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Chapter 9

Chapter 9 Summary

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Department
Psychology
Course
PSYCH 2B03
Professor
Richard B Day
Semester
Winter

Description
Chapter Nine – pg. 319-339 The Inheritance of Personality: Behavioural Genetics and Evolutionary Theory - Inheritance o Inherit wealth: Child’s parents already rich, so children inherit all advantages/disadvantages of wealth (ie. Rockefeller Family). o Inherit personality: traits that your ancestors possessed could have passed on. o How characteristic patterns of behaviour might be encoded on genes and passed from parents to offspring (2 approaches)? I. Behavioural Genetics: individual differences in behaviour (personality traits) passed on by biological relatives. (personality attributes inherited, both ancient and recent ancestors) II. Evolutionary Psychology: patterns of behaviour (characterizing all humans) b/c survival value over the history of species (across generations)  Connection of the 2: BG- inheriting bank account, EP- where did all the money initially come from? Behavioural Genetics - Family resemblance (physical appearance): how you all look shared because of genes shared - Family resemblance (personality): are you psychologically similar (traits) to your biological relatives? o Personality traits: a pattern of behaviour relevant to more than one situation (“trait” genetics but “behavioural” genetics is the traditional term) Controversy (because of notorious ideas): 1) Eugenics: belief that humanity could (and should) be improved through selective breeding o Caused: keep “inferior” immigrants out of some countries (to have the ideal sperm bank) o Adolf Hitler promoted this 2) Cloning: emerged from eugenics. Belief of producing duplicate (physical & psychological) - Neither are feasible, unlikely to breed ppl to specification or duplicate ppl because personality is result of complex interactions of genes and environment. Calculating Heritabilities - Measure who are/aren’t genetically related, or related to different degrees - Phenotype: the observable traits of a person - Genotype: underlying genetic structure - Measuring the degree to which variation in the phenotype, can be attributed to the variation in genotype - Identical Twins: monozygotic/MZ – one fertilized egg splits, identical in all varying genes across individuals - Fraternal Twins: dizygotic/DZ – two fertilized eggs by two different sperm (genetic relatedness: same as any siblings, just born at the same time), identical in ~50% of varying genes across individuals - 99%+ human genes are identical amongst all ppl, 98% in chimpanzees (study of what individual shares is evolutionary biology – inheritance of species) - Behavioural genetics focus on less than 1% of the variation in human genome (focus on personality that differs from one individual to another only) - Research using both twins & twins separated at birth (raised separately =environment variation) - Self-report: Eysenck Personality Questionnaire (EPQ) & California Psychological Inventory (CPI) - Intraclass correlation coefficient: used for correlation coefficient across pairs of twins - Assumption: if a trait/behaviour is influenced by genes, then the trait/behavioural scores of MZ will be more highly correlated than DZ. o Twins: twice the difference between correlation of MZ twins than correlation DZ twins  Heritability quotient = (r MZ – r DZ) x 2  R = average correlation - Assumption: Closer relatives (eg. Siblings) more similar on a gene-influenced inherited trait than distant relatives (eg. Cousins) - Twin Studies: Results: (age and gender controlled) o Avg correlation of MZ twins = 0.60 o Avg correlation of DZ twins = 0.40 o Heritability coefficient = (0.60 – 0.40) X 2 = 0.40  In twin studies, Avg heritability of many traits = 0.40  Proportion of phenotypic (behavioural) variance explained by genetic variance is 40% - Can do more studies: o Parent & Child – share 50% of their variable genes o Parent & Adopted Child – share no more of their personality-relevant genes with their adoptive parents than they would with any other person chosen at random o Siblings– share avg 50% of the genes that vary o Half siblings – share avg only 25% of genes that vary - Two possibilities: I. For most traits the estimates of heritability garnered from nontwin studies are about 20% II. OR half the avg heritability estimated from twin studies. o Difference b/c: maybe the effects of genes are interactive and multiplicative rather than additive.  Twin studies calculation assumes that because DZ twins share half the variable genes that MZ twins do, they are half as similar in genetic expression.  But if genes act not just by independently adding their effects together, but also by interacting with one another, then DZ twins’ similarity in genetic expression will be less than 50%  They share 50% of the genes, they share only 25% of the 2-way interactions among those genes.  Genetic expression: identical twins will be 4x as similar to each other than fraternal twins (instead of only twice)  If true, then 20% for heritability of many traits is a more reasonable o Human genome = 25 000 genes, Fruit flies genome = 13 000 – 14 000 genes, Roundworm genome = 959 cells in its body but over 19 000 genes  Difference btw humans/humans & species: cannot be accounted by adding genetic effect b/c genes interact with each other and with the environment Where Heritabilities Tell You - A heritability number tells you 3 things - Psychologists thought personality only environmentally based (experiences & parent practice) 1) Genes Matter: 1 law of behavioural genetics - Everything is heritable. Not all personality is from experience, some come from genes - Not accepted by everyone 2) Insight into Etiology - Heritability helps tell you if behaviour/disorders are: normal or pathologically abnormal (differ) - Severe mental retardation (IQ<50) not heritable – goes against 1 law (doesn’t run in family- must be something else than inheriting low IQ...relation to environment probably)  Potential non-genetic cause: head injury as child, pregnancy infection, birth trauma - Moderate mental retardation (IQ: 50-69) is heritable (runs in the family) - Genetics of personality vs genetics of personality disorder:  Variation in well ppl in amount of negative emotions experienced  Extreme emotion experienced = depression o Variation of thoughts and interesting activities o Extreme thoughts/interesting activities = psychosis • Variation of impulsiveness and tendency to be uninhibited • Extreme of this = criminal behaviour and family abuse 3) Insight into Effects of the Environment - Growing up in the same home does not make the children similar to each other  Adopted siblings raised together = correlation of 0.05 (5% variation in personality) - Variation in: early environments (ie. first born vs third born treatment by parents), outside friendships, outside activities Does the Family Matter? - Family: little/no impact on personality development? So family environment (neighbours, home atmosphere, income, nutrition, absence of a parent, alcoholic parent, encouraging parents) doesn’t impact one’s personality? - Judith Rich Harris researched this o “Do parents have imp. LT effects on development of child’s personality?” Ans. NO o Implies that: ppl might as well stop trying to be better parents, no need to remove child out of abusive home, it won’t impact their personality. -_-  Denies 50 years of fundamental assumptions guiding developmental studies  Research on how parental styles affect children has been confounded by the fact that parents and their children are genetically related. Thus some effects that psychologists have attributed to the way parents raise their children may instead be just b/c shared genes. o Parents taught how to be better, their children behave better & control emotions o Doesn’t show up as the shared effect: Maybe b/c parents adjusted behaviour to the needs of each child, treating each differently o Family environment matters. o Problematic b/c adopted family is specifically matched by social service agencies o Leads to less variance (incorrectly) being attributed to environment - So was Judith Rich Harris wrong? o Her evidence is not strong enough, limited data, concluded too quickly o Thus conclusions should be repeatable by other researchers o Provocative scientific hypothesizing vs irresponsible overstatement (thin line b/w the 2) - Recent studies: o Heritability calculation were corrected o Results: up to 50% of variance in ppl (ie IQ)
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