10.3 Sexual Behavior, Sexuality, and Gender Identity

Physiological Mechanisms of Sexual Behavior and Motivation

Much of what we know about the physiological mechanisms that underlie sexual behavior and motivation comes from animal research. As you’ve learned, the hypothalamus plays an important role in motivated behaviors, and sex is no exception. In fact, lesions to an area of the hypothalamus called the medial preoptic area completely disrupt a male rat’s ability to engage in sexual behavior. Surprisingly, medial preoptic lesions do not change how hard a male rat is willing to work to gain access to a sexually receptive female (Figure 10.14). This suggests that the ability to engage in sexual behavior and the motivation to do so may be mediated by neural systems distinct from one another.

Figure 10.14 A male rat that cannot engage in sexual behavior still seeks receptive females, suggesting that the ability to engage in sexual behavior and the motivation to do so are mediated by different systems in the brain. (credit: Jason Snyder)

Animal research suggests that limbic system structures such as the amygdala and nucleus accumbens are especially important for sexual motivation. Damage to these areas results in a decreased motivation to engage in sexual behavior, while leaving the ability to do so intact (Figure 10.15) (Everett, 1990). Similar dissociations of sexual motivation and sexual ability have also been observed in the female rat (Becker, Rudick, & Jenkins, 2001; Jenkins & Becker, 2001).

Figure 10.15 The medial preoptic area, an area of the hypothalamus, is involved in the ability to engage in sexual behavior, but it does not affect sexual motivation. In contrast, the amygdala and nucleus accumbens are involved in motivation for sexual behavior, but they do not affect the ability to engage in it.

Although human sexual behavior is much more complex than that seen in rats, some parallels between animals and humans can be drawn from this research. The worldwide popularity of drugs used to treat erectile dysfunction (Conrad, 2005) speaks to the fact that sexual motivation and the ability to engage in sexual behavior can also be dissociated in humans. Moreover, disorders that involve abnormal hypothalamic function are often associated with hypogonadism (reduced function of the gonads) and reduced sexual function (e.g., Prader-Willi syndrome). Given the hypothalamus’s role in endocrine function, it is not surprising that hormones secreted by the endocrine system also play important roles in sexual motivation and behavior. For example, many animals show no sign of sexual motivation in the absence of the appropriate combination of sex hormones from their gonads. While this is not the case for humans, there is considerable evidence that sexual motivation for all genders varies as a function of circulating testosterone levels (Bhasin, Enzlin, Coviello, & Basson, 2007; Carter, 1992; Sherwin, 1988).

Kinsey’s Research

Before the late 1940s, access to reliable, empirically-based information on sex was limited. Physicians were considered authorities on all issues related to sex, despite the fact that they had little to no training in these issues, and it is likely that most of what people knew about sex had been learned either through their own experiences or by talking with their peers. Convinced that people would benefit from a more open dialogue on issues related to human sexuality, Dr. Alfred Kinsey of Indiana University initiated large-scale survey research on the topic (Figure 10.16). The results of some of these efforts were published in two books—Sexual Behavior in the Human Male and Sexual Behavior in the Human Female—which were published in 1948 and 1953, respectively (Bullough, 1998).

Figure 10.16 In 1947, Alfred Kinsey established The Kinsey Institute for Research, Sex, Gender and Reproduction at Indiana University, shown here in 2011. The Kinsey Institute has continued as a research site of important psychological studies for decades.

At the time, the Kinsey reports were quite sensational. Never before had the American public seen its private sexual behavior become the focus of scientific scrutiny on such a large scale. The books, which were filled with statistics and scientific lingo, sold remarkably well to the general public, and people began to engage in open conversations about human sexuality. As you might imagine, not everyone was happy that this information was being published. In fact, these books were banned in some countries. Ultimately, the controversy resulted in Kinsey losing funding that he had secured from the Rockefeller Foundation to continue his research efforts (Bancroft, 2004).

Although Kinsey’s research has been widely criticized as being riddled with sampling and statistical errors (Jenkins, 2010), there is little doubt that this research was very influential in shaping future research on human sexual behavior and motivation. Kinsey described a remarkably diverse range of sexual behaviors and experiences reported by the volunteers participating in his research. Behaviors that had once been considered exceedingly rare or problematic were demonstrated to be much more common and innocuous than previously imagined (Bancroft, 2004; Bullough, 1998).

Among the results of Kinsey’s research were the findings that women are as interested and experienced in sex as men, that both males and females masturbate without adverse health consequences, and that relationships and sexual acts between people of the same sex and/or the same gender are fairly common (Bancroft, 2004). Kinsey also developed a continuum known as the Kinsey scale that is still commonly used today to categorize an individual’s sexual orientation, which is an individual’s emotional, romantic, and erotic attractions to other people or no people (Jenkins, 2010).

Masters and Johnson’s Research

In 1966, William Masters and Virginia Johnson published a book detailing the results of their observations of nearly 700 people who agreed to participate in their study of physiological responses during sexual behavior. Unlike Kinsey, who used personal interviews and surveys to collect data, Masters and Johnson observed people having intercourse in a variety of positions, and they observed people masturbating, manually or with the aid of a device. While this was occurring, researchers recorded measurements of physiological variables, such as blood pressure and respiration rate, as well as measurements of sexual arousal, such as vaginal lubrication and penile tumescence (swelling associated with an erection). In total, Masters and Johnson observed nearly 10,000 sexual acts as a part of their research (Hock, 2008).

Based on these observations, Masters and Johnson divided the sexual response cycle into four phases that are fairly similar for most people: excitement, plateau, orgasm, and resolution (Figure 10.17). The excitement phase is the arousal phase of the sexual response cycle, and it is marked by erection of the penis or clitoris and lubrication and expansion of the vaginal canal. During plateau, the vagina swells further and blood flow to the labia minora increases, and the penis becomes fully erect and may exhibit pre-ejaculatory fluid. People experience increases in muscle tone during this time. Orgasm is marked in females by rhythmic contractions of the pelvis and uterus along with increased muscle tension. In males, pelvic contractions are accompanied by a buildup of seminal fluid near the urethra that is ultimately forced out by contractions of genital muscles, (i.e., ejaculation). Resolution is the relatively rapid return to an unaroused state accompanied by a decrease in blood pressure and muscular relaxation. The refractory period is a period of time that follows an orgasm during which an individual is incapable of experiencing another orgasm. The duration of the refractory period can vary dramatically from individual to individual with some refractory periods as short as several minutes and others as long as a day. As people age, their refractory periods tend to span longer periods of time.

Figure 10.17 This graph illustrates the different phases of the sexual response cycle as described by Masters and Johnson.

In addition to the insights that their research provided with regards to the sexual response cycle and the multi-orgasmic potential of females, Masters and Johnson also collected important information about reproductive anatomy. Their research demonstrated the oft-cited statistic of the average size of a flaccid and an erect penis (3 and 6 inches, respectively) as well as dispelling long-held beliefs about relationships between the size of an erect penis and its ability to provide sexual pleasure to a partner. Furthermore, they determined that the vagina is a very elastic structure that can conform to penises of various sizes (Hock, 2008). In a similar manner to Kinsey’s work and other studies, Masters and Johnson’s research has been criticized, built on, and in some cases proven wrong. The research represents an important element of the history of sexual research, and is not viewed as entirely accurate today.

Sexual Orientation

As mentioned earlier, a person’s sexual orientation is their emotional, romantic, and/or erotic attraction toward other people or no people. People may identify as lesbian, gay, bisexual, pansexual, asexual, heterosexual (straight), or other sexualities. Lesbian and gay people are attracted to people of the same gender or sex; bisexual people are attracted to people of their own gender and another gender; pansexual people experience attraction without regard to sex, gender identity or gender expression; asexual people do not experience sexual attraction or have little or no interest in sexual activity; heterosexual (or straight) people experience attraction to people of a different gender or sex. Other descriptive terms may not refer to a sexual attraction, but rather a romantic one. For example, an aromantic person does not experience romantic attraction; this is different from asexuality, which refers to a lack of sexual attraction. And some sexual orientations do not refer to gender in their description (PFLAG, 2021). It is important to acknowledge and understand that many of these orientations exist on on a spectrum, and there may be no specific term to describe how an individual feels.

Some of these terms have been associated in abbreviations such as LGBTQ (lesbian, gay, bisexual, transgender, and queer or questioning). (Queer is an umbrella term that some LGBTQ people use to describe themselves; questioning refers to people in a process of discovery regarding their gender identity or sexual orientation.) In some cases, people and organizations may add "I" to represent intersex people (described below), and "A" for asexual or aromantic people (or sometimes for "allies"), as well as one "P" to describe pansexual people and sometimes another "P" to describe polysexual people. Finally, some people and organizations add a plus sign (+) to represent other possible identities or orientations. Sexuality and gender terminology are constantly changing, and may mean different things to different people; they are not universal, and each individual defines them for themselves (UC Davis LGBTQIA Resource Center 2020).

Figure 10.18 Between 3% and 10% of the adult population identifies as gay or lesbian. (credit: Till Krech)

For many years, people—including scientists—believed that sexual orientation was largely determined by socialization and familial experiences. However, research has consistently demonstrated that the family backgrounds and experiences are very similar among straight people and LGBTQ people (Bell, Weinberg, & Hammersmith, 1981; Ross & Arrindell, 1988).

Genetic and biological mechanisms have also been proposed, and the balance of research evidence suggests that sexual orientation has an underlying biological component. For instance, over the past 25 years, research has demonstrated gene-level contributions to sexual orientation (Bailey & Pillard, 1991; Hamer, Hu, Magnuson, Hu, & Pattatucci, 1993; Rodriguez-Larralde & Paradisi, 2009), with some researchers estimating that genes account for at least half of the variability seen in human sexual orientation (Pillard & Bailey, 1998). Other studies report differences in brain structure and function among those with different sexual orientations (Allen & Gorski, 1992; Byne et al., 2001; Hu et al., 2008; LeVay, 1991; Ponseti et al., 2006; Rahman & Wilson, 2003a; Swaab & Hofman, 1990), and even differences in basic body structure and function have been observed (Hall & Kimura, 1994; Lippa, 2003; Loehlin & McFadden, 2003; McFadden & Champlin, 2000; McFadden & Pasanen, 1998; Rahman & Wilson, 2003b). In aggregate, the data suggest that to a significant extent, sexual orientations are something with which we are born.

Gender Identity

Many people conflate sexual orientation with gender identity because of misconceptions and attitudes that exist about sexuality. In reality, these are two related, but different, aspects of who we are. Gender identity refers to one’s sense of being male, female, neither of these, both of these, or another gender. Generally, our gender identities correspond to our chromosomal and phenotypic sex, but this is not always the case. Transgender people’s gender identity differs from the sex they were assigned at birth. Transgender people may use a range of terms to describe themselves, including abbreviations (e.g. trans) or terms such as non-binary.

When individuals do not feel comfortable identifying with the gender associated with their biological sex, then they may experience gender dysphoria. Gender dysphoria is a diagnostic category in the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) that describes individuals who do not identify as the gender that most people would assume they are. This dysphoria must persist for at least six months and result in significant distress or dysfunction to meet DSM-5 diagnostic criteria. In order for children to be assigned this diagnostic category, they must verbalize their desire to become another gender. It is important to note that not all transgender people experience gender dysphoria, and that its diagnostic categorization is not universally accepted. For example, in 2019, the World Health Organization reclassified “gender identity disorder” as “gender incongruence,” and categorized it under sexual health rather than a mental disorder. However, health and mental health professionals indicate that the presence of the diagnostic category does assist in supporting those who need treatment or help.

Some transgender individuals may undertake a process of transition, in which they move from living in a way that is more aligned with the sex assigned at birth to living in a way that is aligned with their gender identity. Transitioning may take the form of social, legal, or medical aspects of someone's life, but not everyone undertakes any or all types of transition. Social transition may involve the person's presentation, name, pronouns, and relationships. Legal transition can include changing their gender on government or other official documents, changing their legal name, and so on. Some people may undergo a physical or medical transition, in which they change their outward, physical, or sexual characteristics in order for their physical being to better align with their gender identity (UCSF Transgender Care 2019). Not all transgender individuals choose to alter their bodies: many will maintain their original anatomy but may present themselves to society as another gender. This is typically done by adopting the dress, hairstyle, mannerisms, or other characteristics typically assigned to another gender. It is important to note that people who cross-dress, or wear clothing that is traditionally assigned to a gender different from their biological sex, are not necessarily transgender. Cross-dressing is typically a form of self-expression or personal style, and it does not indicate a person's gender identity or that they are transgender (TSER 2021).

Intersex is a general term used to describe people whose sex traits, reproductive anatomy, hormones, or chromosomes are different from the usual two ways human bodies develop. Some intersex traits are recognized at birth, while others are not recognizable until puberty or later in life (interACT 2021). Intersex and transgender are not interchangeable terms; many transgender people have no intersex traits, and many intersex people do not consider themselves transgender.

Those who identify with the sex they were assigned at birth are often referred to as cisgender, utilizing the Latin prefix "cis," which means "on the same side." (The prefix "trans" means "across.") Many cisgender people do not self-identify as such. As with transgender people, the term or usage of cisgender does not indicate a person's sexual orientation, gender, or gender expression (TSER 2021).

Our scientific knowledge and general understanding about gender identity continue to evolve, and people today have more opportunity to explore and openly express different ideas about what gender means than previous generations. Recent studies indicate that the majority of millennials (those ages 18–34) regard gender as a spectrum instead of a strict male/female binary, and that 12% identify as transgender or gender non-conforming. Additionally, more people know others who use gender-neutral pronouns (such as they/them) (Kennedy, 2017). This change in language may indicate that millennials and Generation Z people understand the experience of gender itself differently. As young people lead this change, other changes are emerging in a range of spheres, from public bathroom policies to retail organizations. For example, some retailers are starting to change traditional gender-based marketing of products, such as removing “pink and blue” clothing and toy aisles. Even with these changes, those who exist outside of traditional gender norms face difficult challenges. Even people who vary slightly from traditional norms are often the target of discrimination and violence.

Figure 10.19 Actress Laverne Cox, who is openly transgender, is the first transgender actress to portray a transgender character on a regular television series. She is also an advocate for LGBTQ+ issues outside of her career, such as in this "Ain't I a Woman?" speaking tour. (credit: modification of work by "KOMUnews_Flickr"/Flickr)

Cultural Factors in Sexual Orientation and Gender Identity

Issues related to sexual orientation and gender identity are very much influenced by sociocultural factors. Even the ways in which we define sexual orientation and gender vary from one culture to the next. While in the United States heterosexuality has historically been viewed as the norm (making it a heteronormative society), there are societies that have different attitudes regarding LGBTQ people. In fact, in some instances, periods of exclusively same-sex sexual behavior are socially prescribed as a part of normal development and maturation. For example, in parts of New Guinea, young boys are expected to engage in sexual behavior with other boys for a given period of time because it is believed that doing so is necessary for these boys to become men (Baldwin & Baldwin, 1989).

There has historically been a two-gendered culture in the United States. We have tended to classify an individual as either male or female according to the sex they were assigned at birth, leading the United States to be considered a cisnormative society. However, in some cultures there are additional genders resulting in more than two gender categories. Some of these identities have been core parts of societies for hundreds or thousands of years, and they carry a deep connection for the culture. For example, the Bugis people in Indonesia have for centuries recognized a gender spectrum that includes at least five identities. One of these, the bissu, are important spiritual figures in the society, and play roles in ceremonies such as weddings and coronations (Davies, 2018). Despite this, these groups may still be persecuted or endure stigma, particularly as cultural, religious, or governmental circumstances change in their regions (Ibrahim, 2019). It is important to consider that many prominent non-binary identities from cultures around the world predate contemporary definitions of gender and gender roles.