第10章感情と動機づけ

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.

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.

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).

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.