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Homosexuals and Heterosexual Brain Structure Differences Essay

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Updated: Jul 24th, 2020


There has been an escalation on the debate whether the homosexual trait is an acquired characteristic or a genetic trait. Majority of the human rights activists sympathizing with gay community argue that homosexuality as congenital is a genetically condition and therefore homosexuals should have the right of association and marriage (Bailey, 2003). They based their arguments on the act scientists in the late 20th century discovered that homosexuality is a genetic or hormonal condition. Scientific studies have correlated sexual orientation to almost everything ranging from the parts of the brain, length of the finger, differences in the inner ear, and hormonal differences among others (LeVay, 1991).

A Psychiatric Professor in the University of Columbia by the name Robert Spitzer contended that humans can alter their sexual orientation from homosexual to heterosexual through reparative therapy counselling (Bailey, 2003). Spitzer was an opponent of the ideology which conceived that homosexuality was an inborn characteristic and could not be changed. Some of the most recent studies carried out on homosexuality suggest that it is not a genetic trait but a fashion among the youths (Bailey, 2003). These studies also suggests that homosexuality among women is based on social interaction, presented as an emotional appeal besides physical attraction that may change with time (Kauth, 2000).

Contrary to the increasing evidence relating to inevitability and impossibility in resisting homosexual behaviour, some studies have been extensively publicized as evidence to a genetic element. However, these studies are either badly constructed or not well presented as to their importance (Bailey, 2003). Other Columbian University professors in the psychiatric department studied the most dominant homosexual gene on the brain structure and found out that most studies have procedural flaws. These professors concluded that there is no evidence to support the genetic aspect of homosexuality. They asserted that the appeal of the present genetic explanation of sexual orientation was purely driven by discontent with the current status of psycho-social explanations than from a considerable body of investigational data (Kauth, 2000)…

Despite of the opposition regarding the biological explanation of sexual orientation, some researchers are very optimistic on the correlation of the above two elements and argue that the past studies have been poorly undertaken (Bailey, 2003). The biological evidence to support the difference between the heterosexuals and homosexuals relates to the brain structure, hormonal difference, similarity of homosexuality among twin and the genetic markers in siblings (Kauth, 2000).

Brain structural difference between homosexuals and heterosexuals

Sex differentiation in the structure of the hypothalamus and the closest brain structures have been found to relate to sexual characteristics of humans such as trans-sexuality and sexual orientation ( Ellis & Ames, 1987). Gender differences in the hypothalamus and other limbic structures are believed to be the reason behind sex dissimilarity in reproduction and sexual traits in humans. Scientific researches show that hypothalamus is the basis to human sexual behaviours (Pilgrim & Reisertm, 1992).

The brain of a homosexual contains double the number of cells as compared to the heterosexual counterpart in the suprachiasmastic (SCN) nucleus-an area within the hypothalamus (Swab et.al 1997). The homosexual traits increase the neuronal digits in the brain structure. The growth of the SCN cell numbers among the gay men is believed to be taking place during the early stages of brain development (Ellis & Ames, 1987).

At birth, the adult SCN cells ranges from 13 to 20 percent, however these cells starts to grow very first at the post natal period (Swab et.al 1997). The total number of the SCN cells in the male adult homosexual is the same as those found in the infants (homosexual) in the postnatal period. In the normal circumstance, the SCN cell number declines by about 35 percent from the summit value as a person approaches adult age. Therefore, among the homosexual men the decline of the SCN cells is prevented (Ellis & Ames, 1987).

A growing number of studies explain that the brains of homosexual men are less masculine than those of the straight males. This is well demonstrated in the visual-spatial work performance. Visual-spatial work performance is used to measure the level of brain masculinity and in normal circumstances male heterosexuals usually exceeds the female counterparts (Swab et.al 1997). Besides, the audio waves of the gay males while processing verbal-spatial tasks are more corresponding to the female heterosexuals as compared to heterosexual males (Ellis & Ames, 1987).

A research at the Texas university revealed that the brain of the gay males and females responds straight to the hearing / auditory stimuli as compared to those of the heterosexuals (Ellis & Ames, 1987). When short auditory stimuli are directed to the ear, a unique series of brain waves is generated. These waves vary in their magnitude or timing among the gay and straight persons. Female homosexuals experience brain waves intermediate to the heterosexuals while in the case of males the brain is shifted away from those of the male and the female heterosexuals (Swab et.al 1997).

Scientific studies also show that the male and female brains demonstrate sexual difference/ dimorphism in the pre-optic zone of the hypothalamus. Males have twice as many cell numbers in this area as compared to the females (Schultz et.al 1996). The same study also established that some of the interstitial nuclei of the anterior Hypothalamus are two times larger in males than in females. The same difference is witnessed among the homosexual and heterosexual males (Ellis & Ames, 1987). Post mortem assessment of the brains of the heterosexual males has shown that interstitial nuclei of the anterior Hypothalamus are twice as many in heterosexual females and homosexual males (Ellis & Ames, 1987).

Other studies on the role of hypothalamus on sexual orientation showed that the sexual dimorphic nucleus reduced in volume plus the cell numbers in females at the immediate post natal age. However, the above findings complicated the study of the brain since the number of sexually dimorphic nucleus and the cells within are also influenced by chemical, hormonal and social factors (Schultz et.al 1996). Another subject that complicates the difference between the brain structure of the gays and the straight persons is the issue of sexual experience which also affects the structure of the brain. This has raised eyebrows on whether homosexuality alters the brain structure or brain alters itself as a result of homosexuality (Bailey, 2003).

Genetics and hormonal influence in homosexuality

Sexual orientation is also a result of hormonal balance in the womb thus homosexuality is attributed to the same hormonal influence. Because hormonal level in the womb is not available, substitutes for hormonal influence have been used to determine how hormones influence sexual orientation (Golombok et.al 1993). These proxies comprise of different skeletal structures, ratio of length of a number of phalanges among others. Homosexual males and straight females have less long bone in their limbs than heterosexual males and gay females (Ellis & Ames, 1987).

Studies on family lineage have shown that homosexual men had more gay relatives in their maternal tree than their paternal pedigree, implying the connection to the X chromosome (LeVay, 1991). Researchers found that the association was at the region of Xq 28. The theory of natural selection also supports the possibility of the connection of X chromosomes with homosexuality. Since homosexual males can not reproduce, their perpetuation has been enhanced by the reproducing females with gay genes in them (Golombok et.al 1993).


There has been a lot of publicity on the origin of the homosexual orientation. A great notion has been created linking homosexuality with genetics instead of the environmental influence. Nevertheless, with the examination of the scientific literatures it is not yet very clear on what courses homosexuality. The origin of homosexuality has led to many debates, with some group proposing the biological influence while others opposing. Major difference between the homosexuals especially men and the heterosexual counterparts is attributed to the difference in the particular cell numbers within the hypothalamus. Homosexuality can also be explained in genetic terms. However, there are no substantial evidence to support all of the above scientific theories on the difference and origin of homosexuality.


Bailey, J.M. (2003). The man who would be queen: The science of gender-bending and transsexualism. Washington, D.C: Joseph Henry Press.

Ellis, B.J., & Ames, M.A. (1987). Neuro-hormonal functioning and sexual orientation: A theory of homosexuality-heterosexuality. Psychol Bull, 101:233–258.

Golombok , S., Spencer, A., & Rutter, M. (1983). Children in lesbian and single-parent households: psychosexual and psychiatric appraisal. J Child Psychol Psychiat, 4 pp. 551-572.

Kauth, M.R. (2000). True nature: A theory of sexual attraction. New York: Kluwer Academic/Plenum Publishers.

LeVay, S. (1991). “A difference in hypothalamic structure between heterosexual and homosexual men”, Science journal 253 pp. 1034-1037.

Pilgrim,C., & Reisertm, I. (1992). Differences between male and female brains – developmental mechanisms and implications. Harm Metab Res, 24 pp. 353-359.

Schultz, C., Braak, H., & Braak, E. (1996). A sex difference in neuro-degeneration of the human hypothalamus. Neurosci Lett, 212 pp.103-106.

Swab, D.S., Zhou,J., &Hoffman, M.A. (1997). Sexual differentiation of the human brain. Biomedical review, 7 pp. 17-32.

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