Sexual Orientation Essay

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.

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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 indicated that sexual orientation may be influenced by the levels of prenatal hormones in humans as well (Balthazart, 2011). Fetal hormonal levels influence the development of sex organs. Prenatal hormones influence the organization of the nervous system including the size of the brain structures, the nerve cells and nerve connections.

These neural systems will be activated later after puberty by the sex hormones resulting in behavioral patterns that have been laid earlier.Heterosexual males’ and homosexual females’ erotic attractions to female partners could be because androgen organized their developing brains in a masculine fashion. This has been supported by Hines (2011) who found out that females –, but not males- who had been exposed to high levels of androgens in the phase of fetal development had a higher likelihood of exhibiting homosexual or bisexual behaviors than those other females who had not been exposed. On the other hand, sexual orientation of gay males and straight females could be due to low levels of prenatal androgens.The levels of hormones during pregnancy can be affected by stress; therefore, stress has also been indicated to influence the sexual orientation of a fetus (Hines, 2011). The prenatal stress theory was been described by Gunter Dorner after observations made in rats (LeVay, 2010). In the early development of males, male hormones (androgens) are known to rise during two periods – early in the fetal development, beginning from the 7th week and peaking in the middle trimester and for about six months after birth.Hines (2011) argues that the surge of these male hormones from the 7th week to the second trimester is essential for the development of male-typical nervous system.

Exposure to testosterone in this stage of fetal development may even influence gender identity. Prenatal stress has been demonstrated to change the timing of the prenatal testosterone rise in male rate fetuses, resulting in demasculinization of the brain which results in atypical sexual behavior in adulthood (Swaab, 2008; Hines 2011). However, such studies are difficult to replicate in humans due to ethical issues.Nevertheless, prenatal stress is known to alter the brain development through various routes. Stress triggers the secretion of endorphins, which antagonizes the effects of testosterone on the hypothalamus (Balthazart, 2011). Stress also increases the levels of corticosterone – an adrenal hormone which decreases the release of testosterone (Hines, 2011). Swaab (2008) explains that prolonged prenatal stress will, therefore, result in some changes of the nervous system making the affected males’ anatomy closer to that of females.

The effects of exposures to prenatal hormones and the sexual orientation have demonstrated by a study on the finger length (LeVay, 2010). Patterns of finger length are different in men and women. The index fingers of straight females have a tendency to be about the equal length as their ring fingers, but straight men’s fingers are often considerably longer than their index fingers. Studies have demonstrated that a significant number of lesbians’ fingers follow the typical straight males’ pattern, but gay males have finger length ratios that exaggerate the traight male pattern (ring finger longer than index finger) (Balthazart, 2011). Bailey and Zuk (2009) attribute the increased masculinization of finger length patterns in homosexual females and males to prenatal exposure to excessive levels of androgens. Being left- or right-handed seems to be determined before birth; through the aid of an ultrasound, a fetus can be known if it will be left- or right-handed by checking the thumb-sucking choice and the arm exhibiting greater movement.In a meta-analysis of studies with a total of about 25,000 individuals, gay participants had 39 percent greater likelihood of being left handed than did straight subjects (Bailey & Zuk, 2009).

All these findings suggest that sexual orientation develops way before birth. Another biological variable that influences sexual orientation is an individual’s birth order as a result of the reaction of the mother’s immune system. Gavrilets and Rice (2006) document that males who have older biological brothers borne of the same mother have a higher probability of homosexual orientation.This does not stem from social experiences since growing up with older stepbrothers or adopted brothers does not influence the sexual orientation, but having biological older brothers has an impact even if the brothers were brought up separately.

The hypothesis of this biological theory is that the when the mother gives bears several sons, her immune system sometimes reacts against a protein in the son and then attacks subsequent male fetuses affecting their prenatal sexual differentiation of the brain enough to influence their sexual orientation.The immune reaction is only evoked by a male fetus and grows stronger after each pregnancy with a male fetus – each older brother increases the chances. This hypothesis is supported by the observation that later-born gay men tend to be shorter than average. Bogaert and Skroska (2011) have documented that having an older brother specifically increases the likelihood of homosexuality among right-handed younger brothers but not among the left-handed younger brothers. Using epidemiological statistics, and the values of 2% to 3% for male homosexuality in the general population, it was determined that 14. % to 15. 8% of homosexual men can attribute their same sex orientation to the fraternal birth order effect or about 1 in 7 (Bogaert & Skroska, 2011).

In addition, for males with 3 older brothers, the fraternal birth order effects accounts for half of the causative factors for a homosexual man’s sexual orientation. The fraternal birth order theory has been supported by a report on the Population Attributable Fraction (PAF) which is the percentage of gay males whose sexual orientation can be attributed to their fraternal birth order.Combining two national probability samples, the PAF was computed for 2,256 straight males and 71 homosexual males and found to be 28. 6 percent, but within the statistical limits of the 15.

2% previously determined (Bogaert & Skroska, 2011). The diversity of male populations in which the fraternal birth order effect has been observed makes it the most prevalent factor in the development of gay sexual orientation that has been identified. Gender nonconformity is the degree to which a person differs for the stereotypical characteristics of masculinity or femininity during childhood.A biological predisposition towards homosexuality in some people is indicated by the strong link between adult homosexuality and gender nonconformity during childhood (Rieger, Linsemeier, Gygax & Bailey, 2008).

Pre-gay children are gender nonconformists in many ways including physical aggressiveness, participation in particular games and sports activities, preference for the company of same- or opposite-sex friends, interests and unconscious behaviors. Majority of studies on gender nonconformity had been reliant on the adult’s memories of their childhood i. . the extent to which they enjoyed conventional girls’ and boys’ activities and their femininity or masculinity. Rieger et al.

(2008) study, however, was not reliant on the adult memories of their childhood, since the accuracy can be uncertain. Conversely, the researchers watched home videos of children from infancy to fifteen years of age. Without knowing the sexual orientation of the adults whose childhood videos they watched, the researchers rated the children on gender conforming and nonconformity characteristics.

The findings show that gay male and female adults exhibited significantly more gender nonconformity as children that did heterosexual adults (Rieger et al. 2008). LeVay (2010) suggest that childhood non-conformity occurs due to genetic predisposition, and subsequent interactions with the environmental factors such as peers push the gender non-conforming child to homosexuality. However, so far there is no evidence that modifying peer interactions and other environmental favors affects the likelihood that the gender-nonconforming child will have homosexual sexual orientation. Childhood gender nonconformity is strongly associated with adult homosexual orientation for males and slightly less for females. Apart from the biological processes, several other studies have demonstrated an association between an individual’s phenotype and his or her sexual orientation. Studies on family and twins gives evidence that genetic differences among individuals explains the substantial fraction of the variations in sexual orientation observed in the population (Gavrilets & Rice, 2006).

Approximations of the heritability of homosexuality are variable but range from 30 to 50 percent for both genders (Bailey & Zuk, 2009). In one study, a cohort of 115 homosexual men who had male twins, 52 percent of the identical twin brothers were also homosexuals, as opposed to only 22 percent of fraternal twin brothers and 11 percent of adopted brothers (Gavrilets & Rice, 2006). In a similar analysis of 115 lesbians, 48 percent of identical twin sisters were also lesbians compared to only 16 percent of fraternal twin sisters and 6 percent of adopted sisters (Gavrilets & Rice, 2006).A subsequent study of about 5000 twins who had been systematically recruited from a twin registry confirmed the heritability of sexual orientation for males and not for women. Bailey and Zuk (2009) in a study of families with two gay brothers implied a link between gay sexual orientation and the inheritance of genetic markers on the X chromosome. In conclusion, a number of empirical research findings indicate that specific biological factors may influence sexual orientation.They include differences in the brains of heterosexual and homosexual men, the effect of prenatal hormones and prenatal stress, gender nonconformity, family and twin studies and also finger length patterns.

It is noteworthy, however, to note that some of these findings have been observed only in males and not females, and vice versa. Thus, there may be different psycho biological pathways in the differentiation of sexual orientation by gender.ReferencesBailey, 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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