Sexual orientation is all about an individual’s preferred sex partners – the sex of the people one is sexually attracted to. One can be sexually attracted to persons of his or her sex (gay, homosexual or lesbian), people of the opposite sex (straight or heterosexual) or both sexes (bisexual). Numerous psychological and biomedical research studies have attempted to identify one or more causes that account for the variation in sexual orientation (LeVay, 2010). The driving question fuelling these studies has been whether sexual orientation is inborn, learned or acquired due to environmental influences. Many factors have been linked with sexual orientation including gender role behavior in childhood, genetics and fraternal birth order yet no single theory can sufficiently account for the sexual-orientation diversity (Bailey & Zuk, 2009). If sexual orientation was solely linked to a genetic trait, homosexuality would have disappeared ages ago since homosexuals are less likely than heterosexuals to have offspring, each successive generation of homosexuals should have become smaller, until the genes for homosexuality disappear from the gene pool. Yet the prevalence of homosexuality has remained constant. Scientific data points out that sexual orientation primarily results from the interaction of genetic factors, sex hormones, and the developing brain and body cells and these biological processes – prenatal sexual differentiation determines a person’s sexual orientation even prior to birth.
LeVay (2010) has conducted experiments investigating the subject of sexual orientation and summarized a wealth of scientific evidence pointing to the counterintuitive conclusion of the role of these biological processes before way before birth. In 1991, he published his highly-publicized research findings on the differences in the brain structure of the homosexual and heterosexual men. The hypothalamus is part of the brain that regulates the sexual behaviors typically exhibited by males. His studies of the hypothalamus from autopsies of dead men and women revealed some differences between the brains of homosexual and heterosexual individuals. The hypothalamus has a rice-grain-sized group of nerve cells known as INAH3, and it usually bigger in males than in females (Swaab, 2008). In his studies, LeVay (2010) found that INAH3 was significantly smaller in the gay subjects compared to the straight. Matter of fact, the size of INAH3 in the homosexual males and women was the same (LeVay, 2010). This indicates that the sexual orientation of a man may be influenced by the biological processes of brain development. Apart from the differences in structure of the INAH3, gay men have also been demonstrated to be similar to heterosexual females by having a larger anterior commissure than heterosexual men (Swaab, 2008). There are also differences in the sizes of both cerebral hemispheres. Moreover, homosexual males and females exhibit gender-shifts in the way their brains respond to sex pheromones and the functional connectivity of their amygdalas. Another research indicated that heterosexual males and homosexual females have similar brain structures just like do the homosexual men and heterosexual women (Swaab, 2008). LeVay (2010) documents that studies also show that homosexual males use both sides of their brain, a pattern similar to straight women.
The biological influences upon the developing nervous systems could be attributed to the development different sexual orientations. Studies have indicated that prenatal steroid exposure influences sexual orientation (Balthazart, 2011). LeVay (2010) documents that scientists have manipulated sex hormones during prenatal development and resulted in those animals mating preferentially with others of the same sex. Injection of certain hormones into pregnant animals during critical periods of fetal growth could cause the offspring to have homosexual behavior. Some studies have...
References: Bailey, N. W. and Zuk, M. (2009). Same-sex sexual behavior and evolution. Trends in ecology and evolution, 24 (8), 439-446.
Balthazart, J. (2011). Minireview: hormones and human sexual orientation. Endocrinology, 152 (8), 2937-2947.
Bogaert, A. F. and Skroska, M. (2011). Sexual orientation, fraternal birth order, and the maternal immune hypothesis: a review. Frontiers in Neuroendocrinology, 32 (2), 247-254.
Gavrilets, S. and Rice. W. R. (2006). Genetic models of homosexuality: generating testable predictions. Proceedings of the Royal Society of Biological Sciences, 273 (1605), 3031-3038.
Hines, M. (2011). Prenatal endocrine influences on sexual orientation and on sexually differentiated childhood behavior. Frontiers in Neuroendocrinology, 32 (2), 170-182.
LeVay, S. (2010). Gay, straight, and the reason why: the science of sexual orientation. New York: Oxford University Press, Inc.
Rieger, G., Linsemeier, J. A., Gygax, L. and Bailey, J. M. (2008). Sexual orientation and childhood nonconformity: evidence from home videos. Development Psychology, 44(1), 46-58.
Swaab, D. F. (2008). Sexual orientation and its basis in brain structure and function. Proceedings of the National Academy of Sciences of the United States of America, 105 (30), 10273-10274.
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