Adolescence - Puberty, Health, and Biological Foundations

Puberty

• Puberty: A brain-neuroendocrine process in early adolescence that stimulates rapid physical changes.

• Marks the beginning of adolescence but ends long before adolescence is over.

Determinants of Puberty

• Initiation of puberty is complex and not fully understood.

• Factors include changes in the endocrine system, weight, and body fat.

• It is unclear whether these factors are causes or consequences of puberty.

• Birth weight, rapid weight gain in infancy, obesity, and sociocultural factors may influence pubertal onset and characteristics.

Heredity

• Timing of puberty is programmed in genes.

• Occurs between 9 and 16 years for most individuals.

• Molecular genetic studies aim to identify specific genes linked to puberty onset and progression.

• Environmental factors can influence onset and duration.

Hormones

• Hormones: Chemical substances secreted by endocrine glands, carried by the bloodstream.

• Androgens: Main class of male sex hormones

  • Testosterone: An androgen important for male pubertal development.

• Estrogens: Main class of female sex hormones

  • Estradiol: An estrogen important for female pubertal development.

Hormones and Physical Changes

• Rising testosterone levels in boys lead to:

  • Development of external genitals.

  • Increased height.

  • Voice changes.

  • Sexual desire and activity.

• Rising estradiol levels in girls lead to:

  • Breast development.

  • Uterine development.

  • Skeletal changes.

  • Hormonal contributions to sexual desire in girls are less clear than in boys.

The Endocrine System

• Puberty onset involves the hypothalamic-pituitary-gonadal (HPG) axis.

  • Hypothalamus: Monitors eating, drinking, and sex.

    • Secretes gonadotropin-releasing hormone (GnRH), linked to pubertal timing.

  • Pituitary gland: Regulates other glands, secretes follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

    • LH regulates estrogen secretion and ovum development in females, and testosterone production in males.

  • Gonads: Sex glands (testes in males, ovaries in females).

Negative Feedback System

• Hormones are regulated by a negative feedback system.

  • High sex hormone levels decrease hypothalamus and pituitary gland stimulation of gonads, reducing sex hormone production.

  • In males, low testosterone levels cause the hypothalamus to produce more GnRH, restarting the cycle.

  • A similar system operates in females, with LH and GnRH regulating ovaries and estrogen production.

Growth Hormones

• Pituitary gland secretes growth hormones, leading to growth and skeletal maturation.

• Growth hormone secreted at night at the beginning of puberty.

• Later in puberty, also secreted during the day; however, daytime levels are usually low.

Adrenarche and Gonadarche

• Two phases of puberty are linked with hormonal changes: adrenarche and gonadarche.

  • Adrenarche: Hormonal changes in the adrenal glands.

    • Occurs from about 6 to 9 years in girls, and a year later in boys, before puberty.

    • Adrenal glands secrete adrenal androgens, such as dehydroepiandrosterone (DHEA).

  • Gonadarche: Maturation of primary and secondary sexual characteristics.

    • Follows adrenarche by about 2 years.

    • Primary sexual characteristics: Ovaries in females, testes in males.

    • Secondary sexual characteristics: Pubic hair, breast and genital development.

    • Begins at approximately 9–10 years in non-Latinx white girls and 8–9 years in African American girls.

    • Begins at about 10–11 years in boys.

Menarche and Spermarche

• Menarche: A girl’s first menstrual period.

  • Occurs in mid- to late gonadarche in girls.

• Spermarche: A boy’s first ejaculation of semen.

  • Occurs in early to mid-gonadarche in boys.

Weight and Body Fat

• Higher weight, especially obesity, is linked to earlier pubertal development.

• Obesity was associated with earlier pubertal onset in boys.

• Menarche influenced by percentage of body fat.

• Anorexic adolescents and female athletes may not menstruate.

• Undernutrition may delay puberty in boys.

Leptin and Kisspeptins

• Reproduction is an energy-demanding function.

• Puberty is “metabolically gated” to prevent fertility when energy conditions are very low.

• Leptin (secreted by fat cells) stimulates the brain to increase metabolism and reduce hunger, playing a role in regulating puberty, especially in females.

• Kisspeptins (products of the Kiss 1 gene) regulate GnRH neurons and play a role in pubertal onset and change.

Weight at Birth and in Infancy

• Link between puberty’s onset and characteristics and birth weight and weight gain during infancy.

• Low-birth-weight girls experience menarche approximately 5–10 months earlier than normal-birth-weight girls.

• Low-birth-weight boys are at risk for small testicular volume during adolescence.

Sociocultural and Environmental Factors

• Cultural variations and early experiences may be related to earlier pubertal onset.

• Adolescents in developed countries and urban areas reach puberty earlier than those in less developed countries and rural areas.

• Children adopted from developing to developed countries often enter puberty earlier.

• In the United States, African American females and males enter puberty earlier than Latinx and non-Latinx white individuals.

Early Experiences

• Early experiences linked to earlier pubertal onset include:

  • Adoption.

  • Father absence.

  • Low socioeconomic status.

  • Family conflict.

  • Maternal harshness.

  • Child maltreatment.

  • Early substance use.

Growth Spurt

• Growth slows throughout childhood, then puberty brings rapid increases in growth.

• Growth spurt occurs approximately 2 years earlier for girls (age 9) than boys (age 11) on average.

• The peak of pubertal change occurs at 11½ years for girls and 13½ years for boys.

• Girls increase in height by about 3½ inches per year; boys, by about 4 inches.

Growth Spurt Details

• For girls, the growth spurt typically begins before menarche and ends earlier.

• For boys, it begins later and ends later.

• At the beginning of adolescence, girls tend to be as tall as or taller than boys; by the end of middle school, boys catch up, and many surpass girls in height.

Weight Gain

• Weight gain follows roughly the same timetable as height gain.

• Fifty percent of adult body weight is gained during adolescence.

• Girls gain an average of 18 lb in 1 year, at roughly 12 years of age.

• Boys gain an average of 20 lb at roughly 13–14 years of age.

• Girls gain hip width, while boys gain shoulder width, as associated with estrogen and testosterone.

• The later growth spurt of boys produces a greater leg length in boys than in girls.

• Boys’ facial structure becomes more angular during puberty, whereas girls’ facial structure becomes rounder and softer.

Sexual Maturation (Males)

• Male pubertal characteristics develop in this order:

  • Increased penis and testicle size (most noticeable).

  • Appearance of straight pubic hair.

  • Minor voice change.

  • First ejaculation (spermarche).

  • Appearance of kinky pubic hair.

  • Onset of maximum growth.

  • Growth of armpit hair.

  • More detectable voice changes.

  • Growth of facial hair (most noticeable).

Sexual Maturation (Females)

• Female pubertal characteristics develop in this order:

  • Breast development (most noticeable).

  • Growth of pubic hair (most noticeable).

  • Growth of armpit hair.

  • Height gain.

  • Hips become wider than shoulders.

  • First menstruation (menarche).

  • No voice changes occur that are comparable to those in pubertal males.

Precocious Puberty

• Precocious puberty: very early onset and rapid progression of puberty.

  • Pubertal onset before the age of 8 in girls and before the age of 9 in boys.

  • Occurs approximately 10 times more often in girls than in boys.

  • Treated by medically suppressing gonadotropic secretions, which temporarily stops pubertal change.

  • The reason for 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.

Secular Trends in Puberty

• Secular trends: patterns of the onset of puberty over historical time, especially across generations.

  • In the United States, 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.

  • 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-Latinx white girls.

  • Puberty is also occurring earlier in a number of other countries in recent years.

Psychological Dimensions of Puberty: Body Image

• Preoccupation with body image is one psychological aspect of puberty for both boys and girls.

• Gender differences:

  • In general, throughout puberty girls are less happy with their bodies and have more negative body images than boys.

  • As pubertal change proceeds, girls often become more dissatisfied with their bodies, probably because their body fat increases.

  • In contrast, boys become more satisfied as they move through puberty, probably because their muscle mass increases.

Social Media and Body Image

• Various aspects of exposure to the internet and social media are increasing the body dissatisfaction of adolescents and emerging adults, especially females.

• Higher social media use was linked to more negative body images among adolescents, especially girls.

• More time on Facebook was related to more frequent body and weight concern comparisons with other women.

• Exposure to attractive female celebrity and peer images on Instagram was detrimental to their body image.

Body Art

• An increasing number of adolescents and college students are obtaining tattoos and getting parts of their body pierced or engaging in scarification.

• Some studies indicate that tattoos and body piercings are markers for risk-taking in adolescence.

• Researchers do not agree whether body art is used to express individuality and self-expression or rebellion.

Hormones and Behavior

• Hormonal factors are thought to account for at least part of the increase in negative and variable emotions that characterize adolescents.

  • In boys, higher levels of androgens are associated with violence and acting-out problems.

  • There is also some indication that increased estrogen levels are linked to depression in adolescent girls.

• Hormonal factors alone are not responsible for adolescent depression or risk-taking behavior.

• Many environmental factors influence hormonal activity:

  • Parent–adolescent relationships.

  • Stress.

  • Eating patterns.

  • Sexual activity.

  • Depression.

Early and Late Maturation

• When adolescents mature earlier or later than their peers, they often perceive themselves differently.

• Early maturation in girls increases girls’ vulnerability to a number of problems, including substance use, depression, eating disorders, antisocial behavior, and earlier sexual experiences.

• Early maturation often has more favorable outcomes in adolescence for boys, especially in early adolescence.

• Later in life, however, boys’ late maturation may be more favorable, especially in terms of identity and career development.

Health

Adolescence: A Critical Juncture in Health

• Adolescence is a critical juncture in the adoption of behaviors that are relevant to health.

• A recent concern is the impact of the COVID-19 pandemic on adolescent health.

  • Parents were less likely to take children to physicians and emergency departments after the pandemic began.

  • The pandemic was associated with increased mental health issues in youth.

Poor Health Habits

• Why might adolescents develop poor health habits?

  • In adolescence, many individuals reach a level of health, strength, and energy that they will never match during the remainder of their lives.

• Experts recognize that health depends on adolescent behavior and propose two goals:

  • Reduce health-compromising behaviors: drug abuse, violence, unprotected sexual intercourse, and dangerous driving.

  • Increase health-enhancing behaviors: exercising, eating nutritiously, wearing seat belts, and getting adequate sleep.

Adolescent Health Risks

• Increasing adolescents’ awareness of health risks doesn’t always work.

  • Effective intervention should focus on treating adolescents with respect and according them higher status.

• Disparities in health related to poverty and ethnicity:

  • homelessness, crime and violence, housing insecurity, hunger, malnutrition, lack of health insurance, compromised health and well-being of parents, racism, and discrimination.

  • Latinx adolescents were 8 times more likely and African American adolescents 5 times more likely to be hospitalized with COVID-19 than non-Latinx white counterparts.

Risk-Taking Behavior

• One type of health-compromising behavior that increases in adolescence is risk-taking.

• Researchers 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 such behavior.

• Parental monitoring and communication skills are linked to a lower level of adolescent risk-taking.

Neurobiological Explanations of Adolescent Risk-Taking

• 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.

• It is important for parents, teachers, mentors, and other responsible adults to effectively monitor adolescents’ behavior.

Health Services

• Adolescents underutilize health care systems.

  • Many adolescents don’t believe providers can help them.

  • Professionals who want to provide better health care for adolescents may lack adequate training and/or time during a health care visit.

  • Of special concern is the low use of health services by high school adolescent males.

  • 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.

Leading Causes of Death

• The three leading causes of death in adolescence are unintentional injuries, suicide, and homicide.

• Almost half of all deaths from 15 to 24 years of age are due to unintentional injuries, the majority involving motor vehicle accidents.

  • In about 50% of motor vehicle fatalities involving adolescents, the driver has a blood alcohol level of 0.10\% or higher.

• Suicide recently replaced homicide as the second- leading cause of death for adolescents.

Emerging Adults’ Health

• Emerging adults have more than twice the mortality rate of adolescents.

• Compared to 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.

• Few emerging adults stop to think about how their personal lifestyles will affect their health later in their adult lives.

Warning Signs Often Ignored by Emerging Adults

• Breast lumps.

• Unexplained weight loss.

• Fever for more than a week.

• Coughing up blood.

• Persistent or severe headaches.

• Fainting spells.

• Unexplained shortness of breath.

Nutrition

• Nutrition is an important aspect of health- compromising and health-enhancing behaviors.

• The eating habits of many adolescents are health- compromising.

• An increasing number of adolescents have an eating disorder.

• Eating regular family meals during early adolescence is linked to healthy eating habits 5 years later.

• Parents play an important role in adolescents’ nutrition, through the food choices they make available, by serving as role models for healthy or unhealthy nutrition, and by including adolescents in regular family meals.

School Nutrition

• Schools can also play an important role in adolescents’ eating patterns.

• One special concern in American culture is the amount of fat in the diet.

• Another special concern is the recent increase in consumption of energy drinks that tend to have high caffeine levels.

  • Research has found this to be linked to more emergency room visits, adverse cardiovascular effects, alcohol use, reduced sleep duration, and fast food consumption.

Exercise and Sports

• Exercise is one of the principal activities that improves the quality of life, both in adolescence and adulthood.

• Researchers have found that individuals become less active as they reach and progress through adolescence.

  • In 2019, 23\% of 9th- through 12th-graders had engaged in physical activity for 60 min or more in each of the last 7 days, compared to 28.7\% in 2011.

  • Adolescent girls were much less likely to engage in physical activity than were boys.

Ethnic Differences in Exercise

• Ethnic differences in the exercise participation rates of U.S. adolescents also occur; and rates also vary by gender.

• A comparison of adolescents in 28 countries found that U.S. adolescents exercised less and ate more junk food.

  • U.S. adolescents are more likely to eat fried food and less likely to eat fruits and vegetables than adolescents in most other countries studied.

Benefits of Exercise

• Exercise is linked to a number of positive outcomes in adolescence.

• Benefits of regular exercise for adolescents include:

  • A positive effect on weight status.

  • Reduced triglyceride levels, lower blood pressure, and a lower incidence of type 2 diabetes.

  • Lower levels of alcohol, cigarette, and marijuana use.

  • Fewer emotional and peer problems.

  • Better connectivity between brain regions than in adolescents who are less fit.

  • Reduced stress and depression.

  • Improvement in cognitive skills.

  • Reduction in the symptoms of attention deficit hyperactivity disorder (ADHD).

Family and School Roles in Exercise

• Parents have an important influence on adolescents’ exercise patterns.

  • 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.

• Peers also often influence adolescents’ physical activity.

  • Peer/friend support of exercise, presence of peers and friends, friendship quality and acceptance, and peer crowds.

Screen Time

• Screen-based activity is associated with lower levels of physical fitness in adolescence.

• Watching television, using computers, talking on the phone, texting, and instant messaging for long hours.

• Adolescents who engage in low physical activity and high screen-based activity are more likely to be overweight/obese.

Sports

• Sports play an important role in the lives of many adolescents.

  • In a 2015 assessment:

    • Boys (62\%%) were more likely to play on a sports team than girls (53\%%).

    • African American boys had the highest participation rate (66.5\%%) and Latinx girls the lowest participation rate (40.7\%%).

    • From 2013 to 2015, the overall girls’ participation rate increased by 4.5\%%, although the rate for Latinx girls decreased by 4.3\%%.

Positive Outcomes of Sports

• Many sports activities can improve adolescents’ physical health and well-being, mental health, self-confidence, motivation to excel, and ability to work with others.

• Adolescents who participate in sports are less likely to engage in risk-taking behaviors such as using drugs, less likely to be overweight or obese, show a lower cardiovascular risk profile, and have higher self-esteem.

Negative Outcomes of Sports

• Pressure to achieve and win, physical injuries, distraction from academics, and unrealistic expectations for success.

• Pressure by parents and coaches to win at all costs, competition anxiety, and self-centeredness.

• Injuries are common when adolescents play sports.

• Use of performance-enhancing drugs such as steroids.

• Coaches who create a performance-oriented motivational climate that is focused on winning, public recognition, and performance relative to others.

• Female athlete triad: disordered eating, amenorrhea, and osteoporosis.

Sleep

• There has been a surge of interest in adolescent sleep.

• In a national survey of youth, only 25\% of U.S. adolescents got 8 or more hours of sleep on an average school night, 7\% less than four years earlier.

• Getting too little sleep is linked to academic deficiencies, less efficient information processing, a greater incidence of emotional, mood, and substance abuse problems, and poorer relationships with peers.

Links Between Lack of Sleep and Adolescent Problems

• Students who sacrificed sleep time to study had difficulty understanding what was taught in class and were more likely to struggle with class assignments.

• In 13- to 19-year-olds, getting less than 7 hours of sleep on school nights was associated with an increased risk of being overweight, having depressive symptoms, being less motivated, difficulty concentrating, high levels of anxiety, and engaging in self-harm/suicidal thoughts.

• A recent study indicated that insufficient sleep was associated with alcohol and marijuana use in adolescents.

Reasons for Lack of Sleep

• Why are adolescents getting too little sleep?

  • Electronic media usage, caffeine, and changes in the brain, coupled with early school start times.

  • Using electronic devices other than television 5 or more hours a day has been linked to getting inadequate sleep.

  • Caffeine consumption and daytime sleepiness are also related to lower academic achievement.

Solutions for Lack of Sleep

• Many adolescents stay up later at night and sleep longer in the morning than when they were children.

• Early school starting times may cause grogginess, inattention, and poor performance on tests.

• The American Academy of Pediatrics recently advocated that schools shift start times from 8:30 to 9:30 a.m. to improve students’ academic performance and quality of life.

Sleep Patterns in Emerging Adulthood

• Sleep patterns are often poor in emerging adulthood.

  • At about 20–22 years of age, a reverse in the timing of bedtimes and rise times occurs.

  • Emotional and academic stress negatively affects sleep, as does smartphone dependence and energy drink consumption.

  • Less sleep is associated with increased suicide risk, lower grade point average, and delayed college graduation.

• The National Sleep Foundation recommends emerging adults get 7–9 hours of sleep.

  • Engaging in more physical activity and maintaining positive social relationships can improve sleep patterns.

Evolution, Heredity, and Environment

The Evolutionary Perspective

• In terms of evolutionary time, humans are relative newcomers to the Earth.

• As our earliest ancestors left the forest to feed on the savannahs and finally to form hunting societies on the open plains, their minds and behaviors changed.

Natural Selection and Adaptive Behavior

• Natural selection: the evolutionary process that favors those individuals of a species who are best adapted to survive and reproduce

  • Charles Darwin: Over the course of many generations, organisms with the characteristics needed for survival would compose a larger and larger percentage of the population, producing a gradual modification of the species.

• Adaptive behavior: a modification of behavior that promotes an organism’s survival in the natural habitat

  • All organisms must adapt to particular places, climates, food sources, and ways of life in order to survive.

Evolutionary Psychology

• Evolutionary psychology emphasizes the importance of adaptation, reproduction, and “survival of the fittest” in explaining behavior.

• The process of natural selection favors those behaviors that increase organisms’ reproductive success and their ability to pass their genes on to the next generation.

Evolutionary Development Psychology

• There is growing interest in using the concepts of evolutionary psychology to understand human development.

  • 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.

  • Many psychological mechanisms are domain-specific—they apply only to the specific aspect of a person’s makeup.

  • Evolved mechanisms are not always adaptive in contemporary society—that is, some behaviors that were adaptive for our prehistoric ancestors may not serve us well today.

Evaluating Evolutionary Psychology

• Albert Bandura (1998) has criticized the “biologizing” of psychology.

  • He rejects what he calls “one-sided evolutionism.”

  • Evolution gave humans body structures and biological potentialities, not behavioral dictates.

• Stephen Jay Gould: In most domains, human biology allows a broad range of cultural possibilities.

• Natural selection leading to human traits and behaviors is difficult to refute or test because it occurs on a time scale that does not lend itself to empirical study.

The Genetic Process

• Our many traits and characteristics that are genetically influenced have a long evolutionary history that is retained in our DNA.

• Each of us carries a “genetic code” that we inherited from our parents.

DNA and the Collaborative Gene

• The nucleus of each human cell contains chromosomes, the threadlike structures that contain DNA.

  • DNA: a complex molecule that contains genetic information.

  • Genes, the units of hereditary information: short segments of DNA that direct cells to reproduce themselves and to assemble proteins.

  • Humans have approximately 20,000–25,000 genes.

  • Humans appear to have far more proteins than they have genes, so there cannot be a one-to-one correspondence between them.

The Collaborative Gene

• Rather than being an independent source of information, DNA collaborates with other sources of information to specify our characteristics.

• 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.

• Stress, exercise, nutrition, respiration, radiation, temperature, sleep, and loneliness can influence gene expression.

• Methylation, in which tiny atoms attach themselves to the outside of a gene, makes a gene more or less capable of receiving and responding to biochemical agents from the body.

Gene–Gene Interaction

• A single gene is rarely the source of a protein’s genetic information, much less the source of a person’s inherited trait.

• Rather than being a group of independent genes, the human genome consists of many collaborative genes.

• The term gene–gene interaction is increasingly used to describe studies that focus on the interdependence of two or more genes in influencing characteristics, behavior, diseases, and development.

Genotype and Phenotype

• A person’s genetic heritage—the actual genetic material—is called a genotype.

• The way an individual’s genotype is expressed in observed and measurable characteristics is called a phenotype.

  • Phenotypes include physical traits and psychological characteristics.

  • For each genotype, a range of phenotypes can be expressed.

Heredity-Environment Interaction

• Heredity and environment interact to produce development.

  • Behavior genetics: the field that seeks to discover the influence of heredity and environment on individual differences in human traits and development

• To study the influence of heredity on behavior, behavior geneticists use either twin or adoption studies.

Twin and Adoption Studies

• Twin study: the behavioral similarity of identical twins is compared with that of fraternal twins

  • Identical twins are monozygotic twins.

  • Fraternal twins are dizygotic twins.

• Adoption study: a study that aims to discover whether the behavior and psychological characteristics of adopted children are more like those of their adoptive parents or those of their biological parents

  • Another form involves comparing adopted and biological siblings.

Heredity-Environment Correlations

• Sandra Scarr described three ways that heredity and environment are correlated:

  • Passive genotype-environment correlations occur because biological parents provide the rearing environment.

  • Evocative genotype-environment correlations occur because an individual’s genetically shaped characteristics elicit certain types of physical and social environments.

  • Active (niche-picking) genotype-environment correlations occur when children seek out environments they find compatible and stimulating.

  • The relative influence of the three correlations changes as children develop from infancy through adolescence.

The Epigenetic View

• The heredity-environment correlation view emphasizes how heredity directs the kind of environmental experiences individuals have.

• In line with the concept of the collaborative gene, the epigenetic view emphasizes that development is the result of an ongoing, bidirectional interchange between heredity and the environment.

Epigenetic Mechanisms

• The epigenetic mechanisms involve the actual molecular modification of the DNA strand as a result of environmental inputs in ways that alter gene functioning.

  • Example: Adolescents who experienced negative life events drank heavily only when they had a particular variation of the CRHR1 gene.

  • This type of research is referred to as gene × environment (G × E) interaction—the interaction of a specific measured variation in DNA and a specific measured aspect of the environment.

Conclusions About Heredity-Environment Interaction

• Heredity and environment operate together.

  • The relative contributions are not quantifiable; nor is it accurate to say that full genetic expression happens once around conception or birth.

  • Genes produce proteins throughout the life span, in many different environments.

  • The emerging view is that many complex behaviors likely have some genetic loading that gives people a propensity for a specific developmental trajectory.

Complex Behaviors

• David Moore: The biological systems that generate behaviors are extremely complex, but too often these systems have been described in overly simplified ways that can be misleading.

  • It is misleading to talk about “genes for” eye color, intelligence, personality, or other characteristics.

  • Adolescents are not only the outcomes of their heredity and the environment they experience; they also author a unique developmental path by changing their environment.