Motivation and emotion ❮ 165Sex
Like hunger and thirst, the sex drive involves the hypothalamus, but unlike hunger and
thirst, the sex drive can be aroused by almost anything at any time and is not necessary
for survival of an individual. The sex drive increases at puberty with an increase in male sex
hormones, such as testosterone, and estrogen, as well as small amounts of testosterone, in
females. Secretion of hormones by the hypothalamus stimulates the pituitary gland to secrete
luteinizing hormone (LH) and follicle stimulating hormone (FSH) into the bloodstream,
which stimulate gonads (testes in males and ovaries in females) to secrete testosterone and
estrogen that initiate and maintain arousal. Without these two hormones, sexual desire is
greatly reduced in all species, but testosterone levels in humans seem related to sexual motiva-
tion in both sexes. Humans seem less instinctively driven to have children than other animals.
Many learned cues are involved in this drive. Societies attempt to regulate sexual behavior by
imposing sanctions against incest and encouraging or discouraging masturbation, premarital
intercourse, marital intercourse, extramarital intercourse, and homosexuality.
In the 1940s, when biology professor Alfred Kinsey coordinated preparation for a marriage
course, he found little scientific information available about sex and decided to pursue that
research. He began to interview people about their sex histories, trained other interviewers,
and founded the Institute for Sex Research, now the Kinsey Institute, at Indiana University.
His popular book Sexual Behavior in the Human Male was based on thousands of interviews,
although participants were not randomly selected. A similar book about females followed.
Sexual orientation refers to the direction of an individual’s sexual interest.
Homosexuality is a tendency to direct sexual desire toward another person of the same
sex, and bisexuality is a tendency to direct sexual desire toward people of both sexes.
Heterosexuality is a tendency to direct sexual desire toward people of the opposite sex.
While most people are heterosexual, about 10 percent are estimated to be homosexual.
Women’s sexuality seems to be oriented and reoriented more easily than men’s, but there
is no evidence that conversion therapy reorients sexuality. The biopsychosocial model
supported by research studies attributes the causes of homosexuality to the interaction of
biological, psychological, and sociocultural factors.
Although the sex drive is not necessary for survival of an individual, it is necessary for
survival of the species. According to evolutionary psychologists, mammalian females lack
incentive to mate with many males because they optimize reproductive success by being
selective in mating, choosing a male who has resources to provide for children. On the
other hand, males optimize reproductive success by mating with many females, choosing
young, healthy, fertile females.
Masters and Johnson described a pattern of four stages in the biological sexual
response cycle of typical men and women, including excitement characterized by sexual
arousal; plateau, which involves increased breathing rate, muscle tension, heart rate, and
blood pressure; orgasm, which is characterized by ejaculation in males and pleasurable
sensations induced by rhythmic muscle contractions in both sexes; and resolution as blood
leaves the genitals and sexual arousal lessens, followed in most males by a refractory period
during which another erection or orgasm is not achieved. Females show less tendency for
a refractory period and are often capable of multiple orgasms.social Motivation
Achievement
According to David McClelland, the achievement motive is a desire to meet some
internalized standard of excellence. McClelland used responses to the Thematic