Biological Basis of Sexual Orientation

Sexual orientation is not a choice to be made; biological factors are believed to effect and determine sexual orientation. People often tend to view breaches of normal behavior such as homosexuality as a choice made by homosexuals to go against the norm. Homosexuals are sometimes asked why they are making things hard on themselves, why they can’t try to be attracted to the opposite sex etc. but despite these beliefs, I hold that sexual orientation and gender identity have been scientifically shown to be biologically based, leaving little room for environmental factors and excluding the possibility of personal choice.

During insemination the male, having both an X and a Y chromosome determines that genetic gender of the fetus. If present in the fetus, the Y chromosome that holds a SRY gene that causes the production of H-Y antigen, which in turn causes the primordial gonads to develop into testes instead of ovaries, indicating that female is the default manifestation. After three moths the testes secrete testosterone, which inhibits feminine and enhance masculine qualities including primary and secondary sex characteristics as well as cortical differences (Pinel 292, 293). The fact that genetic gender, and in turn physical appearance is determined by genetic factors is widely agreed upon.

Gender orientation and behavior is determined by the same factors that cause our bodies to be masculine or feminine, both before and after birth; due to certain abnormalities in this process that will be discussed later, sexual orientation and behavior, and even appearance may not match genetic gender. There are two major hypotheses to a biological basis for sexual orientation; ”Two lines of evidence suggest that sexual orientation is influenced by innate processes: neuroendocrine (including neuroanatomical) and genetic studies”(Pillard).

The greatest proof of a biological basis of sexual orientation can be found when congenital adrenal hyperplasia (CAH) also known as Adreno-genital syndrome causes the adrenal glands to secret testosterone in the female body, where it is naturally non-existent. “Several studies have found high rates of masculine behavior in girls with CAH, including preference for masculine toys, increased rough-and-tumble play activity, and other ‘tomboyish’ behavior. Even more importantly, some studies have found elevated rates of homosexual feelings among adult women with CAH compared to control women“(Pillard). Numerous hormone studies conducted on rats and cats have shown a pre-natal and post-natal change in sexual behavior and orientation. “Research has shown that both male and female rats can be reprogrammed to show the sexual behavior of the opposite gender if they are given the hormones that control sexual arousal in the opposite gender”(Alloy at-el. 362).

The genetic studies are comprised mainly of twin studies. “The largest genetic studies to date have been our own, one with men and one with women…In the male study, MZ twins of our gay index subjects had a 52% chance also of being gay, compared to a 22% rate for their DZ twins and an 11% chance for their adoptive brothers. In the female study, MZ twins had a 48% chance of also being lesbian, compared to a 16% rate for DZ twins and a 6% rate for adoptive sisters. Note that similarity in sexual orientation corresponded closely with genetic similarity in both studies”(Pillard). In 1993, a group from NIH where able to prove a genetic transfer of homosexuality on the X chromosome in a study involving over a hundred families of homosexuals.

The facts presented with both the genetic and hormonal hypotheses can account for the reports of ever-present feelings of homosexuality in very young individuals, regardless of environment or choice. Such information should be considered heavily before accusing homosexuals of being uncivilized, and antagonistic, seeing as it is a natural phenomenon occurring biologically without the person having a say in the matter.

References

Alloy, L. B., Jacobson, N. S. & Acocella J. (1999). Abnormal psychology, Current Perspective. Boston: McGraw-Hill College. 8th edition.

Pillard, R. (No date). NPR Letters on the Biological Basis of Homosexuality. (Nov 22, 2001).

Pinel, J. P. J. (2000). Biopsychology. Boston: Allyn and Bacon. 4th Ed.