1. Unit 9 Developmental Psychology

2. Module 53 Learning Targets Sexual Development
53-1 Describe how sex hormones influence prenatal and adolescent sexual development, and explain intersex conditions.
53-2 Discuss the factors that reduce the risk of sexually transmitted infections.
Sexual Development
53-3 Discuss the factors that influence teenagers’ sexual behaviors and use of contraceptives.
53-4 Synthesize what research has taught us about sexual orientation.

3. How is biological sex determined?
Biological sex is determined by the twenty-third pair of chromosomes.
Whether male or female, the mother’s contribution to that chromosome pair is an X chromosome.

4. Which chromosomes come from the father?
From the father cam the 1 chromosome out of 46 that is not unisex—either
another
X chromosome, making a female, or a Y chromosome, making a male.

5. How does testosterone influence prenatal development?
About 7 weeks after conception, a single gene on the Y chromosome throws a master switch, which triggers the testes to
develop and to produce testosterone, the main androgen (male hormone) that promotes male sex organ development.

6. What changes occur in the fetal stage?
Later, during the fourth and fifth prenatal months, sex hormones bathe the fetal brain and influence its wiring. Different patterns for males and females develop under the influence
of the male’s greater testosterone and the female’s ovarian hormones (Hines, 2004; Udry, 2000)

7. How do sex hormones influence adolescent sexual development?
A flood of hormones triggers another period of dramatic physical change during adolescence, when boys and girls enter puberty. In this two-year period of rapid sexual maturation, pronounced male-female differences emerge. A variety of changes begin at about age 11 in girls and at about age 12 in boys, though the subtle beginnings of puberty, such as enlarging testes, appear earlier.

8. height Throughout childhood, boys and girls are similar in height.
At puberty, girls surge ahead briefly, but then boys typically overtake them at about age 14.
(Data from Tanner, 1978.)

9. What other changes occur?
During these growth spurts, the primary sex characteristics— the reproductive organs and external genitalia that make sexual reproduction possible—develop dramatically. So do the non-reproductive secondary sex characteristics: girls develop breasts and larger hips, boys’ facial hair begins growing and their voices deepen, and pubic and underarm hair emerges in both girls and boys.

10. 1. What Would You Answer?
Which of the following is a primary sex characteristic that changes at puberty? A. a growth spurt in height, especially for boys B. development of breasts for girls C. full development of external genitalia in both sexes D. facial hair and deepened voice for boys E. appearance of pubic and underarm hair in both sexes

11. What is spermarche?
For boys, puberty’s landmark is the first ejaculation, which often occurs first during sleep (as a “wet dream”). This event, called spermarche, usually happens by about age 14.

12. What is menarche?
In girls, the landmark is the first menstrual period, menarche, usually within a year of age 12½.
(Anderson et al., 2003)
Genes play a major role in predicting when girls experience menarche.
(Perry et al., 2014)
But environment matters, too. Early menarche is more likely following stresses related to father absence, sexual abuse, insecure attachments, or a history of a mother’s smoking during pregnancy.
(Rickard et al., 2014; Shrestha et al., 2011; Sung et al., 2016)

13. Physical changes at puberty.

14. What is intersex?
a condition present at birth due to unusual combinations of male and female chromosomes, hormones, and anatomy; possessing biological sexual characteristics of both sexes
For example, a genetic male may be born with normal male hormones and testes but no penis or a micropenis. Such individuals may struggle with their gender identity.

15. sex and gender challenges
Dramatic improvements in South African track
star Caster Semenya’s race times prompted the International Association
of Athletics Federations to undertake sex testing in 2009.

16. What was the resolution?
Semenya was reported to have physical
characteristics not typically male or female.
She was officially cleared
to continue competing
as a woman.

17. Are adolescents at greater risk for sexually transmitted infections(STIs)?
“Compared with older adults,”
reports the Centers for Disease Control
“sexually active adolescents aged 15–19
years and young adults aged 20–24 years
are at higher risk.”
(CDC, 2016)

18. Can condom use prevent sexually transmitted infections (STIs)?
Condoms offer only limited protection against certain skin-to-skin sexually transmitted infections (STIs), such as herpes, but they do reduce other risks.
(NIH, 2001)
When used by people with an infected partner, condoms also have been 80 percent effective in preventing transmission of HIV (human immunodeficiency virus—the virus that causes AIDS)
(Weller & Davis-Beaty, 2002; WHO, 2003)

19. What is acquired immune deficiency syndrome (AIDS)?
a life-threatening, sexually transmitted infection caused by the human immunodeficiency virus (HIV) AIDS depletes the immune system, leaving the person vulnerable to infections.
Although HIV can be transmitted by other means, such as needle sharing during drug use, its sexual transmission is most common. Half of all humans with HIV (and 1/4th of Americans with HIV) are women.

20. How can AIDS be prevented?
Having one sexual partner means also partnering with that partner’s past partners— any one of whom might have unknowingly transmitted an STI. Hence, the first step in preventing STIs is knowing one’s status, and sharing it with one’s sexual partner.

21. What environmental factors contribute to variations in teen sexuality?
communication about birth control
impulsivity
alcohol use
mass media

22. communication about birth control
Teens who talk freely and openly with their parents and with their partner in an exclusive relationship are more likely to use contraceptives. (Aspy et al., 2007; Milan & Kilmann, 1987)
Many teenagers are uncomfortable discussing
contraception with parents, partners, and peers.

23. impulsivity
If passion overwhelms intentions (either to use contraceptives or to delay having sex), unplanned sexual activity may result in pregnancy. (Ariely & Loewenstein, 2006; MacDonald & Hynie, 2008)
Among sexually active 12- to 17-year-old American girls, 72 percent
said they regretted having had sex. (Reuters, 2000)

24. Those who use alcohol prior to sex are less likely to use condoms.
alcohol use
Among late teens and young adults, most sexual hook-ups (casual encounters outside of a relationship) occur after alcohol use, often without knowing consent. (Fielder et al., 2013; Garcia et al., 2013; Johnson & Che, 2015).
Those who use alcohol prior to sex are less likely to use condoms.
(Kotchick et al., 2001)

25. mass media Perceived peer norms influence teens’ sexual behavior.
The more sexual content adolescents and young adults view or read the more likely they are to perceive their peers as sexually active, to develop sexually permissive attitudes, and to experience early intercourse. (Escobar-Chaves et al., 2005; Kim & Ward, 2012; Parkes et al.,2013)
Perceived peer norms influence teens’ sexual behavior.
(Lyons et al., 2015; van de Bongardt et al., 2015)

26. the hypersexualization of female characters
An analysis of the 60 top-selling video games found 489 characters, 86 percent of whom were males.
The female characters were much more likely than the male characters to
be “hypersexualized”—partially nude or revealingly clothed, with large breasts
and tiny waists.
(Downs & Smith, 2010)

27. What environmental factors contribute to sexual restraint in teens?
high intelligence
religious engagement
father presence
service learning participation

28. What is sexual orientation?
our enduring sexual attraction, usually toward members of our own sex (homosexual orientation) or the other sex (heterosexual orientation); variations include attraction toward both sexes (bisexual orientation)
Today’s psychologists view sexual orientation as neither willfully chosen nor willfully changed.

29. Are there environmental factors that influence sexual orientation?
In a search for possible environmental influences on sexual orientation, Kinsey Institute investigators, interviewed nearly 1000 homosexuals and 500 heterosexuals. The bottom line from a half-century’s theory and research: If there are environmental factors that influence sexual orientation after we’re born, we do not yet know what they are.

30. How many people are exclusively homosexual?
According to more than a dozen
national surveys in Europe and the United States, about 3 or 4 percent of men and 2 percent
of women are homosexual.
(Chandra et al., 2011; Herbenick et al., 2010;
Savin-Williams et al., 2012)
When the U.S. National Center for Health Statistics asked 34,557 Americans about their sexual identity, they found that all but 3.4 percent answered “straight,” with 1.6 percent answering “gay” or “lesbian” and 0.7 percent saying “bisexual”. (Ward et al., 2014)

31. What biological factors influence sexual orientation?
Same-sex sexual behaviors have been observed in several hundred species, including grizzlies, gorillas, monkeys, flamingos, and owls. (Bagemihl, 1999)

32. What role might the hypothalamus play in sexual orientation?
LeVay believes that brain anatomy, specifically the hypothalamus, influences sexual orientation. His hunch seems confirmed by the discovery of a similar hypothalamic difference between the male sheep that do and don’t display same-sex attraction. (Larkin et al., 2002; Roselli et al., 2002, 2004)
Researcher Simon LeVay studied sections of the hypothalamus taken from deceased
heterosexual and homosexual people.

33. Are there genetic influences on sexual orientation?
Evidence indicates that “about a third of variation in sexual orientation is attributable to
genetic influences”.
(Bailey et al., 2016)
A same-sex orientation does have some tendency to
run in families. Identical twins are somewhat more likely than fraternal twins to share a homosexual orientation. (Alanko et al., 2010; Långström et al., 2010)

34. Is the prenatal environment an influence on sexual orientation?
Elevated rates of homosexual orientation in identical and fraternal twins suggest an influence not only of shared genes but also a shared prenatal environment. German researcher Gunter Dorner pioneered research on the influence of prenatal hormones by manipulating a fetal rat’s exposure to male hormones, thereby “inverting” its sexual orientation.

35. What is the older brother effect?
Researcher Ray Blanchard offers these approximate curves depicting a man’s likelihood of homosexuality as a function of the number of biological (not adopted) older brothers he has.

36. Learning Target 53-1 Review
Describe how sex hormones influence prenatal and adolescent sexual development.
About 7 weeks after conception, a gene on the Y chromosome triggers the production of testosterone in males. This promotes male sex organ development.
During the 4th and 5th prenatal months, sex hormones bathe the fetal brain. Prenatal exposure of females to unusually high levels of male hormones can dispose them to more male-typical activity interests later on.

37. Learning Target 53-1 Review cont.
Explain intersex conditions.
Another flood of hormones occurs in puberty, triggering a growth spurt, the development of primary and secondary sex characteristics, and the landmark events of spermarche and menarche.
Intersex individuals are born with intermediate or unusual combinations of male and female chromosomes, hormones, and anatomy.

38. Learning Target 53-2 Review
Discuss the factors that reduce the risk of sexually transmitted infections.
Safer sex practices help prevent sexually transmitted infections (STIs).
Condoms, while offering limited protection against skin-to-skin STIs, are especially effective in preventing transmission of HIV, the virus that causes AIDS.
Knowing one’s STI status and sharing it with one’s sexual partner is key to prevention.

39. Learning Target 53-3 Review
Discuss the factors that influence teenagers’ sexual behaviors and use of contraceptives.
Sexual behaviors and attitudes vary from culture to culture and era to era.
Factors contributing to teen pregnancy include minimal communication about birth control with parents, partners, and peers; impulsivity; alcohol use; and mass media influences.
High intelligence, religious engagement, father presence, and participation in service learning programs have been predictors of teen sexual restraint.

40. Learning Target 53-4 Review
Synthesize what research has taught us about sexual orientation.
Sexual orientation is an enduring sexual attraction, usually toward members of one’s own sex (homosexual orientation) or the other sex (heterosexual orientation). Variations include attraction toward both sexes (bisexual orientation).
Today’s psychologists view sexual orientation as neither willfully chosen nor willfully changed.

41. Learning Target 53-4 Review cont.
Synthesize what research has taught us about sexual orientation.
There is no evidence that environmental influences determine sexual orientation.
Evidence for biological influences includes the presence of same-sex attraction in many animal species, straight-gay differences in body and brain characteristics, higher rates of homosexuality in certain families and in identical twins, the effect of exposure to certain hormones during critical periods of prenatal development, and the fraternal birth-order effect.