Ch. 2- Puberty, Health, and Biological Foundations
Families
Parents have an important influence on adolescents' exercise patterns. Children and adolescents benefit when parents engage in regular exercise and are physically fit. Children whose parents got them involved in regular exercise and sports during the elementary school years are likely to continue engaging in exercise on a regular basis as adolescents. One study revealed that 9- to 13-year-olds were more likely to engage in physical activity during their free time if they felt safe, had a number of places to be active, and had parents who participated in physical activities with them (Heitzler & others, 2006).
Genotype
Genetic material of an organism, a person's genetic heritage
Two phases of puberty linked with hormonal changes
-Adrenarche -Gonadarche
Genetic code
Each of us carries a "genetic code" that we inherited from our parents. Because a fertilized egg carries this human code, a fertilized human egg cannot grow into an egret, eagle, or elephant.
Gender differences
In general, throughout puberty girls are less happy with their bodies and have more negative body images than do boys, which to some extent may be due to media portrayals of the attractiveness of being thin and the increase in body fat in girls during puberty
Evocative genotype-environment correlations
Occur because an adolescent's genetically shaped characteristics elicit certain types of physical and social environments. For example, active, smiling children receive more social stimulation than passive, quiet children do. Cooperative, attentive adolescents evoke more pleasant and instructional responses from the adults around them than uncooperative, distractible adolescents do. Athletically inclined youth tend to elicit encouragement to engage in school sports. As a consequence, these adolescents tend to be the ones who try out for sports teams and go on to participate in athletically oriented activities.
Extended childhood period
One important concept is that an extended childhood period evolved because humans require time to develop a large brain and learn the complexity of human societies. Humans take longer to become reproductively mature than any other mammal (see Figure 11). During this extended childhood period, they develop a large brain and acquire the experiences needed to become competent adults in a complex society.
Hormones
Powerful chemical substances secreted by the endocrine glands and carried throughout the body by the bloodstream
The Endocrine System
Puberty onset involves the activation of the hypothalamic-pituitary-gonadal (HPG) axis (see Figure 2). The hypothalamus is a structure in the higher portion of the brain that monitors eating, drinking, and sex. The pituitary gland is the endocrine gland that controls growth and regulates other glands. The gonads are the sex glands—the testes in males, the ovaries in females. How does the endocrine system work? The pituitary gland sends a signal via gonadotropins (hormones that stimulate sex glands) to the testes or ovaries to manufacture the hormone. Then, through interaction with the hypothalamus, the pituitary gland detects when the optimal level of hormones has been reached and maintains it with additional gonadotropin secretions
Male pubertal characteristics
Researchers have found that male pubertal characteristics develop in this order: increased penis and testicle size; appearance of straight pubic hair; minor voice change; first ejaculation (spermarche—this usually occurs through masturbation or a wet dream); appearance of kinky pubic hair; onset of maximum growth; growth of hair in armpits; more detectable voice changes; and growth of facial hair
Screen-Based Activity
Screen-based activity (watching television, using computers, talking on the phone, texting, and instant messaging for long hours) is associated with lower levels of physical fitness in adolescence (Bassett & others, 2015; Mitchell, Pate, & Blair, 2012).
Shared environmental experiences
Siblings' common experiences, such as their parents' personalities or intellectual orientation, the family's socioeconomic status, and the neighborhood in which they live
Schools
Some of the blame for the poor physical condition of U.S. children and adolescents falls on U.S. schools, many of which fail to provide physical education classes on a daily basis
FSH (follicle-stimulating hormone)
Stimulates follicle development in females and sperm production in males
Estrogens
The main class of female hormones
Chromosomes
Thread-like structures that contain the remarkable substance deoxyribonucleic acid, or DNA
Three leading causes of death in adolescence and emerging adults
-Accidents -Homicide -Suicide
Two hormones secreted by the pituitary gland that regulate levels of sex hormones
-FSH (follicle-stimulating hormone) -LH (luteinizing hormone)
Contextual factors influence whether adolescents engage in regular exercise
-Families - Peers -Schools - Screen-based activity
Spermarche
A boy's first ejaculation of semen, occurs in early to mid-gonadarche.
Puberty
A brain-neuroendocrine process occurring primarily in early adolescence that provides stimulation for the rapid physical changes that take place during this period of development
DNA
A complex molecule that contains genetic information. It has a double helix shape, like a spiral staircase.
Adaptive behavior
A modification of behavior that promotes an organism's survival in the natural habitat. All organisms must adapt to specific places, climates, food sources, and ways of life in order to survive (Hoefnagels, 2015; Johnson, 2015). In humans, attachment ensures an infant's closeness to the caregiver for feeding and protection from danger. This behavioral characteristic promotes survival just as an eagle's claw, which facilitates predation, ensures the eagle's survival.
Sports
A recent national study revealed that in 2013, 54 percent of ninth- through twelfth-grade U.S. students played on at least one sports team at school or in the community (Kann & others, 2014). The 54 percent figure represents a 4 percent drop from 2011. In the 2013 assessment, boys (60 percent) were more likely to play on a sports team than girls (48.5 percent). African American boys had the highest participation rate (66 percent) and Latino females the lowest participation rate (45 percent) (Kann & others, 2014). In another recent assessment, high school girls' participation increased between 1971 and 2012 (Bassett & others, 2015).
Twin study
A study in which the behavioral similarity of identical twins is compared with the behavioral similarity of fraternal twins
Adoption study
A study where investigators seek to discover whether the behavior and psychological characteristics of adopted children are more like those of their adoptive parents, who have provided a home environment, or more like those of their biological parents, who have contributed their heredity
Critical Juncture in Health
Adolescence is a critical juncture in the adoption of behaviors that are relevant to health (Kadivar & others, 2014; Latt & others, 2015; Quinlan-Davidson & others, 2014). Many of the behaviors that are linked to poor health habits and early death in adults begin during adolescence (Feinstein, Richter, & Foster, 2012). Conversely, the early formation of healthy behavior patterns, such as regular exercise and a preference for foods low in fat and cholesterol, not only has immediate health benefits but helps in adulthood to delay or prevent disability and mortality from heart disease, stroke, diabetes, and cancer (Schiff, 2015).
Peers
In a recent research review, peer/friend support of exercise, presence of peers and friends, peer norms, friendship quality and acceptance, peer crowds, and peer victimization were linked to adolescents' physical activity (Fitzgerald, Fitzgerald, & Aherne, 2012). Consider these studies described in the review: Peer/friend support. Friend support for physical activity was a stronger predictor of adolescent physical activity than support from parents or siblings (Duncan & others, 2007). Presence of peers and friends. Adolescent boys at risk for being overweight were less active than thin boys when alone but as active as thin boys when a peer was present (Rittenhouse, Salvy, & Barkley, 2011). Friendship quality and acceptance. Higher levels of friendship quality and acceptance were linked to youths' continued participation in youth soccer (Ulrich-French & Smith, 2009). Peer crowd affiliation. Adolescents who affiliated with "jocks" and "populars" exercised considerably more than their counterparts who affiliated with other crowds (MacKey & La Greca, 2007). Peer victimization. Being victimized by peers predicted less willingness to engage in physical activity in overweight youth (Gray & others, 2008).
Female Athlete Triad
Involves a combination of disordered eating (weight loss), amenorrhea (absent or irregular menstrual periods), and osteoporosis (thinning and weakening of bones)
Adrenarche
Involves hormonal changes in the adrenal glands, located just above the kidneys. These changes occur surprisingly early, from about 6 to 9 years of age in girls and about one year later in boys, before what is generally considered the beginning of puberty (Dorn & others, 2006). During adrenarche and continuing through puberty, the adrenal glands secrete adrenal androgens, such as dehydroepiandrosterone (DHEA).
Adolescent sleep patterns
Mary Carskadon and her colleagues (Carskadon, 2002, 2004, 2006, 2011; Carskadon & Tarokh, 2014; Crowley & Carskadon, 2010; Jenni & Carskadon, 2007; Kurth & others, 2010; Tarokh & Carskadon, 2008, 2010; Tarokh, Carskadon, & Achermann, 2014) have conducted a number of research studies on adolescent sleep patterns. They found that when given the opportunity adolescents will sleep an average of 9 hours and 25 minutes a night. Most get considerably less than 9 hours of sleep, especially during the week. This shortfall creates a sleep deficit, which adolescents often attempt to make up on the weekend. The researchers also found that older adolescents tend to be sleepier during the day than younger adolescents. They theorized that this sleepiness was not due to academic work or social pressures. Rather, their research suggests that adolescents' biological clocks undergo a shift as they get older, delaying their period of wakefulness by about one hour. A delay in the nightly release of the sleep-inducing hormone melatonin, which is produced in the brain's pineal gland, seems to underlie this shift (Eckerberg & others, 2012). Melatonin is secreted at about 9:30 p.m. in younger adolescents and approximately an hour later in older adolescents.
Weight at Birth and in Infancy
Might puberty's onset and characteristics be influenced by birth weight and weight gain during infancy? There is increasing research evidence for this link (Ibanez & others, 2011). Low-birth-weight girls experience menarche approximately 5 to 10 months earlier than normal-birth-weight girls, and low-birth-weight boys are at risk for small testicular volume during adolescence (Ibanez & de Zegher, 2006). A recent study confirmed that rapid weight gain in infancy was associated with earlier menarche (Salgin & others, 2015). A recent research review concluded that early growth acceleration soon after birth that reaches a peak in the first 2 to 4 years of life predicts very early pubertal onset for girls (Papadimitriou & others, 2010). This review also noted that this early growth acceleration is present in children who become overweight or obese later in childhood and adolescence
Conclusions about changes in pubertal onset
More specific conclusions about changes in pubertal onset have recently been proposed. For example, a recent research review concluded that early puberty does seem to be occurring only in overweight girls but that obesity delays pubertal onset in boys (Walvoord, 2010). In this review, it was concluded that earlier puberty in girls is directly linked to the increase in overweight and obesity.
Nutrition
Nutrition is an important aspect of health-compromising and health-enhancing behaviors (Schiff, 2015). The eating habits of many adolescents are health-compromising, and an increasing number of adolescents have an eating disorder (Donatelle, 2015; Finistrella & others, 2015; Langsford & others, 2015). A comparison of adolescents in 28 countries found that U.S. and British adolescents were more likely to eat fried food and less likely to eat fruits and vegetables than adolescents in most other countries that were studied (World Health Organization, 2000). A recent national survey found that only 37 percent of U.S. adolescents ate breakfast every day during the week before they took the survey (Kann & others, 2014). A research review found that two family factors were linked to increased fruit and vegetable consumption by adolescents: availability of fruits and vegetables in the home and consumption of fruits and vegetables by parents (Pearson, Biddle, & Gorely, 2009). And one study revealed that eating regular family meals during early adolescence was linked to healthy eating habits five years later (Burgess-Champoux & others, 2009). Thus, parents play an important role in adolescents' nutrition through the food choices they make available to adolescents, by serving as models for healthy or unhealthy nutrition, and by including adolescents in regular family meals
Passive genotype-environment correlations
Occur because biological parents, who are genetically related to the child, provide a rearing environment for the child. For example, the parents might have a genetic predisposition to be intelligent and read skillfully. Because they read well and enjoy reading, they provide their children with books to read. The likely outcome is that their children, given their own inherited predispositions from their parents, will become skilled readers.
Active (niche-picking) genotype-environment correlations
Occur when children seek out environments that they find compatible and stimulating. Niche-picking refers to finding a setting that is suited to one's abilities. Adolescents select from their surrounding environment some aspect that they respond to, learn about, or ignore. Their active selections of environments are related to their specific genotype. For example, attractive adolescents tend to seek out attractive peers. Adolescents who are musically inclined are likely to select musical environments in which they can successfully perform their skills.
Help adolescents satisfy their motivation for risk taking without compromising their health
One strategy is to increase the social capital of a community, as was recommended in the study previously described (Youngblade & others, 2006). As Laurence Steinberg (2004, p. 58) argues, another strategy is to limit opportunities for immature judgment to have harmful consequences. ... Thus, strategies such as raising the price of cigarettes, more vigilantly enforcing laws governing the sale of alcohol, expanding access to mental health and contraceptive services, and raising the driving age would likely be more effective in limiting adolescent smoking, substance abuse, suicide, pregnancy, and automobile fatalities than strategies aimed at making adolescents wiser, less impulsive, and less short-sighted. It also is important for parents, teachers, mentors, and other responsible adults to effectively monitor adolescents' behavior (Williams, Burton, & Warzinski, 2014). In many cases, adults decrease their monitoring of adolescents too early, leaving them to cope with tempting situations alone or with friends and peers (Masten, 2004). When adolescents are in tempting and dangerous situations with minimal adult supervision, their inclination to engage in risk-taking behavior combined with their lack of self-regulatory skills can make them vulnerable to a host of negative outcomes.
Secular trends
Patterns of pubertal onset over historical time, especially across generations. For example, in Norway, menarche now occurs at just over 13 years of age, compared with 17 years of age in the 1840s (Ong, Ahmed, & Dunger, 2006). In the United States, where children mature physically up to a year earlier than in European countries, menarche now occurs at about 12½ years of age compared with over 14 years of age a century ago (see Figure 7). An increasing number of U.S. girls are beginning puberty at 8 and 9 years of age, with African American girls developing earlier than non-Latino White girls (Herman-Giddens, 2007). A recent research review concluded that age at menarche has not fallen as much as the onset of puberty (Dorn & Biro, 2011). Further, a recent study concluded that boys also are entering puberty earlier (Herman-Giddens & others, 2012). In this study, non-Latino White boys entered puberty on average at 10 years of age, a year earlier than had been documented previously. However, this study has been criticized for aspects that could have skewed the results toward earlier pubertal onset. For example, the sample was obtained by having physicians volunteer to participate, meaning that earlier maturing boys may have been overrepresented as parents brought their sons to the physicians because of health concerns.
Risk Taking Behavior
One type of health-compromising behavior that increases in adolescence is risk taking (Heneghan & others, 2015; Steinberg, 2015a; Telzer, Ichien, & Qu, 2015). One study revealed that sensation seeking increased from 10 to 15 years of age and then declined or remained stable through the remainder of adolescence and into early adulthood (Steinberg & others, 2008). However, even 18-year-olds are "more impulsive, less future-oriented, and more susceptible to peer influence" than adults in their mid- to late twenties (Steinberg, 2008). Researchers also have found that the more resources there are in the community, such as youth activities and adults as role models, the less likely adolescents are to engage in risky behavior (Yancey & others, 2011). One study found that a higher level of what was labeled social capital (in this study, number of schools, number of churches/temples/synagogues, and number of high school diplomas) was linked with lower levels of adolescent risky behavior (in this study, gunshot wounds, pregnancy, alcohol and drug treatment, and sexually transmitted infections) (Youngblade & Curry, 2006). Parental monitoring and communication skills are linked to a lower level of adolescent risk taking (Chen & others, 2008). A recent study revealed that perceiving parents as strong monitors and rule setters was linked to less risky driving by adolescents
Onset of Puberty
Other scientists have hypothesized that the onset of menarche is influenced by the percentage of body fat in relation to total body weight, although a precise percentage has not been consistently verified. However, both anorexic adolescents whose weight drops dramatically and females who participate in certain sports (such as gymnastics and swimming) may not menstruate. In boys, undernutrition may delay puberty (Susman, Dorn, & Schiefelbein, 2003).
Studies on gender differences in body image during adolescence
Adolescent girls placed a higher aesthetic value on body image but had a lower aesthetic satisfaction with their bodies than did adolescent boys (Abbott & Barber, 2010). The profile of adolescents with the most positive body images was characterized by health-enhancing behaviors, especially regular exercise (Frisen & Holmqvist, 2010). Among non-Latino White, Latino, African American, and Asian American adolescents, the psychological well-being (self-esteem and depression, for example) of non-Latino White girls was the most influenced and that of non-Latino White boys the least influenced by body perceptions (Yuan, 2010). The negative aspects of puberty for girls appeared in a study that explored 400 middle school boys' and girls' perceptions of the best and worst aspects of being a boy or a girl (Zittleman, 2006). In the views of the middle school girls, at the top of the list of the worst things about being a girl was the biology of being female, which included such matters as childbirth, PMS, periods, and breast cancer. The middle school boys said certain aspects of discipline—getting into trouble, being disciplined, and being blamed more than girls even when they were not at fault—were the worst things about being a boy. However, another aspect of physical development was at the top of the girls' list of the best things about being a girl—appearance (which included choosing clothes, hairstyles, and beauty treatments). Boys said the best thing about being a boy was playing sports.
Health Services
Adolescents underutilize health-care systems (Hoover & others, 2010). Of special concern is the low use of health services by older adolescent males (Hoover & others, 2010). A U.S. study found that 16- to 20-year-old males have significantly less contact with health-care services than 11- to 15-year-old males (Marcell & others, 2002). In contrast, 16- to 20-year-old females have more contact with health-care services than do younger females. And one study found that adolescents were much more likely to seek health care for problems related to disease than problems related to mental health, tobacco use, or sexual behavior (Marcell & Halpern-Felsher, 2007). Among the chief barriers to better health care for adolescents are cost, poor organization and availability of health services, lack of confidentiality, and reluctance on the part of health-care providers to communicate with adolescents about sensitive health issues (Hoover & others, 2010; Tebb & others, 2015). Few health-care providers receive any special training in working with adolescents. Many say they feel unprepared to provide services such as contraceptive counseling or to evaluate what constitutes abnormal behavior in adolescents. Health-care providers may transmit to their patients their discomfort in discussing topics such as sexuality and drugs, causing adolescents to avoid discussing sensitive issues with them (Marcell & Millstein, 2001).
Nonshared environmental experiences
An adolescent's unique experiences, both within the family and outside the family; these are not shared with a sibling
Testosterone
An androgen that plays an important role in male pubertal development (Werner & Holterhus, 2014). Testosterone is primarily secreted from testes in boys. Throughout puberty, rising testosterone levels are associated with a number of physical changes in boys, including the development of external genitals, an increase in height, and voice changes (Goji & others, 2009). Testosterone level in adolescent boys is also linked to sexual desire and activity (Cameron, 2004)
Evoluntionary psychology
An approach to, and subfield of psychology that is concerned with the evolutionary origins of behaviors and mental processes, their adpative value, and the purposes they continue to serve. David Buss' (2000, 2008, 2012, 2015) ideas on evolutionary psychology have produced a wave of interest in how evolution can explain human behavior. Buss argues that just as evolution shapes our physical features such as our body shape and height, it also influences our decision making, our aggressive behavior, our fears, and our mating patterns.
Estradiol
An estrogen that plays an important role in female pubertal development. Estradiol is primarily secreted from ovaries in girls. As estradiol levels rise, breast development, uterine development, and skeletal changes occur
Body image
Preoccupation with one's body image is strong throughout adolescence, but it is especially acute during puberty, a time when adolescents are more dissatisfied with their bodies than in late adolescence
Heredity
Programmed into the genes of every human being is the timing for the emergence of puberty (Tu & others, 2014). Puberty does not take place at 2 or 3 years of age and it does not occur in the twenties. Recently, scientists have begun to conduct molecular genetic studies in an attempt to identify specific genes that are linked to the onset and progression of puberty (Amstalden & others, 2014). Nonetheless, as you will see later, puberty takes place between about 9 and 16 years of age for most individuals
Physical Exercise as a Stress Buffer
An exciting possibility is that physical exercise might act as a buffer against the stress adolescents experience and improve their mental health and life satisfaction (Wood & others, 2012). Consider the following support for this possibility: A recent study of depressed adolescents with low levels of exercise revealed that a 12-week exercise intervention lowered their rates of depression (Dopp & others, 2012). Higher levels of physical activity at 9 and 11 years of age predicted higher self-esteem at 11 and 13 years of age (Schmalz & others, 2007). A nine-month physical activity intervention with sedentary adolescent girls improved their self-image (Schneider, Dunton, & Cooper, 2008). High school seniors who exercised frequently had higher grade-point averages, used drugs less frequently, were less depressed, and got along better with their parents than those who rarely exercised (Field, Diego, & Sanders, 2001).
Collaboration of DNA
Rather than being an independent source of developmental information, DNA collaborates with other sources of information to specify our characteristics (Moore, 2013, 2015). The collaboration operates at many points. Small pieces of DNA are mixed, matched, and linked by the cellular machinery. That machinery is sensitive to its context—that is, it is influenced by what is going on around it. Whether a gene is turned "on," working to assemble proteins, is also a matter of collaboration. The activity of genes (genetic expression) is affected by their environment (Kahn & Fraga, 2009; Lickliter & Honeycutt, 2015; Moore, 2015). For example, hormones that circulate in the blood make their way into the cell, where they can turn genes "on" and "off." And the flow of hormones can be affected by environmental conditions such as light, day length, nutrition, and behavior. Numerous studies have shown that external events outside the cell and the person, and internal events inside the cell, can excite or inhibit gene expression (Craft & others, 2014; Dedon & Begley, 2014).
Factors influencing gene expression
Recent research has documented that factors such as stress, exercise, nutrition, respiration, radiation, temperature, and sleep can influence gene expression (Craft & others, 2014; Dedon & Begley, 2014; Donnelly & Storchova, 2015; McInnis & others, 2015)
The human genome
An important step in this direction was accomplished when the Human Genome Project and the Celera Corporation completed a preliminary map of the human genome—the complete set of instructions for making a human organism. One of the big surprises of the Human Genome Project was a report indicating that humans have only about 30,000 genes (U.S. Department of Energy, 2001). More recently, the number of human genes has been revised downward again to approximately 21,500 (Ensembl Human, 2008). Further, recent analysis proposes that humans may actually have fewer than 20,000 protein-producing genes (Abyzov & others, 2014; Ezkurdia & others, 2014). Scientists had thought that humans had as many as 100,000 or more genes. They had also believed that each gene programmed just one protein. In fact, humans appear to have far more proteins than they have genes, so there cannot be a one-to-one correspondence between them (Commoner, 2002; Moore, 2015). Each segment of DNA is not translated, in automaton-like fashion, into one and only one protein. It does not act independently, as developmental psychologist David Moore (2001) emphasized by titling his book The Dependent Gene.
Body Art
An increasing number of adolescents and college students are obtaining tattoos and getting parts of their bodies pierced (Mayers & Chiffriller, 2008). Many of these youth engage in such body modifications to be different, to stamp their identity as unique. In one study of adolescents, 60 percent of the students with tattoos had academic grades of A's and B's (Armstrong, 1995). In this study, the average age at which the adolescents got their first tattoo was 14 years of age. Some studies indicate that tattoos and body piercings are markers for risk taking in adolescence (Deschesnes, Fines, & Demers, 2006). One study revealed that having multiple body piercings is especially a marker for risk-taking behavior (Suris & others, 2007). However, other researchers argue that body art is increasingly used to express individuality and self-expression rather than rebellion (Armstrong & others, 2004).
Issues in Girls' Early Maturation
An increasing number of researchers have found that early maturation increases girls' vulnerability to a number of problems (Blumenthal & others, 2011; Hamilton & others, 2014; Sontag-Padilla & others, 2012). Early-maturing girls are more likely to smoke, drink, be depressed, have an eating disorder, engage in delinquency, struggle for earlier independence from their parents, and have older friends; and their bodies are likely to elicit responses from males that lead to earlier dating and earlier sexual experiences (Copeland & others, 2010; Negriff, Susman, & Trickett, 2011; Verhoef & others, 2014). For example, a recent study confirmed that early maturation was linked to depression in young adolescent girls (Rudolph & others, 2014). Further, recent research has found that early-maturing girls tend to have sexual intercourse earlier and have more unstable sexual relationships (Moore, Harden, & Mendle, 2014). And early-maturing girls are less likely to graduate from high school and more likely to cohabit and marry earlier (Cavanagh, 2009). Apparently the combination of their social and cognitive immaturity and early physical development result in early-maturing girls being more easily lured into problem behaviors, not recognizing the possible long-term effects of these on their development.
Domain-specific
Another key idea is that many evolved psychological mechanisms are domain-specific. That is, the mechanisms apply only to a specific aspect of a person's makeup. According to evolutionary psychology, information processing is one example. In this view, the mind is not a general-purpose device that can be applied equally to a vast array of problems. Instead, as our ancestors dealt with certain recurring problems such as hunting and finding shelter, specialized modules evolved that process information related to those problems: for example, a module for physical knowledge for tracking animals, a module for mathematical knowledge for trading, and a module for language. Evolved mechanisms are not always adaptive in contemporary society. Some behaviors that were adaptive for our prehistoric ancestors may not serve us well today. For example, the food-scarce environment of our ancestors likely led to humans' propensity to gorge when food is available and to crave high-caloric foods, a trait that that might lead to an epidemic of obesity when food is plentiful.
Sleep
Another study also found that adolescents are not getting adequate sleep. The National Sleep Foundation (2006) conducted a U.S. survey of 1,602 caregivers and their 11- to 17-year-olds. Forty-five percent of the adolescents got inadequate sleep on school nights (less than 8 hours). Older adolescents (ninth- to twelfth-graders) got markedly less sleep on school nights than younger adolescents (sixth- to eighth-graders)—62 percent of the older adolescents got inadequate sleep compared with 21 percent of the younger adolescents.
Coaches in adolescent sports
Coaches play an important role in youth sports (Bosselut & others, 2012; Cushion, Ford, & Williams, 2012). Too often youth coaches create a performance-oriented motivational climate that is focused on winning, receiving public recognition, and performing better than other participants. But other coaches place more emphasis on mastery motivation that focuses adolescents' attention on developing their skills and meeting self-determined standards of success. Researchers have found that athletes who have a mastery focus are more likely than others to see the benefits of practice, to persist in the face of difficulty, and to show significant skill development over the course of a season (Roberts, Treasure, & Kavussanu, 1997).
Emerging adults' sleeping patterns
Do sleep patterns change in emerging adulthood? Research indicates that they do (Galambos, Howard, & Maggs, 2011; Kloss & others, 2011, 2014; Wolfson, 2010). In a recent study which revealed that more than 60 percent of college students were categorized as poor-quality sleepers, it appears that the weekday bedtimes and rise times of first-year college students are approximately 1 hour and 15 minutes later than those of seniors in high school (Lund & others, 2010). However, the first-year college students had later bedtimes and rise times than third- and fourth-year college students, indicating that at about 20 to 22 years of age, a reverse in the timing of bedtimes and rise times occurs.
Emerging adults' health
Emerging adults have more than twice the mortality rate of adolescents (Park & others, 2008). Males are mainly responsible for the higher mortality rate of emerging adults. Also, compared with adolescents, emerging adults engage in more health-compromising behaviors, have more chronic health problems, are more likely to be obese, and are more likely to have a mental health disorder (Irwin, 2010). In a recent analysis, most health and health care indicators changed little across the last decade for adolescents and young adults (Park & others, 2014). In this analysis, improvements for adolescents and young adults occurred in rates of unintentional injury, assault, and tobacco use, and also adolescents improved in sexual/reproductive health. Also in this analysis, young adults continued to engage in greater health risks and have worse health outcomes than did adolescents.
Epigentic view
Emphasizes that development is the result of an ongoing, bidirectional interchange between heredity and the environment
Positive Benefits of Exercise in Adolescence
Exercise is linked with a number of positive outcomes in adolescence (Hoare & others, 2014; Peykari & others, 2015). One study revealed that physical fitness in adolescence was linked to physical fitness in adulthood (Mikkelsson & others, 2006). Regular exercise has a positive effect on adolescents' weight status (Ten Hoor & others, 2014). One study revealed that regular exercise from 9 to 16 years of age especially was associated with normal weight in girls (McMurray & others, 2008). Other positive outcomes of exercise in adolescence are reduced triglyceride levels, lower blood pressure, and a lower incidence of type 2 diabetes (Anyaegbu & Dharnidharka, 2014; Koozehcian & others, 2014). One study found that adolescents in the lowest 20 percent of cardiorespiratory fitness were at risk for cardiovascular disease (Lobelo & others, 2010). Other recently reported research indicated that eighth-, tenth-, and twelfth-grade students who engaged in higher levels of exercise had lower levels of alcohol, cigarette, and marijuana use (Terry-McElrath, O'Malley, & Johnston, 2011). Also, a recent study revealed that a daily morning running program for three weeks improved the sleep quality, mood, and concentration of adolescents (Kalak & others, 2012).
Psychological Aspects of Puberty
Far less research has been conducted on the psychosocial aspects of male pubertal transitions than on female pubertal transitions, possibly because of the difficulty o detecting when the male transitions occur. Wet dreams are one marker, yet there has been little research on the topic. Not only are the effects of puberty easier to study in girls, they also are more likely to have a strong effect on girls because they are more obvious than the pubertal changes in boys. For example, female breast enlargement is much easier to see in most societies than male genital growth.
Factors determining adolescent development
If heredity and environment interact to determine the course of development, is that all there is to answering the question of what causes development? Are adolescents completely at the mercy of their genes and environment as they develop? Genetic heritage and environmental experiences are pervasive influences on adolescents' development. But in thinking about what causes development, adolescents not only are the outcomes of their heredity and the environment they experience, but they also can author a unique developmental path by changing the environment.
Natural selection
The evolutionary process that favors those individuals of a species who are best adapted to survive and reproduce To understand natural selection, let's return to the middle of the nineteenth century, when the British naturalist Charles Darwin (1809-1882) was traveling the world, observing many different species of animals in their natural habitats. In his groundbreaking book, On the Origin of Species (1859), Darwin noted that most species reproduce at rates that would cause enormous increases in their population and yet populations remained nearly constant. He reasoned that an intense struggle for food, water, and resources must occur among the many young born in each generation, because many of them do not survive. Darwin believed that those who do survive to reproduce and pass on their genes to the next generation are probably superior to others in a number of ways. In other words, the survivors are better adapted to their world than the nonsurvivors (Raven & others, 2014). Over the course of many generations, Darwin reasoned, organisms with the characteristics needed for survival would compose a larger and larger percentage of the population, producing a gradual modification of the species. If environmental conditions changed, however, other characteristics might be favored by natural selection, moving the evolutionary process in a different direction.
Behavior genetics
The field that seeks to discover the influence of heredity and environment on individual differences in human traits and development (Krushkal & others, 2014; Lickliter & Honeycutt, 2015).
Menarche
The first menstrual period, occurs in mid- to late gonadarche in girls
Growth Spurt
The growth spurt associated with puberty occurs approximately two years earlier for girls than for boys. For girls, the mean beginning of the growth spurt is 9 years of age; for boys, it is 11 years of age. The peak of pubertal change occurs at 11½ years for girls and 13½ years for boys. During their growth spurt, girls increase in height about 3½ inches per year; boys, about 4 inches. The growth spurt typically begins before menarche and ends earlier for girls. The growth spurt for boys, as indicated earlier, begins later and ends later than it does for girls.
GnRH (gonadotropin-releasing hormone)
The hypothalamus secretes a substance called GnRH (gonadotropin-releasing hormone), which is linked to pubertal timing
Gene x environment (G x E) interaction
The interaction of a specific measured variation in the DNA and a specific measured aspect of the environment
Androgens
The main class of male sex hormones
Neurobiological explanations of adolescent risk taking
The prefrontal cortex, the brain's highest level that is involved in reasoning, decision making, and self-control, matures much later (continuing to develop in late adolescence and emerging adulthood) than the amygdala, which is the main structure involved in emotion in the brain. The later development of the prefrontal cortex combined with the earlier maturity of the amygdala may explain the difficulty younger adolescents have in putting the brakes on their risk-taking adventures. These developmental changes in the brain provide one explanation of why risk taking declines as adolescents get older (Steinberg, 2015a, b).
Genes
The units of hereditary information, are short segments composed of DNA
Phenotype
The way an individual's genotype is expressed in observed and measurable characteristics
Negative feedback system
These hormones are regulated by a negative feedback system. If the level of sex hormones rises too high, the hypothalamus and pituitary gland reduce their stimulation of the gonads, decreasing the production of sex hormones. If the level of sex hormones falls too low, the hypothalamus and pituitary gland increase their production of the sex hormones. In males, the pituitary gland's production of LH stimulates the testes to produce testosterone. When testosterone levels rise too high, the hypothalamus decreases its production of GnRH, and this decrease reduces the pituitary's production of LH. When the level of testosterone falls as a result, the hypothalamus produces more GnRH and the cycle starts again. The negative feedback system operates in a similar way in females, except that LH and GnRH regulate the ovaries and the production of estrogen.
Male Sexual Maturation
Three of the most noticeable signs of sexual maturation in boys are penis elongation, testes development, and growth of facial hair.
Growth Hormones
We know that the pituitary gland releases gonadotropins that stimulate the testes and ovaries. For example, a recent study documented that the pituitary gland grows in adolescence and that its volume is linked to circulating blood levels of estradiol and testosterone (Wong & others, 2014). In addition, through interaction with the hypothalamus, the pituitary gland also secretes hormones that lead to growth and skeletal maturation either directly or through interaction with the thyroid gland, located in the neck region (see Figure 2). At the beginning of puberty, growth hormone is secreted at night. Later in puberty, it also is secreted during the day, although daytime levels are usually very low (Susman, Dorn, & Schiefelbein, 2003). Cortisol, a hormone that is secreted by the adrenal cortex, also influences growth, as do testosterone and estrogen (Kang & others, 2014; Stroud & others, 2011).
Female Pubertal Characteristics
What is the order of appearance of physical changes in females? On average, breast development occurs first, followed by the appearance of pubic hair. Later, hair appears in the armpits. As these changes occur, the female grows in height, and her hips become wider than her shoulders. Her first menstruation (menarche) occurs rather late in the pubertal cycle.
Gonadarche
Which follows adrenarche by about two years, is the period most people think of as puberty. Gonadarche involves the maturation of primary sexual characteristics (ovaries in females, testes in males) and secondary sexual characteristics (pubic hair, breast, and genital development) (Dorn & others, 2006). "The hallmark of gonadarche is reactivation of the hypothalamic-pituitary-gonadal axis (HPG). ... The initial activation of the HPG axis was during the fetal and neonatal period" (Dorn & others, 2006, p. 35). In the United States, the gonadarche period begins at approximately 9 to 10 years of age in non-Latino White girls and 8 to 9 years in African American girls (Herman-Giddens, Kaplowitz, & Wasserman, 2004). In boys, gonadarche begins at about 10 to 11 years of age.
Precocious puberty
the term used to describe the very early onset and rapid progression of puberty. Judith Blakemore and her colleagues (2009) described the following characteristics of precocious puberty. Precocious puberty is usually diagnosed when pubertal onset occurs before 8 years of age in girls and before 9 years of age in boys. Precocious puberty occurs approximately 10 times more often in girls than in boys. When precocious puberty occurs, it usually is treated by medically suppressing gonadotropic secretions, which temporarily stops pubertal change (Alikasifoglu & others, 2015; Neely & Crossen, 2014). The reason for this treatment is that children who experience precocious puberty are ultimately likely to have short stature, early sexual capability, and the potential for engaging in age-inappropriate behavior
Sociocultural and Environmental Factors
Recent research indicates that cultural variations and early experiences may be related to earlier pubertal onset. Adolescents in developed countries and large urban areas reach puberty earlier than their counterparts in less-developed countries and rural areas (Graham, 2005). For example, a recent study of more than 15,000 girls in China revealed that menarche occurred much earlier in urban than rural girls (Sun & others, 2012). Children who have been adopted from developing countries to developed countries often enter puberty earlier than their counterparts who continue to live in developing countries (Teilmann & others, 2002). African American females enter puberty earlier than Latina and non-Latina females, and African American males enter puberty earlier than non-Latino males (Talpade, 2008). Early experiences that are linked to earlier pubertal onset include adoption, father absence, low socioeconomic status, family conflict, maternal harshness, child maltreatment, and early substance use (Arim & others, 2011; Deardorff & others, 2011; Ellis & others, 2011). In many cases, puberty comes months earlier in these situations, and this earlier onset of puberty is likely explained by high rates of conflict and stress in these social contexts (Behie & O'Donnell, 2015). One study revealed that maternal harshness in early childhood was linked to early maturation as well as sexual risk taking in adolescence (Belsky & others, 2010). Another study found that early onset of menarche was associated with severe child sexual abuse (Boynton-Jarrett & others, 2013).
LH (luteinizing hormone)
Regulates estrogen secretion and ovum development in females and testosterone production in males
Developmental Changes Regarding Exercise
Researchers have found that individuals become less active as they reach and progress through adolescence (Pate & others, 2009). A national study of U.S. 9- to 15-year-olds revealed that almost all 9- and 11-year-olds met the federal government's moderate to vigorous exercise recommendations per day (a minimum of 60 minutes a day), but only 31 percent of 15-year-olds met the recommendations on weekdays and only 17 percent met the recommendations on weekends (Nader & others, 2008). Also, a longitudinal study found that total physical activity (in school and out of school) was stable from 5 to 8 years of age but fell progressively from 9 to 15 years of age (Metcalf & others, 2015). And a recent national study found that adolescent boys were much more likely to engage in 60 minutes or more of vigorous exercise per day than were girls (Kann & others, 2014). Yet another national study of U.S. adolescents revealed that physical activity increased until 13 years of age in boys and girls but then declined through 18 years of age (Kahn & others, 2008). In this study, adolescents were more likely to engage in regular exercise when they wanted to present a positive body image to their friends and when exercise was important to their parents.