Sexual Development Thesis

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Human sexuality

Orientation and brain development: Continuing controversies

The search for a so-called 'gay gene' that conclusively determines an individual's sexual orientation remains elusive. In fact, very likely it does not exist at all. Current genetic studies indicate that while homosexuality seems to have a clear biological component, there is equally compelling evidence that gayness cannot be entirely attributed to an individual's genetic code alone. Even in pairs of identical twins, often one twin is gay and the other twin is heterosexual. Even the most generous estimates "suggest there is a genetic basis for homosexuality in only 50% of gay men" (Kunzig 2008). Studies of brain development do suggest a strong biological predisposition for homosexuality, but not a singular cause-and-effect pattern.

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"In 2005 a study conducted at the University of Illinois at Chicago and published in Human Genetics indicated there were three different chromosomes that appeared to be linked to sexual orientation" (Graceffo 2008). These chromosomes are influential in determining sexual orientation, but only create a tendency, not a final determination of an individual's orientation. Genetics and environmental factors before and after birth have a complex interplay that can often be difficult to calculate. In Sweden, where researchers conducted the world's largest twin study of 3,826 same-gender twin pairs focusing on sexual orientation, they "concluded that genetics accounted for around 35% of the difference between men in homosexual behavior. The remainder was due to environmental factors after birth and factors operating during fetal development. For women, genetics explained about 18% of the variation in same-sex behavior" (Graceffo 2008).

Thesis on Sexual Development Assignment

Hormonal theories about influences, genetic and environmental, upon the developing fetus have been proposed in various forms, but with no clear and conclusive evidence yet emerging to favor one over the other. So-called 'gay genes' could refer to the genes that control certain hormones, "enzymes that modify hormones, or receptors on the surface of brain cells that bind to those hormones. A mutation in any one of those genes might make a person gay" or various hormonal influences could arise depending on drugs and other eccentric environmental stressors suffered by the mother while pregnant (Kunzig 2008). One theory is that there is "a gene that helps time the release of testosterone from the testes of a male fetus. Testosterone masculinizes the fetal genitalia -- and presumably also the brain. Without it, the fetus stays female. It may be that the brains of gay men don't feel the full effects of testosterone at the right time during fetal development, and so are insufficiently masculinized" (Kunzig 2008).

Studies of women have shown that there is an "increased incidence of non-heterosexual sexual orientations among women with congenital adrenal hyperplasia (CAH), an inherited disorder which causes higher than normal secretion of adrenal androgens," which also suggests a hormonal influence in the opposite direction, namely a masculinizing one (Hall & Schaeff 2008, p.158). However, female studies of the genetic components of sexuality have proven more difficult for researchers to construct, given that women are more apt to identify as sexually 'fluid' than their male heterosexual or homosexual counterparts.

Furthermore, the theory of hormonal influence upon the developing male fetus reflects the fact that the developing male fetus 'begins' as a female, and only becomes male later on, and thus homosexuality is conceptualized as a deviation from the process of masculinzation. This tends to emphasize the importance of the development of male homosexuality vs. lesbianism in understanding orientation. Still, this phenomenon of under-or over-masculinzation of the fetus has also be noted in non-human animals, namely that animals with insufficient masculinizing hormones will exhibit same-sex attraction: "The organization-activation theory posits that the nervous system of a developing fetus responds to prenatal androgens so that, at a postnatal time, it will determine how sexual behavior is manifest" (Diamond 2009). A study by Hall and Schaeff (2008) proposed that as shifts in hormonal levels and fetal stress are often correlated to asymmetry of morphological structures (such as left-handedness, or length of various fingers and limbs) in offspring, gays and lesbians would exhibit more asymmetry than their heterosexual counterparts. "FA refers to small, non-directional deviations from perfect symmetry in the development of bilateral traits" such as finger length (Hall & Schaeff 2008). Hall and Schaeff conducted comparative fluxuating asymmetry (FA) studies upon gay, lesbian, and non-gay and lesbian men and women and found a greater tendency to exhibit FA in gays and lesbians, although not in all of the components they studied.

Other researchers have suggested that having homosexual offspring conveys an evolutionary advantage, as "by interfering with the masculinization of the brain, gay genes might promote feminine behavior traits, making men who carry them kinder, gentler, more nurturing-'less aggressive and psychopathic than the typical male,'" and "compared the family trees of gay men to those of straight men" they found "homosexuals had more gay male relatives on their mother's side than on their father's side-which suggests an X-linked trait" (Kunzig 2008). This means that having a homosexual male offspring can be advantageous to female survival. Having sons who do not find mates could also provide protection for older females after their reproductive years have ended. However, this also fails to explain lesbianism, much like the 'insufficiently masculinized' fetus theory.

There are certain problematic aspects to all of these masculinization theories, not the least of which is that it assumes that femininity and male homosexuality are synonymous. In another example, one popular circulating theory originates in birth order studies. It has been substantiated that younger brothers tend to be disproportionally gay than older brothers, a phenomenon that cannot be attributed to nurture alone, given that the tendency persists even in gay men whose older brothers are deceased. It is though that the older-brother effect could result the mother's immune system reacting against her male, developing offspring. "During her first male pregnancy, the mother's body reacts against some factor related to male fetal development. Her immune system detects male-specific proteins produced by the boy's Y chromosome-perhaps proteins located on the surface of his brain cells -- and deems them foreign invaders. As a result, her body generates antibodies against them. Each successive male pregnancy strengthens this immune response. The next time she's pregnant, the anti-male antibodies cross through the placenta and influence the fetus's brain, interfering with the masculinization of his brain and making him gay" (Kunzig 2009). And once again, this presupposes that gay men are more feminized by definition than heterosexual males.

Virtually all studies of hormonal influence upon gay men and lesbians presuppose a fairly rigid black-and-white definition of sexual orientation -- even though women are far more apt to change their sexual identification throughout their lives, sometimes several times. "A second common implicit assumption is that heterosexuality and homosexuality are mutually exclusive. This assumption contributes to the practice of not examining people who experience attraction to both sexes or treating them as quasi-homosexuals. Furthermore, such studies presuppose that heterosexuality is the norm and needs no explaination for coming into being, unlike homosexuality, although not all heterosexuals are fertile (Kauth 2008, p.2). Many cultures have different methods of conceptualizing sexuality -- in ancient Greece and even in some all-male environments today, male homosexuality is normal in adolescence, and seen as a transition phase, but biologically oriented research assumes that "contemporary sexual categories -- heterosexual / straight, homosexual/gay/lesbian, and bisexual -- represent natural kinds of things -- that is, distinct kinds of people -- rather than nominal kinds of things or socially constructed ways of being (Kauth 2008, p.3).

Additionally, many of the studies supporting homosexuality and biological factors are problematic upon more rigorous scientific analysis. In another FA (fluxuating asymmetry) study correlating maternal stress, fetal exposure to shifting levels of hormones, homosexuality, and left-handedness the authors concluded "that left-handedness is associated with number of older brothers and is sometimes… [END OF PREVIEW] . . . READ MORE

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How to Cite "Sexual Development" Thesis in a Bibliography:

APA Style

Sexual Development.  (2009, September 23).  Retrieved May 27, 2020, from

MLA Format

"Sexual Development."  23 September 2009.  Web.  27 May 2020. <>.

Chicago Style

"Sexual Development."  September 23, 2009.  Accessed May 27, 2020.