertheless, it is worth pointing out that several authors (e.g. Kuroda, 1979, 1980; Dahl, 1986) have described some of the behavioral features of P. paniscus as paedomorphic and resembling juvenile patterns of P. troglodytes. Examples here include play behavior, food sharing frequency, decreased social differentiation by sex, ventro-ventral copulation, and the characteristic genito-genital (GG) rubbing of females. Several of these behaviors may be directly linked to the morphological features of the juvenilized external genitalia discussed above (see Dahl, 1985, 1986). I have argued elsewhere (Shea, 1983a, 1984) that the most important link among the morphological and behavioral distinctions between P. paniscus and P. troglodytes is the reduced social differentiation by sex. The most notable morphological change associated with neotenic facial growth in P. paniscus is the marked reduction in sexual dimorphism of the gnathic and total facial region. Although the canine teeth of P. paniscus are significantly sexually dimorphic, they are much less so than is the case in P. troglodytes, and the same holds true for a comparison of dimorphism in facial dimensions between the species (Fenart and Deblock, 1972, 1973, 1974). While we have much to learn regarding the intriguing behavioral distinctions between these two chimpanzee species (see Wrangham, 1986, for one recent discussion), it seems likely that the reduced sexual dimorphism in the facial region of P. paniscus is related to social factors, such as lowered male-male and male-female aggression, increased female bonding, increased food sharing, and perhaps aspects of sexual behavior." (Shea, B.T. (1989) Heterochrony in human evolution: the case for neoteny reconsidered. Yearbook of Physical Anthropology 32: pp. 93-4)
"In addition, few, if any, of the pervasive morphological changes associated with our extremely specialized form of bipedal locomotion can be interpreted as the result of neotenic paedomorphism (Gould, 1977). (Shea, B.T. (1989) Heterochrony in human evolution: the case for neoteny reconsidered. Yearbook of Physical Anthropology 32: pp. 88)