10.3 Sexual Behavior

Overview of Human Sexual Behavior

Evolutionary Perspective of Sexual Behavior

  • The primary reason for sexual behavior from an evolutionary perspective is the perpetuation of species.

  • However, human sexual behavior involves more than reproduction.

  • This section discusses research on human sexual behavior, motivation, and a concluding discussion on gender and sexual orientation.

Physiological Mechanisms of Sexual Behavior and Motivation

Animal Research Insights

  • Much knowledge about the physiological mechanisms underlying sexual behavior and motivation derives from animal studies.

  • The hypothalamus plays a critical role in motivated behaviors, including sexual behavior.

    • Lesions in the medial preoptic area of the hypothalamus disrupt a male rat's sexual behavior.

    • However, these lesions do not change the level of effort a male rat will exert to access a sexually receptive female.

    • This indicates that the ability to engage in sexual behavior and the motivation for it are mediated by different neural systems.

Important Brain Structures

  • Research suggests that specific limbic system structures are crucial for sexual motivation:

    • Amygdala

    • Nucleus accumbens

  • Damage to these areas lowers sexual motivation while preserving the ability to engage in sexual acts.

  • Similar findings of dissociations between sexual motivation and ability have been observed in female rats.

Implications for Human Sexual Behavior

  • While complexity increases in humans compared to rats, parallels can still be drawn.

  • The popularity of erectile dysfunction drugs reflects that sexual motivation can be dissociated from sexual functioning in humans.

  • Disorders with hypothalamic dysfunction are linked to hypogonadism (reduced gonadal function) and decreased sexual function.

  • Hormones secreted by the endocrine system have significant roles in sexual motivation.

    • Many animals demonstrate no sexual motivation in the absence of a specific blend of sex hormones.

    • In humans, there is substantial evidence that sexual motivation is responsive to circulating testosterone levels (Bhasin et al., 2007; Carter, 1992; Sherwin, 1988).

Kinsey's Research

Historical Context

  • Before the late 1940s, access to empirical information regarding sexuality was limited; physicians lacked proper training in sexual issues.

  • Dr. Alfred Kinsey initiated extensive surveys on human sexuality, aiming to promote open dialogue.

    • Results were published in two seminal books:

    • Sexual Behavior in the Human Male (1948)

    • Sexual Behavior in the Human Female (1953)

Impact of Kinsey’s Work

  • Kinsey's reports were groundbreaking, unveiling the private sexual behaviors of the American public for the first time.

  • His books sold well; public discussions about sexuality increased significantly.

  • Some backlash arose, leading to the banning of his books in various countries and loss of funding for future research.

  • Kinsey's research faced criticism due to sampling errors but has significantly shaped future sexual behavior research.

  • Kinsey highlighted a wide range of sexual behaviors that were more common than previously believed (Bancroft, 2004; Bullough, 1998).

Kinsey Scale

  • Kinsey established a continuum, known as the Kinsey scale, which is utilized to categorize an individual's sexual orientation (Jenkins, 2010).

Masters and Johnson's Research

Methodology

  • In 1966, William Masters and Virginia Johnson studied the physiological responses during sexual behavior among 700 participants.

  • They employed observations of sexual activities rather than surveys, noting physiological variables:

    • Blood pressure

    • Respiration rate

    • Measurements of sexual arousal (e.g., vaginal lubrication, penile tumescence)

  • A total of nearly 10,000 sexual acts were observed (Hock, 2008).

Human Sexual Response Cycle

  • Masters and Johnson defined the human sexual response cycle as consisting of four phases:

    1. Excitement: Characterized by erection in men and lubrication in women.

    2. Plateau: Increased swelling in women and full erection in men; sexual tension heightens.

    3. Orgasm: Women experience rhythmic contractions of the pelvis, and men experience ejaculation.

    4. Resolution: The body returns to an unaroused state; blood pressure decreases and muscles relax.

    • Refractory Period: Post-orgasm period during which men cannot achieve another orgasm; duration varies greatly between individuals and increases with age.

  • Figure 4 illustrates the stages of the sexual response cycle.

Significance of Masters and Johnson’s Research

  • Their findings played a crucial role in understanding sexual dysfunctions related to arousal and orgasm phases.

  • They provided significant anatomical insights, including average sizes of flaccid and erect penises (3 inches and 6 inches respectively).

  • They debunked myths regarding penis size and sexual satisfaction, emphasizing the vagina's elasticity and capacity to accommodate various sizes (Hock, 2008).

Conclusion

  • Understanding human sexual behavior requires integrating insights from animal research, historical studies, and physiological data.