Homosexuality is an issue that has sparked tumultuous debate in the United States, and has been brought to the forefront in the last fifty to sixty years. While the legal and social implications has captured the attention of the media, the lingering question of biology remains at the core of the debate. Is it possible that one is born with the characteristic of being homosexual, or is it solely a learned behavior embedded in cultural norms? Researchers since the nineteen-fifties have studied homosexuality in a variety of ways, through genetics, animal behavior, and even birth order. While few have come to a conclusive answer, important progress has been made since the time homosexuality was merely considered a mental disorder that could be cured.
In the March 2004, Health and Medicine Week, research findings from the study of homosexuality in rams was published. Scientists at Oregon Health and Science University School of Medicine had looked at the biological foundations of a male sheep's homosexuality. They used the animals since they had been consistently and thoroughly studied in the past, and provided for a controllable experiment. They studied the oSDN, "an irregularly shaped, densely packed cluster of nerve cells in the hypothalamus of the sheep brain." The hypothalamus is an important part of the brain that regulates body temperature, blood pressure, as well as sexual behavior. Researchers found that the ovine sexually dimorphic nucleus (oSDN) was larger and contained more neurons in male- oriented rams (1). This information is important in several different ways. While it is solely a study on ram behavior, it is believed that homosexuality can be found in many different species, not limited to humans. This is also important because it is the first study to show a relationship between variations in sexual partner preference and brain structure in an animal, which could provide insight into how humans are studied and what should be looked for in humans to unlock the clues of biological causes of homosexuality.
While the rams are an interesting case study, there are also research findings directly relating to humans. The prenatal hormone theory is a provocative explanation of the link between biology and homosexual tendencies. It is based on the idea that hormones can affect a fetus in the womb and can influence brain development. Studies on the neuroendocrine function in homosexuality has shown that while levels of testosterone and estrogen do not typically vary along the lines of homo and heterosexuality, it is one's response mechanisms to these hormones that can play a role in sexual orientation. It is far too basic to attribute homosexuality with a lack of testosterone in males and a lack of estrogen in women, and many studies have negated this idea. However, the central nervous system, which mediates behavior and physiological responses, can be heavily affected by the level of hormones present (2).
It is also believed that birth order has a direct relation to whether or not one is gay. It is possible that a woman's fetus builds up certain antibodies in her first pregnancy, if it is with a male, to male antibodies, and these affect the development of male fetuses in subsequent pregnancies (4). For each older brother, humans are believed to be approximately 33% more likely to be homosexual. In other studies, it has been found that homosexuals are 39% more likely to be left- handed than heterosexuals (3).
Biological study of sexual orientation is not without its flaw. It has been criticized in the scientific world for reducing the subject to simplistic sides of homo and hetero sexual behavior. Simon LeVay is a scientist who has published extensive research on the difference in biology between homo and heterosexuals. In Science magazine in1991, Thomas A. Schoenfeld writes about his work and the faults he finds with LeVays work. Schoenfeld states that biology cannot always be viewed as something that runs against social environment and upbringing, "It is all too common to see early experience, social learning, or choice pitted against biology, but these are false dichotomies" (5). Rather it is the genetic and biological traits that lead to predisposition towards certain behavior characteristics. This approach allows for the biological factors in homosexuality, without limiting the subject to exclusively culture or biology.
All of the research that has surfaced in the past century reflects an interesting pattern of social acceptability of homosexuality. What was once thought of as a negative and controllable defect, is now recognized and embraced by many. While society is far from fully accepting homosexuality as a cultural norm, it has entered the public sphere as a subject worthy of discourse, rather than feared and ignored. It is in this sense that scientists are able to invest more of their time and money into researching homosexuality. In addition, the study of homosexuality itself both in its cultural causes and social effects, such as AIDS, depression, gender roles, marriage laws, has gained world wide attention. The research presented is far from conclusive, and generally generates more questions than it answers. It is uncertain whether or not humans will truly understand the relationship between nature and nurture and the intricate balance of biological or genetic effects and learned cultural behavior. After seeing some of the evidence about biological theories of homosexuality, I am not completely convinced of researchers conclusions. However, I do believe that it presents the interesting point that one cannot consider homosexuality to be a purely psychological or behavioral characteristic, completely disregarding any evidence of biological or genetic influence. After all, in our society, where in some places homosexuals are treated with little respect, and often times, are met with hostility, why would one choose to be gay?
1) "Biology is Behind Homosexuality in Sheep, Study Confirms." Health and Medicine Week (2004): 422. ProQuest. Bryn Mawr College Canaday Library. 25 Sept. 2006 <http://proquest.umi.com/pqdweb?did=588863761&Fm t=3&clientId= 42764&RQT=309&VName=PQD>. 
2) Diamant, Louis. Male and Femal Homosexuality: Psychological Approaches. Cambridge: Hemisphere Corporation, 1987. 129-153.
3) Kristof, Nicholas D. "Gay At Birth?" New York Times (2003): a19. ProQuest. Bryn Mawr College Canaday Library. 24 Sept. 2006 <http://proquest. umi.com /pqdweb ?did=430686171&Fmt=2&clientId=42764&RQT=309&V Name=PQD 
4) Levay, Simon. "The Biology of Sexual Orientation." Homepage of Simon LeVay. Feb. 2006. 25 Sept.2006 <http://members.aol.com/slevay /page22.html#_Brain _stud ies%97function> .
5) Schoenfeld, Thomas A. "Biology and Homosexuality." Science 254 (1991): 630. JStor. Bryn Mawr College Canaday Library. 25 Sept. 2006 <http://links.js tor.org/sici?sici= 0036-8075%2819911101%2 93%3A254%3A503 2%3C630%3ABAH %3E2.0.CO%3B2-9>.