ABSTRACT
Testosterone secretion before birth causes the differentiation of male sexual organs and characteristics. The species-typical sexual behavior of female mammals other than primates is triggered by the presence and behavior of a male of the same species, but only when she is at the receptive stage of her estrus cycle. Similarly, castration of male animals leads quickly to cessation of sexual activity, which can be reinstated by testosterone injection. Testosterone levels in men also respond to sexual behavior: viewing erotic films increases blood testosterone levels. However, most research finds no relationship between the amount of testosterone and the intensity of sexual desire or amount of sexual activity. Thus, perinatal testosterone levels have sex-specific organizing effects on behavior and brain structures in rodents. Despite some early claims, homosexual men do not have lower levels of circulating testosterone than do heterosexual men, and neither does the injection of androgens affect their orientation..
