Traditional theories on sexual orientation have argued for biological causation and then focused on finding evidence for this perspective in physiological and psychological studies. While some evidence suggests that biology may play some small role in sexual orientation development, theorists recognize the complex interplay between nature and nurture in the formation of both gender orientation and sexual orientation. After a discussion of research on gender orientation, this article presents a multidisciplinary review of the literature on sexual orientation development. As greater professional and public acceptance of homosexuality and bisexuality emerge in our culture, our awareness of the wide diversity of sexual expression is expanding.
Keywords Androphilia; Bisexual; Gonad; Gynephilia; Heterosexual; Homosexual; Monozygotic Twins; Neurology; Polysexual
The nature versus nurture debate is a central theme in any review of contemporary theories of sexual orientation. It centers on the question of whether a person is born heterosexual or homosexual, or if people develop their sexual orientation through childhood interactions with family members and playmates. In part, the answer to this question depends upon how one approaches the issue. Experts in genetics, neurology, and related biological sciences tend to develop perspectives based upon more innate physical qualities that impact human behavior, while social scientists and psychologists tend to focus on human interactions as a basis of social development. Likewise, some individual scholars view one factor as causal in the development of sexual orientation, while others seek a more integrated theoretical analysis that considers several factors.
Thus, although the balance of this article looks at the various factors individually, it is important to consider how complex and interconnected biology and psychology can be. It is also important to consider how most scholars believe that one's sexual orientation is not a fixed or absolute concept. Rather, they believe that one's sexual orientation can differ over time and according to one's life experiences. Many people, for example, have had both homosexual and heterosexual experiences during their lifetime. And though a person may identify himself or herself as homosexual, heterosexual, or bisexual, even this self-definition may differ from that of an outside observer. In thinking about sexual orientation, therefore, it is important to keep one's mind open to the complexities of the human experience.
One important way to deepen our understanding of sexual orientation is to first expand our knowledge of gender orientation. Traditionally, people in Western cultures have believed that there are two genders: male and female. However, Harbeck (2007) and others have argued that "male" and "female" represent two extreme points on a continuum of gender identity. Their work suggests that this continuum can be described in an integrated theory that takes into account a variety of causal factors like:
- Genetic and other biological predispositions;
- Biological and environmental modifications (hormones, surgery, pollution);
- Developmental experiences (family, peers, social institutions);
- Psychological dispositions/trait factors (temperament, identity, lifespan);
- Social and cultural structures and process (masculinity, femininity, gender, and other learned behaviors); and
- Contextual factors (availability, acceptability).
The World Health Organization, for example, indicates that in approximately one out of every 2,000 births in this country, the baby is born visibly intersex. In these cases, a specialist in sex differentiation is to be consulted in order to begin the process of defining the baby's gender. Similar anomalies can be found in internal sex organs, genetic markers, and other neurological and biological materials. Scholars have referred to these conditions as "intersex" or "disorders of sex development," but those eager to abolish the negative connotations of these labels use the phrase "variations of sex development."
While we know that a significant number of individuals have physiological gender variations, little is known about the number of individuals who have psychological gender variations or identify with a gender variation. Additionally, we now know that environmental pollution plays a role in gonad function as well as in the sex development of various species such as green mussels, frogs, sea bass, roaches, rodents, and swallows (Nagarajappa, 2006; Thomas, 1982; Sitzlar, 2008). Thus, some scholars have begun arguing that gender may be more diverse than previously thought, and may even be becoming more diverse.
Thus, bridging the discussion of gender identity and sexual orientation is the topic of intersexuality or transgender identities. Transgender is an umbrella term that encompasses both transvestites and transsexuals. Transvestites are individuals who wear the clothing normally ascribed to the opposite gender in a given society, and adopt the stereotypical mannerisms associated with that gender. For example, a male transvestite might wear a dress, high heeled shoes, and makeup to adopt the persona of a woman. Individuals may engage in this behavior for emotional satisfaction, sexual arousal, or self-identification. Since their pleasure in wearing clothes of the opposite gender is not necessary linked with sexual orientation, transvestites may be heterosexual, homosexual or bisexual.
Transsexuals, or intersexuals, are individuals who identify with a physical sex different from the one with which they were born and raised. These individuals may have aspects of the male/female duality or they may have been assigned the wrong gender at birth. Transsexuals may choose to ignore these feelings, or they may choose to wear the clothing of and pass as the opposite gender. They may or may not choose to undergo gender reassignment through hormone therapy or surgery. Transsexuals and their advocates are somewhat divided over this last point, as some question the need for hormone therapy and surgery to change the gender of an individual, arguing that this process enhances traditional, distorted views of gender in our society rather than supports gender diversity. In terms of their sexual orientation, transgendered individuals who are attracted to women express gynephilia, while individuals attracted to men express androphilia.
Sexual orientation can be defined in many ways, but the most familiar definitions are also the legal definitions: heterosexuality, homosexuality and bisexuality. Heterosexuality is a sexual attraction to individuals of the opposite gender, while homosexuality is an attraction to individuals of the same gender. Bisexuality is an attraction to both men and women, although some individuals choose to use the words "polysexual" or "pansexual" to avoid bisexuality's implicit assumption that only two genders exist. Asexuality is a lack of sexual interest altogether. In 2013 a Gallup study estimated that the nationwide average of lesbian, gay, bisexual, and transgender individuals in the United States is between 3.5 and 4 percent; estimates in different states range from 1.7 percent (North Dakota) to 10 percent (District of Columbia).
Kauth described sexual orientation as "a biologically based processing bias continuously exploited or challenged by social and cultural conditions," taking into account both sides of the nature versus nurture debate on sexual orientation (2000; LeVay, 2008). Rather than identifying any one factor as a determinant of sexual orientation, such a definition takes in several factors: anatomical brain studies, functional brain studies, genetics/chromosomal, birth order, anatomical, cognitive, developmental, psychoanalytic theories, behaviorism/socialization, sexual experiences, social constructionism, sociocultural, and personal identity.
Anatomical Brain Studies
A number of studies on the anatomical aspects of sexual orientation have focused on the brain. One of the more well-known studies was conducted by LeVay, who argued that the hypothalamus, a part of the underside of the brain which controls hormone production and release, is different in gay and straight men (1991). However LeVay's critics have pointed out that since all of his research was conducted on the brains of individuals who died of AIDS, the results of his study may be invalid. More recently, Savic and Lindstrom suggested that when comparisons are made of left and right brain hemispheres, differences can be seen between heterosexual and homosexual individuals (2008). Similarly, Gorski reported that "the anterior commissure, a bundle of fibers running across the midline of the brain, is larger in women and gay men than heterosexual men" (1978; Odent & Odent, 2006, ¶10).
LeVay has suggested that these differences in brain anatomy may be caused by some prenatal factor (like hormone levels) that affects the fetus' development and, thus, the baby's sexual orientation (2003, 2008). This theory is called the early fixation hypothesis. While studies have failed to find a link between adult's hormone levels and sexual orientation, Dorner and others have argued that prenatal hormone levels may impact the sexual orientation of an individual in later life (1969). Although...
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