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Summary: Sexual Behavior

Sexual development begins with the sexual differentiation of the fetus in the womb. If no male hormones are present, the fetus will develop as a female, even if it has the male XY genetic pattern.

The events of early sexual develop­ment proceed in a series of stages that produce abnormalities if disrupted. After a baby is born, it initially has no detect­able gender-specific behavioral characteristics.

Experiments show people take their cues from a baby's hair and clothes. These superficial cues can elicit gender stereotyped responses.

Puberty is accompanied by development of secondary sex characteristics such as a deepening voice (in males), breast devel­opment (in females) and develop­ment of pubic hair (in both sexes). Menstruation may be delayed in girls who are very thin and who exercise vigorously, such as ballerinas.

Adult sexual arousal was not systematic­ally studied until the work of Masters and Johnson. They fitted volunteers, some of whom were prostitutes, with measuring devices.

Masters and Johnson came up with a four-stage model of sexual arousal. It received some criticism (as "prematurely enshrined"). A highly regarded sex thera­pist, Helen Singer Kaplan, suggested they had left out the first and most important stage: desire.

Hormones can be influenced by classical conditioning if stimuli predict sex. Novelty increases arousal in both non-humans and humans. As yet, there is no firm evidence of chemical sexual attractants or pheromones in humans, despite many claims.

Deep kissing is common before sex among married couples. Affection­ate mouth-play is common in all human cultures. It may have evolved out of nose-touching, the universal greeting display of mammals.

Drugs boosting dopamine levels, such as cocaine and metham­phetamine, can cause hypersexuality or, in addicts, substitute for sex altogether. Alcohol lessens sexual inhibitions but reduces a male's ability to have sex. An attempt to study the effect of marijuana on sexual arousal was halted after being ridiculed by congressmen.

Most psychologists no longer consider homosexuality a psychological abnormality. Signs of homosexuality are present in many individuals from early life. Researchers have found both genetic and epigenetic influences on homosexuality in humans as well as non-human animals.

Surveys of early childhood experiences show that homosexuality is more common when the opposite-sexed parent is dysfunctional. Same-sex crushes as well as early sexual encounters are correlated with adult homosexuality.

Untangling causal factors is difficult because childhood sexual experiences are more common in families that have other problems as well. Crushes may be due to natural preferences, but might also lead to early "imprinting" experiences that influence adult preferences.

Historically, gay men and lesbians showed somewhat different patterns of behavior. Lesbians are more likely to regard their sexual orientation as volun­tary. In one study, only about 1 in 333 women reported exclusively homosexual attraction, while about 1 in 26 men reported the same. Gay men are more likely to feel their sexual orientation is natural and inevitable.

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