Testosterone is a male sex hormone (also found in smaller quantities in females) produced mainly in the testes, but also the adrenal glands and ovaries. It is responsible for many physical characteristics specific to adult males including facial hair, reproductive organs and sexual function. In both sexes, it is involved in sex drive, aggression, bone/muscle mass and red blood cell production.Hormone Health Network. (n.d.). Testosterone. [online] Available at: http://www.yourhormones.info/hormones/testosterone/ [Accessed 15 Nov. 2018]. Delville, Y., Mansour, K. M., & Ferris, C. F. (1996). Testosterone facilitates aggression by modulating vasopressin receptors in the hypothalamus. Physiology and Behavior, 60, 25-29. Archer, J. (2006). Testosterone and human aggression: an evaluation of the challenge hypothesis. Neuroscience & Biobehavioral Reviews, 30(3), 319-345.