Adolescence Chapter 1 PDF

Part 1 The Fundamental Changes of Adolescence 1 Biological Transitions 2 Cognitive Transitions 3 Social Transitions 1 Puberty: An Overview...

Part 1 The Fundamental Changes of Adolescence 1 Biological Transitions 2 Cognitive Transitions 3 Social Transitions 1 Puberty: An Overview Biological Transitions The Psychological and Social Impact of The Endocrine System Puberty What Triggers Puberty? The Immediate Impact of Puberty How Hormones Influence Adolescent The Impact of Specific Pubertal Events Development The Impact of Early or Late Maturation Somatic Development Obesity and Eating Disorders The Adolescent Growth Spurt Obesity Sexual Maturation Anorexia Nervosa, Bulimia, and Binge Eating The Timing and Tempo of Puberty Disorder Variations in the Timing and Tempo of Puberty Genetic and Environmental Influences on Pubertal Timing ©Image Source/Getty Images 14  CHAPTER 1 Biological Transitions 15 According to an old joke, there are only two things some traditional societies, pubertal maturation brings with it in life that one can be sure of—death and taxes. To this a series of public initiation rites that mark the passage of the brief list, we might add puberty—the physical changes of young person into adulthood, socially as well as physically. adolescence. Not all adolescents experience identity cri- In other societies, recognition of the physical transformation ses, rebel against their parents, or fall madly in love, but from child into adult takes more subtle forms. Parents may virtually all go through puberty, the biological changes that merely remark, “Our little boy has become a man,” when change our appearance and ultimately make us capable they discover that he needs to shave, or “Our little girl has of sexual reproduction. grown up,” when they learn that she has gotten her first Puberty, however, is greatly affected by the context period. Early or late maturation may be cause for celebra- in which it occurs. Physical development is influenced tion or cause for concern, depending on what is admired by a host of environmental factors, and the timing and or made fun of in a given peer group at a given point in rate of pubertal growth vary across regions of the world, time. The fifth-grader who is developing breasts might be socioeconomic classes, ethnic groups, and historical eras. embarrassed, but the ninth-grader who has not developed Today, in contemporary America, the average girl has her breasts might be equally self-conscious. first period at about age 12. At the turn of the 20th century, In sum, even the most universal aspect of adolescence— she was around 14½. puberty—is hardly universal in its impact on the young Physical and sexual maturation profoundly affect the person. In this chapter, we examine just how and why the ways in which adolescents view themselves and are viewed environment in which adolescents develop exerts its influ- and treated by others. But the social environment exerts a ence even on something as fundamental as puberty. As tremendous impact on the psychological and social conse- you will learn, the adolescent’s social environment even quences of going through puberty (Skoog & Stattin, 2014). In affects the age at which puberty begins. Puberty: An Overview The Endocrine System Puberty derives from the Latin word pubertas, which The endocrine system produces, circulates, and regulates means “adult.” Technically, the term refers to the period levels of hormones. Hormones are highly specialized sub- during which an individual becomes capable of sexual stances that are secreted by one or more endocrine glands reproduction. More broadly, however, puberty encom- and then enter the bloodstream and travel throughout passes all the physical changes that occur in adolescents the body. Glands are organs that stimulate particular as they pass from childhood into adulthood (Dorn & parts of the body to respond in specific ways. Many Biro, 2011). of the hormones that play important roles at puberty Puberty has three chief physical manifestations: carry their instructions by activating certain brain cells, called gonadotropin-releasing hormone (GnRH) neurons 1. A rapid acceleration in growth, resulting in dramatic (Romeo, in press). increases in height and weight. endocrine system The system of the body that 2. The development of primary sex characteristics, The Hormonal Feedback produces, circulates, and including the further development of the gonads Loop The endocrine sys- regulates hormones. (sex glands), which results in a series of hormonal tem receives its instructions to hormones changes. increase or decrease circulating Highly specialized substances 3. The development of secondary sex characteristics, levels of particular hormones secreted by one or more including changes in the genitals and breasts, and the from the central nervous sys- endocrine glands. growth of pubic, facial, and body hair. tem, mainly through the firing glands of GnRH neurons. The sys- Organs that stimulate Each of these sets of changes is the result of devel- tem works like a thermostat. particular parts of the body opments in the endocrine and central nervous sys- Hormonal levels are “set” at a to respond in specific ways to tems, many of which begin years before the signs of certain point, which may differ particular hormones. puberty are evident—some actually occur at conception depending on the stage of devel- gonadotropin-releasing (Susman & Dorn, 2009). No new hormones are pro- opment, just as you might set hormone (GnRH) neurons duced at puberty. Rather, the levels of some hormones a thermostat at a certain tem- Specialized neurons that are that have been present since before birth increase, perature (and use different set- activated by certain pubertal hormones. whereas others decline. tings during different seasons 16 PART 1 The Fundamental Changes of Adolescence or different times of the day). set point By setting your room’s thermo- Hypothalamus A physiological level or stat at 60°F, you are instructing setting (e.g., of a specific your heating system to go into The hypothalamus inhibits hormone) that the body The hypothalamus the pituitary gland unless attempts to maintain action when the room becomes monitors levels of sex hormone levels fall through a self-regulating colder than that. Similarly, sex hormones to below a set point. system. when a particular hormonal maintain the correct set point. feedback loop level in your body dips below A cycle through which two or the endocrine system’s set point Pituitary more bodily functions respond for that hormone, secretion of gland to and regulate each other, the hormone increases; when such as that formed by the the level reaches the set point, When signalled by the hypothalamus, the pituitary hypothalamus, the pituitary gland, and the gonads. secretion temporarily stops. gland signals the gonads to And, as is the case with a ther- release more sex hormones. pituitary gland mostat, the setting level, or set One of the chief glands point, for a particular hormone When signaled by the responsible for regulating Gonads can be adjusted up or down, pituitary gland, the levels of hormones in depending on environmental or gonads (testes in males, the body. ovaries in females) release internal bodily conditions. sex hormones. hypothalamus A part of the brain that Such a feedback loop— the controls the functioning of the HPG axis (for hypothalamus, Sex hormones pituitary, gonads)—becomes (androgens and pituitary gland. estrogens) increasingly important at the gonads The glands that secrete sex onset of puberty. Long before Figure 1.1 Levels of sex hormones are regulated by hormones: in males, the testes; adolescence— in fact, before a feedback system (the HPG axis) composed of the in females, the ovaries. birth—the HPG axis develops hypothalamus, pituitary gland, and gonads. (Grumbach, Roth, Kaplan, & Kelch, 1974) testes involving three structures: the The male gonads. pituitary gland (which controls hormone levels in general), the ovaries stops inhibiting the pituitary, permitting it to stimu- hypothalamus (the part of the The female gonads. brain that controls the pitu- late the release of sex hormones by the gonads. When androgens itary gland, and where there hormone levels reach the set point, the hypothalamus A class of sex hormones is a concentration of GnRH responds by once again inhibiting the pituitary gland. secreted by the gonads, neurons), and the gonads (in Just as you might change the setting on your heating found in both sexes, but in higher levels among males males, the testes; in females, thermostat automatically every November 1, or when than females following the ovaries), which release the your utility bill has become too expensive, your brain puberty. “sex” hormones— androgens is constantly monitoring a variety of signals and adjust- estrogens and estrogens (see Figure 1.1). ing your hormonal set points in response. Puberty A class of sex hormones Although you may think of begins when several different signals— genetic as well secreted by the gonads, androgens as “male” hormones as environmental—instruct the brain to change the set found in both sexes, but and estrogens as “female” hor- point (Sisk & Romeo, 2018). in higher levels among mones, both types of hormones females than males following puberty. are produced by each sex, and Adrenarche Just before puberty, the pituitary begins both are present in males and to secrete hormones that act on the thyroid and on the HPG (hypothalamic- females at birth. During ado- adrenal gland, as well as hormones that stimulate growth pituitary-gonadal) axis lescence, however, the average more generally (which is why we grow taller and heavier The neurophysiological pathway that creates a male produces more andro- during puberty). As with sex hormones, the release of feedback loop involving the gens than estrogens, and the these substances is also under the control of the hypo- hypothalamus, the pituitary average female produces more thalamus. The thyroid and adrenal gland, in turn, secrete gland, and the gonads. estrogens than androgens hormones that cause various bodily changes to take (Susman & Dorn, 2009). place. Your HPG axis is set to maintain certain levels of Do you remember the first time you felt sexually androgens and estrogens. It is under the control of the attracted to someone? Maybe it was a tingly feeling that hypothalamus, which inhibits the pituitary gland when you didn’t yet have words for. It turns out that most indi- hormonal levels get too high. When these hormone viduals report that their first sexual attraction took place levels fall below their set points, the hypothalamus before they went through puberty. These early sexual  CHAPTER 1 Biological Transitions 17 feelings may be stimulated by maturation of the adrenal glands, called adrenarche (Herdt & McClintock, 2000), which also contributes to the development of body odor, signaling the beginning of sexual maturation to others (Campbell, 2011). Changes at puberty in the brain system that regulates the adrenal gland are also important because this is the brain system that controls how we respond to stress (Del Giudice, Angeleri, & Manera, 2009). One reason ado- lescence is a period of great vulnerability for the onset of many serious mental disorders is that the hormonal changes of puberty make us more responsive to stress (Burke, McCormick, Pellis, & Lukkes, 2017; Monahan, Guyer, Silk, Fitzwater, & Steinberg, 2016; Romeo, Patel, Pham, & So, 2016; Sisk & Romeo, in press; Susman, Peckins, Bowes, & Dorn, 2017). This leads to excessive secretion of the stress hormone cortisol, a substance that at high and chronic levels can cause brain cells to Early feelings of sexual attraction to others are stimulated die (Carrion & Wong, 2012; Gunnar, Wewerka, Frenn, by adrenarche, the maturation of the adrenal glands, which Long, & Griggs, 2009). Exposure to stress in adoles- takes place before the outward signs of puberty are evident. cence is also associated with physical health problems ©Glow Images and later cardiovascular illness (Crestani, 2017; Lippold, McHale, Davis, Almeida, & King, 2016). Keep in mind, production of kisspeptin in the brain is affected by other though, that there is a difference between saying that chemicals, most importantly leptin, which stimulates it, adolescence is an inherently stressful time (which it is and melatonin, which suppresses it. Leptin is a protein not) and saying that adolescence is a time of heightened produced by fat cells, and which exists in our body in vulnerability to stress (which it is). levels proportionate to our amount of body fat. It plays a critical role in the regulation of hunger and appetite, by suppressing our desire to eat when we’re full. In some making the personal senses, leptin serves to signal the brain not just that we connection are full enough, but that we are “fat enough.” Melatonin Do you remember your first feelings of sexual attraction is a hormone that helps regulate the sleep cycle, which for someone? How old were you? we’ll discuss later in this chapter. Your genes predispose you to go through puberty around a particular age, but the more fat cells you have, and the more What Triggers Puberty? light to which you have been adrenarche The maturation of the adrenal Although the HPG axis is active before birth, it is rela- exposed during childhood, the glands that takes place during tively quiet during childhood. Something happens during more likely it is that you will go adolescence. middle childhood, though, that reawakens the HPG axis through puberty on the early cortisol and signals it that the body is ready for puberty. Some of side of your inherited propensity. A hormone produced when a this is due to a clock whose “puberty alarm” is set very Someone with the same genes, person is exposed to stress. early in life by information coded in our genes (the age but who is thin and doesn’t get kisspeptin at which someone goes through puberty is largely inher- as much light exposure, will go A brain chemical believed to ited). But some of the reawakening of the HPG axis at through puberty later (Lomniczi trigger the onset of puberty. puberty is due to multiple signals that tell the brain it et al., 2013). This is why puberty leptin is time to start preparing for childbearing. These sig- starts earlier among overweight A protein produced by the fat nals indicate whether there are sexually mature mating children and among children cells that may play a role in the partners in the environment, whether there are suffi- who grow up closer to the equa- onset of puberty through its cient nutritional resources to support a pregnancy, and tor (Lee et al., 2016). Obese impact on kisspeptin. whether the individual is physically mature and healthy children have more body fat and melatonin enough to begin reproducing. therefore produce a lot more A hormone secreted by the The onset of puberty is stimulated by an increase in leptin, which stimulates kiss- brain that contributes to sleepiness and that triggers a brain chemical called kisspeptin (Roseweir & Millar, peptin production. Children who the onset of puberty through 2009) (so named because it was discovered in Hershey, live near the equator are exposed its impact on kisspeptin. Pennsylvania, the birthplace of chocolate kisses). The to relatively more sunlight each 18 PART 1 The Fundamental Changes of Adolescence How Hormones Influence Adolescent Development Most people understandably think that changes in behav- ior at puberty result from changes in hormones at that time. But this is only partially correct. Long before ado- lescence—in fact, before birth—hormones organize the brain in ways that may not be manifested in behavior until childhood or even adolescence (Sisk & Romeo, in press). Generally, until about eight weeks after conception, the human brain is “feminine” unless and until it is exposed to certain “masculinizing” hormones, like testosterone. Because levels of testosterone are higher among males than females while the brain is developing, males usually end up with a more “masculinized” brain than females. This sex difference in brain organization predetermines certain patterns of behavior, many of which may not actu- ally appear until much later (Sisk & Romeo, in press). Studies of sex differences in aggression, for example, show that even though some of these differences may not appear until adolescence, they likely result from the impact of prenatal hormones, rather than from hormonal changes at puberty. For instance, my dog, Benson, a male who was neutered shortly after birth, and therefore didn’t have testicles when he reached “adolescence” (which in dogs begins sometime between six months and one year, Even though our dog, Benson, was neutered soon after he was with smaller dogs maturing earlier than larger ones), still born, he still displayed stereotypic “humping” behavior when displayed stereotypic male “humping” behavior when he he reached adolescence, as a result of the impact of prenatal reached this age. This was likely due to the way his brain testosterone on his brain. He is pictured here with his favorite was programmed by sex hormones before he was born. romantic partner, Lambie. ©Wendy Steinberg In other words, the presence or absence of certain hor- mones early in life “program” the brain and the central nervous system to develop in certain ways and according year, and they have lower melatonin levels as a result, so to a certain timetable (Sisk & Romeo, in press). Because their kisspeptin production is not suppressed as much as we may not see the resulting changes in behavior until it is among children who live closer to the poles. Exposure adolescence, it is easy to mistakenly conclude that the to artificial light, especially the kind of light emitted from behaviors result from hormonal changes that take place electronic gadgets, can also suppress melatonin levels and at the time of puberty. In reality, however, exposure to cer- hasten puberty (Greenspan & Deardorff, 2014). Children tain hormones before birth may set a sort of alarm clock who spend a lot of time in front of electronic screens may that does not go off until adolescence. Just because the be inadvertently speeding up the onset of puberty. alarm clock rings at the same time that puberty begins The reason that body fat and light exposure affect the does not mean that puberty caused the alarm to go off. timing of puberty is found in our evolutionary history. Many changes in behavior at adolescence do occur Humans evolved when resources were scarce, and it was because of changes in hormone levels at puberty, how- adaptive to conceive and bear as many offspring as pos- ever (Schulz & Sisk, 2016). For instance, the increase in sible, since not all of them would survive. If the ultimate certain hormones at puberty is thought to stimulate the goal is to bear as many healthy children as possible, once development of secondary sex characteristics, such as someone has developed enough fat and senses that the the growth of pubic hair. There is also growing evidence season is right for gathering food, it is time to start matur- that puberty affects the brain in ways that increase ado- ing physically. Our genes don’t know that we no longer lescents’ emotional arousal and desire for highly reward- live in a resource- scarce world and can store food in our ing, exciting activities, which may make teenagers who cupboards and refrigerators so that we have plenty to eat are especially sensitive to rewards more prone to emo- in the dark of winter. Although conditions have changed, tional and behavioral problems (Forbes & Dahl, 2010; our brains evolve much more slowly, and the timing of Harden & Mann, 2015; Icenogle et al., 2017; LeMoult, puberty is still affected by how much fat we have accumu- Colich, Sherdell, Hamilton, & Gotlib, 2015; Spielberg lated and how much light we’ve been exposed to. et al., 2015).  CHAPTER 1 Biological Transitions 19 Still other changes during puberty are likely to be gain of height and weight that adolescent growth spurt results of an interaction between prenatal and pubertal typically occurs but the speed The dramatic increase in height hormones (Collaer & Hines, 1995). Hormones that are with which the increases take and weight that occurs during present prenatally may organize a certain set of behav- place. Think for a moment of puberty. iors (for example, our brains may be set up to have us how quickly very young children peak height velocity later engage in sexual behavior), but certain changes in grow. At the time of peak height The point at which the those hormones at puberty may be needed to activate the velocity—the time at which the adolescent is growing most pattern; that is, individuals may not become motivated to adolescent is growing most rap- rapidly. engage in sex until puberty. idly—he or she is growing at the epiphysis same rate as a toddler. For boys, The closing of the ends of peak height velocity averages the bones, which terminates Somatic Development about 4 inches (10.3 centime- growth after the adolescent growth spurt has been ters) per year; for girls, it’s about The effects of the hormonal changes of puberty on the completed. 3.5 inches (9.0 centimeters). adolescent’s body are remarkable. The individual enters One marker of the conclusion of puberty looking like a child but within four years or so puberty is the closing of the ends of the long bones in the has the physical appearance of a young adult. During this body, a process called epiphysis, which terminates growth relatively brief period, the average individual grows about in height. Puberty is also a time of significant increase in 10 inches taller, matures sexually, and develops an adult- weight—nearly half of one’s adult body weight is gained proportioned body. Along with many other organs, the during adolescence (Susman & Dorn, 2009). brain changes in size, structure, and function at puberty, Figure 1.2 shows just how remarkable the growth a series of developments we’ll discuss in Chapter 2. spurt is with respect to height. The graph on the left shows changes in absolute height and indicates, as you would expect, that the average individual grows through- The Adolescent Growth Spurt out infancy, childhood, and adolescence. As you can see, The simultaneous release of growth hormones, thyroid there is little gain in height after age 18. But look now at hormones, and androgens stimulates rapid acceleration in the right-hand graph, which shows the average increase height and weight. This dramatic increase in stature is called in height per year (i.e., the rate of change) over the same the adolescent growth spurt. What is most incredible about age span. Here you can see the acceleration in height at the adolescent growth spurt is not so much the absolute the time of peak height velocity. (a) (b) 24 22 190 180 Boy 20 170 18 Girl 160 16 Height gain (cm/year) 150 140 14 130 Height (cm) 12 120 110 10 Boy 100 8 Girl 90 6 80 70 4 60 2 50 1 3 5 7 9 11 13 15 17 19 1 3 5 7 9 11 13 15 17 19 Age Age Figure 1.2 (a) Height (in centimeters) at different ages for the average male and female youngster. (b) Gain in height per year (in centimeters) for the average male and female youngster. Note the adolescent growth spurt. (Adapted from Marshall, 1978) 20 PART 1 The Fundamental Changes of Adolescence Figure 1.2 also indicates that the growth spurt occurs, girls to become overly concerned about their weight— on average, about two years earlier among girls than even when their weight is within the normal range for boys. In general, as you can see by comparing the two their height and age (Calzo et al., 2012). As you will graphs, boys tend to be somewhat taller than girls before read later in this chapter, adolescence is the period of age 11; then girls tend to be taller than boys between greatest risk for the development of eating disorders ages 11 and 13; and finally, boys tend to be taller than such as anorexia, bulimia, and binge eating disorder. girls from about age 14 on. Sex differences in height can One study of college undergraduates found that women be a concern for many young adolescents when they who recalled being unprepared for and disliking going begin socializing with members of the opposite sex, through puberty were at relatively greater risk for devel- especially if they are tall, early-maturing girls or short, oping an eating disorder many years later (Moore, late-maturing boys. McKone, & Mendle, 2016). The sequence in which various parts of the body grow Although the majority of girls diet unnecessarily is fairly regular. Extremities—the head, hands, and feet— during this time in response to the increase in body fat, are the first to accelerate in growth. Accelerated growth the girls who are most susceptible to feelings of dissat- occurs next in the arms and legs, followed by the torso isfaction with their bodies during this phase of develop- and shoulders. ment are those who mature early and begin dating early Because different parts of the body do not all grow at (Smolak, Levine, & Gralen, 1993). Girls who spend a lot the same rate or at the same time during puberty, young of time talking about their looks with their friends, who adolescents often appear to be out of proportion phys- are teased about their weight (especially by boys), or who ically—as though their nose or legs were growing faster are pressured to be thin are especially vulnerable to feel- than the rest of them (which may actually be the case). ings of body dissatisfaction (Webb & Zimmer- Gembeck, This is why young adolescents often look clumsy or 2013; Webb et al., 2015). Girls’ body dissatisfaction is gawky. It is probably little consolation for someone going often blamed on the impact of the mass media’s exces- through the awkward phase of puberty to be told that an sively positive portrayal of thinness, but studies show that attractive balance probably will be restored within a few it is comparing themselves with their friends, and not just years, but, fortunately, this is what usually happens. being exposed to media imagery, that leads to unhappi- ness about their appearance (Ferguson, Muñoz, Garza, & Body Dissatisfaction Among Adolescent Girls. Galindo, 2014), and that adolescent girls’ conversations Sex Differences in Muscle and Fat The spurt about their looks are affected by the media images they in height during adolescence is accompanied by an are exposed to in a way that leads them to reinforce increase in weight that results from an increase in both each other (Rousseau & Eggermont, 2017; Trekels & muscle and fat, but there are important sex differences Eggermont, 2017), in part because girls who are espe- in adolescent body composition. Before puberty, there cially weight-conscious often hang around with peers who are relatively few sex differences in muscle development share the same concerns (O’Connor, Burt, VanHuysse, & and only slight sex differences in body fat. In both sexes, Klump, 2016). muscular development is rapid during puberty, but mus- There are also important ethnic and cross-cultural dif- cle tissue grows faster in boys than girls (Bogin, 2011). ferences in the ways in which adolescent girls feel about In contrast, body fat increases for both sexes during their changing bodies. In many parts of the world, includ- puberty, but more so for females than for males, espe- ing North and South America, Europe, and Asia, there cially during the years just before puberty. (For boys, is strong pressure on girls to be thin (Jones & Smolak, there is actually a slight decline in body fat just before 2011). Black adolescents seem less vulnerable to these puberty.) The end result of these sex differences is feelings of body dissatisfaction than other girls (Ali, that boys finish adolescence with a muscle- to- fat ratio Rizzo, & Heiland, 2013; Jung & Forbes, 2013), and con- of about 3 to 1, but the comparable ratio for girls is sequently they are less likely to diet, in part because of approximately 5 to 4. This has important implications ethnic differences in conceptions of the ideal body type for understanding why sex differences in strength and (Granberg, Simons, & Simons, 2009). Consistent with athletic ability often appear for the first time during ado- this, a recent study of Black girls found that early matur- lescence. According to one estimate, about half of the ers who were not dating were more likely to be depressed sex difference in athletic per- than those who were romantically involved (Carter, secondary sex formance during early adoles- Caldwell, Matusko, & Jackson, 2015). characteristics The manifestations of cence results simply from the difference in body fat (Smoll & sexual maturity at puberty, including the development of Schutz, 1990). Sexual Maturation breasts, the growth of facial The rapid increase in body Puberty brings with it a series of developments associ- and body hair, and changes in fat among females in early ado- ated with sexual maturation. In both boys and girls, the the voice. lescence frequently prompts development of secondary sex characteristics is typically  CHAPTER 1 Biological Transitions 21 Table 1.1 The sequence of physical changes at puberty Girls Boys Age of First Appearance Age of First Appearance (Years) Characteristic (Years) Characteristic 1. 7–13 Growth of breasts 1. 10–13½ Growth of testes, 2. 7–14 Growth of pubic hair scrotal sac 3. 9½–14½ Body growth 2. 10–15 Growth of pubic hair 4. 10–16½ Menarche 3. 10½–16 Body growth 5. About two years after Underarm hair 4. 11–14½ Growth of penis pubic hair 5. About the same time Change in voice (growth 6. About same time as Oil- and sweat-producing as penis growth of larynx) underarm hair glands 6. About two years after Facial and underarm hair pubic hair appears 7. About same time as Oil- and sweat-producing underarm hair glands, acne Source: Goldstein, B. (1976). divided into five stages, often called Tanner stages, after Sexual Maturation in Girls The sequence of develop- the British pediatrician who devised the categorization ment of secondary sex characteristics among girls (shown in system. Table 1.1) is less regular than it is among boys. Usually, the first sign of sexual maturation in girls is the elevation of the Sexual Maturation in Boys The sequence of devel- breast—the emergence of the “breast bud.” In about one-third opments in secondary sex characteristics among boys is of all adolescent girls, however, the appearance of pubic hair fairly orderly (see Table 1.1). Generally, the first stages precedes breast development. The development of pubic of puberty involve growth of the testes and scrotum, hair in females follows a sequence similar to that in males— accompanied by the first appearance of pubic hair. generally, from sparse, downy, light-colored hair to denser, Approximately 1 year later, the growth spurt in height curlier, coarser, darker hair. Breast development often occurs begins, accompanied by growth of the penis and further concurrently with the growth of pubic hair and generally development of pubic hair—now coarser and darker. The proceeds through several stages during which the shape and five Tanner stages of penis and pubic hair growth in boys definition of the nipple and areola change. The female breast are shown in Figure 1.3. undergoes these changes at puberty regardless of changes in The emergence of facial and body hair are relatively late breast size (which is why breast size alone is a poor indicator developments. The same is true for the deepening of the of pubertal maturation). The five Tanner stages of breast and voice, which is gradual and generally does not occur until pubic hair growth in girls are shown in Figure 1.4. very late adolescence. During puberty, there are changes As is the case for boys, puberty brings important inter- in the skin as well. The skin becomes rougher, especially nal changes for adolescent girls that are associated with around the upper arms and thighs, and there is increased the development of reproductive capacity. In girls, these development of the sweat glands, which often gives rise to changes involve development and growth of the uterus, acne, pimples, and increased oiliness of the skin. vagina, and other aspects of the reproductive system. In Other, internal changes that permit ejaculation occur addition, there is enlargement of the labia and clitoris. that are important elements of sexual maturation. At the As is apparent in Table 1.1, the growth spurt is likely time that the penis develops, the seminal vesicles, the to occur during the early and middle stages of breast prostate, and the bulbourethral glands also enlarge and and pubic hair development. Menarche, the beginning develop. The first ejaculation of seminal fluid generally of menstruation, is a relatively occurs about one year after the beginning of accelerated late development. Generally, Tanner stages penis growth, although this is often determined culturally full reproductive function does A widely used system that rather than biologically, since for many boys’ first ejacula- not occur until several years describes the five stages of tion occurs as a result of masturbation (J. Tanner, 1972). after menarche, and regular pubertal development. One interesting observation about the timing and sequence ovulation follows menarche by menarche of pubertal changes in boys is that they are generally fertile about two years (Bogin, 2011). The time of first menstruation, (i.e., capable of fathering a child) before they have devel- Unlike boys, therefore, girls one of the most important changes to occur among oped an adultlike appearance (Bogin, 2011). As you will generally appear physically females during puberty. read in the next section, the opposite is true for girls. mature before they are fertile. 22 PART 1 The Fundamental Changes of Adolescence Penis and Scrotum Pubic Hair Stage 1: The infantile Stage 1: There is no true stage that persists from pubic hair, although there birth until puberty begins. may be a fine vellus over During this time the pubes similar to that the genitalia increase over other parts of the slightly in overall size but abdomen. there is little change in general appearance. Stage 2: Sparse growth of lightly pigmented hair, Stage 2: The scrotum has which is usually straight or begun to enlarge, and only slightly curled. This there is some reddening usually begins at either and change in texture of side of the base of the the scrotal skin. penis. Stage 3: The penis has Stage 3: The hair spreads increased in length and over the pubic symphysis there is a smaller increase and is considerably darker in breadth. There has been and coarser and usually further growth of the more curled. scrotum. Stage 4: The length and Stage 4: The hair is now breadth of the penis have adult in character but increased further and the covers an area glans has developed. The considerably smaller than scrotum is further enlarged in most adults. There is no and the scrotal skin has spread to the medial become darker. surface of the thighs. Stage 5: The genitalia are Stage 5: The hair is Penis adult in size and shape. distributed in an inverse Scrotum The appearance of the triangle as in the female. It Glans genitalia may satisfy the has spread to the medial (Head) criteria for one of these surface of the thighs but Testes stages for a considerable not elsewhere above the time before the penis and base of the triangle. scrotum are sufficiently developed to be classified as belonging to the next stage. Figure 1.3 The five pubertal stages for penile and pubic hair growth. (From Morris & Udry, 1980) different changes on puberty are, and how adolescents The Timing and Tempo of Puberty perceive their own pace of development all have import- Thus far, no mention has been made of the “normal” ages ant mental health implications (Mendle, 2014). at which various pubertal changes are likely to take place. This is because variations in the timing of puberty (the Variations in the Timing and Tempo age at which puberty begins) and in the tempo of puberty (the rate at which maturation occurs) are so great that it of Puberty is misleading to talk even about average ages. As you’ll The onset of puberty can occur as early as age 5 in girls read, differences among adolescents in when and how and 6 in boys, or as late as age 13 in girls and 13 in boys. quickly they go through puberty, how synchronized the In girls, the interval between the first sign of puberty and  CHAPTER 1 Biological Transitions 23 Breasts 1 Stage 1: No breast development. Stage 2: The first sign of breast development has appeared. This stage is sometimes 2 referred to as the breast budding stage. Some palpable breast tissue under the nipple; the flat area of the nipple (areola) may be somewhat enlarged. Stage 3: The breast is more distinct although 3 there is no separation between contours of the two breasts. Stage 4: The breast is further enlarged and there is greater contour distinction. The 4 nipple, including the areola, forms a secondary mound on the breast. Stage 5: Size may vary in the mature stage. The breast is fully developed. The contours are distinct and the areola has receded 5 into the general contour of the breast. Pubic Hair 1 2 3 Stage 1: No pubic hair. Stage 2: There is a small amount of long pubic hair chiefly along the vaginal lips. Stage 3: The hair is darker, coarser, and curlier and spreads sparsely over the skin around the vaginal lips. 4 5 Stage 4: The hair is now adult in type, but the area covered is smaller than in most adults. There is no pubic hair on the inside of the thighs. Stage 5: The hair is adult in type, distributed as an inverse triangle. There may be hair on the inside of the thighs. Figure 1.4 The five pubertal stages for breast and pubic hair growth. (From Marshall & Tanner, 1969) complete physical maturation can be as short as a year a late-maturing youngster has even begun puberty, and and a half or as long as 6 years. In boys, the comparable 8 years before a late-maturing, slow-maturing youngster interval ranges from about 2 to 5 years (J. Tanner, 1972). has matured completely! Think about it: Within a totally normal population of There is no relation between the age at which puberty young adolescents, some individuals will have completed begins and the rate at which pubertal development pro- the entire sequence of pubertal changes before others ceeds. The timing of puberty may have a small effect have even begun. In more concrete terms, it is possible on one’s ultimate height or weight, however, with late for an early-maturing, fast-maturing youngster to com- maturers, on average, being taller than early matur- plete pubertal maturation by age 10—3 years before ers as adults, and early maturers, on average, being 24 PART 1 The Fundamental Changes of Adolescence Individual Differences in Pubertal Maturation Comparisons of identical and nonidentical twins, which allow scientists to estimate how much a given trait is genetically determined, indicate that the timing and tempo of an individual’s pubertal maturation are largely inherited (Mustanski, Viken, Kaprio, Pulkkinen, & Rose, 2004). A specific region on chromosome 6 has been identified as one of the markers for pubertal timing in both boys and girls (Bogin, 2011). Despite this powerful influence of genetic factors, the environment plays an important role. In all likelihood, every individual inherits a predisposition to develop at a certain rate and to begin pubertal maturation at a cer- tain time. But this predisposition is best thought of as an upper and lower age limit, not a fixed absolute. Whether the genetic predisposition that each person has to mature around a given age is actually realized, and when within the predisposed age boundaries she or he actually goes Individuals vary considerably in when puberty begins and the through puberty, is influenced by many external factors. rate with which it progresses. ©Peathegee Inc/Getty Images In other words, the timing and tempo of pubertal matu- ration are the product of an interaction between nature and nurture. somewhat heavier—at least among females (St. George, By far the two most important environmental influ- Williams, & Silva, 1994). Adult height and weight are far ences on pubertal maturation are nutrition and health. more strongly correlated with height and weight during Puberty occurs earlier among individuals who are bet- childhood than with the timing of puberty, however ter nourished and grow more throughout their prenatal, (Pietiläinen et al., 2001). infant, and childhood years, whereas delayed puberty Within the United States, there are ethnic differences in is more likely to occur among individuals with a his- the timing and rate of pubertal maturation. Several large- tory of protein and/or caloric deficiency (Terry, Ferris, scale studies of U.S. youngsters indicate that Black girls Tehranifar, Wei, & Flom, 2009). Chronic illness during mature significantly earlier than Mexican American girls, childhood and adolescence is also associated with who, in turn, mature earlier than White girls (Chumlea delayed puberty, as is excessive exercise. Generally, then, et al., 2003; Herman- Giddens et al., 1997). Although the after genetic factors, the most important determinant of reasons for this ethnic difference are not known, it does not the timing of puberty is the overall physical well-being of appear to be due to ethnic differences in income, weight, or the individual from conception through preadolescence area of residence (S. E. Anderson, Dallal, & Must, 2003). (Susman & Dorn, 2009). One possible explanation for the earlier maturation of non- White girls is that they may be more frequently exposed to Familial Influences on Pubertal Timing A number chemicals in the environment that stimulate earlier puberty, of studies have shown that social factors in the home such as those contained in certain hair care products and environment also influence the onset of maturation, espe- cosmetics (Susman & Dorn, 2009). cially in girls. Puberty occurs somewhat earlier among girls who grew up in father-absent families, in less cohe- Genetic and Environmental Influences sive or more conflict-ridden households, or with a step- father (Culpin, Heron, Araya, & Johnson, 2015; Ellis, on Pubertal Timing 2004); early puberty is also more common among girls Why do some individuals mature relatively early and who were sexually abused during childhood (Mendle, others relatively late? Researchers who study variability Leve, Van Ryzin, & Natsuaki, 2014; Mendle, Ryan, & in the onset and timing of puberty approach the issue McKone, 2016; Negriff, Blankson, & Trickett, 2014). in two ways. One strategy involves the study of differ- One explanation for the finding that family conflict ences among individuals (i.e., studying why one individ- may accelerate pubertal maturation is that tension ual matures earlier or faster than another). The other in the family may induce stress, which, in turn, may involves the study of differences among groups of adoles- affect hormonal secretions in the adolescent (Belsky, cents (i.e., studying why puberty occurs earlier or more Steinberg, Houts, & Halpern- Felsher, 2010; Belsky, rapidly in certain populations than in others). Both sets Ruttle, Boyce, Armstrong, & Essex, 2015; Saxbe, of studies point to both genetic and environmental fac- Negriff, Susman, & Trickett, 2015), especially among tors (Ge, Natsuaki, Neiderhiser, & Reiss, 2007). girls who are genetically susceptible to this influence  CHAPTER 1 Biological Transitions 25 (Ellis, Shirtcliff, Boyce, Deardorff, & Essex, 2011; The Secular Trend We can pheromones Hartman, Widaman, & Belsky, 2015). (Other types of also examine environmental A class of chemicals secreted stress, like economic stress, hasten the onset of puberty, inf luences on the timing of by animals that stimulate too; Sun, Mensah, Azzopardi, Patton, & Wake, 2017.) puberty by looking at changes certain behaviors in other Interestingly, having a secure infant-mother attachment in the average age of menarche members of the species. seems to protect against the impact of harsh parenting over the past two centuries. secular trend on pubertal timing (Sooyeon et al., 2016). In addition, Because nutritional conditions The tendency, over the past the presence of a stepfather may expose the adolescent have improved during the past two centuries, for individuals girl to pheromones (a class of chemicals secreted by to be larger in stature and to 150 years, we would expect to reach puberty earlier, primarily animals that stimulate certain behaviors in other mem- find a decline in the average because of improvements in bers of the species) that stimulate pubertal maturation. age at menarche over time. health and nutrition. In general, among humans and other mammals, living This is indeed the case, as can in proximity to one’s close biological relatives appears be seen in Figure 1.5. This pat- to slow the process of pubertal maturation, whereas tern, known as the secular trend, is attributable not only exposure to unrelated members of the other sex may to improved nutrition but also to better sanitation and accelerate it. better control of infectious diseases. In most European Although it may seem surprising that something as countries, maturation has become earlier by about 3 to biological as puberty can be influenced by factors in the 4 months per decade. For example, in Norway 150 years social environment, scientists have long known that our ago, the average age of menarche may have been about social relationships affect our biological functioning. 17 years. Today, it is between 12 and 13 years. Similar One of the best-known examples of this is that women declines have been observed over the same period in who live together—such as dormitory roommates—find other industrialized nations and, more recently, in devel- that their menstrual periods begin to synchronize over oping countries as well. In China, for example, the aver- time (McClintock, 1980). age age of menarche dropped by nearly 2 years between 1991 and 2011 (Meng, Li, Duan, Sun, & Jia, 2017). Group Differences in Pubertal Maturation Unlike The secular trend is less well documented among differences among adolescents growing up in the same boys, in part because there is no easily measured marker environment, which are mainly due to genetics, differ- ences among countries in the average rate and timing of puberty are more likely to reflect differences in their environments (Bogin, 2011). The influence of the broader environment on the tim- ing and tempo of puberty can be seen in more concrete terms by looking at two sets of findings: (1) comparisons of the average age of menarche across countries and (2) changes in the average age of menarche over time. Although menarche does not signal the onset of puberty, researchers often use the average age of menarche when comparing the timing of puberty across different groups or historical eras, because it can be measured more reli- ably than other indicators. And while the age of men- arche doesn’t directly reflect when males in that same group are going through puberty, it does so indirectly, because in places where girls mature early, boys mature early, too (Steinberg, 2014a). Given the importance of nutrition and health as influences on pubertal timing, it comes as no surprise that menarche generally is earlier in countries where individuals are less likely to be malnourished or to suf- fer from chronic disease (Bogin, 2011). For example, in Western Europe and in the United States, the median age of menarche ranges from about 12 to 13½ years. In Africa, however, the median age ranges from about Scientists have expressed concern about the continuing decline 14 to 17 years. The range is much wider across Africa in the age when puberty begins, because pubertal hormones because of the greater variation in environmental condi- affect the developing brain in ways that increase sensation tions there. seeking. ©Rose Hayes/Shutterstock 26 PART 1 The Fundamental Changes of Adolescence Figure 1.5 The age at menarche has declined considerably over Germany the past 150 years. This decline is 17.0 Norway known as the secular trend. Sweden (Adapted from Eveleth & Tanner, 1990) Denmark United States 16.0 Finland Age at menarche (years) 15.0 14.0 14.0 13.5 13.0 13.0 1950 1960 1970 12.0 1840 1860 1880 1900 1920 1940 1960 1980 Year of menarche of puberty, like menarche. One unusual factoid that is the secular trend has not affected the age at which the consistent with the decline in the age of puberty among maturation of impulse control takes place. If the increase boys over many centuries, though, is the observation in sensation seeking is taking place before children are that the average age at which boys experience their voice able to regulate urges to do exciting things, it may lead to breaking (a sign of male pubertal development), based increases in risky and reckless behavior, especially when on reports from European children’s choirs, dropped the risk taking is impulsive (Khurana et al., 2012). The from about 18 in the mid-1700s to around 10 today end result is that, as the age of puberty has dropped, the (Mendle & Ferrero, 2012). The drop in the age of male amount of time elapsed between the arousal of sensation puberty appears to be continuing, and has fallen during seeking and the maturation of self-control has grown, the past three decades (Herman- Giddens et al., 2012). creating a larger window of vulnerability to risky behav- Interestingly, although puberty is starting earlier, there is ior (Steinberg, 2014). Consistent with this, as the age some evidence that it is taking longer to complete, mean- of puberty has fallen, rates of adolescent mortality have ing that children are spending more time in the midst of risen (Mendle, 2014). puberty than ever before (Mendle, 2014). The average age of puberty among American adoles- cents has continued to decline, most probably because making the scientific of increased rates of obesity, which affects leptin levels connection (Currie et al., 2012); exposure to certain man- made Some studies indicate that the secular trend has been chemicals in cosmetics, food, and the environment that more dramatic among females than males. Why might this affect development by mimicking actual pubertal hor- be the case? mones; and increased exposure to artificial light, which affects melatonin secretion (Greenspan & Deardorff, 2014). One reason scientists have expressed concern about The Psychological and Social the continuing decline in the age when puberty begins is that pubertal hormones affect the developing brain in Impact of Puberty ways that make adolescents more inclined to engage in Puberty can affect the adolescent’s behavior and psycho- sensation seeking (Steinberg, 2014). Brain systems that logical functioning in a number of ways (Hollenstein & govern self-regulation are less influenced by puberty, so Lougheed, 2013). First, the biological changes of puberty  CHAPTER 1 Biological Transitions 27 Researchers have generally cross-sectional study taken two approaches to study- A study that compares two or ing the psychological and social more groups of individuals at consequences of puberty. One one point in time. approach is to look at individ- longitudinal study uals who are at various stages A study that follows the same of puberty, either in a cross- group of individuals over time. sectional study (in which groups of individuals are compared at different stages of puberty) or in a longitudinal study (in which the same individuals are tracked over time as they mature through the different stages of puberty). Studies of this sort examine the impact of puberty on young people’s psychological development and social relations. Researchers might ask, for example, whether youngsters’ self-esteem is higher or lower during puberty than before or after. A second approach compares the psychological Contrary to widespread belief, there is little evidence that the development of early and late maturers. Because there hormonal changes of puberty contribute in a dramatic way to is large variation in pubertal timing, individuals of the adolescent moodiness. ©Westend61/Getty Images same chronological age and who are in the same grade in school may be at very different stages of puberty. How does being early or late to mature affect the adolescent’s can have a direct effect on behavior. For example, psychological development? Here, a typical question increases in testosterone at puberty are directly linked to might be whether early maturers are more popular in the an increase in sex drive and sexual activity among ado- peer group than are late maturers. lescent boys (Halpern, Udry, & Suchindran, 1996). (The impact of hormonal change on girls’ sex drive and sexual activity is more complicated, because girls’ sexual activ- The Immediate Impact of Puberty ity is significantly influenced by contextual factors.) Studies of the psychological and social impacts of Second, the biological changes of puberty may change puberty indicate that physical maturation, regardless of the adolescent’s self-image, which, in turn, may affect whether it occurs early or late, affects the adolescent’s how he or she behaves. For example, a boy who has self-image, mood, and relationships with parents. recently gone through puberty may feel more grown up as a result of his more adultlike appearance. This, in turn, Puberty and Self-Esteem Although puberty can be may make him seek more independence from his parents. a potential stressor with temporary adverse psychological He may ask for a later curfew, a larger allowance, or the consequences, this is true only when it is coupled with right to make decisions about things that previously were other changes that necessitate adjustment (Susman & decided by his parents. As we will see later in this chap- Dorn, 2009). The impact of puberty on self-esteem var- ter, the physical changes of puberty often spark conflict ies by gender and across ethnic groups, with girls more between teenagers and their parents, in part because of adversely affected than boys, and with White girls, in the ways in which puberty affects the adolescent’s desire particular, at greatest risk for developing a poor body for autonomy. image (J. Siegel, Yancey, Aneshensel, & Schuler, 1999). Finally, biological change at puberty transforms Given the premium in contemporary American society the adolescent’s appearance, which, in turn, may elicit placed on thinness, the increase in body dissatisfaction changes in how others react to the teenager (Lougheed, among White girls that takes place at puberty is, not Hollenstein, & Lewis, 2016). These changes in reactions surprisingly, linked to specific concerns that girls have may provoke changes in the adolescent’s behavior. An about their hips, thighs, waist, and weight. Interestingly, adolescent girl who has recently matured physically may the way adolescents feel about their physical appearance find herself suddenly receiving the attention of older when they begin adolescence remains remarkably stable boys who had not previously noticed her. She may feel over time, regardless of whether their actual attractive- nervous about all the extra attention and confused about ness changes (Rosenblum & Lewis, 1999). how she should respond to it. Moreover, she must now make decisions about how much time she wishes to Puberty and Adolescent Moodiness Although an devote to dating and how she should behave when out adolescent’s self-image can be expected to change during with someone who is sexually interested in her. a time of dramatic physical development, self-esteem 28 PART 1 The Fundamental Changes of Adolescence 3 3 2.8 2.8 2.6 2.6 2.4 2.4 Happiness Variability Anger Variability 2.2 2.2 2 2 1.8 1.8 1.6 1.6 1.4 1.4 1.2 1.2 1 1 Age13/14 Age14/15 Age15/16 Age16/17 Age17/18 Age13/14 Age14/15 Age15/16 Age16/17 Age17/18 3 3 2.8 2.8 2.6 2.6 2.4 2.4 Sadness Variability Anxiety Variability 2.2 2.2 2 2 1.8 1.8 1.6 1.6 1.4 1.4 1.2 1.2 1 1 Age13/14 Age14/15 Age15/16 Age16/17 Age17/18 Age13/14 Age14/15 Age15/16 Age16/17 Age17/18 Figure 1.6 Children become less moody as they get older. (Figure 1, from Maciejewsk, van Lier, Branje, Meeus, & Koot, 2015) or self-image is reasonably stable over time, with long behavior, the direct connection between hormones and and sturdy roots reaching back to childhood. For this mood is not very strong (Duke, Balzer, & Steinbeck, reason, some researchers have turned their attention 2014). When studies do find a connection between to the impact of puberty on more transient states, such hormonal changes at puberty and adolescent mood or as mood. One reason for this focus is that adolescents behavior, the effects are strongest early in puberty, when are thought to be moodier, on average, than either chil- the process is being “turned on” and when hormonal dren or adults. One classic study, in which adolescents’ levels are more likely to fluctuate. However, pubertal moods were monitored repeatedly by electronic pagers, hormones affect brain systems responsible for emotional for example, showed that their moods fluctuate during arousal in ways that make adolescents more respon- the course of the day more than do the moods of adults sive to what is going on around them socially (Forbes, (Csikszentmihalyi & Larson, 1984). Teenagers become Phillips, Silk, Ryan, & Dahl, 2011; Masten et al., 2011; less moody as they get older (Maciejewski, van Lier, Motta-Mena & Scherf, 2017; Op de Macks et al., 2017). Branje, Meeus, & Koot, 2015) (see Figure 1.6). For example, rapid increases in many of the hormones Many adults assume that adolescent moodiness is associated with puberty—such as testosterone, estrogen, directly related to the hormonal changes of puberty and various adrenal androgens—may be associated with (Buchanan, Eccles, & Becker, 1992). Is there any sci- increased irritability, impulsivity, aggression (in boys) entific evidence that the hormonal changes of puberty and depression (in girls), especially when the increases cause adolescents to be moody or, for that matter, that take place very early in adolescence. One interpretation these hormonal changes affect the adolescent’s psycho- of these findings is that it is not so much the absolute logical functioning or behavior at all? increases in these hormones during puberty but their According to several comprehensive reviews of rapid fluctuation early in puberty that may affect ado- research on hormones and adolescent mood and lescents’ moods. Once the hormone levels stabilize at  CHAPTER 1 Biological Transitions 29 12:30 pattern—called a delayed phase Weekday bedtime delayed phase preference Bedtime (P.M.) and wake time (A.M.) preference—is driven by the bio- A pattern of sleep Weekend bedtime logical changes of puberty, and characterized by later sleep 11:30 Weekday wake time it is seen not only in humans, and wake times, which usually Weekend wake time but in other mammals as well emerges during puberty. 10:30 (Carskadon, 2011). Falling asleep is caused by 9:30 a combination of biological and environmental factors. One of the most important is the secretion of melatonin, 8:30 which, as you know, plays a role in triggering puberty. Melatonin levels change naturally over the course of the 7:30 24-hour day, mainly in response to the amount of light in the environment. Feelings of sleepiness increase and decrease with melatonin levels—as melatonin rises, we 6:30 3 5 7 9 11 13 15 17 feel sleepier, and as it falls, we feel more awake. Over the Child’s age in years course of the day, we follow a sleep–wake cycle that is calibrated to changes in light and regulated by melatonin Figure 1.7 Children’s weekday and weekend bedtimes secretion. and wake times, by age. (Adapted from Snell, Adam, & Duncan, 2007) During puberty, the time of night at which melatonin levels begin to rise changes, becoming later and later as individuals mature physically. In fact, the nighttime higher levels, later in puberty, their negative effects wane increase in melatonin starts about 2 hours later among (Buchanan et al., 1992). adolescents who have completed puberty than among Although rapid increases in hormones early in puberty those who have not yet begun (Carskadon & Acebo, are associated with depressed mood in girls, it turns out 2002). As a result of this shift, individuals become able that stressful life events, such as problems in the family, to stay up later before feeling sleepy (Hummer & Lee, in school, or with friends, play a far greater role in the 2016). In fact, when allowed to regulate their own sleep development of depression and negative moods than do schedules (as on weekends), most teenagers will stay up hormonal changes (Brooks- Gunn, Graber, & Paikoff, until around 1:00 A.M. and sleep until about 10:00 A.M. 1994; Santiago et al., 2017). Similarly, while high levels Because the whole cycle of melatonin secretion is shifted of testosterone have been associated with impulsivity and later at puberty, this also means that once adolescents aggression and low levels with depression, these associ- have gone through puberty, they are more sleepy early in ations are weaker among adolescents who have positive the morning than they had been before puberty. family relationships or strong self-control (A. Booth, Johnson, Granger, Crouter & McHale, 2003; Reardon, Herzhoff, & Tackett, 2016). In other words, there is little evidence that adoles- cents’ moodiness results exclusively from the “storm and stress” of raging hormones. Over the course of a day, a teenager may shift from elation to boredom, back to happiness, and then to anger. But these shifts in mood appear to have more to do with shifts in activities— elated when seeing a girlfriend, bored during biology, happy when having lunch with friends, and angry when assigned extra chores around the house—than with inter- nal, biological changes (Schneiders et al., 2006). Not sur- prisingly, adolescents’ moods fluctuate over the course of the school year, too, with teenagers reporting the high- est levels of anxiety and stress at the end of the school year (Verma, Allen, Trinder, & Bei, 2017). Puberty and Changes in Patterns of Sleep Many parents complain that their teenage children go to bed too Important changes in the sleep cycle take place after puberty. late in the evening and sleep in too late in the morning, This “delayed phase preference” causes adolescents to want a pattern that begins to emerge in early adolescence (see to stay up later at night and makes them feel more tired in the Figure 1.7). It now appears that the emergence of this early morning hours. ©CORBIS/AGE Fotostock 30 PART 1 The Fundamental Changes of Adolescence Falling asleep is affected by the environment as well— using eyeglasses that block the blue- wavelength light it’s much easier to fall asleep when a room is dark than emitted by these screens can help reduce the adverse when it’s bright. When preadolescents get into bed at effects of screen light on sleep (van der Lely et al., 2015). night, they tend to fall asleep very quickly—even if there It has also been suggested that the demands of school is something that they want to stay up for—because their and extracurricular activities are taking their toll on ado- melatonin levels are already high. After going through lescents’ sleep by keeping them busy into the late hours. puberty, though, because of the delayed timing of the Whatever the reason, because teenagers’ wake time has increase in melatonin, it is easier for individuals to stay not changed, but their bedtime has gotten later, today’s up later, so that if there is something more exciting to teenagers get significantly less sleep than their counter- do—check an Instagram post, play a video game, text