Defines five layers related to human sexuality: Sexual identity, orientation, preference, role, and performance. Believes that the deeper the layer (e.g., core sexual identity) the more difficult it would be to achieve change. (Seligman, Martin E P., PhD. What You Can Change…and What You Can’t. p 148-173. NY: Fawcett Books, 1993.)

The preoptic anterior nucleus seems to regulate masculine brain functions (e.g., mounting in response to female signals). In humans this area of the hypothalamus is about twice as large in males as in females. (Wilson, Glenn. The Great Sex Divide. p 35-36. England: Peter Owen Publishers, 1989.)

Homosexual males tend to have fewer neurons in the 3rd interstitial nuclei of the anterior hypothalamus (INAH-3) as compared to the straight male brain (but more than in the female brain). (Blum, Deborah. Sex on the Brain. p 42-48. NY: Penguin Books, 1997.)

The hypothalamus is the sex center. Less than an ounce in weight and about the size of a cherry, it is larger in the male brain than in the female brain or in the brains of homosexuals or transsexuals. (Pease, Barbara and Allan. Why Men Don’t Listen and Women Can’t Read Maps. p 190-200. NY:Broadway Books, 1998.

The third interstitial nucleus of the anterior hypothalamus is of similar size in the brains of females and homosexual males; twice as large in heterosexual males. (Howard, Pierce J., PhD. The Owner’s Manual for the Brain. p 223-226. GA: Bard Press, 1994, 2000.)