UNIT 6: Developmental Psychology
Learning Targets
50-1 Describe how sex hormones influence prenatal and adolescent sexual development, and explain intersex conditions.
50-2 Discuss the factors that reduce the risk of sexually transmitted infections.
50-3 Discuss the factors that influence teenagers’ sexual behaviors and use of contraceptives.
50-4 Synthesize what research has taught us about sexual orientation.
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.
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.
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.
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)
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.
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.)
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.
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
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.
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)
Physical changes at puberty.
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.
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.
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.
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)
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)
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.
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.
What environmental factors contribute �to variations in teen sexuality?
communication about birth control
impulsivity
alcohol use
mass media
communication about birth control
Many teenagers are uncomfortable discussing
contraception with parents, partners, and peers.
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)
impulsivity
Among sexually active 12- to 17-year-old American girls, 72 percent
said they regretted having had sex. (Reuters, 2000)
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)
alcohol use
Those who use alcohol prior to sex are less likely to use condoms.
(Kotchick et al., 2001)
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).
mass media
Perceived peer norms influence teens’ sexual behavior.
(Lyons et al., 2015; van de Bongardt et al., 2015)
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)
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)
What environmental factors contribute �to sexual restraint in teens?
high intelligence
religious engagement
father presence
service learning participation
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.
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.
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)
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)
What role might the hypothalamus play in sexual orientation?
Researcher Simon LeVay studied sections of the hypothalamus taken from deceased
heterosexual and homosexual people.
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)
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)
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.
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.
Learning Target 50-1 Review
Describe how sex hormones influence
prenatal and adolescent
sexual development.
Learning Target 50-1 Review cont.
Explain intersex conditions.
Learning Target 50-2 Review
Discuss the factors that reduce the
risk of sexually transmitted infections.
Learning Target 50-3 Review
Discuss the factors that
influence teenagers’ sexual behaviors
and use of contraceptives.
Learning Target 50-4 Review
Synthesize what research has
taught us about sexual orientation.
Learning Target 50-4 Review cont.
Synthesize what research has
taught us about sexual orientation.