Between childhood and adulthood is an extended developmental stage that may not qualify for a “hood” of its own, but that is clearly distinct from the stages that come before and after. Adolescence is the period of development that begins with the onset of sexual maturity (about 11 to 14 years of age) and lasts until the beginning of adulthood (about 18 to 21 years of age). Unlike the transition from embryo to fetus or from infant to child, this transition is sudden and clearly marked. In just 3 or 4 years, the average adolescent gains about 18 kg and grows about 20 cm. For girls, all this growing starts at about the age of 10 and ends when they reach their full heights at about the age of 15.5. For boys it starts at about the age of 12 and ends at about the age of 17.5.

The beginnings of this growth spurt signals the onset of puberty, which refers to the bodily changes associated with sexual maturity. These changes involve primary sex characteristics, which are bodily structures that are directly involved in reproduction, for example, the onset of menstruation in girls and the enlargement of the testes, scrotum, and penis and the emergence of the capacity for ejaculation in boys. They also involve secondary sex characteristics, which are bodily structures that change dramatically with sexual maturity but that are not directly involved in reproduction, for example, the enlargement of the breasts and the widening of the hips in girls and the appearance of facial hair, pubic hair, underarm hair, and the lowering of the voice in both genders. This pattern of changes is caused by increased production of estrogen in girls and testosterone in boys.

Just as the body changes during adolescence, so too does the brain. For example, there is a marked increase in the growth rate of tissue connecting different regions of the brain just before puberty (Thompson et al., 2000). The Czech–Canadian researcher Tomáš Paus and his colleagues have demonstrated that the connections between two regions essential for language function—Broca’s area and Wernicke’s area in the left hemisphere—become stronger and denser between the ages of 4 and 17 (Paus et al., 1999). These connections presumably allow brain areas to share information faster and more efficiently (see FIGURE 11.11).

But the most important neural changes occur in the prefrontal cortex, the part of the brain associated with the ability to regulate emotions, and to control attention and behaviour. An infant’s brain forms many more new synapses than it actually needs, and by the time children are 2 years old they have about 15 000 synapses per neuron, which is roughly twice as many as the average adult (Huttenlocher, 1979). This early period of synaptic proliferation is followed by a period of synaptic pruning in which the connections that are not frequently used are eliminated. This is a clever system that allows the brain’s wiring to be determined in part by its experience in the world. Scientists used to think that this process ended early in life, but recent evidence suggests that the prefrontal cortex undergoes a second wave of synaptic proliferation just before puberty, and a second round of synaptic pruning during adolescence (Giedd et al., 1999). During this period, the prefrontal cortex also seems to be forming faster, more efficient connections with the rest of the brain (Paus, 2005). Clearly, the adolescent brain is a work in progress.

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The age at which puberty begins varies across individuals (e.g., people tend to reach puberty at about the same age as their same-sexed parent did) and across cultures (e.g., African American girls tend to reach puberty before European American girls do). It also varies across generations (Malina, Bouchard, & Beunen, 1988). For example, in Scandinavia, the United Kingdom, and the United States, the age of first menstruation was between 16 and 17 years in the nineteenth century but was approximately 13 years in 1960. A more recent study found that the average age of breast development for Danish girls has decreased by an entire year since 1992 alone (Aksglaede et al., 2009). The average age at which American boys begin puberty has now fallen to between 9 and10 years old (Herman-Giddens et al., 2012). Why so much earlier now than just a few decades ago? Puberty is accelerated by body fat (Kim & Smith, 1998), and the decrease in the age of the onset is largely due to improved diet and health (Ellis & Garber, 2000). But puberty in girls can also be hastened by exposure to environmental toxins that mimic estrogen (Buck Louis et al., 2008) or by stressful family situations (Belsky, 2012).

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The increasingly early onset of puberty has important psychological consequences. Just two centuries ago, the gap between childhood and adulthood was relatively brief because people became physically mature at roughly the same time that they were ready to accept adult roles in society, and these roles did not normally require them to have extensive schooling. But in modern societies, people typically spend 3 to 10 years in school after they reach puberty. Thus, while the age at which people become physically adult has decreased, the age at which they are prepared or allowed to take on adult responsibilities has increased, and so the period between childhood and adulthood has become protracted. What are the consequences of a protracted adolescence?

Adolescence is often characterized as a time of internal turmoil and external recklessness, and some psychologists have speculated that the protraction of adolescence is in part to blame for its sorry reputation (Moffitt, 1993). According to these theorists, adolescents are adults who have temporarily been denied a place in adult society, mostly through the school system and through restrictions on the types of work that adolescents in Western countries like Canada and the United States are permitted to do (Epstein, 2007a). American teenagers are subjected to 10 times as many restrictions as adults, and twice as many restrictions as American Marines on active duty or incarcerated felons (Epstein, 2007a). As such, they feel especially compelled to do things to protest these restrictions and demonstrate their adulthood, such as smoking, drinking, using drugs, having sex, and committing crimes. In a sense, adolescents are people who are forced to live in a strange gap between two worlds, and the pathologies of adolescence are partly a result of this predicament. As one researcher noted, “Trapped in the frivolous world of peer culture, they learn virtually everything they know from one another rather than from the people they are about to become. Isolated from adults and wrongly treated like children, it is no wonder that some teens behave, by adult standards, recklessly or irresponsibly” (Epstein, 2007b).

But the storm and stress of adolescence is by no means inevitable (Steinberg & Morris, 2001). Research suggests that the “moody adolescent” who is a victim of “raging hormones” is largely a myth. Adolescents are no moodier than children (Buchanan, Eccles, & Becker, 1992), and fluctuations in their hormone levels have only a tiny impact on their moods (Brooks-Gunn, Graber, & Paikoff, 1994). Although they can be more impulsive and susceptible to peer influence than adults (see FIGURE 11.12), they are just as capable of making wise decisions based on good information (Steinberg, 2007). It is true that the majority of adolescents dabble in misbehaviour, but they do not actually major in it. For example, more than 60 percent of 15 to 17 year olds in Canada report having used alcohol in the last year (Canadian Public Health Association, n.d.), but few develop drinking problems or allow alcohol to impair their academic success or personal relationships (Hughs, Power, & Francis, 1992; Johnston, Bachman, & O’Malley, 1997). Most adolescent experiments have no long-term consequences, and the vast majority of adolescents who try drugs or break the law end up becoming sober, law-abiding adults (Steinberg, 1999). In short, the hijinks of adolescence are typically minor and temporary, and in some cultures they barely occur at all (Epstein, 2007b). Adolescence is not a terribly troubled time for most people, and most adolescents “age out” of any troubles they get themselves into (Sampson & Laub, 1995).

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Puberty can be a difficult time, but it is especially difficult for girls who reach it earlier than their peers. These girls are more likely to experience a range of negative consequences, from distress and depression to delinquency and disease (Mendle, Turkheimer, & Emery, 2007) (see FIGURE 11.13). This happens for several reasons (Ge & Natsuaki, 2009). First, early bloomers do not have as much time as their peers do to develop the skills necessary to cope with adolescence (Petersen & Grockett, 1985), but because they look so mature, people expect them to act like adults. In other words, early puberty creates unrealistic expectations and demands that the adolescent may have trouble fulfilling. Second, early blooming girls draw the attention of older men, who may lead them into a variety of unhealthy activities (Ge, Conger, & Elder, 1996). Some research suggests that for girls, the timing of puberty has a greater influence on emotional and behavioural problems than does the occurrence of puberty itself (Buchanan et al., 1992). The timing of puberty does not have such consistent effects on boys: Some studies suggest that early maturing boys do better than their peers, some show they do worse, and some show that there is no difference at all (Ge, Conger, & Elder, 2001). Interestingly, recent research suggests that for boys, tempo, the speed with which they transition from the first to the last stages of puberty, may be a better predictor of negative outcomes than is timing (Mendle et al., 2010).

For some adolescents, puberty is additionally complicated by the fact that they are attracted to members of the same sex. Most gay men report having become aware of their sexual orientation between the ages of 6 and 18, and most lesbians report having become aware between the ages of 11 and 26 (Calzo et al., 2011). Not only does their sexual orientation make gay adolescents different from the vast majority of their peers (a mere 2 percent of Canadian adults identify themselves as lesbian, gay, or bisexual) (Statistics Canada, 2004), but it can also subject them to disapproval from family, friends, and community. In a recent survey (Pew Research Center Global Attitudes Project, 2013), almost 1 in 5 Canadians said that homosexuality is a way of life that should not be accepted by society, and Canada is much more accepting of homosexuality than are many other nations (see FIGURE 11.14). In some countries, gay citizens are imprisoned or sentenced to death.

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Given so much social disapproval, it is little wonder that the happiness and well-being of homosexual adolescents is a great concern to mental-health professionals. Several provincial legislatures have enacted anti-bullying laws in the last decade, aimed at reducing and ending bullying against students. For example, the Ontario Accepting Schools Act is aimed at reducing gender-based violence and acts of homophobia in primary and secondary schools, and allows students at any school in the province to set up clubs called “Gay Straight Alliances.” The hope that this will promote tolerance of all people, regardless of sexual orientation.

What determines whether a person’s sexuality is primarily oriented toward the same or the opposite sex? For a long time, psychologists believed that a person’s sexual orientation depended primarily on his or her upbringing. For example, psychoanalytic theorists claimed that boys who grow up with a domineering mother and a submissive father are less likely to identify with their father and are therefore more likely to become homosexual. Okay. Nice theory. But the fact is that scientific research has failed to identify any aspect of parenting that has a significant impact on a child’s ultimate sexual orientation (Bell, Weinberg, & Hammersmith, 1981). Perhaps the most telling fact is that children raised by homosexual couples and children raised by heterosexual couples are equally likely to become heterosexual adults (Patterson, 1995). There is also little support for the idea that a person’s early sexual encounters have a lasting impact on his or her sexual orientation (Bohan, 1996).

So what does determine a person’s sexual orientation? There is now considerable evidence to suggest that biology plays the major role. Not only do gay people have a larger proportion of gay siblings than do heterosexuals (Bailey et al., 1999), but the identical twin of a gay man (with whom he shares 100 percent of his genes) has a 50 percent chance of being gay, whereas the fraternal twin or non-twin brother of a gay man (with whom he shares 50 percent of his genes) has only a 15 percent chance (Bailey & Pillard, 1991; Gladue, 1994). A similar pattern has emerged in studies of lesbians (Bailey et al., 1993). Some evidence suggests that the fetal environment may play a role in determining sexual orientation and that high levels of androgens in the womb may predispose a person—whether male or female—later to develop a sexual preference for women (Ellis & Ames, 1987; Meyer-Bahlberg et al., 1995). Perhaps this is why the brains of gay people tend to look like the brains of straight people of the opposite sex (Savic & Lindstrom, 2008). For example, the brain’s two hemispheres tend to be unequally sized among straight men and lesbians (both of whom are attracted to women), but equally sized among straight women and gay men (both of whom are attracted to men).

Of course, genes and prenatal biology cannot be the sole determinant of a person’s sexual orientation because many homosexual men and women have identical twins who shared both their fetal environment and their genes, and who are nonetheless heterosexual. There must be other factors and, at present, we just do not know what they are. But one thing we do know is that regardless of what leads people to have a particular sexual orientation, there is no evidence that it can be changed by so-called conversion therapy (American Psychological Association, 2009). It is also worth noting that about 1 percent of people claim to have no sexual orientation of any kind and have never experienced sexual attraction to either gender (Bogaert, 2004). The science of sexual orientation is still young and fraught with conflicting findings, but one thing that seems abundantly clear is that sexual orientation is not simply a matter of choice.

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In 2005, 43% of Canadian teens aged 15 to 19 reported having had sexual intercourse at least once, with no difference between men and women (Rotermann, 2008). Interestingly, the rate at which young Canadian women engage in sex is dropping. In 1996/1997, 51% of young women aged 15 to 19 reported having sexual intercourse at least once, compared to 43% in 2005. The proportion of adolescents reporting experience with sexual intercourse was higher among 18 to 19 year olds (approximately 67%) than among 15 to 17 year olds (approximately 33%) and was higher in Quebec (58%) than in the other Canadian provinces (see TABLE 11.2). FIGURE 11.15 shows the general trends in sexual activity among male and female teens from 1996 to 2005.

The best scientific evidence suggests that sex education leads teens to delay having sex for the first time, increases the likelihood they will use birth control when they do have sex, and lowers the likelihood that they will get pregnant or catch a sexually transmitted disease (Mueller, Gavin, & Kulkarni, 2008; Satcher, 2001). Although young people between the ages of 15 to 24 years have among the highest rates of sexually transmitted infections, condom use is increasing: in 2003, 62% of sexually active people aged 15 to 24 reported than they had used condoms the last time they had intercourse. This proportion increased to 68% in 2009–2010 (Rotermann, 2012).

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“Who am I?” is a question asked by amnesiacs and adolescents, who tend to ask it for different reasons. Children’s views of themselves and their world are tightly tied to the views of their parents, but puberty creates a new set of needs that begins to snip away at those bonds by orienting adolescents toward peers rather than parents. Psychologist Erik Erikson (1959) characterized each stage of life by the major task confronting the individual at that stage. His stages of psychosocial development (shown in TABLE 11.3) borrow from the work of Sigmund Freud, and suggest that the major task of adolescence is the development of an adult identity. Whereas children define themselves almost entirely in terms of their relationships with parents and siblings, adolescence marks a shift in emphasis from family relations to peer relations.

Two things can make this shift difficult. First, children cannot choose their parents, but adolescents can choose their peers. As such, adolescents have the power to shape themselves by joining groups that will lead them to develop new values, attitudes, beliefs, and perspectives. In a sense, the adolescent has the opportunity to invent the adult he or she will soon become, and the responsibility this opportunity entails can be overwhelming. Second, as adolescents strive for greater autonomy, their parents naturally rebel. For instance, parents and adolescents tend to disagree about the age at which certain adult behaviours—such as staying out late or having sex—are permissible, and you do not need a scientist to tell you which position each party in this conflict tends to hold (Holmbeck & O’Donnell, 1991). Because adolescents and parents often have different ideas about who should control the adolescent’s behaviour, their relationships become more conflictive and less close, and their interactions become briefer and less frequent (Larson & Richards, 1991). Even so, adolescents and their parents have surprisingly few conflicts (Chung, Flook, & Fuligni, 2009), and when they do argue it tends to be over minor issues, such as dress and language (which may explain why teenagers argue more with their mothers, who are typically in charge of such issues, than with their fathers) (Caspi et al., 1993).

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Adolescents pull away from their parents, but more importantly, they move toward their peers. Studies show that across a wide variety of cultures, historical epochs, and even species, peer relations evolve in a similar way (Dunphy, 1963; Weisfeld, 1999). Young adolescents initially form groups or “cliques” with same-sexed peers, many of whom were friends during childhood (Brown, Mory, & Kinney, 1994). Next, male cliques and female cliques begin to meet in public places, such as town squares or shopping malls, and they begin to interact—but only in groups and only in public. After a few years, the older members of these same-sex cliques peel off and form smaller, mixed-sex cliques, which may assemble in private as well as in public, but usually assemble as a group. Finally, couples (typically a male and a female) peel off from the small, mixed-sex clique and begin romantic relationships.

Studies show that throughout adolescence, people spend increasing amounts of time with opposite-sex peers while maintaining the amount of time they spend with same-sex peers (Richards et al., 1998), and they accomplish this by spending less time with their parents (Larson & Richards, 1991). Although peers exert considerable influence on the adolescent’s beliefs and behaviours, this influence generally occurs because adolescents respect, admire, and like their peers and not because their peers pressure them (Susman et al., 1994). In fact, as they age, adolescents show an increasing tendency to resist peer pressure (Steinberg & Monahan, 2007). Acceptance by peers is of tremendous importance to adolescents, and those who are rejected by their peers tend to be withdrawn, lonely, and depressed (Pope & Bierman, 1999). Fortunately for those of us who were seventh-grade nerds, individuals who are unpopular in early adolescence can become popular in later adolescence as their peers become less rigid and more tolerant (Kinney, 1993).

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