Nature, Nurture, and Human Diversity

Transcription

1 CHAPTER 4 Preview Natre, Nrtre, and Hman Diversity Members of the hman family share common behavioral tendencies bt are also strikingly diverse. To what extent are we shaped by or heredity and to what degree by or life history? The conclsions that both natre and nrtre are crcially important are central to today s psychology. Genes provide the bleprints that design both or niversal hman attribtes and or individal traits. Behavior geneticists explore individal differences. By sing twin, adoption, and temperament stdies, they assess the heritability of varios traits and disorders. Their research indicates that we are prodcts of interactions between or genetic predispositions and or srronding environments. Moleclar geneticists search for genes that pt people at risk for genetically inflenced disorders, which has potential benefits as well as risks. Evoltionary psychologists focs on what makes s alike as hmans. They stdy how natral selection favored behavioral tendencies that contribted to the srvival and spread of or genes. For example, in explaining gender differences in sexal behavior, they arge that women most often send their genes into the ftre by pairing wisely, men by pairing widely. Critics maintain that evoltionary psychologists make too many hindsight explanations. Althogh genetic inflences are pervasive, so are environmental inflences. Nrtre begins in the womb as embryos receive differing ntrition and varying levels of exposre to toxic agents. Sclpted by experience, neral connections mltiply rapidly after birth. Parental inflence is more important when it comes to edcation, discipline, responsibility, orderliness, charitableness, and interacting with athority figres. Peers are important in learning cooperation, for finding the road to poplarity, and for inventing styles of interaction among people of the same age. Cltral grops evolve norms or rles that govern members behaviors. They vary in their child-raising practices. Individalist and collectivist cltres have different effects on personal identity. Yet, despite or many cltral differences, we hmans are more alike than different. Differing sex chromosomes and differing concentrations of sex hormones lead to significant physiological sex differences. Yet, gender differences vary widely depending on cltre. Cltral variations in gender roles demonstrate or capacity for learning and adapting. Both social and cltral factors contribte to gender identity and gender typing. The biopsychosocial approach to development recognizes that we are prodcts of both natre and nrtre, of genes and environment. We are also architects of or ftre. Introdctory Exercise: Fact or Falsehood? The correct answers to Handot 4 1 are as follows: 1. T 2. F 3. F 4. T 5. F 6. F 7. T 8. T 9. T 10. T 31

2 32 Chapter 4 Natre, Nrtre, and Hman Diversity HANDOUT 4 1 Fact or Falsehood? T F 1. People everywhere retrn favors. T F 2. Even complex hman traits are determined by a single gene. T F 3. Adoptees traits sch as extraversion and agreeableness bear more similarities to their adoptive parents than to their biological parents. T F 4. The most emotionally intense preschoolers tend to be relatively intense yong adlts. T F 5. If after a worldwide catastrophe only Icelanders or Kenyans srvived, the hman species wold sffer a hge redction in its genetic diversity. T F 6. In many places arond the world, females are more likely than males to initiate sexal activity. T F 7. A child who hears English spoken with one accent at home and another in the neighborhood and at school invariably adopts the accent of his or her peers, not the parents. T F 8. Compared with Westerners, people in Japanese and Chinese cltres exhibit greater concern for social harmony and loyalty. T F 9. Seven weeks after conception, males and females remain anatomically indistingishable. T F 10. Even when families discorage traditional gender typing, children sally organize themselves into boy worlds and girl worlds, each gided by rles for what boys and girls do.

3 Chapter 4 Natre, Nrtre, and Hman Diversity 33 Gide Objectives Every qestion in the Test Banks is keyed to one of these objectives. Behavior Genetics: Predicting Individal Differences 4-1. Define chromosomes, DNA, genes, and the hman genome, and describe how behavior geneticists explain or individal differences Discss how twin and adoption stdies help s nderstand the effects and interactions of natre and nrtre Describe what psychologists have learned abot temperament Define heritability, and discss how it relates to individals and grops Discss how moleclar genetics research is changing or nderstanding of the effects of natre and nrtre Identify some benefits and risks of prenatal genetic testing. Evoltionary Psychology: Understanding Hman Natre 4-7. Describe evoltionary psychologists se of natral selection to explain behavior tendencies Discss how an evoltionary psychologist might explain male-female differences in sexality and mating preferences Smmarize the key criticisms of evoltionary explanations of hman sexality, and describe how evoltionary psychologists respond. Cltre, Gender, and Other Environmental Inflences Describe how early experiences modify the brain Describe the ways in which parents and peers shape children s development Describe how cltre affects or behavior Discss how individalist and collectivist cltres differ in their vales and goals Explain how the meaning of gender differs from the meaning of sex Describe some ways in which males and females tend to be alike and to differ Explain how sex hormones inflence prenatal and adolescent sexal development, and describe a disorder of sexal development Explain how gender roles and gender identity differ Identify what is inclded in the biopsychosocial approach to development. Behavior Genetics: Predicting Individal Differences Lectres: Why Is It Important to Answer the Natre/Nrtre Qestion?; Natre/Nrtre and Pblic Policy Members of the hman family differ in personality, interests, cltre, and family backgrond. At the same time, or shared brain architectre predisposes s to sense the world, develop langage, and experience hnger throgh the same mechanisms. Hmans everywhere affiliate, conform, reciprocate favors, pnish offenses, and grieve a child s death. Or genes and or environment contribte to or striking diversity and shared hman natre. Genes: Or Codes for Life Lectre: The Genetic Revoltion Exercise: Genetic Factors Exercise/Project: Genetic Inflences LanchPad: Behavioral Genetics 4-1. Define chromosomes, DNA, genes, and the hman genome, and describe how behavior geneticists explain or individal differences. Behavior geneticists stdy or differences and aim to determine the relative importance of heredity and environment on behavior. Environment incldes every nongenetic inflence, from prenatal ntrition to the people and things arond s.

4 34 Chapter 4 Natre, Nrtre, and Hman Diversity Every cell ncles contains the genetic master code for the body. Within each cell are 46 chromosomes with 23 donated by each parent. Each chromosome is composed of a coiled chain of a molecle, called DNA (deoxyriboncleic acid). Genes are DNA segments that, when trned on (active or expressed), provide the code for the prodction of protein molecles. By directing the manfactre of proteins, the approximately 20,000 to 25,000 genes that compose the hman body determine or development. The genome provides the complete instrctions for making an organism, consisting of all the genetic material in the organism s chromosomes. Variations at particlar gene sites in the DNA give cles to or niqeness. Hman traits are inflenced by many genes interacting with the environment. Lectre: Behavioral Genetics Exercise: Striking Similarities LanchPad: Natre Verss Nrtre: Growing Up Apart; 100-Years-Old and Conting: Psychological and Biological Factors 4-2. Discss how twin and adoption stdies help s nderstand the effects and interactions of natre and nrtre. Comparisons of identical twins, who are genetic clones, and fraternal twins, who develop from separate eggs, help behavior geneticists tease apart the effects of heredity and environment. On both extraversion and neroticism, identical twins report mch greater similarity than fraternal twins. The discovery that identical twins separated at birth show remarkable similarities also sggests genetic inflence. Indeed, separated fraternal twins do not exhibit similarities comparable to those of separated identical twins. However, shared genes can translate into shared experiences. Adoption stdies enable comparisons with both genetic and environmental relatives. Adoptees personality traits bear more similarities to their biological parents than to their caregiving adoptive parents. Nonetheless, the latter do inflence their children s attitdes, vales, manners, faith, and politics. Clearly, natre and nrtre shape one s developing personality. Temperament and Heredity Exercise: EAS Temperament Srvey 4-3. Describe what psychologists have learned abot temperament. An infant s temperament is his or her characteristic emotional reactivity and intensity. From the first weeks of life, some babies are more relaxed and cheerfl, while others are difficlt (more tense and irritable). Still others are slow to warm p. These differences in temperament tend to persist. For example, the most emotionally intense preschoolers tend to be relatively intense yong adlts. Anxios, inhibited infants have high and variable heart rates and a reactive nervos system. Heritability Lectre: Genetic Inflences on Psychological Traits Exercise: Explaining Heritability 4-4. Define heritability, and discss how it relates to individals and grops. Heritability describes the extent to which variation among individals can be attribted to their differing genes. If the heritability of intelligence is 50 percent, this does not mean that one s intelligence is 50 percent genetic. Instead, it means that we can attribte to genetic inflence 50 percent of the observed variation among people. Gene-Environment Interaction Lectres: Gene-Environment Correlation; Epigenetic Video; Epigenetic Inflences on Psychological Disorders LanchPad: The Natre Nrtre Isse

5 4-5. Discss how moleclar genetics research is changing or nderstanding of the effects of natre and nrtre. Or genes affect how or environment reacts to and inflences s. Natre enables nrtre. Becase of hman adaptability, most psychologically interesting traits are expressed in particlar environments. In other words, genes are self-reglating; they can react differently in different environments. Epigenetics is stding the moleclar mechanisms by which environments trigger or block genetic expression. Or experiences lay down epigenetic marks, which are often organic methyl molecles attached to part of a DNA strand. We are all the prodcts of interactions between or genetic predispositions and or srronding environments. For example, a baby who is genetically predisposed to be social and easygoing may, in contrast to one who is less so, attract more affectionate and stimlating care and ths develop into a warmer and more otgoing person. The new frontier of behavior-genetic research draws on bottom-p moleclar genetics, which stdies the moleclar strctre and fnction of genes. Genes typically are not solo players. So, one goal of moleclar behavior genetics is to find some of the many genes that together orchestrate complex traits sch as body weight, sexal orientation, and implsivity Identify some benefits and risks of prenatal genetic testing. Chapter 4 Natre, Nrtre, and Hman Diversity 35 In labs worldwide, moleclar geneticists are teaming with psychologists to pinpoint genes that pt people at risk for genetically inflenced disorders. Potentially, steps may be taken to prevent problems before they happen. With this benefit, however, also comes risks of labeling people in ways that may lead to discrimination. Prenatal screening poses hopefl possibilities bt also difficlt problems as parents become able to select their children s traits. In China and India, where boys are highly valed, testing for an offspring s sex has enabled selective abortions. Millions of parents will select for health and perhaps for brains and beaty. However, by selecting ot certain traits, we may deprive orselves of ftre Handels, van Goghs, Lincolns, and Dickinsons, who were all trobled people. Evoltionary Psychology: Understanding Hman Natre Natral Selection and Adaptation and Evoltionary Sccess Helps Explain Similarities Lectre: Misnderstanding Evoltionary Theory and Psychology Exercise: Darwinian Grandparenting PsychSim 6: Lonely Crowd LanchPad: Evoltionary Psychology 4-7. Desribe evoltionary psychologists se of natral selection to explain behavior tendencies. Evoltionary psychologists focs on what makes s so mch alike as hmans. They stdy how natral selection has shaped or niversal behavioral tendencies. Natral selection is Charles Darwin s principle that, among the range of inherited trait variations, those that lead to increased reprodction and srvival will most likely be passed on to scceeding generations. Natre selects beneficial variations from among the mtations (random errors in gene replication) and the new gene combinations prodced at each hman conception. Dring hman ancestry, genes that enable today s capacity to learn and adapt had srvival vale. Similarly, we love the taste of fats and sweets, which once were hard to come by bt which prepared or ancestors to srvive famines. This particlar natral disposition is mismatched with today s fast-food environment.

6 36 Chapter 4 Natre, Nrtre, and Hman Diversity An Evoltionary Explanation of Hman Sexality Lectres: Gender Differences in Sexality; Evoltionary Theory and Gender Differences in Motivation Exercise: Brief Sexal Attitdes Scale PsychSim 6: Dating and Mating LanchPad: Openness to Casal Sex: A Stdy of Men Verss Women 4-8. Discss how an evoltionary psychologist might explain male-female differences in sexality and mating preferences. One of the largest reported differences between men and women is women s greater disapproval of and lesser willingness to engage in casal, ncommitted sex. In comparison to women, men think more abot sex, mastrbate more often, are more likely to initiate sex, and desire more freqent sex. Evoltionary psychologists apply the principle of natral selection to explain women s more relational and men s more recreational approaches to sex. Compared with eggs, sperm are cheap. While a woman mst conceive and protect a fets inside her body for p to nine months, a man can spread his genes throgh other females. Women most often send their genes into the ftre by pairing wisely, men by pairing widely. Women increase their own and children s chances of srvival by searching for mates with economic resorces and social stats. Being attracted to healthy, fertile-appearing partners increases men s chances of spreading their genes widely Smmarize the key criticisms of evoltionary explanations of hman sexality, and describe how evoltionary psychologists respond. Critics arge that evoltionary psychologists start with an effect (for example, gender sexality difference) and work backward to propose an explanation. Other critics ask why we shold try to explain today s behavior based on decisions or distant ancestors made thosands of years ago. They believe social learning theory offers a better, more immediate explanation for these reslts. Perhaps women learn social scripts their cltre s gide to how people shold act in certain sitations. Still others sggest that evoltionary explanations may nderct moral responsibility. In response, evoltionary psychologists point to the explanatory and predictive power of their theoretical principles. They also note that nderstanding or tendencies may help s to overcome them. Cltre, Gender, and Other Environmental Inflences How Does Experience Inflence Development? Describe how early experiences modify the brain. From conception onward, we are the prodct of a cascade of interactions between or genetic predispositions and or srronding environments. In the womb, embryos receive different ntrition and varying levels of exposre to toxic agents. Normal stimlation dring the early years is critical for optimal brain development. After brain matration provides s with an abndance of neral connections, experience preserves or activated connections and nsed connections degenerate (a process called prning). Throghot life, or actions strengthen some neral pathways, while others weaken from disse. Dring early childhood while excess connections are still on call yongsters can most easily master sch skills as the grammar and accent of another langage. Althogh normal stimlation dring the early years is critical, the brain s development does not end with childhood. Thanks to the brain s amazing plasticity, or neral tisse is ever changing and reorganizing, in response to new experiences.

7 Chapter 4 Natre, Nrtre, and Hman Diversity 37 Lectres: Where Parents Matter; Peer Inflence Exercise/Project: Stdent/Parent Similarities Describe the ways in which parents and peers shape children s development. Parental inflence is clearest at the extremes, for example, in the absed who become absive and in the loved bt firmly handled children who become self-confident and socially competent. Parental inflence is also reflected in the remarkable academic and vocational sccess of people who fled from Vietnam and Cambodia. However, environmental inflences typically accont for less than 10 percent of children s personality differences. This finding sggests that parents be given less credit for their children s sccesses as well as less blame for their failres. Parental and peer inflences are complementary. Parents are more inflential when it comes to edcation, discipline, responsibility, orderliness, charitableness, and ways of interacting with athority figres. Peers are more important for learning cooperation, for finding the road to poplarity, and for inventing styles of interaction among people of the same age. Parents can inflence their children by selecting their neighborhood and schools. Cltral Inflences Lectres: Understanding Cltre Differences in Relation to Individal Differences; The Geography of Time Exercise: English and Chinese Proverbs Describe how cltre affects or behavior. Cltre is the behaviors, ideas, attitdes, vales, and traditions shared by a grop of people and transmitted from one generation to the next. Cltre enables the preservation of innovation and the efficient division of labor. All cltral grops evolve their own norms rles for accepted and expected behaviors. Althogh sometimes social expectations seem oppressive, they also grease the social machinery. When cltres collide, their differing norms may make s ncomfortable, and we may experience cltre shock. Over time, cltres change. For example, with greater economic independence, today s women are less likely to endre absive relationships ot of economic need. Many minority grops enjoy expanded hman rights. Not all cltre change is positive. For example, within the last 50 years or so, the United States has seen sharply increased rates of divorce and depression. Changes in the hman gene pool evolve far too slowly to accont for these rapid cltral changes. Lectre: Individalism Verss Collectivism Arond the World Exercises: Assessing Individalism/Collectivism; Cltre, Child Raising, and Sleeping Arrangements Discss how individalist and collectivist cltres differ in their vales and goals. Individalist cltres give relatively greater priority to personal goals and define their identity mostly in terms of personal attribtes. They strive for personal control and individal achievement. Individalism s benefits can come at the cost of more loneliness, divorce, homicide, and stress-related disease. Collectivist cltres vale grop goals and solidarity. Relationships tend to be close and endring. Maintaining social harmony is important, and dty to family may trmp personal career preferences. Collectivists derive their identity from belonging, and one s life task is to maintain social connections, fit in, and perform one s role. While people in individalist cltres encorage independence in their children, those in collectivist cltres focs on emotional closeness. Children in collectivist cltres grow p with a stronger sense of family self. The diversity of child-raising practices makes it clear that children can thrive nder varios systems. Regardless of or cltre, we hmans are more alike than different.

8 38 Chapter 4 Natre, Nrtre, and Hman Diversity Gender Development Explain how the meaning of gender differs from the meaning of sex. Or sex, or biological stats, is defined by or chromosomes and anatomy. For most people, those biological traits help define their gender, their cltre s expectations abot what it means to be male or female. Or gender is the prodct of the interplay among or biological dispositions, or developmental experiences, and or crrent sitations. Lectres: Gender Differences in Personality?; Are Women More Social? Exercise: Gender Differences on a Motor-Skills Task Describe some ways in which males and females tend to be alike and to differ. Men and women are similar in genetic makep, and, on average, have comparable creativity and intelligence and feel the same emotions and longings. Men and women differ in life expectancy. Women are more vlnerable to depression, anxiety, and eating disorders. In contrast, men are more likely to die by sicide and develop alcohol se disorder. They are also mch more likely to be diagnosed with atism spectrm disorder, color-blindness, and attention-deficit/hyperactivity disorder as children, and antisocial personalities as adlts. In srveys, men admit to more aggression than women, and experiments confirm that men tend to behave more aggressively, sch as by blasting people with what they believed was intense and prolonged noise. The same difference is reflected in violent crime rates. The gender gap in physical aggression appears in many cltres and across varios ages. However, women are slightly more likely than men to commit relational aggression. In most societies men place more importance on power and achievement and are socially dominant. In grops, leadership tends to go to men. Men and women also lead differently. Men tend to be more directive; women tend to be more democratic. In everyday behavior, men are more likely to talk assertively, to interrpt, to initiate toching, to smile less, to stare, and to apologize less. Compared with men, women are more concerned with making social connections. Men are more independent; women are more interdependent. This gender difference srfaces early, in children s play. As teens, girls spend more time with friends and less time alone. In coping with stress, women more often trn to others for spport. They tend and befriend. Women emphasize caring. Both men and women indicate that their friendships with women tend to be more intimate, enjoyable, and nrtring. Lectre: Atypical Sex Chromosome Patterns Exercise: Writing Abot Pberty LanchPad: Gender Development Explain how sex hormones inflence prenatal and adolescent sexal development, and describe a disorder of sexal development. Biological sex is determined by the twenty-third pair of chromosomes, the sex chromosomes. The member of the pair inherited from the mother is an X chromosome. The X (female) or Y (male) chromosome that comes from the father determines the child s sex. The Y chromosome triggers the prodction of the principal male sex hormone, testosterone, which in trn triggers the development of external male sex organs in the fets and the development of male sex characteristics dring pberty. Dring the forth and fifth prenatal months, the male s greater testosterone and the female s ovarian hormones have an impact on the brain s wiring. Research confirms male-female differences in brain areas with abndant sex hormone receptors dring development. Dring pberty, the reprodctive organs, or primary sex characteristics, develop dramatically. So do the secondary sex characteristics, sch as the breasts and hips in girls, facial hair and a deep-

9 ened voice in boys, and pbic and nderarm hair in both sexes. The landmarks of pberty are the first ejaclation (spermarche) in boys, which sally occrs by abot age 14, and the first menstral period (menarche) in girls, sally within a year of age 12 1 /2. Sometimes natre blrs the biological line between males and females. When a fets is exposed to nsal levels of sex hormones, or is especially sensitive to those hormones, the individal may develop a disorder of sexal development, with chromosomes or anatomy not typically male or female. Lectre: Who Does the Hosework Arond the World? Exercise: Learning Gender Roles Explain how gender roles and gender typing differ. Althogh biology inflences or gender, gender is also socially constrcted, as the biopsychosocial approach reminds s. Cltre shapes or roles: a role is a clster of prescribed actions. For example, gender roles or expectations abot the way men and women behave vary across cltres and time, as well as across generations. For instance, in nomadic societies of food-gathering people, there is little division of labor by sex. Ths, boys and girls receive mch the same pbringing. In agricltral societies, women stay close to home, while men often roam more freely. Sch societies typically socialize children into more distinct gender roles. Even among indstrialized contries, gender roles vary greatly. Society assigns each of s to the social category of male and female. The reslt is or gender identity, or sense of being male, female, or a combination of the two. Social learning theory assmes that children learn gender-linked behaviors by observing and imitating significant others and by being rewarded and pnished. To varying degrees, we also become gender typed, acqiring a traditional male or female role. No matter how mch parents encorage or discorage traditional gender behavior, children may drift toward what feels right to them. Some organize themselves into boy worlds and girl worlds, each gided by rles. Others seem to prefer androgyny: A blend of male and female roles feels right to them. Thinking also matters. From their cltre, children learn a concept or gender schema of what it means to be male or female and adjst their behavior accordingly. For some people, however, comparing themselves with the tranditional concept of gender prodces feelings of confsion and discord. Transgender people s sense of being male or female differs from their birth sex. Reflections on Natre, Nrtre, and Their Interaction Exercise: Biopsychosocial Inflences Chapter 4 Natre, Nrtre, and Hman Diversity Identify what is inclded in the biopsychosocial approach to development. Natre and nrtre jointly form s. That is, we are prodcts of natral selection and heredity as well as cltral, family, and peer inflences. Bt we are also open systems that is, creators as well as creatres of or worlds. We respond to the world s response to s, and the stream of casation rns throgh or present choices. Or hopes, goals, and expectations inflence or ftre. Or decisions today design or environments tomorrow.

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