Abstract
Human gender/sexual differentiation is very complicated combination of following five factors: 1) true biological or genetic sex, that is, the gonad to be testis or ovary; 2) body sex in appearance which is judged mainly with form of the external genitalia; 3) sex type of the brain; 4) gender identity; and 5) sexual orientation. The sex type of the brain does not seem to determine gender identity, since some persons suffering from intense female-to-male (FTM) gender identity disorder have menstrual cycles, suggesting their brain possibly not to be male type. The gender identity, in turn, may not determine sexual orientation; there are persons who are living as male with completely male gender identity but are seduced sexually only by males (true homosexual). It is still mysterious what determines gender identity or sexual orientation. Any combination of the above five factors can be developed, and the situation is complicated more by the presence of hermaphrodites and persons with bisexual orientation. Besides, gender identity disorder, especially MTF, varies in intensity from transvestism to a core type disorder requiring sex reassignment surgery. By the way, why eating disorders, for example, are mostly seen in women? Here I try to discuss gender difference of such addicted behaviors, which develop after adolescence in very hard psychological conditions without any control by consciousness. Is a type of these behaviors induced by biological, environmental or cultural factors? [Jpn J Physiol 54 Suppl:S41 (2004)]
