Chapter 3 Nature, Nurture, and Human Diversity

Transcription

1 Myers PSYCHOLOGY Chapter 3 Nature, Nurture, and Human Diversity C3:1 C3:2 The Nature and Nurture of Behavior Behavior Genetics: Predicting Individual Differences Evolutionary Psychology: Understanding Human Nature Parents and Peers Cultural Influences Gender Development Reflections on Nature and Nurture Nature and Nurture Basic question is origin of commonalities and differences among individuals and groups in psychological characteristics Two categories of variables - 1. Nature: Inherited tendencies Genes, heredity - 2. Nurture: Environmental variables Biological: intrauterine, nutrition,... Psychological: child-rearing, schooling,... Both important Begin with Nature side of equation Precedes environmental influences C3:3 Behavior Genetics Outline Genes: Our Codes for Life Twin Studies Temperament Studies Heritability Gene-Environment Interaction The New Frontier: Molecular Genetics Begin with a bit of a warning C3:4 Genetic Does Not Equal Immutable! C3:5 People sometimes think wrongly that genetic causes for some condition means that condition (or trait in psychology) is immutable (i.e., unchangeable) Not true. Many genetic conditions can be ameliorated (i.e., improved) by environmental factors Example of PKU (recessive genetic disorder): untreated PKU people have very low IQs (less than 50 by one source), but with dietary treatment (+1 +2) Diet and Adult IQ of PKU Children C3:6 1

2 C3:7 C3:8 Genes: Our Codes for Life See Diagram (+1) Chromosomes: Threadlike structures made of DNA that contain genes DNA (deoxyribonucleic acid): Molecule with genetic information making chromosomes (double helix) Genes: Segment of DNA capable of synthesizing proteins Genome: Complete instructions to make organism C3:9 C3:10 Comparison of Relative Size Karyotype of normal male fetus C3:11 C3:12 Karyotype of Down s Syndrome (Trisomy 21) Male 2

3 C3:13 Genes Genes and Inheritance of traits Offspring receive half of chromosomes from mother and half from father Some traits associated with single or few genes - Traits dominant or recessive, some sex linked (+1 +2) Other traits associated with multiple genes - Produce quantitative differences on trait, often approximated by normal curve (e.g., height, intelligence, aggression, sociability) (+3) From Genes to Behavior - Missing link is often what and how biochemical processes controlled by Genes lead to psychological traits and behaviors C3:14 Dominant & Recessive Genes Genes and Colour Blindness What shapes and numbers do you see in figures below? C3:15 Polygenic Traits C3: x Imagine trait influenced by 10 independent genes, each of which is 0 half the time or 1 half the time Trait strength is determined by the number of 1s: scores could range from 0 (all 0s) to 10 (all 1s) Probability of different strengths shown in graph Genetic mutations In addition to normal inheritance, mutations influence transmission/acquisition of traits Conditions possibly related to mutations include schizophrenia: e.g., children of older fathers more susceptible (3%) than children of younger fathers (1%) Some mutations adaptive: e.g., sickle cell anemia more common in Africans and their descendents because sickle cell mutation protects somewhat against malaria C3:17 Behaviour Genetics Twin Studies Identical and Fraternal twins (+1) Identical more similar in many areas (+2) - Alzheimer s - Personality traits (extraversion) - Divorce - Abilities (later slide) - Schizophrenia (later slide) Separated Twin Studies: MZ more similar than DZ even if reared apart on many traits studied C3:18 3

4 C3:19 Behavior Genetics Identical Twins: single zygote (fertilized egg) that splits in two, creating two genetic replicas Fraternal Twins: separate zygotes, genetically no closer than brothers and sisters, but share fetal environment C3:20 Genetic Influences Similarity of 1.0 intelligence 0.9 scores (correlation) Identical twins reared together Identical twins reared apart Fraternal twins reared together Siblings Unrelated reared individuals together reared together C3:21 Most genetically similar people have most similar scores Recall that r varies from 0 indicating no relation to +/- 1, indicating perfect relation Schizophrenia Lifetime risk of developing schizophrenia for relatives of schizophrenic General population Siblings Children Fraternal twin Children of two Identical twin schizophrenia victims C3:22 Behaviour Genetics C3:23 Genetic Influences C3:24 Adoption Studies Similarity of offspring to biological (genetic) and adoptive (environmental) parents In many traits, children more similar to biological parents (+1) Child-parent correlation in verbal ability scores Children and their birth parents Adopted children and their birth parents years 16 years Adopted children and their adoptive parents 4

5 Temperament Studies Person s characteristic emotional reactivity and intensity Even young infants show differences in temperament (+1) - Some excitable and emotionally reactive - Others calm and easygoing C3:25 Survey of parents in mid 1990s measured difficult C3:26 temperament with questions such as: "How easy or difficult is it for you to calm or soothe him or her when he or she is upset? "How many times per day, on average, does he or she get fussy and irritable? "How much does he or she smile and make happy sounds? Final score out of 50 determined by adding up values for each question Correlates with adult behaviour Also observed in animals Some cultural differences perhaps explained by genetic differences - Asian infants more calm, Aboriginal babies and restraint (above) Behavior Genetics Heritability Proportion of variation among individuals attributed to genes: 40-50% in many areas Depends on range of populations and environments studied Within-group variation: may not explain between-group differences (+1) Interaction Effect of one factor (such as environment) depends on another factor (such as heredity) C3:27 C3:28 Genetic Influences Group differences below due to environmental factor (soil fertility), not heritability (within-group variation) Variation within group Poor soil Seeds Variation within group Fertile soil Difference between groups Gene by Environment Interaction Cooper & Zubeck Bred maze-bright and maze-dull rats Reared them in various environments - Impoverished, Normal, Rich Observed number of errors on mazelearning task Strong Gene x Environment interaction C3:29 New Frontier: Molecular Genetics Attempt to identify specific genes associated with behaviours and disorders Compare genetic make-up of affected and nonaffected people Identify gene or genes that distinguish groups Important to remember that genes influence underlying biochemical processes; they do not transmit traits directly C3:30 5

6 Evolutionary Psychology: Understanding Human Nature Outline Natural Selection An Evolutionary Explanation of Human Sexuality Critiquing Evolutionary Perspective Introduction Explains universal behaviours in terms of shared biological foundations arising from Natural Selection Based on Darwinian model, which is widely accepted by scientists but still controversial among public (+1) C3:31 Religiousness and Evolution C3:32 Evolutionary Psychology Variation + Natural Selection Random combinations and mutations produce variation in members of species Genes that promote reproductive success favoured Results in physical and behavioural adaptations that persist today - Fear of spiders and snakes (+1) - Gender differences in sexual behaviours (later) 40 years of breeding foxes for tameness (bottom right) C3:33 Charles Darwin Biological Preparedness: Fears Do organisms have innate fear of some objects (e.g., snakes, spiders, )? C3:34 Wild monkeys show intense fear of snakes, but not captive raised monkeys. Suggest fear learned, but Nonfearful Monkeys who see single example of another monkey responding fearfully to snake acquire fear (but not flowers or other non-dangerous objects) Suggests organisms have innate preparedness to fear snakes, but this predisposition needs to be activated by single exposure to appropriate model Genes and Human Variation C3:35 Peoples of world remarkably similar in genetic make-up and numerous behaviors E.g., emotional expressions largely universal Genes also contribute to ways in which groups differ from one another Groups of people differ with respect to genetic similarity depending on evolutionary migration (+1) Much current research on genetic bases for ethnic differences in disease, drug treatment, and other medical domains Less research on psychological implications Some resistance among social scientists to attribute group differences to genetic differences C3:36 6

7 C3:37 Evolutionary Explanation of Human Sexuality Gender and Human Sexuality Males more likely to initiate sexual activity Males more accepting of casual sex - FSU researchers: Would you go to bed with me tonight? asked of strangers - 0% of women accepted, and 75% of men Males more likely to masturbate, and more often Males 80% of customers of adult video stores Males think about sex more often Males higher risk takers (attracting mate) Gender differences in mating preferences around world (+1) Evolutionary Psychology Mating Preferences Men everywhere preferred attractive physical features suggesting youth and health Women preferred men with resources and status C3:38 Evolutionary Explanation Biologically, sperm cheap relative to eggs Male can spread sperm around to multiple recipients, while female must incubate and nurse one infant at a time Hence, men pair widely while women pair wisely C3:39 C3:40 Critiquing Evolutionary Perspective Scientific Criticisms Hindsight explanations can explain anything Fail to explain some findings: e.g., some female monkeys mate with numerous males Lack of mediating mechanisms Societal Criticisms Perpetuate gender stereotypes and other negative social consequences. Evolutionary psychology proposes genetic determinism and undercuts morality in establishing society. Universal results (e.g., preferences) may result from universal inequities in status of men and women around world Ignores commonalities, such as preference of both males and females for similar traits in partners Environmental Influences What explains other 50-60% of variability? Various Environmental influences Parents and Early Experiences - Prenatal environment - Experience and brain development - Role of Parents Peer influence Culture C3:41 Prenatal Environment Some identical twins (below) share more similar intrauterine environment than other identical and fraternal twins and non-twins C3:42 7

8 Prenatal Environment Teratogens More in Ch. 4 C3:43 Environmental Influence Experience affects brain development (also +1) C3:44 Cocaine and Heroin miscarriage or premature birth birth defects Alcohol Fetal Alcohol Syndrome Motor development problems Impoverished environment Rat brain cell Enriched environment Rat brain cell Environmental Influence A trained brain: left=before and right=after finger-tapping practice C3:45 Parents Surprisingly (to many people) parental influence appears to be rather weak: see works by Judith Harris Plomin & Daniels (1987) wrote: Two children in the same family [are on average] as different from one another as are pairs of children selected randomly from the population C3:46 Environment: Peer Influence Peers powerful socializing factor on children C3:47 e.g., immigrant children strongly influenced by school-mates and friends; often dramatic and sudden changes from parent s generation e.g., peer influence on adolescent smoking (below) C3:48 Environment: Culture Culture Behaviours, ideas, attitudes, and traditions shared by large group of people and transmitted from one generation to next Some cultures homogeneous (e.g., traditional Japan) Cultures vary in many ways - Norms (e.g., for eating) - Personal space - Expressiveness - Pace of life - Child-rearing (e.g., collectivism vs. individualism and promotion of independence in children) Cultures also evolve over time, sometimes quickly 8

9 Culture C3:49 C3:50 Individualism-Collectivism A major distinction between cultures Individualist cultures - Independent self, abstract principles of morality, confrontation allowed in relationships, - E.g., Canada and other English-speaking nations, Northern Europe, Collectivist cultures - Interdependent self, morality defined by social networks (duty), harmony important in groups, - Mediterranean Europe, Asia,. Other contrasts (+1) Marked differences in child-rearing practices across cultures, perhaps Culture and associated with Child-rearing individualism-collectivism Sleep alone vs. with Mother and perhaps other family members Promote Independence vs. strong Emotional attachment to care-giver(s) and Obedience Nuclear family vs. Extended family C3:51 Gender Development Consider example of Gender Similarities and Differences in more detail Biological and Environmental influences Biological Factors C3:52 X and Y Chromosomes: Sex chromosomes for women (XX) and men (XY) Testosterone - Primary male sex hormone - Present in both males and females, but more in males Influences brain development in fetus Development of male sex characteristics at puberty Related to some traits (e.g., aggression) The Nature and Nurture of Gender C3:53 The Nature and Nurture of Gender C3:54 Nurture of Gender What is acquired? - Gender Role: expected behaviors for males and for females - Gender-typing: acquisition of a traditional masculine or feminine role - Gender Identity: one s sense of being male or female Differences across cultures (+1) Changes in Western cultures (+2) Gender and Culture (1994) 9

10 The Nature and Nurture of Gender C3:55 Gender Theories C3:56 Two theories (above) Social Learning Theory: learn social behavior by observing & imitating and by being rewarded or punished Gender Schema Theory: children learn what it means to be male and female, and adjust behavior Reflections on Nature and Nurture C3:57 C3:58 Genes and Experience together form who we are (+1) We are both creatures and creators of our worlds Some troubled by naturalism of science Appears to leave little room for Spirituality Interestingly, Myers himself is deeply religious person (he has many religious writings that can be found on www), so science and religion can be reconciled by some people. Even Pope John Paul endorsed evolution as more than a theory. Also true, however, that many who accept science do tend to leave religion behind Evolution and Religion C3:59 Myers (p ) Some positive dialogue between representatives of religious groups and science - Pope John Paul, 1996: evolution more than just a theory Myers also cites some scientists (?) - Quotes could be interpreted as consistent with intelligent design (nature cunningly devised ) - ID viewed by many scientists, even believers, as pseudoscience Also states - On most of these matters, science is silent - But, supposed limits of science have never lasted Science and Religion Important and much-discussed issue Googling science religion reveals 30,000,000 hits Many have to do with conflict between and / or reconciliation of two One of issues you may face as university student is difference of worldview presented in psychology and other university classes from your traditional views acquired from family, past teachers, society, C3:60 10