Answering these easy Psycology questions

I need someone who can save my time answering these 10 questions. Please if you disagree with the budget, or you have not time to do it do not even bet. Thanks.

Questions:

Chapter 13

1. What helps children thrive in difficult family or neighborhood conditions?

2. Should parents marry, risking divorce, or not marry, risking separation?

3. What can be done to stop a bully?

4. How might siblings raised together not share the same family environment?

5. What is the difference between family structure and family function?

Chapter 14

1. What are the first visible signs of puberty?

2. How are girls affected by early puberty?

3. How are boys affected by off-time puberty?

4. What are the problems with adolescent pregnancy?

5. Among sexually active people, why do adolescents have more STIs than adults?

Adolescence

CHAP

T

ER

1

4

CHAPTER

1

5

CHAPTER

1

6

361

W
ould you ride with an unskilled

driver? When my daughter

Bethany had her learner’s permit

,

I tried to convey confidence. Not

until a terrified “Mom! Help!” did I grab the wheel to

avoid hitting a subway kiosk. I should have helped

sooner, but it is hard to know when children become

adults, able to manage without their mothers.

As an adolescent, Bethany was neither child nor

adult. A century ago, puberty began later: Soon after

puberty, many teenage girls married and boys found

work. Depending on customs and family income,

some married or entered the labor force even before

adolescence and some much later. Even today, in

some developing nations, by age 10 some boys are

working and some girls are betrothed.

It has been said that adolescence begins with

biology and ends with society. Today, adolescence

tends to begin earlier biologically and end later

sociologically than it once did. Growth is uneven in

both domains; some aspects of the brain mature at

puberty (emotional excitement) and some much

later (reflection). This led one observer to liken

adolescence to “starting turbo-charged engines

with an unskilled driver” (Dahl, 2004, p. 17).

In the next three chapters (covering ages 11–18),

we begin with biology (the growth increases of

puberty) and move toward society (the roles that

teenagers take on). Understanding adolescence is

more than an intellectual challenge: Those turbo-

charged engines need skilled guidance. Get ready

to grab the wheel.

PA R T V

Adolescence:
Biosocial Development

T
he body changes of early adolescence rival those of infancy in
speed and drama but differ in one crucial way: Adolescents are
aware. Even tiny changes (a blemish, a fingernail) matter when a
person watches his or her own body transforming.

I once overheard a conversation among three teenagers, including my
daughter Rachel. All three were past the awkward years, now becoming
beautiful. They were discussing the imperfections of their bodies. One
spoke of her fat stomach (what stomach? I could not see it), another of her
long neck (hidden by her silky, shoulder-length hair), and my Rachel com-
plained not only about a bent finger but also about her feet!

The reality that children grow into men and women is no shock to any
adult. But for teenagers, heightened self-awareness often triggers surprise
and even horror, joy, or despair. This chapter describes normal biosocial
changes, including growing bodies, emerging sexuality, and maturing brains,
and then two possible problems.

14

36

3

CHAPTER OUTLINE

c Puberty Begins

Hormones

When Will Puberty Start?

Too Early, Too Late

Nutrition

c The Transformations of Puberty

Growing Bigger and Stronger

Sexual Maturation

Brain Development

A CASE TO STUDY:
What Were You Thinking?

ISSUES AND APPLICATIONS:

Calculus at 8 A.M.?

c Possible Problems

Sex Too Soon

Drug Use and Abuse

Learning from Experience

That’s What Friends Are For Jennifer’s

preparations for her prom include pedi-

cure and hairstyle, courtesy of her good

friends Khushbu and Meredith. In every

generation and society the world over,

teenagers help their same-sex friends

prepare for the display rituals involved in

coming of age, but the specifics vary by

cohort and culture. M
IK

E
K

IN

G

/
A

P
P

H
O

T
O

Puberty Begins
Puberty refers to the years of rapid physical growth and sexual maturation that
end childhood, eventually producing a person of adult size, shape, and sexual
potential. The forces of puberty are unleashed by a cascade of hormones that
produce external signs as well as the heightened emotions and sexual desires that
many adolescents experience. The process normally starts between ages 8 and 14.
The biological changes follow a common sequence (see Table 14.1).

For girls, puberty begins with growth of the nipples and initial pubic hair, then
a peak growth spurt, widening of the hips, the first menstrual period (menarche),
final pubic-hair pattern, and full breast development. The current average age of
menarche among well-nourished girls is about 12 years, 8 months (Malina et al.,
2004), although, as you will soon see, variation in timing is quite normal.

For boys, the usual sequence is growth of the testes, initial pubic hair, growth
of the penis, first ejaculation of seminal fluid (spermarche), facial hair, peak
growth spurt, voice deepening, and final pubic-hair growth (Biro et al., 2001;
Herman-Giddens et al., 2001). The modal age of spermarche is just under

13

years, the same as for menarche.

Typically, physical growth and maturation are complete four years after the first
signs appear, although some individuals (usually late developers) add height, and
most (especially early developers) gain more fat and muscle in their late teens or
early 20s.

Hormones

Just described are the visible changes of puberty. An invisible event begins the
entire process, namely a marked increase in certain hormones, which are natural

puberty The time between the first onrush

of hormones and full adult physical devel-

opment. Puberty usually lasts three to five

years. Many more years are required to

achieve psychosocial maturity.

menarche A girl’s first menstrual period,

signaling that she has begun ovulation.

Pregnancy is biologically possible, but ovu-

lation and menstruation are often irregular

for years after menarche.

spermarche A boy’s first ejaculation of

sperm. Erections can occur as early as

infancy, but ejaculation signals sperm pro-

duction. Spermache occurs during sleep

(in a “wet dream”) or via direct stimulation.

hormone An organic chemical substance

that is produced by one body tissue and

conveyed via the bloodstream to another

to affect some physiological function. Vari-

ous hormones influence thoughts, urges,

emotions, and behavior.

364 C H A P T E R 14 ■ Adolescence: Biosocial Development

TABLE 14.1

AT ABOUT THIS TIME: The Sequence of Puberty

Approximate

Girls Average Age*

Boys

Ovaries increase production of

estrogen and progesterone†

Uterus and vagina begin to grow

larger

Breast “bud” stage

Pubic hair begins to appear; weight

spurt begins

Peak height spurt

Peak muscle and organ growth (also,

hips become noticeably wider)

Menarche (first menstrual period)

First ovulation

Voice lowers

Final pubic-hair pattern

Full breast growth

9

91⁄

2

1

0

11

111⁄2

12

121⁄2

13
14

15

16

1

8

Testes increase production of

testosterone†

Testes and scrotum grow larger

Pubic hair begins to appear

Penis growth begins

Spermarche (first ejaculation); weight

spurt begins
Peak height spurt

Peak muscle and organ growth (also,

shoulders become noticeably broader)

Voice lowers; visible facial hair

Final pubic-hair pattern

*Average ages are rough approximations, with many perfectly normal, healthy adolescents as much as three years

ahead of or behind these ages.

†Estrogens and testosterone influence sexual characteristics, including reproduction. Charted here are the in-

creases produced by the gonads (sex glands). The ovaries produce estrogens and the testes produce androgens,

especially testosterone. Adrenal glands produce some of both kinds of hormones (not shown).

chemicals in the bloodstream that affect every body cell. Hormones regulate
hunger, sleep, moods, stress, sexual desire, and much more.

At least 23 hormones affect human growth and maturation, several of which in-
crease markedly in the months before the first signs of puberty. Technically, those
first straggly pubic hairs are “a late event” in the process (Cameron, 2004, p. 116).

You learned in Chapter 8 that the production of many hormones is regulated
deep within the brain, where biochemical signals from the hypothalamus signal
another brain structure, the pituitary. The pituitary produces hormones that
stimulate the adrenal glands, small glands located above the kidneys at either
side of the lower back. The adrenal glands produce more

hormones.

This HPA
axis (hypothalamus-pituitary-adrenal) is the route followed by hormones that reg-
ulate stress, growth, sleep, appetite, and sexual excitement as well as puberty (see
Figure 14.1).

Sex Hormones

At adolescence, the pituitary also activates the gonads, or sex glands (ovaries in
females; testes, or testicles, in males). One hormone in particular, GnRH
(gonadotropin-releasing hormone), causes the gonads to enlarge and dramatically
increase their production of sex hormones, chiefly estradiol in girls and testos-
terone in boys. These hormones affect the entire body shape and function.

Estrogens (including estradiol) are considered female hormones, and andro-
gens (including testosterone) are considered male hormones, but the adrenal
glands produce both in everyone. Unlike those produced by the adrenal glands,
the hormones produced by the gonads are sex-specific. After a decrease during
childhood, testosterone skyrockets in boys—up to 20 times the pre-pubescent
level (Roche & Sun, 2003). For girls, estradiol increases to about 8 times the
childhood level (Malina et al., 2004).

The activated gonads eventually produce gametes (sperm and ova), whose mat-
uration and release are heralded by spermarche or menarche, signifying that the
young person has the biological potential to become a parent. (Peak fertility comes
years later, but ovulation and ejaculation signify the possibility of pregnancy.)

Sudden Emotions

Remember that the HPA axis leads from brain to body to behavior. The behaviors
that adolescents are best known for are emotional and sexual—moodiness and
lust that overtake the formerly predictable, seemingly asexual, child. Hormones
influence this. To be specific:

■ Testosterone at high or accelerating levels stimulates rapid arousal of emo-
tions, especially anger.

■ Hormonal bursts lead to quick emotional extremes (despair, ecstasy).
■ For many boys, the increase in androgens causes sexual thoughts and a desire

to masturbate.
■ For many girls, the fluctuating estrogens increase happiness in the middle of

the menstrual cycle (at ovulation) and sadness or anger at the end.

pituitary A gland in the brain that responds

to a signal from the hypothalamus by pro-

ducing many hormones, including those

that regulate growth and control other

glands, among them the adrenal and sex

glands.

adrenal glands Two glands, located above

the kidneys, that produce hormones

(including the “stress hormones” epineph-

rine [adrenaline] and norepinephrine).

HPA axis The hypothalamus-pituitary-adrenal

axis, a route followed by many kinds of

hormones to trigger the changes of

puberty and to regulate stress, growth,

sleep, appetite, sexual excitement, and

various other bodily changes.

gonads The paired sex glands (ovaries in

females, testicles in males). The gonads

produce hormones and gametes.

estradiol A sex hormone, considered the

chief estrogen. Females produce more

estradiol than males do.

testosterone A sex hormone, the best

known of the androgens (male hormones);

secreted in far greater amounts by males

than by females.

Puberty Begins 365

Hypothalamus
Hormones

Pituitary Adrenal glands

HPA axis

Growth spurt

Primary sex characteristics

Secondary sex characteristics

Gonads

(ovaries or

testicles)

Increase

in many

hormones,

including

testosterone

and estrogen

Growth

hormone

(GH)

Gonadotropin-
releasinghormone < >

FIGURE 14.1

Biological Sequence of Puberty Puberty

begins with a hormonal signal from the hypo-

thalamus to the pituitary gland. The pituitary,

in turn, signals the adrenal glands and the

ovaries or testes to produce more of their

hormones.

Although adults experience these same hormonal effects, during puberty hor-
mones are more erratic and powerful, less familiar and controllable, and they come
in bursts, not a steady flow (Cameron, 2004; Susman & Rogol, 2004). Further,
when adults experience hormonal changes (especially during pregnancy and birth),
cognitive maturation helps control the effects.

Hormones sometimes make adolescents seek sexual activity and sometimes
arouse excitement, pleasure, and frustration. But human thoughts and emotions
not only result from physiological and neurological processes—they also cause
them (Damasio, 2003). An adolescent’s reactions to how other people respond to
breasts, beards, and body shapes evoke emotions that, in turn, affect hormones—
just as hormones affect emotions—with the particular emotional reaction not di-
rectly tied to specific hormones (Alsaker & Flammer, 2006).

This is clearer with an example. Suppose a 13-year-old girl hears a lewd remark,
provoked by her developing breasts in a too-tight shirt. She might feel a surge of
anger, fear, or embarrassment, but it is the remark, not her hormones, that arouses
her. Her emotions might cause a rise in stress hormones and sexual ones as well.

Evidence for a complex link between hormones and emotions came from a
study of 56 adolescents who were late to begin puberty (Schwab et al., 2001).
Doctors prescribed treatment every 3 months: injections of hormones (low,
medium, or high doses of testosterone or an estrogen) alternating with injections
of a placebo (which had no hormones). Gradually, the outward signs of puberty
appeared.

Every three months, other measures were taken: the level of sex hormones
(measured via blood tests) and the emotions felt by the adolescents (via a ques-
tionnaire). An emotional shift occurred, indirectly caused by the hormones. Over
the two years, moods became more positive, not directly because of hormones in
the body but presumably because the teenagers were happy with their physical
development.

Surprisingly, happiness and sadness did not correlate with shifting hormonal
levels. The teenagers did not seem emotionally aroused by the level of hormones
in their systems—with one exception. Both boys and girls reported more anger

when they had had moderate amounts of hormones, not the highest
levels of testosterone (for the boys) or estrogens (for the girls) (Sus-
man & Rogol, 2004).

When Will Puberty Start?

Hormones cascading into the bloodstream always trigger the changes
of puberty. However, age of onset varies. Age 11 or 12 is most likely,
but a rise in hormones is still considered normal in those as young as
age 8 or as old as age 14. This variation is not random but is affected
by genes, body fat, and stress (Ellis, 2004).

Genes

The genes on the sex chromosomes markedly affect the onset of
puberty. Among well-nourished children, at least one girl (XX) in a
fifth-grade class has already developed breasts and begun to grow to
adult height. Not until age 18 or so has her last male classmate (XY)
sprouted facial hair and grown to man-size.

On average, girls are about two years ahead of boys in height.
However, hormonally and sexually girls are ahead by only a few
months, not by years (Malina et al., 2004), because the height spurt
occurs about midway in female pubescence (before menarche) but
is a late event (after spermarche) for boys.

Especially for Parents of Teenagers

Why would parents blame adolescent moods

on hormones?

366 C H A P T E R 14 ■ Adolescence: Biosocial Development

S

K

J
O

LD
P

H
O

T
O

G
R

A
P
H

S
/

T
H

E

I
M

A
G

E
W

O
R

K
S

Both 12 The ancestors of these two

Minnesota 12-year-olds came from northern

Europe and West Africa. Their genes have

dictated some differences between them,

including the timing of puberty, but these

differences are irrelevant to their friendship.

Genes influence the timing of puberty in other ways as well. Monozygotic twins
are more alike than same-sex dizygotic twins (Roche & Sun, 2003). Ethnic varia-
tions in pubertal timing are partly genetic (see Figure 14.2). In the United States,
African Americans tend to reach puberty earlier than do European Americans or
Hispanic Americans (see Figure 14.3). Asian Americans average several months
later (Herman-Giddens et al., 2001; Malina et al., 2004).

Ages in Europe also vary, probably for genetic reasons. Northern European girls
are said to reach menarche at 13 years, 4 months, on average, and southern Euro-
pean girls do so at an average age of 12 years, 5 months (Alsaker & Flammer, 2006).

Body Fat

The genetic differences noted above are apparent only when every child is well
fed. Puberty starts earlier in the cities of India and China than in the remote
villages, probably because rural children are often hungry. In Poland and Greece,
urban–rural differences are shown in that puberty occurs a year earlier in Warsaw

Puberty Begins 36

7

11.8

11.6

12

12.2

12.4

12.6

12.8

13Age
(years)

Median Age of Menarche, by U.S. Ethnic Group

Median age at menarche

African American girls

Asian American girls

Mexican American girls

European American girls

Source: Chumlea et al.,

2003.

FIGURE 14.2

Usually by Age 13 The median age of

menarche (when half the girls have begun to

menstruate) differs somewhat among ethnic

groups in the United

States.

2
0
4
6
8

10

12

14Age
(years)

Timing of Menarche, by U.S. Ethnic Group

Timing of menarche

African American girls
Mexican American girls
European American girls

Earliest 10 percent Latest 10 percent

Source: Chumlea et al., 2003.

FIGURE 14.3

Almost Always by Age 14 This graph shows

the age of menarche for the earliest and lat-

est 10 percent of girls in three U.S. ethnic

groups. Note that, especially for the slow de-

velopers (those in the 90th percentile), ethnic

differences are very small.

Observation Quiz (see answer, page 368):

At first glance, ethnic differences seem

dramatic in Figure 14.2 but minimal in Figure

14.3. Why is this first glance deceptive?

than in Polish villages and 3 months earlier in Athens than in the rest of Greece
(Malina et. al, 2004).

Worldwide, stocky individuals begin puberty before those with thinner builds.
Some believe that hormones in the food supply cause earlier puberty, and others
believe that hormones cause weight gain rather than vice versa (Ellison,

2002).

Neither of these theories has been proven. Nonetheless, it is apparent that
menarche occurs later in girls who have little body fat (because they are under-
nourished or overexercised) and that most girls weigh at least 100 pounds (

45

kilograms) before their first period (Berkey et al., 2000).

In both sexes, chronic malnutrition delays puberty. This probably explains why
puberty did not occur until about age 17 in the sixteenth century. In the early
twentieth century, menarche occurred on average at age 15 in Norway, Sweden,
and Finland (Tanner, 1990), compared with age 12 or 13 today.

These are examples of the secular trend, a term that refers to earlier and
greater growth of children over the last two centuries as nutrition and medical care
have improved. Over the twentieth century, each generation experienced puberty
a few months earlier than did the preceding one (Alsaker & Flammer, 2006).

The secular trend seems to have stopped in developed nations (Roche & Sun,
2003). This has a specific application. Probably, after considering the gender dif-
ferential (men are on average about 5 inches taller than women), today’s young
adults will be about as tall as their parents unless chronic illness or undernourish-
ment as a child is a factor.

Stress

The production of many hormones is directly connected to stressful experiences
via the HPA axis (Sanchez et al., 2001). Because stress affects reproductive
hormones, many young women experience irregular menstruation when they leave
home for college or take trips abroad, and many couples find it easier to become
pregnant on vacation than when they are working.

Stress affects pubertal hormones as well, paradoxically by increasing (not
decreasing) them. Puberty tends to arrive earlier if a child’s parents are sick,
addicted, or divorced, or when the neighborhood is violent and impoverished
(Herman-Giddens et al., 2001; Hulanicka, 1999; Moffitt et al., 1992).

Before concluding that stress causes early puberty, however, you need to know
that not every scientist agrees that this is the case (Ellis, 2004). Since puberty is
partly genetic, it could be that adults who reached puberty early are likely to marry
and become parents young, which might make them more likely to be under-
educated, depressed, angry, and divorced. Consequently, their children would live
with conflicted, divorce-prone parents and thus experience early puberty not be-
cause of the conflict but because of their genes.

However, at least one careful longitudinal study of 87 girls did find a direct link
between stress and puberty (Ellis & Garber, 2000). Those girls who fought with
their mothers and who lived with an unrelated man (stepfather or mother’s
boyfriend) also had earlier puberty, even when genes and weight were taken into
account. The longer a girl lived with a man who was not her father, the earlier she
reached menarche.

Animal research also implicates stress. Mice, rats, and opossums under stress
become pregnant at younger ages than do other members of their species
(Warshofsky, 1999). Further, female mice reach puberty earlier if, as infants, they
were raised with unrelated adult male mice (Caretta et al., 1995).

The evidence for the stress hypothesis is sufficiently strong to wonder why
stress would trigger puberty. Logically, conflicted or stepfather families would
benefit if the opposite happened—if teenagers looked and acted like children and

secular trend A term that refers to the ear-

lier and greater growth of children due to

improved nutrition and medical care over

the last two centuries.

368 C H A P T E R 14 ■ Adolescence: Biosocial Development

➤Response for Parents of Teenagers

(from page 366): If something causes

adolescents to shout “I hate you,” to slam

doors, or to cry inconsolably, parents may

decide that hormones are the problem.

This makes it easy to disclaim personal

responsibility for the teenager’s anger.

However, research on stress and hormones

suggests that this comforting attribution is

too simplistic.

➤Answer to Observation Quiz (from

page 367): The major reason is the vertical

axis, which covers a total of 11⁄2 years in

Figure 14.2 and 14 years in Figure 14.3. In

addition, the outliers (top and bottom 10

percent) in Figure 14.2 show less variation

than the median in Figure 14.3

could not reproduce. But that does not happen. One explanation comes from evo-
lutionary theory:

Over the course of our natural selective history, ancestral females growing up
in adverse family environments may have reliably increased their reproductive
success by accelerating physical maturation and beginning sexual activity and
reproduction at a relatively early age.

[Ellis & Garber, 2000, p. 486]

In other words, in past stressful times, adolescent parents could replace them-
selves before they died, passing on family genes. Natural selection favored genes
that adapted to wars, famine, and sickness by initiating early puberty. Currently,
early sexuality and reproduction lead to social disruption, not social survival, but
the human genome has been shaped over millennia. Although many explanations
are possible for the link between stress and early puberty, the evidence continues
to find the correlation (Romans et al., 2003).

Too Early, Too Late

For most adolescents, only one aspect of timing is important: their friends’ sched-
ules. No one wants to be early or late, with early particularly hard for girls, late for
boys. Why?

Think about the early-maturing girl. If she has visible breasts in the fifth grade,
the boys tease her; they are awed by the sexual creature in their midst. She must
fit her womanly body into a school chair designed for younger children, and she
may hide her breasts in large T-shirts and bulky sweaters and refuse to undress
for gym. Early-maturing girls tend to have lower self-esteem, more depression,
and poorer body image than later-maturing girls (Compian et al, 2004; Mendle
et al., 2007).

Some early-maturing girls have boyfriends several years older, which adds status
but more complications, including drug and alcohol use (Weichold et al., 2003).
They are “isolated from their on-time-maturing peers [and] tend to associate with
older adolescents. This increases their emotional distress” (Ge et al., 2003, p. 437).

Cohort is crucial for boys. Early-maturing boys who were born around 1930 often
became leaders in high school and beyond (M. C. Jones, 1965). Early-maturing
boys also tend to be more successful as adults (Taga et al., 2006). However, if
early-maturing boys live in stressful urban neighborhoods (with poverty, drugs, and
violence) and if their parents are unusually strict, they are likely to befriend
law-breaking, somewhat older boys (Ge et al., 2002). For both sexes, early puberty
currently correlates with early romance, sex, and parenthood, which lead to later
depression and other psychosocial problems (B. Brown, 2004; Siebenbruner et al.,
2007).

Late puberty may also be difficult, especially for boys. Ethnic differences in age
of puberty can add to ethnic tensions in high school. Remember that Asian Amer-
ican youth tend to experience later puberty. In one multiethnic high school, the
“quiet Asian boys” were teased because they were shorter and thinner than their
classmates, much to their dismay (Lei, 2003). This is a likely explanation for the
greater peer discrimination experienced by the Chinese youth in another school
(Greene et al., 2006; see Research Design). In a third multiethnic high school,
Samoan students were small numerically but advanced in puberty. As a result,
they were respected by their classmates of all backgrounds, able to moderate ten-
sions between African and Mexican Americans (Staiger, 2006). Interactions
among students in all three of these schools illustrate the importance of physical
appearance for many adolescents. Puberty can enhance or diminish a person’s
status with peers, depending partly on when it occurs.

Especially for Parents Worried About

Early Puberty Suppose your cousin’s 9-year-

old daughter has just had her first period, and

your cousin blames hormones in the food

supply for this “precocious” puberty. Should

you change your young daughter’s diet?

Puberty Begins 369

Research Design
Scientists: Melissa L. Greene, Niobe

Way, and Kerstin Pahl.

Publication: Developmental Psychology

(2006).

Participants: A total of 136 high school

students at a multiethnic high school in

New York City.

Design: Six times over the four years of

high school, students answered ques-

tionnaires about discrimination, ethnic

identity, depression, and self-esteem.

Major conclusion: For all four ethnic

groups (Black, Asian American, Puerto

Rican, and other Latino), perceived peer

discrimination had a greater impact on

self-esteem than did perceived adult

discrimination. The Asian Americans

averaged higher levels of perceived

discrimination than any other group;

the Black Americans were second.

Comment: This study is a welcome step

toward multifaceted, multiethnic, longi-

tudinal research on adolescents. More is

needed to provide, as the researchers

write, “a thorough examination of the

impact of experiences of discrimination

on well-being.”

Nutrition

All the changes of puberty depend on nutrition, yet many adolescents are deficient
in necessary vitamins or minerals. A five-year longitudinal study found that eating
habits get worse throughout the teen years (N. I. Larson et al., 2006).

Diet Deficiencies

Fewer than half of all teenagers consume the recommended daily dose of 15 mil-
ligrams of iron, found in green vegetables, eggs, and meat—all spurned in favor of
chips, sweets, and fast food. Because menstruation depletes the body of iron,
more adolescent girls are anemic than those in any other age or gender group
(Belamarich & Ayoob, 2001). Adolescent boys also suffer from anemia, especially
if they engage in physical labor or competitive sports, because muscles need iron
(Blum & Nelson-Mmari, 2004).

Calcium is another example. About half of adult bone mass is acquired from
ages 10 to 20, yet few adolescents consume enough calcium to prevent osteoporo-
sis, which causes disability, injury, and death among older adults. Milk drinking
has declined; most North American children once drank at least a quart a day. In
2005 among ninth-graders, only 14 percent of U.S. girls and 24 percent of boys
drank even 24 ounces (3⁄4 liter) of milk a day. By twelfth grade, the rates were 10
and 18 percent (MMWR, June 9, 2006).

Nutritional deficiencies result from the choices young adolescents are allowed,
even enticed, to make. There is a direct link between deficient diets and the
availability of vending machines in schools (Cullen & Zakeri, 2004). Fast-food
establishments cluster around high schools, if zoning permits, and many such
places are hangouts for teenagers.

One reason is price. At least experimentally, 10- to 14-year-olds choose healthy
foods if they are cheaper than unhealthy ones (Epstein et al., 2006), but milk and
fruit juice are more expensive than fruit punch or soda, and McDonald’s charges
more for a salad than a hamburger. Only 20 percent of high school students in
2005 ate five or more servings of fruits or vegetables a day (MMWR, June 9,
2006), worse than a decade ago (29 percent) (MMWR, August 14, 1998).

Body Image

Another reason for poor nutrition is anxiety about body image—that is, a person’s
idea of how his or her body looks. Since puberty alters the entire body, it is almost
impossible for teenagers to welcome every change. Unfortunately, their percep-
tions are distorted; they tend to focus on and exaggerate the problems.

Girls diet because they want to be thinner, and they notice that boys tend to
date thinner girls (Halpern et al., 2005). Many boys want to look taller and
stronger, a concern that increases from ages 12 to 17 (D. Jones & Crawford,
2005). Children of ethnic minorities are bombarded with faces and bodies in films
and advertisements that have features and shapes quite different from those their
genes will produce.

Many stressed teenagers eat erratically or ingest drugs (especially diet pills or
steroids), hoping to lose weight (the girls) or to gain muscles (the boys). Their
obsession can backfire. Some adolescents give up, becoming flabby and fat
instead of strong and thin. About 12 percent of all U.S. teenagers are overweight
according to international standards, more than in any other nation that has
been studied (Lissau et al., 2004). As bad as that is, almost two-thirds (62 per-
cent) of all U.S. adolescent girls and almost a third of the boys are trying to lose
weight, according to a nationwide U.S. survey of 14,000 high school students
(MMWR, June 9, 2006).

body image A person’s idea of how his or

her body looks.

370 C H A P T E R 14 ■ Adolescence: Biosocial Development

➤Response for Parents Worried About

Early Puberty (from page 369): Probably

not. If she is overweight, her diet should

change, but the hormone hypothesis is

speculative. Genes are the main factor; she

shares only 1/8 of her genes with her cousin.

Some social scientists believe that the epidemic of obesity
(discussed in detail in Chapters 11 and 20) can be a direct result
of the wish to be thinner (e.g., P. F. Campos, 2004). Adolescent
obesity increases the risk of premature death, at least for women,
partly because overweight women are more likely to be suicidal
(van Dam et al., 2006). Girls are more likely than boys to be
obsessed with weight, an obsession that can lead to extreme
dieting. Eating disorders typically begin in early adolescence and
grow worse by young adulthood. (Anorexia and bulimia nervosa
are discussed in detail in Chapter 17.)

S U M M I N G U P

Puberty usually begins between ages 8 and 14 (typically at about 11)

in response to hormones deep within the brain, from the hypothala-

mus to the pituitary to the adrenal and sex glands. Hormones affect the emotions as

well as the physique, with adolescent outbursts caused by the combination of hormones

and sociocultural reactions to visible body changes. Many factors, including genes, body

fat, and probably stress, affect when puberty begins. Generally, puberty begins earlier

than in past centuries, although this aspect of the secular trend is stopping. Early

puberty (especially for girls) or late puberty (especially for boys) is problematic. All

adolescents are vulnerable to poor nutrition and body image worries.
■

The Transformations of Puberty
Every body part changes during puberty. For simplicity, the transformation from a
child into an adult is traditionally divided into two parts: growth and sexuality. We
will use that division here and add a third aspect, the transformation of the brain.
In actuality, however, every aspect of pubescent growth involves all three.

For example, suppose a young adolescent suddenly notices darker and thicker
hair growing on his or her legs, which everyone experiences as part of puberty. If
the child is a girl, she will probably shave her legs, feeling quite womanly when
she nicks herself before developing a light touch or buying a depilatory. If the child
is a boy, he may search for new hair on his upper lip, his chin, and his chest, to
mark his manhood. Thus a sexless sign of maturity (hair on the legs) is seen as sex-
ual, and thoughts and memories stored in the brain affect the adolescent’s proud
reaction.

Growing Bigger and Stronger

The first set of changes during puberty is the growth spurt—a sudden, uneven
jump in the size of almost every part of the body, turning children into adults.
Growth proceeds from the extremities to the core (the opposite of the proximal-
distal growth of the prenatal and infant periods). Thus, fingers and toes lengthen
before hands and feet; hands and feet before arms and legs; arms and legs before
the torso.

Because the torso is the last body part to grow, many pubescent children are
temporarily big-footed, long-legged, and short-waisted, appearing to be “all legs and
arms” (Hofmann, 1997, p. 12). If young teenagers complain that their jeans don’t
fit, they are probably correct, even if those same jeans fit their shorter-waisted,
thinner body when their parents paid for them a month before. (Parents had
advance warning when they had to buy shoes for their children in adult shoe sizes.)

growth spurt The relatively sudden and

rapid physical growth that occurs during

puberty. Each body part increases in size

on a schedule: Weight usually precedes

height, and the limbs precede the torso.

The Transformation of Puberty 371

Does He Like What He Sees? During ado-

lescence, all the facial features do not de-

velop at the same rate, and the hair often

becomes less manageable. If B. T. here is typ-

ical, he is not pleased with the appearance of

his nose, lips, ears, or hair.

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Sequence: Weight, Height, Muscles

As the bones lengthen and harden (visible on an X-ray) and the growth spurt
begins, children eat more and gain weight. Exactly when, where, and how much
weight is gained depends on heredity, diet, exercise, and gender, with girls gaining
much more fat than boys. By age 17, the average girl has twice as much fat as her
male classmate, whose increased weight is mostly muscle (Roche & Sun, 2003).

A height spurt follows the weight spurt, burning up some fat and redistributing
the rest. A year or two after the height spurt, the muscle spurt occurs. Thus, the
pudginess and clumsiness of early puberty is usually gone by late adolescence. On
average, a boy’s arm muscles are twice as strong at age 18 than at age 8, enabling
him to throw a ball four times as far (Malina et al., 2004). Arm muscles show the
most sex difference (see Figure 14.4); other muscles are more gender-neutral. For
instance, running speed increases over adolescence in both sexes, with boys not
much faster than girls (see Figure 14.5).

Other Body Changes

For both sexes, organs grow and become more efficient. Lungs triple in weight,
and adolescents breathe more deeply and slowly. The heart doubles in size and
beats more slowly (which decreases the pulse), while blood pressure and volume
both increase (Malina et al., 2004). These changes increase physical endurance,
enabling many teenagers to run for miles or dance for hours.

Note that both weight and height increase before the growth of muscles and
internal organs, which means that athletic training and weight lifting should be
tailored to an adolescent’s size the previous year, to spare their immature muscles
and organs. Sports injuries are the most common school accidents, increasing at
puberty. One reason is that, because height precedes increases of bone mass,
young adolescents are more vulnerable to fractures than are adults until old age
(Roche & Sun, 2003).

372 C H A P T E R 14 ■ Adolescence: Biosocial Development

Meters

6 8 12 14 16 1810

Age (years)

60

50

40

30

20

10
0

Source: Malina et al., 2004, p. 221.

Throwing Performance of Boys and Girls, Age 6 to 18

Girls

Boys

Ball throw for distance

FIGURE 14.4

Big Difference All children experience an increase in muscles

during puberty, but gender differences are much more apparent

in some gross motor skills than others. For instance, upper-arm

strength increases dramatically only in boys.

Running time

(seconds)

6 8 12 144 16 1810

Age (years)
3
4
5
6
7

Source: Malina et al., 2004, p. 222.

Running Speed of Girls and Boys, Age 5 to 18

30-yard (27.4-m) dash

Girls
Boys

FIGURE 14.5

Little Difference Both sexes develop longer and stronger legs

during puberty.

Observation Quiz (see answer, page 374): At what age does

the rate of increase in the average boy’s muscle accelerate?

Only one organ system, the lymphoid system (which includes the tonsils and
adenoids), decreases in size, thus making teenagers less susceptible to respiratory
ailments. Mild asthma, for example, often switches off at puberty (Busse &
Lemanske, 2005), and teenagers have fewer colds than younger children do.

Another organ system, the skin, changes in marked ways, making bodies oilier,
sweatier, and more prone to acne. Hair also changes. During puberty, hair on the
head and limbs becomes coarser and darker, and new hair grows under arms, on
faces, and above sex organs (pubic hair, from which puberty was named). Visible
facial and chest hair is sometimes considered a sign of manliness, although hairi-
ness in either sex depends on genes as well as hormones.

Sexual Maturation

The second set of changes turns boys into men and girls into women. Sexual char-
acteristics signify this transformation, as do many impulses and behaviors.

Sexual Body Changes

Primary sex characteristics are defined as those parts of the body that are
directly involved in conception and pregnancy. During puberty, every primary sex
organ (the ovaries, the uterus, the penis, and the testes) increases in size and ma-
tures in function. By the end of the process, reproduction is possible.

At the same time as maturation of the primary sex characteristics, secondary
sex characteristics develop. Secondary sex characteristics are bodily features
that do not directly affect fertility (hence they are secondary) but that signify mas-
culinity or femininity. One obvious secondary sexual characteristic is body shape,
virtually unisex in childhood. At puberty, males grow taller than females (by 5
inches, on average) and become wider at the shoulders, while girls develop breasts
and a wider pelvis.

Breasts and hips are often considered signs of womanhood; but neither is re-
quired for conception, and thus both are secondary, not primary, sex characteris-
tics. Secondary sex characteristics may be important psychologically, if not
biologically. For example, many girls buy “minimizer,” “maximizer,” “training,” or
“shaping” bras. Many boys are horrified to notice a swelling around their nipples—
a normal and temporary result of the erratic hormones of early puberty.

A welcome secondary sex characteristic is a lower voice as the lungs and larynx
grow, a change most noticeable in boys. Girls also develop lower voices, which is
why throaty female voices are considered sexy.

The pattern of growth at the scalp line differs for the two sexes, but few people
notice that. Instead, they notice gender markers in hair length and style, which
can attain the status of a secondary sex characteristic. Adolescents spend consid-
erable time, money, and thought on their visible hair—growing, shaving, curling,
straightening, brushing, combing, styling, dyeing, wetting, drying . . .

Sexual Activity

The primary and secondary sex characteristics just described are not the only
manifestations of the sexual hormones. Fantasizing, flirting, hand-holding, staring,
displaying, and touching are all done in particular ways to reflect gender, availabil-
ity, and culture. As already explained, hormones trigger thoughts and emotions,
but the social context shapes thoughts into enjoyable fantasies, shameful preoccu-
pations, frightening impulses, or actual contact.

Some experts believe that boys are more influenced by hormones and girls by
culture (Baumeister et al., 2007). Perhaps. When a relationship includes sexual
intimacy, girls seem more concerned about the depth of the romance than boys do

primary sex characteristics The parts of the

body that are directly involved in reproduc-

tion, including the vagina, uterus, ovaries,

testicles, and penis.

secondary sex characteristics Physical

traits that are not directly involved in repro-

duction but that indicate sexual maturity,

such as a man’s beard and a woman’s

breasts.

The Transformation of Puberty 373

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Male Pride Teenage boys typically feel serious

pride when they first need to shave. Although

facial hair is taken as a sign of masculinity, a

person’s hairiness is actually genetic as well as

hormonal. Further evidence that the Western

world’s traditional racial categories have no

genetic basis comes from East Asia: Many

Chinese men cannot grow beards or mus-

taches, but most Japanese men can.

(Zani & Cicognani, 2006). However, both sexes
are influenced by hormones and society. All
have sexual interests they did not previously
have (biology), which produce behaviors that
teenagers in other nations would not necessarily
engage in (culture) (Moore & Rosenthal, 2006).

Cultural norms affect who is likely to be a
person’s first sexual partner. Individuals might
think that this is a very private and personal
choice, but evidence suggests not.

For example, North American adolescents of
both sexes tend to express sexual impulses with
partners about the same age, which is also true
in many European nations (Zani & Cicognani,
2006). However, in Finland and Norway, girls
tend to become sexually experienced later than
boys. In Greece and Portugal, the opposite is
true (Teitler, 2002). Men in Nigeria are expected
to seek inexperienced younger teens for sexual

partners and to give them gifts. By contrast, emerging adult males in Thailand are
expected to seek older, experienced women (World Health Organization, 2005).

These generalities do not apply to everyone within those nations. Subgroups as
well as cohorts always differ, again for cultural reasons. One specific was found in
a survey of 704 adolescents in Ghana: More 16-year-old girls than boys were sexu-
ally experienced, but those experienced girls usually had only one partner whereas
the boys had several. Muslim youth were less often experienced than Christians,
who were less experienced than those of neither faith (Glover et al., 2003).

As in Ghana, religious teachings affect sexual behavior for many teenagers
worldwide; this was apparent in a study of adolescents in Israel and the United
States, with many youth being influenced by their faith. For Muslim teenagers,
romances seldom included sexual intimacy, even in thought (Magen, 1998). For
example, one Arab Israeli boy reported on “the most wonderful and happiest day
of my life”:

A girl passed our house. And she looked at me. She looked at me as though I
were an angel in paradise. I looked at her, and stopped still, and wondered and
marveled. . . . [Later] she passed near us, stopped, and called my friend, and
asked my name and who I am. I trembled all over and could hardly stand on my
feet. I used my brain, since otherwise I would have fallen to the floor. I couldn’t
stand it any longer and went home.

[quoted in Magen, 1998, pp. 97–98]

Cohort as well as culture have notable effects on sexual activity. For most of
the twentieth century, surveys in North America have reported increasing propor-
tions of adolescents becoming sexually active. This trend reversed in 1990. For
example, according to the CDC’s Youth Risk Behavior Survey (MMWR, 2006),
62 percent of eleventh-graders in the United States had had intercourse in 1991,
but only 51 percent had in 2005. The double standard (with boys expected to be
more sexually active than girls) also declined, as male rates came closer to female
ones (see Figure 14.6). Ethnic differences among high school students were also
apparent. Rates of sexual experience for African Americans were down 13 per-
centage points (from 81 to 68 percent), for European Americans down 7 percent-
age points (from 50 to 43 percent), and for Latinos down 2 percentage points
(from 53 to 51 percent).

374 C H A P T E R 14 ■ Adolescence: Biosocial Development

A Woman at 15 Dulce Giovanna Mendez

dances at her quinceañera, the traditional

fifteenth-birthday celebration of a Hispanic

girl’s sexual maturity. Dulce lives in Ures,

Mexico, where many older teenagers marry

and have children. This was the expected out-

come of puberty in earlier decades in the

United States as well.

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➤Answer to Observation Quiz (from

page 372): About age 13. This is most obvious

in ball throwing (see Figure 14.4), but it is also

apparent in the 30-yard dash.

All these examples demonstrate that a universal experience (specifically, rising
hormones) that produces another universal experience (specifically, growth of
primary and secondary sex characteristics) takes many forms, depending on cohort
and culture.

Brain Development

As with all the other changes of puberty, adolescent brain growth is the conse-
quence of hormones, maturation, and experience, which together cause uneven
yet rapid growth. The limbic system (fear, emotional impulses) matures before
the prefrontal cortex (planning ahead, emotional regulation). Neuroscientists and
developmentalists are working to understand exactly how emotions and logic con-
nect, as the following explains.

The Transformation of Puberty 3

75

40
45
50

55

60

Percent

1991 1993 1995 1997 1999 2001 2003 2005

Year

Percent of U.S. Eleventh-Grade Students Who Say They Have Had Sexual Intercourse

Source: MMWR Surveillance Summaries, June 9, 2006.

Girls
Boys

FIGURE 14.6

Surprise! Two trends are apparent from this

graph. First, fewer adolescents are sexually

experienced than was the case 15 years ago.

Second, the gap between the sexes is shrink-

ing. This is confirmed by other data, including

the number of eleventh-graders who say

they have had four or more partners, which

showed a 10 percent male–female gap in

1991 and a 5 percent gap in 2005. Both

trends (decline and sexual convergence) are

found in other nations, and neither was pre-

dicted by researchers a few decades ago.

a case to study
What Were You Thinking?

Laurence Steinberg is a noted expert on adolescent thinking.

He is also a father.

When my son, Benjamin, was 14, he and three of his friends de-

cided to sneak out of the house where they were spending the

night and visit one of their girlfriends at around two in the morn-

ing. When they arrived at the girl’s house, they positioned them-

selves under her bedroom window, threw pebbles against her

windowpanes, and tried to scale the side of the house. Modern

technology, unfortunately, has made it harder to play Romeo these

days. The boys set off the house’s burglar alarm, which activated a

siren and simultaneously sent a direct notification to the local

police station, which dispatched a patrol car. When the siren

went off, the boys ran down the street and right smack into the

police car, which was heading to the girl’s home. Instead of stop-

ping and explaining their activity, Ben and his friends scattered

and ran off in different directions through the neighborhood. One

of the boys was caught by the police and taken back to his home,

where his parents were awakened and the boy questioned.

I found out about this affair the following morning, when the

girl’s mother called our home to tell us what Ben had done. . . .

After his near brush with the local police, Ben had returned to

the house out of which he had snuck, where he slept soundly

until I awakened him with an angry telephone call, telling him to

gather his clothes and wait for me in front of his friend’s house.

On our drive home, after delivering a long lecture about what he

had done and about the dangers of running from armed police in

the dark when they believe they may have interrupted a burglary,

I paused.

“What were you thinking?” I asked.

“That’s the problem, Dad,” Ben replied, “I wasn’t.”

[Steinberg, 2004, pp. 51, 52]

Steinberg finds his son insightful. “The problem is not that

Ben’s decision-making was deficient. The problem is that it was

nonexistent” (Steinberg, 2004, p. 52). In his analysis, Steinberg

points out a characteristic of adolescent thought: When emotions

Caution Versus Thrills

Much more interdisciplinary research is needed to integrate neurology and psy-
chology. Caution is needed, lest “incomplete brain development [becomes] an ex-
planation for just about everything about teens that adults have found perplexing,
from sleep patterns to risk taking and mood swings” (Kuhn, 2006, p. 59). The
fMRI, the PET, and other measures are expensive and complex, and longitudinal,
reliable, multifactorial research on the brains of typical 10- to 17-year-olds is not
yet extensive. As one expert explains:

We stand at the edge of very exciting new research developments as new neuro-
imaging technologies come online, but at present we are groping in the dark in
many respects. . . . The work on adolescent development is particularly recent.

[Keating, 2004, p. 69]

With excitement tempered by caution, scientists trace many hallmarks of ado-
lescent thinking and behavior to the brain. It is thrilling to learn that the frontal
lobes are the last part of the brain to mature, with ongoing myelination from ages
10 to 25. In the words of a leading neuroscientist:

The frontal lobes are essential for . . . response inhibition, emotional regulation,
planning, and organization, which may not be fully developed in adolescents . . .
[which suggests that brain immaturity underlies much] troublesome adolescent
behavior.

[Sowell et al., 2007, p. 59]

Uneven Growth

You learned in Chapter 11 that the brain functions well in middle childhood, as
dendrites, myelination, and the corpus callosum allow “a massively interconnected
brain” (Kagan & Herschkowitz, 2005, p. 220). Yet you just read that the immature
prefrontal cortex may allow “troublesome adolescent behavior.” Is this a contradic-
tion? Regression? Eight-year-olds would probably not sneak out at 2 A.M. to throw
pebbles at a girl’s window. If the idea occurred to them, they would probably think
twice and stay in bed.

Actually, there is no contradiction. Adolescents are quite capable of rational
thinking. However, they don’t necessarily use that capacity to “think twice” before
acting. As in the rest of the teenager’s body, brain growth is uneven. Myelination
and maturation proceed from inside to the cortex and from back to front (Sowell
et al., 2007).

376 C H A P T E R 14 ■ Adolescence: Biosocial Development

are intense, especially with peers, the logical part of the brain

shuts down.

This is not reflected in questionnaires that require teenagers

to respond to paper-and-pencil questions regarding hypothetical

dilemmas. On those tests, teenagers think carefully and answer

correctly. They know the risks of sex and drugs. However,

the prospect of visiting a hypothetical girl from class cannot pos-

sibly carry the excitement about the possibility of surprising

someone you have a crush on with a visit in the middle of the

night. It is easier to put on a hypothetical condom during an act

of hypothetical sex than it is to put on a real one when one is in

the throes of passion. It is easier to just say no to a hypothetical

beer than it is to a cold frosty one on a summer night.

[Steinberg, 2004, p. 43]

Steinberg believes that, to understand how the brain actually

works, abstract questionnaires are inadequate. Adolescent think-

ing is more variable than earlier researchers believed (Kuhn,

2006). Now that scientists realize the limitations of prior

research, and neuroscientists have data from fMRI and other

brain scans, new discoveries about adolescent brain functioning

are on the horizon.

Ben reached adulthood safely. Some other teenagers, with

less cautious police or less diligent parents, do not. Ideally, re-

search on adolescent brains will help protect adolescents from

their own dangerous ones (Monastersky, 2007).

Especially for Parents Worried About

Their Teenager’s Risk Taking You

remember the risky things you did at the

same age, and you are alarmed by the

possibility that your child will follow in your

footsteps. What should you do?

Further, the hormones of puberty seem to affect the amygdala more directly
than they affect the cortex, which is more influenced by age and experience. The
combination of the sequence of brain maturation and the effects of early puberty
mean that the limbic system (deep inside) matures years before the prefrontal
cortex.

Since the amygdala specializes in quick emotional reactions—sudden anger,
joy, fear, despair—and the prefrontal cortex (called the executive) coordinates,
inhibits, and strategizes, this uneven maturation puts adolescents

at increased risk for emotional problems and disorders because the brain systems
that activate emotions . . . are developed before the capacity for volitional effort-
ful control of these emotions is fully in place.

[Compas, 2004, p. 283]

The maturing limbic system is particularly attracted to strong, immediate sen-
sations, unchecked by the slowly maturing prefrontal cortex. For this reason,

Adolescents like intensity, excitement, and arousal. They are drawn to music
videos that shock and bombard the senses. Teenagers flock to horror and slasher
movies. They dominate queues waiting to ride the high-adrenaline rides at
amusement parks. Adolescence is a time when sex, drugs, very loud music, and
other high-stimulation experiences take on great appeal. It is a developmental
period when an appetite for adventure, a predilection for risks, and a desire for
novelty and thrills seem to reach naturally high levels.

[Dahl, 2004, pp. 7, 8]

Such intense experiences are sought because they short-circuit the emotional
regulation of the prefrontal cortex.

When stress, arousal, passion, sensory bombardment, drug intoxication, or dep-
rivation are extreme, the brain is overtaken by impulses that might shame adults.
Teenagers brag about being so drunk they were “wasted,” “bombed,” “smashed,”
describing a state most adults would try to avoid. Some teenagers choose to spend
a night without sleep, a day without eating, or to exercise in pain.

The consequences may be especially severe in the twenty-first
century, because puberty precedes adult employment and family
life by a decade or more and because guns, drugs, and sex can turn
a momentary lapse of judgment into a lethal mistake. It seems that
the hormones that trigger the body changes of puberty do not also
trigger the brain changes, which are more affected by birth date
than body size.

Neurological Advances

With increased myelination, reactions become lightning fast. The
white matter, which includes the axons and dendrites that link one
neuron to another, increases throughout adolescence, again from

The Transformation of Puberty 377
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Front Front

Back Back

(a) (b)

Twisted Memorial This wreck was once a

Volvo, driven by a Colorado teenager who

ignored an oncoming train’s whistle at a rural

crossing. The car was hurled 167 feet and

burst into flames. The impact instantly killed

the driver and five teenage passengers. They

are among the statistics indicating that acci-

dents, many of which result from unwise risk

taking, kill 10 times more adolescents than

diseases do.

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The Prefrontal Cortex Matures These are composite scans of

normal brains of (a) children and adolescents and (b) adolescents

and adults. The red areas indicate both an increase in brain size

and a decrease in gray matter (cerebral cortex). The red areas in (b)

are larger than in (a) and are concentrated in the frontal area of the

brain, which is associated with complex cognitive processes. The

growth of brain areas as their gray matter decreases is believed to

reflect an increase in white matter, which consists of myelin—the

axon coating that makes the brain more efficient.

back to front (Sowell et al., 2007). Additional pruning occurs, and the dopamine
system (neurotransmitters that bring pleasure) is very active.

Before these advances are complete (about age 25), new connections between
one synapse and another ease acquisition of new ideas, words, memories, person-
ality patterns, or dance steps (Keating, 2004). As you might imagine, values ac-
quired during adolescence are more likely to endure than those learned later, after
brain links are more firmly established.

Adolescent brain immaturity can be used positively or negatively. The fact that
“the prefrontal cortex is still developing . . . confers benefits as well as risks. It
helps explain the creativity of adolescence and early adulthood, before the brain
becomes set in its ways. But it also makes adolescents more prone to addiction”
(Monastersky, 2007, p. A17).

One expert bemoans “the deleterious consequences of drug use [which] appear
to be more pronounced in adolescents than in adults, a difference that has been
linked to brain maturation” (Moffit et al., 2006, p. 12). Another scholar celebrates
adolescent passion that “intertwines with the highest levels of human endeavor:
passion for ideas and ideals, passion for beauty, passion to create music and art”
(Dahl, 2004, p. 21).

Thus, adolescent experiences can teach compassion or mistrust, political par-
ticipation or isolation. Those who care about the next generation need attend to
the life lessons that adolescents are learning, providing “scaffolding and monitor-
ing” until brains and skills can function well on their own (Dahl, quoted in
Monastersky, 2007, p. A18).

Body Rhythms

Brain rhythms affects body rhythms (Buzsáki, 2006). The hypothalamus and pitu-
itary regulate hormones that affect stress, appetite, sleep, and so on. As you know,
the brain of every living creature responds to natural changes.

Seasons affect reproduction (more births occur in spring), weight (gains in
winter), and, in some species, migration and hibernation. Diurnal (daily) rhythms
affect tiredness, hunger, alertness, elimination, body temperature, nutrient balance,
blood composition, moods, and so on. (Some people wake up cheery and others

cranky, switching moods by nightfall.)
All creatures have a day–night cycle. That’s why jet lag affects people

who fly east–west across the globe, changing time zones, but not those
who fly the same distance north–south. Because of diurnal rhythms,
people cannot get their recommended 60 hours of sleep per week by
staying awake 24 hours for four days and then sleeping 20 hours on
each of the other three. The diurnal rise and fall of body chemicals,
melatonin among them, make sleep elusive sometimes and impossible
to postpone at other times.

Puberty alters biorhythms. Hormones from the pituitary often cause
a “phase delay” in sleep–wake patterns: Many teens are wide awake at
midnight but half-asleep all morning. Because adult brains are naturally
alert in the morning and sleepy at night, social patterns set by adults do
not necessarily accommodate adolescent rhythms.

One consequence is sleep deprivation for many teenagers, who
naturally stay up late but who nonetheless are forced to wake up early.
Evidence for this is that teenagers seldom waken spontaneously on
weekdays (see Figure 14.7) and often “sleep in” on weekends (Andrade
& Menna-Barreto, 2002).

Uneven sleep schedules (more sleep on weekends, with later bed-
times and daytime sleeping) are common among teenagers, yet this

378 C H A P T E R 14 ■ Adolescence: Biosocial Development

Reasons for Waking Up on School Mornings

Percentage

of age group

100

75
50

25

0

Source: Carskadon, 2002a, p. 7.

10–11 12–13

Age group

14–18

Parent

Alarm clock

Spontaneous

FIGURE 14.7

Sleep Deprivation Humans naturally wake up once they’ve

had enough sleep. Few high school students wake up spon-

taneously, and many sleep later on weekends than on school

days. These facts suggest that most teenagers need more

sleep. Depression and irritability correlate with insufficient

sleep.

➤Response for Parents Worried About

Their Teenager’s Risk Taking (from page

376): You are right to be concerned, but you

cannot keep your child locked up for the next

decade or so. Since you know that some

rebellion and irrationality are likely, try to

minimize them by not boasting about your

own youthful exploits, by reacting sternly to

minor infractions to nip worse behavior in the

bud, and by making allies of your child’s

teachers.

Especially for Those Who Appreciate

Folk Wisdom What is meant by “The early

bird catches the worm” and “Early to bed

and early to rise, makes a man healthy,

wealthy, and wise”?

unevenness decreases well-being just as overall sleep deprivation does (Fuligni &
Hardway, 2006). Girls are particularly likely to be sleep-deprived, which decreases
their grades and happiness (Fredriksen et al., 2004).

The Transformation of Puberty 379

Calculus at 8 A.M.?

Biology designs teenage bodies to be alert at midnight and tired

all morning, perhaps falling asleep in school (see Figure 14.8).

School schedules reflect culture, not biorhythms.

Some parents fight biology. They command their wide-awake

teen to “go to sleep,” they hang up on classmates who phone

after 10 P.M., they set early curfews, and they drag their off-

spring out of bed for school. (An opposite developmental clash

occurs when parents tell their toddlers to stay in their cribs after

dawn.)

Data on the phase delay of adolescence led social scientists

at the University of Minnesota to ask 17 school districts to con-

sider a later starting time for high school. Most adults opposed

the idea.

Teachers generally thought that early morning was the best

time to learn. Many (42 percent) parents of adolescents thought

school should begin before 8 A.M. In fact, some (20 percent)

wanted their teenagers out of the house by 7:15 A.M., as did

only 1 percent of those with younger children. Bus drivers hated

rush hour; cafeteria workers wanted to leave by mid-afternoon;

police said teenagers should be off the streets by 4 P.M.; coaches

needed sports events to end before dark; employers hired teens

to staff the afternoon shift; community program directors

wanted to schedule the gym for nonschool events (Wahlstrom,

2002).

Despite the naysayers, one school district experimented. In

Edina, Minnesota, high school began at 8:30 A.M. (previously

7:25 A.M.) and ended at 3:10 P.M., not 2:05 P.M. After one year,

most (93 percent) parents and virtually all students approved.

One student said, “I have only fallen asleep in school once this

whole year, and last year I fell asleep about three times a week”

(quoted in Wahlstrom, 2002, p. 190). The data showed fewer

absent, late, disruptive, or sick students (the school nurse be-

came an advocate) and higher grades.

Other school districts reconsidered. Minneapolis, which had

started high school at 7:15 A.M., changed the starting time to

8:40 A.M. Again, attendance improved, as did graduation rate.

School boards in South Burlington (Vermont), West Des

Moines (Iowa), Tulsa (Oklahoma), Arlington (Virginia), and

Milwaukee (Wisconsin) voted in favor of later starting times,

switching on average from 7:45 A.M. to 8:30 A.M. (Tonn, 2006).

Unexpected advantages appeared: financial savings (more effi-

cient energy use) and, at least in Tulsa, unprecedented athletic

championships.

But change is hard. Researchers believe that “without a

strategic approach, the forces to maintain the status quo in the

schools will prevail” (Wahlstrom, 2002, p. 195). Few college stu-

dents choose 8 A.M. classes. Why?

issues and applications

5
0
10
15
20
25
30

35Percent

Fatigue Among Middle- and High School Students

Grades 9–12

Grades 6–8

Too tired
to exercise

Asleep in
school

Source: National Sleep Foundation, 2006.

FIGURE 14.8

Dreaming and Learning? This graph shows the percent of U.S.

students who, once a week or more, fall asleep in class or are too

tired to exercise. Not shown are those who are too tired overall

(59 percent for high school students) or who doze in class “almost

every day” (8 percent).

Sleep deprivation and irregular sleep schedules are associated with many other
difficulties, such as falling asleep while driving, insomnia in the middle of the
night, distressing dreams, and mood disorders (depression, conduct disorder,
anxiety) (Carskadon, 2002b; Fredriksen et al., 2004; Fuligni & Hardway, 2006).

S U M M I N G U P

The growth spurt, sexual differentiation, and brain maturation are notable during the

years after the first signs of puberty. Physical growth proceeds from the extremities to

the center, so the limbs grow before the internal organs. Weight precedes height, which

precedes muscles and growth of the internal organs. Both boys and girls increase in

sexual interest as their bodies develop and their hormone levels rise, with sexual behav-

ior and thoughts powerfully affected by culture.

The hormones of puberty probably cause the brain’s emotional hot spots to further

myelinate as well as grow. Adult functioning of the prefrontal cortex depends less on

specific hormones and more on age and experience; thus it matures later. Uneven

neurological advancement may be one reason adolescents take irrational risks and enjoy

intense sensory experiences. Reactions quicken and emotional memories endure. The

brain affects body rhythms, notably in the phase delay that makes adolescents stay up

late at night. As a result of school schedules, many adolescents are sleep-deprived.
■

Possible Problems
Growth and sexual awakening, emotional intensity and hormonal rushes—all of
this can be quite wonderful. However, as you will read in each of the chapters on
adolescence and emerging adulthood, maturation can bring problems. Typically, if
a young person has one problem, he or she also has several others—true for about
20 percent of all young people. That means that 80 percent are not bedeviled by
problems; for them, adolescence is more joyful than troubled. Remember that as
we look at sex and drugs, serious problems for a minority.

Sex Too Soon

Adolescent sexuality in the twenty-first century can be problematic for three reasons:

■ Puberty occurs at young ages. Early sexual experiences correlate with depres-
sion and drug use.

■ Raising a child has become more complex, which means that teenage preg-
nancy is no longer welcomed or expected.

■ Sexually transmitted infections are more common and dangerous.

The first item on this list, sexual relationships, is discussed in Chapter 16, where the
main discussion of teen romance and friendship occurs. The other two items, preg-
nancy and infections, each have specific health impacts, so they are discussed below.

Teenage Pregnancy

There is good news about pregnancy under age 18: It is about half as common as it
was 20 years ago in the United States and in many other nations (MMWR, Febru-
ary 4, 2005). Not only are teen births less frequent, the abortion rate has also de-
creased. Contraception use is higher and teen intercourse is lower.

Nonetheless, if a girl under age 15 becomes pregnant, as about 25,000 U.S. girls
did in 2002 (a rate higher than in any other developed nation), she is at greater risk
of almost every complication—including spontaneous and induced abortion, high
blood pressure, stillbirth, cesarean section, a low-birthweight baby, and even death—
than she would have been if she had waited five years or more (Menacker et al., 2004).

In some nations (notably sub-Saharan Africa), inadequate medical care makes
pregnancy the leading cause of death for teenage girls (Reynolds et al., 2006). In
regions where almost everyone is malnourished, the youngest mothers die of birth
complications three times more often than do older women (Blum & Nelson-
Mmari, 2004).

380 C H A P T E R 14 ■ Adolescence: Biosocial Development

If a pregnant teenager has an abortion (as two-thirds of all pregnant U.S. girls
under age 15 do), she avoids the problems of a sustained pregnancy and birth, but
she encounters other complications, partly because the younger a woman is, the
later in pregnancy she is likely to abort (MMWR, November 24, 2006).

Throughout puberty, bodies add bone, redistribute weight, and gain height,
while the inner organs (including the uterus) mature. Pregnancy interferes with
this, because another set of hormones directs the body to sustain new life. Nature
protects the fetus, which may take essential nutrients (especially calcium and
iron) from the mother. If normal pubescent growth is deflected, that causes the
girl to become a shorter and sicker woman than she otherwise would have been.

If a young woman lives in a developed nation and obtains good medical care, the
serious biological consequences of adolescent pregnancy are rare. Unfortunately,
the youngest teenagers are likely to postpone seeing a doctor, which increases the
risk of complications. Even in Sweden, with good nutrition and free prenatal care,
an early teen birth impairs health and achievements lifelong (Olausson et al., 2001).

If a baby of a teen mother is born healthy, he or she is still likely to experience
numerous complications later on, including poor health; inadequate education; low
intelligence; and anger at his or her family, community, and society (Borkowski
et al., 2007). That takes a greater toll on the mother as she cares for her child.

Many college students reading this book know teenage mothers. Such young
women may obtain good medical care, stay in school, and get help from her family
and the child’s father. In such a case, adolescent mothers are likely to be resilient,
becoming competent young women by age 30 or so (Borkowski et al., 2007). As
with the other problems of life, no single burden is insurmountable, although it
would be easier on the body to postpone pregnancy until all growth is complete.

Sexual Infections

A sexually transmitted infection (STI) (formerly known as a sexually transmit-
ted disease [STD] or venereal disease [VD]) is any infection transmitted through
sexual contact (oral or genital). Worldwide, sexually active teenagers have higher
rates of the most common STIs (gonorrhea, genital herpes, and chlamydia) than any
other age group (World Health Organization, 2005).

The most lethal STIs, specifically AIDS and syphilis, are more commonly caught
by people in their 20s, but teenagers are vulnerable to them as well, especially if
they already have an STI or if they have sex with an older person. One statistic
makes the point: In the United States, young persons aged 15–24 constitute only
one-fourth of the sexually active population but account for half of all sexually
transmitted infections (MMWR, October 20, 2006).

One reason is purely biological. Fully developed women have some natural bio-
logical defenses against STIs, but this is less true for pubescent girls, who are more
likely to catch every STI, including AIDS, from an infected partner (World Health
Organization, 2005). It is not known whether adolescent boys are also more vulner-
able to infection.

It is known that, for many reasons, sexually active boys and girls under age 16
are particularly likely to contract an STI (Kaestle et al., 2005) but are unlikely to
seek immediate treatment and alert their sexual partners. Not only are they
ashamed and afraid, but many do not recognize symptoms, nor do they believe
that medical treatment will be

confidential.

An added complication occurs for partners of the same sex. Especially for youths
in the United States, such relationships are usually kept secret; thus it is even
more difficult for them to seek treatment than it is for heterosexual teenagers.

Many STIs have no symptoms but severe consequences (MMWR, August 4,
2006). For example, chlamydia, the most frequently reported disease (more often
than any other sexual or nonsexual disease), can cause lifelong infertility. Another

sexually transmitted infection (STI) A dis-

ease spread by sexual contact, including

syphilis, gonorrhea, genital herpes,

chlamydia, and HIV.

Possible Problems 381

➤Response for Those Who Appreciate

Folk Wisdom (from page 379): Folk wisdom

is a good way to understand popular culture.

In this case, adults enshrined their natural

rhythms with aphorisms approving adult

sleep–wake patterns.

child sexual abuse Any erotic activity that

arouses an adult and excites, shames, or

confuses a child, whether or not the victim

protests and whether or not genital con-

tact is involved.

common STI is human papillomavirus (HPV), which increases the chances of fatal
uterine cancer. Human immunodeficiency virus (HIV) can have no symptoms for
years, and then cause AIDS and death. There are literally hundreds more STIs
(James, 2007).

Unless a teenager has regular checkups with lab testing (which few do), he or
she may not realize that an STI is at work. Many STIs can be prevented with
immunization and confidential counseling. Although most of the research has
been done on girls, the problem may be even worse for boys, who are particularly
unlikely to see a doctor unless they are seriously injured.

Protection

Preventing and treating STIs is only one of many reasons teenagers should have
regular medical care. Basic information is no longer the usual problem. Almost
every teenager knows that pregnancy and STIs can be prevented by abstinence or
regular and proper use of condoms, but whether that information is translated into
practice depends on peers, partners, and adults. Confidence in a familiar medical
provider can be crucial.

National differences are striking. In France, 91 percent of adolescents use con-
traception (usually a condom) at first intercourse (Michaud et al., 2006), partly
because every French high school is required to provide free, confidential medical
care. However, far fewer Italian, German, and U.S. teenagers use condoms. For
instance, in the United States, only 46 percent of sexually active high school
senior girls used a condom during their most recent sexual encounter (MMWR,
June 9, 2006).

Sex education is discussed in Chapter 16. Before leaving this topic, however,
we need to note one mistake especially common in early adolescence, already
apparent in our discussion of body image. Teenagers tend to confuse appearance
and reality, not realizing that a polite, well-dressed partner could have an STI. For
example, one girl in Malawi (where AIDS is epidemic) thought she was safe
because her partner was known to her and “my mother knows his mother” (quoted
in World Health Organization, 2005, p. 11).

Sexual Abuse

We should not leave the topic of sexuality without noting that child sexual
abuse, which includes any sexual activity between a juvenile and an older person,
is most common just after puberty. Every study finds that virtually every adoles-
cent problem (including drug abuse, eating disorders, suicide, and pregnancy) is
more common in adolescents who are sexually abused. Some eventually become
abusers as well (Barbaree & Marshall, 2006).

Young people who are sexually exploited have difficulty establishing sexual rela-
tionships. This is true during the abuse, because the abuser often isolates the
victim from his or her peers, and later on, because past memories interfere with
normal sexuality.

Sex abuse is more common between the ages of 10 and 15 than at any other
time, and it is a major problem in every nation. The United Nations reports that
millions of young adolescents are forced into marriage, genital surgery, and prosti-
tution (often across national borders) each year (Pinheiro, 2006). Exact numbers
are elusive. Almost every nation has laws against sexual abuse, but these laws are
rarely enforced, and adults often let disgust and sensationalism crowd out efforts
to prevent, monitor, and eliminate the problem (Davidson, 2005).

Data on substantiated childhood sexual abuse in the United States confirm that,
as elsewhere, the rate is higher among 12- to 15-year-olds than among younger chil-
dren (U.S. Department of Health and Human Services Administration on

Especially for Health Practitioners How

might you encourage adolescents to seek

treatment for STIs?

382 C H A P T E R 14 ■ Adolescence: Biosocial Development

No Safer? Educational posters and even in-

tense educational programs have little proven

effect on the incidence of AIDS among ado-

lescents. This poster was displayed outside

an HIV testing center in Windhoek, Namibia,

a country that has one of the highest HIV in-

fection rates in the world.

S
E
A

N
S

P
R

A
Q

U
E
/

T
H

E
I
M

A
G
E
W
O
R
K
S

Children, Youth, and Families, 2006). Girls are particularly vulnerable, although
boys are also at risk. But overall rates are declining, perhaps because adolescents
are becoming better informed about sexual activity (Finkelhor & Jones, 2004).
Nonetheless, almost thirty thousand 12- to 15-year-olds were substantiated victims
of sexual abuse in the United States in 2005 (see Table 14.2), a statistic that under-
scores that teenagers need protection, not just information (U.S. Department of
Health and Human Services Administration on Children, Youth, and Families, 2006).

Drug Use and Abuse

Innocence is also reflected in drug use, as few adolescents imagine that they could
become addicted. Most experiment and observe no immediate harm, enjoying the
thrill of doing something that adults think they are too young to do. Worldwide,
most young people use at least one drug before age 18.

An annual nationwide survey of U.S. high school seniors called Monitoring the
Future began in 1975 and continues to this day (see Research Design). In 2006,
many seniors drank alcohol (73 percent), puffed a cigarette (47 percent), and
smoked marijuana (42 percent) (Johnston et al., 2007) (see Figure 14.9). Drug
use is down in the United States over the life of the survey, but the number of
available drugs has increased, as have prescription-type drugs (e.g., barbiturates
and tranquilizers).

Possible Problems 383

TABLE 14.2

Age and Sex Abuse: United States, 2005

Age Number of Substantiated Victims Percent of Maltreatment That Is Sex Abuse

0–3 5,407 2.1

4–7 18,547 8.2

8–11 19,136 11.2

12–15 29,768 17.3

16–18 8,676 16.8

Source: U.S. Department of Health and Human Services Administration on Children, Youth, and Families, 2006

Research Design
Scientists: Lloyd D. Johnston, Patrick M.

O’Malley, Jerald G. Bachman, and John

E. Schulenberg.

Publication: Monitoring the Future is

online. Print copies are available from

the National Institute on Drug Abuse in

Bethesda, Maryland.

Participants: In 2006, 48,500 students in

410 high schools, throughout the United

States.

Design: Beginning in 1975, scientists

from the University of Michigan sur-

veyed adolescents each year, asking

about drug use, drug availability, and

personal attitudes. The basic questions

have remained the same, with new

drugs added (e.g., Vicodin, OxyContin).

Data are reported by age, sex, ethnicity,

and region.

Major conclusion: Over the 32 years of

the survey, drug use declined, rose, and

recently declined again. New drugs con-

tinue to appear, and sometimes old

drugs become more popular again. Use

is more affected by attitudes than by

availability.

Comment: This study tracks many co-

hort changes within the United States.

Interested readers should access the

latest reports online. Note that other

nations often show different patterns

and that Monitoring the Future does not

usually include high school dropouts.

40
30
20
10

0
1976 ’78 ’80 ’82 ’84 ’86 ’88 ’90 2000’92 ’94 ’96 ’98 ’02 ’04 ’06

Percent

reporting

use of drug

Drug Use by U.S. High School Seniors in the Past 30 Days

Year

Source: Johnston et al., 2007.

Cocaine

Other

illicit drugs

(not marijuana)

Marijuana

Amphetamines

CigarettesFIGURE 14.9

Rise and Fall By asking the

same questions year after year,

the Monitoring the Future study

shows notable historical effects.

It is encouraging that something

in society, not in the adolescent,

makes drug use increase and de-

crease and that the most recent

data show a decline. However,

as Chapter 1 emphasized, survey

research cannot prove what

causes change.

Variations by Nation, Gender, and Ethnicity

One of the fascinating aspects of adolescent drug use is how variable it is, which
indicates that much more than biology is involved. In some nations, young adoles-
cents drink alcohol more often than they use any other drug; in others, smoking
is more common than drinking. In many places (especially eastern Europe),
teenagers use both alcohol and tobacco more than in the United States; in still
other places, teenagers rarely use any drugs at all (Buelga et al., 2006; Eisner,
2002).

Laws and family practices are part of the reason for these variations, but not the
only reasons. For example, in many Arab nations, alcohol is strictly forbidden; in
many European nations, children drink wine with dinner; in many Asian nations,
anyone may smoke anywhere; in the United States, smoking is forbidden in many
public places.

Even nations with common boundaries differ radically (Buelga et al., 2006).
For example, among 15-year-olds, 9.4 percent of those in Switzerland were heavy
users of marijuana compared with only 3.3 percent in Italy. More Canadian youth
smoke marijuana, but fewer smoke cigarettes, than in the United States. Laws are
only part of the explanation: Although marijuana is legal and widely available in the
Netherlands, Dutch 15-year-olds are among the lowest heavy users (2.8 percent)
of any developed nation (Buelga et al., 2006).

Gender differences are apparent for most drugs in most nations, with boys hav-
ing higher rates of use than girls. In the United States, cigarette smoking is unisex,
but an international survey (131 nations) of 13- to 15-year-olds found that more
boys than girls are smokers (except in some European nations), including three
times as many boys as girls in Southeast Asia (Warren et al., 2006). According to
another international survey, this one of 31 nations, boys are also almost twice as
likely as girls to have tried marijuana (26 versus 15 percent) (ter Bogt et al., 2006).

For North Americans, the good news is that adolescents begin drug use later
than in many other nations. A significant minority (about 20 percent) never use
any drugs, usually because of religious values (C. Smith, 2005). However, the
United States leads the world in the number of available drugs, including syn-
thetic narcotics, unknown in most nations. During 2006, 10 percent of U.S. high
school seniors used Vicodin and 4 percent used OxyContin (Johnston et al.,
2007).

A particular problem is using drugs before age 13, because doing so is more
likely to interfere with brain and body growth as well as to lead to serious problems

Especially for Older Brothers and

Sisters A friend said she saw your 13-year-

old sister smoking. Should you tell your

parents?

384 C H A P T E R 14 ■ Adolescence: Biosocial Development

The Same Event, A Thousand Miles Apart:

Teen Approaches to Drinking Adolescents

everywhere drink alcohol, including these

girls at a high school prom in New York City

(left) and at a sidewalk café in Prague (right).

Cultural differences affect the specifics but

not the general trend toward teenage experi-

mentation with drugs and alcohol.

Observation Quiz (see answer, page 386):

Can you spot three cultural differences

between these two groups?

M
A

R
K

P
E
T
E
R

S
/
C
O

R
B

IS

S
T
U

A
R

T
F

R
A

N
K

LI
N

/
M

A
G

N
U

M
P

H
O
T
O
S

➤Response for Health Practitioners

(from page 382): Many adolescents are

intensely concerned about privacy and fearful

of adult interference. This means your first

task is to convince the teenagers that you are

nonjudgmental and that everything is

confidential.

later on. One large U.S. survey revealed that, among ninth-graders, 34
percent said that they had begun drinking before age 13, 19 percent
that they had smoked a cigarette, and 11 percent that they had tried
marijuana (MMWR, June 9, 2006). Monitoring the Future found that
16 percent of eighth-graders reported past use of inhalants (which can
be unexpectedly and rapidly fatal), again beginning before the teen
years (Johnston et al., 2007).

Rates also vary among U.S. ethnic groups (see Figure 14.10). Euro-
pean American teens use the most drugs and African and Asian Ameri-
cans the least. Hispanic adolescent drug use may be increasing,
especially marijuana smoking by younger teens who speak English well
(Delva et al., 2005).

Why would any teenager, in any nation, use drugs, especially if
forbidden by law and against parental wishes? One reason is that, for
many adolescents, peers are more important than parents. “In young
adolescence, use of substances . . . provides a form of commerce with the social
world” (Dishion & Owen, 2002, p. 489). In other words, socially awkward pubes-
cent children (especially boys) use drugs to establish friendships and be part of a
peer group.

Another reason is that the neurological drive for intense sensations without
the caution of a fully mature prefrontal cortex makes adolescents seek a quick and
intense rush, as explained by a Spanish expert:

Teenagers and young adults use licit and illicit drugs to look for states of excite-
ment that make their relationships with others more intense and satisfying and
that make their spare time activities more stimulating.

[Buelga et al., 2006, p. 351]

Possible Problems 385

Looking Cool The tight clothing, heavy

makeup, multiple rings, and cigarettes are

meant to convey to the world that Sheena,

15, and Jessica, 16, are mature, sophisticated

women.

Observation Quiz (see answer, page 386):

Did these girls buy their own cigarettes?

LA
U

R
E
N

G
R

E
E
N

FI
E
LD

Percent

1997 2001 2003 20051999

Year
50
40
30
20
10
0

Source: MMWR, June 9, 2006 (Tables 22 and 28), and previous years.

Recent Trends in Drinking and Smoking Among U.S. High School Students

White females Hispanic females Black females

Hispanic males Black malesWhite males

Heavy Drinking

Percent
1997 2001 2003 20051999
Year
30
20
10
0

Regular Smoking
FIGURE 14.10

Less Drinking, Still Too Much Smoking The

overall downward trend in both binge drinking

and regular smoking by adolescents is good

news, but changing many high school students’

minds about getting drunk or smoking daily

remains difficult.

Observation Quiz (see answer, page 387):

Which of these categories of people is least

likely to drink alcohol during adolescence?

Which category seems most affected by

cohort changes in regular smoking?

Harm from Drugs

Since drugs are widely used and bring peer bonding and excitement, many adoles-
cents think adults exaggerate the harm of teen drug use. That may be, but devel-
opmentalists see many immediate and long-term consequences. It would be far
better if adolescents and their communities could postpone experimentation and
never get to steady use. Here are some of the reasons.

During puberty, the body and the brain are destined to grow. Drugs interfere
with healthy eating and digestion, particularly important during puberty. All
psychoactive drugs impair the appetite, but tobacco is worst of all. Smoking or
chewing tobacco decreases food consumption and interferes with the absorption
of nutrients. This is one reason adolescent smokers become shorter and heavier
adults.

In fact, all kinds of tobacco (bidis, cigars, pipes, chewing tobacco) decrease
growth, a particularly serious problem in India, where undernutrition is chronic
and tobacco use (typically not via cigarettes) is widespread (Warren et al., 2006).
Since internal organs mature after the height spurt, drug-using teenagers who
appear full-grown may still damage their hearts, lungs, brains, and reproductive
systems.

For North Americans, alcohol is the most commonly abused drug, which is par-
ticularly harmful for the brain. Steady drinking impairs memory and self-control
(not just temporarily) by damaging the hippocampus and the prefrontal cortex
(S. A. Brown et al., 2000; De Bellis et al., 2005; White & Swartzwelder, 2004).

When nonhuman animals are forced to drink alcohol, addiction occurs and
brain abnormalities result, with animals choosing the drug rather than nourish-
ment. Among rats, adolescents likely drank more than adults in the same con-
dition, and they were slower to solve problems (De Bellis et al., 2005; Sircar &
Sircar, 2005).

Many adolescents know the damage of alcohol and cigarettes from observing
adults, but they remain oblivious to the dangers of marijuana. Johanna explained:

I started off using about every other weekend, and pretty soon it increased to
three to four times a week. . . . I started skipping classes to get high. I quit soccer
because my coach was a jerk. My grades dropped, but I blamed that on my not
being into school. . . . Finally some of my friends cornered me and told me how
much I had changed, and they said it started when I started smoking marijuana.
They came with me to see the substance-abuse counselor at school.

[quoted in Bell, 1998, p. 199]

Adolescents who regularly smoke marijuana are likely to drop out of school, become
teenage parents, and be unemployed (Chassin et al., 2004). Marijuana affects
memory, language proficiency, and motivation (Lane et al., 2005)— all especially
crucial during adolescence.

For decades, researchers have noted that many drug-using adolescents distrust
their parents, injure themselves, hate their schools, and get in trouble with the
law. One hypothesis was that the psychic strains of adolescence led to drug use.
However, longitudinal research suggests that drug use causes more problems than
it solves, often preceding anxiety disorders, depression, and rebellion (Chassin
et al., 2004).

Perhaps because drugs appear to make problems better but actually make them
worse, more drugs are sought for those worse problems, which leads to abuse and
addiction. Like Johanna above, many adolescents do not notice when they move
past use (experimenting) to abuse (causing harm) and then addiction (needing the
drug to feel normal). Addiction may take years, but Monitoring the Future reports
that, in 2006, 25 percent of high school seniors were binge drinkers (5 or more

Especially for College Roommates

You and your roommate respect each other’s

privacy, but your roommate is jeopardizing his

or her health by getting drunk every weekend

and practicing unsafe sex. What should you

do?

386 C H A P T E R 14 ■ Adolescence: Biosocial Development

➤Answer to Observation Quiz (from

page 384): The most important difference is

that, because moderate alcohol use during

adolescence is accepted in most European

countries, the girls in the Czech Republic are

casual about drinking in public. In addition,

the American girl is drinking straight from the

bottle, and she is drinking hard liquor—both

generally frowned upon in Europe.

➤Response for Older Brothers and

Sisters (from page 384): Smoking is very

addictive; urge your sister to stop now,

before the habit becomes ingrained. Most

adolescents care more about immediate

concerns than about the distant possibility of

cancer or heart disease, so tell your sister

about a smoker you know whose teeth are

yellow, whose clothing and hair reek of

smoke, and who is shorter than the rest of

his or her family. Then tell your parents; they

are your best allies in helping your sister have

a healthy adolescence.

➤Answer to Observation Quiz (from

page 385): No; they bummed them off a

stranger at this San Jose, California, shopping

mall. If you answered no, you probably had in

mind the fact that most states, including

California, are strictly enforcing their laws

against selling cigarettes to minors. You may

also have noticed the awkward way the girls

are holding their cigarettes and realized that

they have not yet been smoking long enough

to have become addicted to nicotine.

alcoholic drinks in a row in the past two weeks), 12 percent were daily cigarette
smokers, and 5 percent were daily marijuana users (Johnston et al., 2007). All
these suggest addiction.

Indeed, all psychoactive drugs are addictive, physically or psychologically, with
addiction more likely the younger a person is at first use (see Table 14.3). Com-
pared with nonusing high school students, users think they are using drugs as a
temporary respite, but early users often use the same drug at age 35, when most
people who first try drugs in college have quit (Merline et al., 2004). For example,
adolescent binge drinkers are almost four times more likely to drink heavily at
midlife than those who did not binge in high school (even if they drank heavily
at age 20).

Learning from Experience

As you just read, any drug that affects the brain is more harmful and yet more
attractive during adolescence than later. Herein lies another example of the
“unskilled driver,” referenced in the beginning of these chapters. Wisdom about
use and abuse, about moderation versus addiction, about tolerance and impair-
ment, and about particular risks comes with experience. A common phenomenon
is generational forgetting, the idea that each new generation forgets what the
previous generation learned about harmful drugs (Chassin et al., 2004; Johnston
et al., 2007).

Why does generational forgetting occur? One reason is that teenagers tend to
distrust adults, who experienced a different drug scene. For example, the most
widely used drug prevention program in U.S. high schools, project DARE, fea-
tures adults (usually police officers) telling high school students about the dangers
of drugs. DARE has no impact on later drug use, according to several reliable
studies (West & O’Neal, 2004).

Similarly, some antidrug advertisements and scare tactics (“your brain on
drugs”) have the opposite effect from that intended, probably because they make
the drug seem exciting (Block et al., 2002; Fishbein et al., 2002).

This does not mean that trying to halt early drug use is hopeless. Massive ad
campaigns in Florida and California have cut adolescent smoking in half, in part
by having teenagers help design the publicity. Throughout the United States,
higher prices and better law enforcement have led to a marked decline in smoking
among younger adolescents. In 2006, only 9 percent of eighth-graders had smoked
cigarettes in the past month, compared with 21 percent 10 years earlier (Johnston
et al., 2007).

Possible Problems 387

Still Smoking? Binge drinkers in high

school are 3.7 times more likely to be-

come heavy drinkers at midlife compared

with those who were not binge drinkers.

Adults generally stick to the same drugs

they used in high school (very seldom

crossing over from smoking cigarettes to

using cocaine, for instance), except that

illicit drug users often switch to abusing

prescription drugs.

TABLE 14.3

Adolescent Drug Use Predicts Adult Drug Use

As High School Senior Odds Ratio at Age 35

Binge drinking 3.7 for heavy drinking

Marijuana use 8.7 for marijuana use

Other illicit drugs 5.3 for cocaine use

3.4 for abuse of prescription drugs

Cigarette smoking, tried 3.3 for regular smoking

Cigarette smoking, in past month 12.7 for regular smoking

Cigarette smoking, regular 42.5 for regular smoking

Source: Merline et al., 2004.

generational forgetting The idea that each

new generation forgets what the previous

generation learned about harmful drugs.

➤Answer to Observation Quiz (from

page 385): Black females are least likely to

drink alcohol, with Black males the next-

lowest group. The White males’ and females’

rate of smoking dropped from 21 percent to

10 percent in just the four years from 1999 to

2003.

388 C H A P T E R 14 ■ Adolescence: Biosocial Development

Puberty Begins
1. Puberty refers to the various changes that transform a child’s
body into an adult one. Even before the teenage years begin, bio-
chemical signals from the hypothalamus to the pituitary gland to
the adrenal glands (the HPA axis) increase testosterone, estrogen,
and various other hormones. These hormones cause the body to
grow and change.

2. Puberty is accompanied by many emotions. Some, such as
quick mood shifts and thoughts about sex, are directly caused by
hormones, but most are only indirectly hormonal. Instead, they
are caused by reactions (from others and from the young persons
themselves) to the body changes of adolescence.

3. The visible changes of puberty normally occur anytime from
about age 8 to 14; puberty most often begins between ages 10 and
13. The young person’s sex, genetic background, body fat, and
level of family stress all contribute to this variation.

4. Girls generally begin and end the process before boys do.
Adolescents who do not reach puberty at about the same age as
their friends experience additional stresses. Generally (depending
on culture, community, and cohort), early-maturing girls have the
most difficult time of all.

5. To sustain body growth, most adolescents consume large quan-
tities of food, although they do not always make healthy choices.
One reason for poor nutrition is anxiety about body image.

The Transformations of Puberty
6. The growth spurt is an acceleration of growth in every part of
the body. Peak weight increase usually precedes peak height,
which is then followed by peak muscle growth. The lungs and the
heart also increase in size and capacity, and body rhythms (espe-
cially sleep) change.

7. Sexual characteristics emerge at puberty. The maturation of
primary sex characteristics means that by age 13 or so, menarche
and spermarche have occurred, and the young person is soon
capable of reproducing. In many ways, the two sexes experience
the same sexual characteristics, although they emerge in different
ways.

8. Secondary sex characteristics are not directly involved in re-
production but do signify that the person is a man or a woman.
Body shape, breasts, voice, body hair, and numerous other fea-
tures differentiate males from females. Sexual activity is influ-
enced more by culture than by physiology.

9. Various parts of the brain mature during puberty, each at its
own rate. The neurological areas dedicated to emotional arousal
(including the amygdala) mature ahead of the areas that regulate
and rationalize emotional expression (the prefrontal cortex). Con-
sequently, many adolescents seek intense emotional experiences,
untempered by rational thought.

10. The prefrontal cortex matures by early adulthood, allowing
better planning and analysis. Throughout this period, ongoing
myelination and experience allow faster and deeper thinking.

Possible Problems
11. Among the problems that adolescents face is sex before their
bodies and minds are ready. Pregnancy before age 16 takes a
physical toll on a growing girl, and STIs at any age can lead to
infertility and even death.

12. Most adolescents use drugs, especially alcohol and tobacco,
although such substances impair growth of the body and of the
brain. Prevention and moderation are possible, but programs
need to be carefully designed to avoid generational forgetting.

SUMMARY

Similarly, the declining U.S. rates of adolescent sex, birth, and abortion, as well
as all the variations in drug use just described, suggest that adolescent biology is
far from destiny, that the emotions and sexual impulses of puberty need not be
harmful.

As you will see in the next two chapters, experiences of peers, guidance from
elders, and application of research together have helped most young people avoid
the hazards of this age period. The energy and sexuality of the teen years are
fondly remembered by many adults. So it should be for everyone.

S U M M I N G U P

Although many adolescents are not yet sexually active or users of drugs, others are,

with a substantial minority involved in such activities before age 15. Early pregnancy

takes a physiological as well as psychological toll; early sexually transmitted infections

are particularly likely to spread; early use of alcohol, nicotine, or marijuana is particularly

likely to slow down development of the brain and body. Because of generational forget-

ting, adolescents learn best from other members of the same generation, which makes

it more difficult to warn them about the hazards of sex and drugs.
■

➤Response for College Roommates

(from page 386): Think about how you would

feel if your roommate died because you kept

quiet. Discuss your concerns with your

roommate, presenting facts as well as

feelings. You cannot make anyone change,

but you must raise the issue. You might also

consult the college health service.

Summary 389

parenthood? What would have been different had the baby been
born three years earlier or three years later?

4. Adults disagree about the dangers of drugs. Find two people
with very different opinions (e.g., a parent who would be horrified
if his or her child used any drug and a parent who believes that
young people should be allowed to drink or smoke at home).
Ask them to explain their reasons, and write these down without
criticism or disagreement. Later, present each with the arguments
from the other person. What is the response? How open, flexible,
and rational does it seem to be? Why are beliefs about drugs so
deeply held?

1. Visit a fifth-, sixth-, or seventh-grade class. Note variations in
the size and maturity of the students. Do you see any patterns
related to gender, ethnicity, body fat, or self-confidence?

2. Interview two to four of your friends who are in their late teens
or early 20s about their memories of menarche or spermarche,
including their memories of others’ reactions. Do their comments
indicate that these events are emotionally troubling for young
people?

3. Talk with someone who became a parent before the age of 20.
Were there any problems with the pregnancy, the birth, or the
first years of parenthood? Would the person recommend young

APPLICATIONS

puberty (p. 364)
menarche (p. 364)
spermarche (p. 364)
hormone (p. 364)
pituitary gland (p. 365)

adrenal glands (p. 365)
HPA axis (p. 365)
gonads (p. 365)
estradiol (p. 365)
testosterone (p. 365)
secular trend (p. 368)

body image (p. 370)
growth spurt (p. 371)
primary sex characteristics

(p. 373)

secondary sex characteristics

(p. 373)

sexually transmitted infection
(STI) (p. 381)

child sexual abuse (p. 382)
generational forgetting (p. 387)

KEY TERMS

8. Why is body image particularly likely to be distorted in adoles-
cence?

9. Almost all neuroscientists agree about certain aspects of brain
maturation. What are these aspects?

10. Why are sexually active adolescents more likely to contract
STIs than are sexually active adults?

11. What can help prevent teenage drug abuse?

1. What aspects of puberty are under direct hormonal control?

2. What psychological responses result from the physical changes
of puberty?

3. How do nature and nurture combine to enable young people
to become parents?

4. Why is experiencing puberty “off time” especially difficult?

5. What are the similarities of puberty for males and females?

6. What are the differences of puberty for males and females?

7. Name three reasons many adolescents have nutritional defi-
ciencies.

KEY QUESTIONS