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.
"It is also now clear that high plasma levels of testosterone are immunosuppressive (fig 2). This may have first arisen as a mechanism to suppress actions of the immune system within the testes, because as developing spermatozoa become haploid, they develop surface proteins that are recognized as foreign by cells of the immune system. Thus, suppression of immune responses within the testes enhances fertility. Problems arise when testosterone is secreted into the blood and then has the potential to inhibit the immune system throughout the organism." (Wingfield, J.C., Jacobs, J. & Hillgarth, N. (1997) Ecological constraints and the evolution of hormone-behavior interrelationships. Annals of the N. Y. Academy of Science 807: pp. 25)