Adolescence and Emerging Adulthood: A Cultural Approach Chapter 2 Biological Foundations Adolescence and Emerging Adulthood: A Cultural Approach by Jeffrey

Adolescence and Adolescence and Emerging Adulthood: A Emerging Adulthood: A

Cultural ApproachCultural Approach

Chapter 2 Chapter 2

Biological Biological FoundationsFoundations

Adolescence and Emerging Adulthood: A Cultural Approach by Jeffrey Jensen Arnett. Copyright © 2004 by Pearson Education. All rights reserved.


Hormonal ChangesHormonal Changes

Physical ChangesPhysical Changes

Primary Sex CharacteristicsPrimary Sex Characteristics

Secondary Sex CharacteristicsSecondary Sex Characteristics

Cultural, Social, Psychological Cultural, Social, Psychological Responses to PubertyResponses to Puberty

Chapter OverviewChapter Overview


PubertyPuberty

derived from the Latin derived from the Latin word ‘word ‘pubescere’pubescere’ which which means to “grow hairy”means to “grow hairy”

The body undergoes a The body undergoes a biological revolution biological revolution that dramatically that dramatically changes the changes the adolescent’s adolescent’s anatomyanatomy, , physiologyphysiology, and , and physical physical appearanceappearance

The Endocrine SystemThe Endocrine System


Hormonal changes begin here

Gradually increases production of gonadotropin-releasing hormone (GnRH)

Recent evidence indicates that this occurs once a threshold

level of body fat is reached

Fat cells produce leptin that provides the signal

to the hypothalamus

Pituitary Gland and GonadotropinsPituitary Gland and Gonadotropins

Increase in GnRH affects the pituitary gland

Gonadotropins influence production of sex hormones

Gonadotropins stimulate development of gametes

Pituitary gland releases gonadotropins


Sex HormonesSex Hormones


Compare the differences in hormone production Compare the differences in hormone production between boys and girls during pubertybetween boys and girls during puberty

Testosterone

Estradiol

Endocrine System Feedback LoopEndocrine System Feedback Loop


Monitor levels of androgens and estrogens in the bloodstream

Responds to the reduction in GnRH by reducing production

of FSH, LH and ACTH

Respond to lower levels of FSH and LH by reducing the amount

of sex hormones produced

“SET POINT” – when sex hormones reach an optimal level and the hypothalamus reduces GnRH to

begin this process

Physical Growth during PubertyPhysical Growth during Puberty


Notice the differential timing in when growth spurts begin

Notice when the difference in final height is achieved

Growth SpurtsGrowth Spurts Not all parts of the Not all parts of the

body grow at the body grow at the same pacesame pace

AsynchronicityAsynchronicity in in growth explains the growth explains the “gangly look” in early “gangly look” in early adolescenceadolescence

Extremities are the first to hit the

growth spurt


Muscle Mass and Body FatMuscle Mass and Body Fat


Notice prior to puberty boys and girls are very similar in muscle mass

During puberty body fat increases more for

girls than for boys

Cultural ExpectationsCultural Expectations In many cultures gender differences exist for In many cultures gender differences exist for

physical activityphysical activity

Girls are sometimes discouraged from Girls are sometimes discouraged from participating in sports (not confirming to participating in sports (not confirming to “feminine” stereotypes)“feminine” stereotypes)

Boys are more likely to exercise in Boys are more likely to exercise in adolescenceadolescence

This gender difference contributes to This gender difference contributes to differences in athletic performance between differences in athletic performance between adolescent boys and girlsadolescent boys and girls



Is This True?Is This True?

Reaction time is slower in emerging

adulthood.

Is this true?

Reaction time is actually faster in the

early twenties than at any other time of life

Is this true?

Grip Strength in men peak in emerging

adulthood

Yes … and followed by a steady decline

Cardiac output peaks at 18 years of age

Is this true?

Cardiac output, the quantity of blood flow from the heart, peaks

at age 25

Physical Functioning in Physical Functioning in Emerging AdulthoodEmerging Adulthood

Emerging adulthood is the period of Emerging adulthood is the period of the life span with the least the life span with the least susceptibility to physical illnesssusceptibility to physical illness

… … but that’s not the whole but that’s not the whole storystory


Physical Functioning in Physical Functioning in Emerging AdulthoodEmerging Adulthood

Lifestyles of many emerging adults often include a Lifestyles of many emerging adults often include a variety of factors that variety of factors that undermine healthundermine health such as such as• Poor nutritionPoor nutrition• Lack of sleepLack of sleep• Stress of juggling school/work/multiple jobsStress of juggling school/work/multiple jobs

Automobile accidentsAutomobile accidents are the leading cause of are the leading cause of death among emerging adults in the United Statesdeath among emerging adults in the United States

HomicideHomicide is another common cause of death in the is another common cause of death in the U.S. during emerging adulthoodU.S. during emerging adulthood

Rates of contracting Rates of contracting sexuallysexually transmitted diseases, transmitted diseases, including HIV are highest in the early twentiesincluding HIV are highest in the early twenties


Sex CharacteristicsSex CharacteristicsPrimary Sex Primary Sex

CharacteristicsCharacteristicsSecondary Sex Secondary Sex

CharacteristicsCharacteristics

BoysBoys Production of Production of spermsperm

Development of Development of sex organssex organs

Hair growthHair growth in pubic areas, underneath in pubic areas, underneath arms, chests, face, shoulders and backarms, chests, face, shoulders and back

SkinSkin becomes rougher becomes rougher

Sweat glandsSweat glands increase production increase production

GirlsGirls Production of Production of eggseggs

Development of Development of sex organssex organs

Hair growthHair growth in public areas, underneath in public areas, underneath arms and a slight amount of facial hairarms and a slight amount of facial hair

SkinSkin becomes rougher becomes rougher

Sweat glandsSweat glands increase production increase production

Slight enlargement of breasts known as Slight enlargement of breasts known as breast budsbreast buds


… … the facts about femalesthe facts about females

Women are born with about 400,000 Women are born with about 400,000 immature eggs (follicles) in each ovaryimmature eggs (follicles) in each ovary

Once a girl reaches her first menstrual Once a girl reaches her first menstrual period (menarche) one follicle develops period (menarche) one follicle develops into a mature egg (ovum) about every 28 into a mature egg (ovum) about every 28 daysdays

Females release about 400 eggs over the Females release about 400 eggs over the course of their reproductive livescourse of their reproductive lives


… … the truth about menthe truth about men Males have no sperm in their testes when Males have no sperm in their testes when

they are born and do not produce any until they are born and do not produce any until they reach pubertythey reach puberty

The average age that sperm production The average age that sperm production begins (spermarche) is approximately 12 begins (spermarche) is approximately 12 years oldyears old

Boys produce sperm in astonishing Boys produce sperm in astonishing quantities – there are between 30 and 500 quantities – there are between 30 and 500 million sperm in the typical male million sperm in the typical male ejaculation, which means they produce ejaculation, which means they produce millions of sperm everydaymillions of sperm everyday


The Order of Pubertal EventsThe Order of Pubertal Events

GIRLS

BOYS

Downy pubic hair

Appearance of breast buds

Growth spurt

Growth of sexual and

reproductive organs

Menarche

Secretion of increased

skin oil and sweat

Development of underarm

hair

Appearance of pubic hair

Deepening of the voice

Development of facial hair

Growth of testes

Growth spurt

Increased growth of

penis

Secretion of increased

skin oil and sweat


Pubertal CaveatPubertal Caveat

Virtually all the studies considered in the Virtually all the studies considered in the order of pubertal development have been order of pubertal development have been conducted with White adolescents in the conducted with White adolescents in the WestWest

Three studies demonstrate the variations Three studies demonstrate the variations that may exist in other groups that may exist in other groups • Worthman, 1987Worthman, 1987• Lee, Chang, and Chan, 1963Lee, Chang, and Chan, 1963• Herman-Giddens et al., 1997; 2001Herman-Giddens et al., 1997; 2001


Kikuyu culture in KenyaKikuyu culture in Kenya(Worthman, 1987)(Worthman, 1987)

Boys show the first physical changes of Boys show the first physical changes of puberty puberty beforebefore their female peer their female peer

a reversal of the Western patterna reversal of the Western pattern

African American GirlsAfrican American Girls(Herman-Giddens et al., 1997; 2001)(Herman-Giddens et al., 1997; 2001)

Many Black girls were found to begin Many Black girls were found to begin developing breast buds and pubic hair developing breast buds and pubic hair considerably earlier than White girlsconsiderably earlier than White girls


Pubic hair began to develop in most girls about 2 years Pubic hair began to develop in most girls about 2 years afterafter the the development of breast buds and only a few months before development of breast buds and only a few months before menarchemenarche

In sharp contrast to the Western studies that found pubic hair and In sharp contrast to the Western studies that found pubic hair and breast buds developed together about 2 years before menarchebreast buds developed together about 2 years before menarche

Chinese GirlsChinese Girls(Lee, Chang, and Chan, 1963)(Lee, Chang, and Chan, 1963)

These three studies show the importance of investigating ethnic differences in the rates, timing,

and order of pubertal events


Culture and Pubertal TimingCulture and Pubertal Timing


The secular trend downward in the age of

menarche has occurred in every Western country for

which records exist


Discussion StopDiscussion Stop

Why is the Why is the secular trendsecular trend for the age of menarche for the age of menarche going down in Western going down in Western countries?countries?

How do your answers compare to the following slide?

Downward Secular Trend of MenarcheDownward Secular Trend of Menarche

Puberty begins earlier in cultures where Puberty begins earlier in cultures where good nutrition and medical care are widely good nutrition and medical care are widely availableavailable

Illness and thinness tend to inhibit the Illness and thinness tend to inhibit the development of body fat resulting in development of body fat resulting in delayed pubertydelayed puberty

Advances in food production have Advances in food production have enhanced nutrition and therefore puberty enhanced nutrition and therefore puberty has come soonerhas come sooner


Cultural Responses to Puberty: RitualsCultural Responses to Puberty: RitualsTraditional CulturesTraditional Cultures

68%68% of cultures had of cultures had puberty rituals puberty rituals for boysfor boys

Typically rituals require the Typically rituals require the young man to display young man to display courage, strength and courage, strength and enduranceendurance

The rituals are often The rituals are often violent, requiring boys to violent, requiring boys to submit to and sometimes submit to and sometimes engage in bloodletting of engage in bloodletting of various kindsvarious kinds

• 79%79% of cultures had of cultures had puberty rituals puberty rituals for girlsfor girls

• Menarche is the pubertal Menarche is the pubertal event that is most often event that is most often marked by ritualmarked by ritual

• Cultural views are mixed Cultural views are mixed as to whether menstrual as to whether menstrual blood is an omen or a blood is an omen or a positive sign of fertilitypositive sign of fertility


NOTE: Globalization has been credited with the decline in frequency of these rituals

How do parent-adolescent relations How do parent-adolescent relations change at puberty?change at puberty?

Conflict increasesConflict increases

Closeness decreases Closeness decreases

Parents and adolescents seem less Parents and adolescents seem less comfortable in each other’s comfortable in each other’s presencepresence

Distancing hypothesis:Distancing hypothesis: it may be it may be adaptive for young people to move adaptive for young people to move away from closeness to their parents away from closeness to their parents once they reach sexual maturity so once they reach sexual maturity so that they mate and reproduce with that they mate and reproduce with persons outside the family, thus persons outside the family, thus avoiding the genetic problems that avoiding the genetic problems that often result from incestoften result from incest


Frequency of Adolescent-Mother Frequency of Adolescent-Mother Touching and TalkingTouching and Talking


Research based on 122 pairs of mother and

children aged 6 to 16

Mothers and early adolescents talked

more than mothers and younger children,

suggesting that parent-child communication styles shift toward

talking and away from touching when puberty

is reached

Early Maturation - GirlsEarly Maturation - Girls• The effects of early maturation are The effects of early maturation are

especially especially negativenegative for girls for girls

• Early maturing girls are at risk for a Early maturing girls are at risk for a variety of problems:variety of problems:

Depressed moodDepressed mood Negative body imageNegative body image Eating disordersEating disorders Substance useSubstance use DelinquencyDelinquency School problemsSchool problems Conflicts with parentsConflicts with parents


Late Maturation - GirlsLate Maturation - Girls• Late maturing girls have few of the problems Late maturing girls have few of the problems

that early-maturing girls havethat early-maturing girls have

• Although they can suffer from:Although they can suffer from: TeasingTeasing Negative body image (during the years when Negative body image (during the years when

other girls have begun to develop)other girls have begun to develop)

• However, by their late teens they tend to However, by their late teens they tend to have a more favourable body image than have a more favourable body image than other girlsother girls

• They are more likely to end up with the lean They are more likely to end up with the lean body build that tends to be regarded as body build that tends to be regarded as attractive in Western majority cultures.attractive in Western majority cultures.


Early Maturation - BoysEarly Maturation - Boys• The effects of early maturation tend to The effects of early maturation tend to

be be positivepositive for boys for boys

• Early maturing boys have:Early maturing boys have: More favorable body imageMore favorable body image Higher popularityHigher popularity

• Although not everything is favorable. Although not everything is favorable. They tend to be involved in:They tend to be involved in:

Substance useSubstance use DelinquencyDelinquency SexSex


Late Maturation - BoysLate Maturation - Boys

• Late maturing boys show evidence of Late maturing boys show evidence of problemsproblems

• Compared with boys who mature “on Compared with boys who mature “on time” late maturing boys have higher time” late maturing boys have higher rates of:rates of:

Alcohol useAlcohol use DelinquencyDelinquency Lower grades in schoolLower grades in school


GenotypeGenotype• A person’s inherited genesA person’s inherited genes

According to the theoryAccording to the theory• Both genotype and environment make Both genotype and environment make

essential contributions to human developmentessential contributions to human development

Genotype-environment interactions take Genotype-environment interactions take three forms:three forms:• PassivePassive• EvocativeEvocative• ActiveActive

Genotype-Environment InteractionsGenotype-Environment Interactions



DescriptionInteraction

ActiveOccur when people seek out environments that correspond to their genotypic characteristics

EvocativeOccur when a person’s inherited characteristics evoke responses from others in their environment

Passive Occur in biological families when parents provide both genes and environment

Genotype-Environment InteractionsGenotype-Environment Interactions

Unravelling genotype-environment Unravelling genotype-environment interactionsinteractions

Adoption studiesAdoption studies

• These studies avoid the problem of These studies avoid the problem of passive genotype-environment effects passive genotype-environment effects because one set of parents provided the because one set of parents provided the adolescent’s genes but a different set of adolescent’s genes but a different set of parent provided the environmentparent provided the environment


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Adolescence and Emerging Adulthood: A Cultural Approach Chapter 2 Biological Foundations Adolescence and Emerging Adulthood: A Cultural Approach by Jeffrey