Same Sex Attraction Is Hard Wired

Tri-Valley Relationship Therapy, Inc. in Dublin & Oakland offers sex positive counseling to LGBTQQI individuals and couples all over the East Bay.

Tri-Valley Relationship Therapy, Inc. in Dublin & Oakland offers sex positive counseling to LGBTQQI individuals and couples all over the East Bay.

This article is the first part of a two part series devoted to the presentation of research that discusses the biological, physiological, sensory and genetic predisposition for same-sex attraction. In this post, the hormonal factors and differences in brain structure are discussed. The next post will include the sensory and genetic factors for same-sex attraction.

Same sex attraction manifests itself in the form of homosexuality or bisexuality. The physiological etiology of same sex attraction has always been an area of great interest for sexologists. But bisexuality as a differentiation of human sexual orientation has been little studied. Most of the research done on bisexuality usually generalizes the results from homosexuality to bisexuality. But researchers who have studied bisexuality individually have consistently observed that bisexuals are often unlike homosexuals or heterosexuals (Angelides, 2001).

Many studies have pointed out that some bisexuals usually have a strong inclination towards homosexual or heterosexual orientation. But the manifestation of the bisexual tendencies become possible due to high erotic responsiveness or predominance of masculine behaviors leading to versatility in sexual behavior (Angelides, 2001).

According to Ritter & Terndrup (2002), currently there are three lines of physio-biological research that has attempted to explain sexual orientation. The first theoretical perspective is the prenatal hormone theory that puts forward the hypothesis that the endocrine system is responsible for the hormonal masculinization or feminization of the brain, which in turn determines the sexual orientation.

The second line of research suggests that the study of sexual orientation at the molecular level of synapses and neurons point to basic differences in the brain between the homosexual and heterosexual population. The last thread of inquiry explores the heritability of sexual orientation, which includes the study of family genetics and twin studies (Ritter & Terndrup, 2002).


Congenital Adrenal Hyperplasia:

CAH or Congenital Adrenal Hyperplasia refers to a group of inherited adrenal gland disorders. People with CAH don’t produce enough of the hormones cortisol and aldosterone but produce the hormone androgen in excess (Popov & Bekhterev, 1992).

Bisexuality often appears in women with congenital adrenal hyperplasia than in women with normal levels of androgen. Innate adrenal hyperplasia leads to masculinization of the female fetus. Patient exams have shown that all subjects develop sexual orientation corresponding to their gender of education, which means the gender they are assigned and brought up as. However they manifest bisexuality more often than average (Heino, 2004).

There is also a form of postnatal androgenization, which is called Acquired Adrenal Hyperplasia and females with this condition are documented to usually have either bisexual or homosexual orientation (Heino, 2004).

DES Exposure:

DES or Diethylstilbestrol is a non-steroidal synthetic estrogen, which in the past was prescribed to pregnant mothers. A study done by Ehrhardt et al (2002) indicated that exposure to DES increased the likelihood of bisexual or homosexual orientations.

DHT Levels:

According to Harvey (2004), women who produce more dihydrotestosterone (DHT) than testosterone are more sexually expressive as well as sexually ambiguous. They are distinguished by having a bisexual or homosexual orientation in comparison to women who produce normal levels of DHT.

Digital Ratio:

The ratio of the length of the index finger and the ring finger is sexually dimorphic. There is evidence that higher levels of testosterone during the critical development stage of the fetus facilitate the growth of the ring finger. On the other hand, higher levels of estrogen during the critical development stage effects the length of the index finger. For men, the ratio of the length of the index and the ring finger is the same whereas for women the index finger is usually longer. This ratio predicts hyper masculinization, which increases the likelihood of homosexuality and bisexuality in males as well as females (Manning, 2002).

Testosterone Levels:

Studies indicate that male bisexuals have also been exposed to high levels of testosterone in their prenatal environment. This is in turn leads to higher levels of post natal testosterone levels. These elevated levels of testosterone are associated with male bisexual orientation because they promote sensation-seeking behavior (James, 2004).


INAH Difference: 

The INAH is the interstitial nuclei of the human anterior hypothalamus and it is considered to by sexually dimorphic (Byne et al, 2001). It is the human analogue of SDN-POA or Sexually Dimorphic Nucleus of the Preoptic Area in rats which if low in volume suggest demasculinization. According to Le Vay (1991), the INAH3, which is the third nuclei of the anterior hypothalamus, varies in volume in relation to sexual orientation. His studies indicated that the volume of INAH3 is smaller in homosexual men than heterosexual men and comparable to heterosexual women (Byne et al, 2001).

SCN Difference:

The SCN is the Suprachiasmatic nucleus and it is a region in the brain that controls the body’s temperature, sleep and secretion of hormones (Mbugua, 2003). A study by Swab and Hofman (1990) indicated that the volume of the SCN was much larger in the homosexual males than heterosexual males. Hall and Kimura (1993) studied the differences in sleep pattern among homosexuals and heterosexuals and came to the conclusion that the homosexual males had similar “rise and retire” patterns as heterosexual females. They got up and went to bed earlier than heterosexual males (Mbugua, 2003).

AC Difference:

The AC is the Anterior Commissure, which is one of the two clusters of nerve fibers that connect the two hemispheres of the brain. A study by Allen et al (1992) had shown that the anterior commissure is sexually dimorphic. The anterior commissure in homosexual males is 18% larger than heterosexual males and 34% larger than heterosexual females (Mbugua, 2003).


Byne, W., Tobet, S., Mattiace, L.A., Lasco, M.S., Kemether, E., Edgar, M.A., Morgello, S., Buchsbaum, M.S. & Jones, L.B. (2001) The Interstitial Nuclei of the Human Anterior Hypothalamus: An Investigation of Variation with Sex, Sexual Orientation and HIV Status. Hormones and Behavior 86-92.

Dorner, G., Gotz, F., Rohde, W., Plagemana, A., Lindner, R., Peters, H. & Ghanaati, Z. (2001) Genetic and Epigenetic Effects on Sexual Brain Organization Mediated by Sex Hormones.Neuroendocrinology 403-409.

Hatcher, R.A. (2004) Contraceptive Technology NY: Ardent Media, Inc.

Hyde, J.S. (2005) Biological Substrates of Human Sexuality Washinton D.C: American    Psychological Association.

Jones, R. (2006) Human Reproductive Biology San Diego CA: Academic Press.

Le Vay, S. (1994) The Sexual Brain. MIT Press.

Written by: Nagma V. Clark, Ph.D., L.P.C.C. specializing in sex therapy,  couples therapy & marriage counselingpremarital counselingindividual relationship therapy LGBTQQI couples counseling at Tri-Valley Relationship Therapy, Inc. in the East Bay, in Dublin & Oakland.

Tri-Valley Relationship Therapy, Inc. is a queer friendly & trans-informed practice. LGBTQ counseling is offered to individuals & couples residing all over the East Bay, South Bay & Central Valley. Dr. Clark is especially trained in treating the emotional & mental health issues impacting the LGBTQ community. In her practice, she works with LGBTQ & poly couples.

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