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Chapter 9

PSYB30 Chapter 9 Textbook Notes.docx

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University of Toronto St. George
Michael Inzlicht

Chapter 9: The Inheritance of Personality:  Behavioural Genetics and Evolutionary Theory My Abbreviations • ~ = most recent bolded+underlined word (usually a subheading), Behv = behaviour, P = personality, evol = evolution, psy = psychology, concn = concentration, dev = development, hypoth = hypothesis, gen = genetic, w/ = with, w/o = without, enviro = environment, exp = experience, E = emotion, C = culture, R = relationships, sitn = situation, thru = through, diff = different, avg = average, exp’t = experiment, exp’tl = experimental, corr= correlation, coeff= coefficient, stat = statistic, tho = though, btwn = between, imp = important, var = variance Intro • Rockefeller = ruthless businessman whose name is now synonymous w/ wealth o His children inherited his money • 2 approaches to understand how characteristic patterns of behv (P) might be encoded in genes and passed on and inherited across generations: o Behv genetics: attempts to show how traits are heritable. (i.e. how genes can influence broad patterns of behv)  Controversial studies trying to show the molecular basis of P  Also research on enviro changing gen expression o Evol psy: attempts to show how traits have emerged in all humans bc of their survival value, over the entire history of our species • These 2 approaches are connected o Behv gen shows how “money can be inherited” and evol psy asks “Where did money come from in the first place?” • P trait = a pattern of behaviour relevant to more than one sitn • Behv gen may more accurately be called trait gen Behv Gen: Controversy • Historic association w/ some very notorious ideas like: • Eugenics: belief that humanity could be improved thru selective breeding. To be done by keeping “inferior” immigrants out, set up sperm banks w/ deposits from Nobel Prize winners o Hitler promoted ~ • Cloning: emerged from the idea of eugenics. • Another concern for controversy is that the general public will have the belief that fate is predetermined, i.e. outcomes like intelligence, criminality, etc. are primarily bc of genes and cannot be changed by the individual no matter what exp’s they go through in their life • Modern behv geneticists are generally quick to dissociate themselves from the above o Rather, they say they are pursuing knowledge for its own sake, avoiding ignorance, etc. o And they do not believe that genetically influenced traits are inevitably fixed • And cloning, eugenics aren’t very feasible anyways because P = genes + enviro interacting Calculating Heritabilities • Degree to which variation in the phenotype (= observable traits of a person) can be attributed to variation in the genotype (= underlying genetic structure) • Common research method is twin studies o Compares monozygotic twins (MZ = identical twins, from the splitting of a single fertilized egg, share all the same genes) vs. dizygotic (DZ = fraternal twins, two eggs fertilized by diff sperm that are no more genetically related than any other two siblings and share roughly 50% of their genes on avg) • More than 99% of all human genes are identical among all human beings o 98% shared with chimpanzees • Thus, behv gen concentrates on the less than 1 percent of the human genome that varies • Therefore, behv gen is about diffs whereas evol bio is about similarities among humans • MZ and DZ twins are found for these studies and it is especially helpful if they are separated at birth and reared apart. Mostly self-report measures. Especially these: o EPQ = Eysenck Personality Questionnaire o CPI = California Psychological Inventory o NEO-PI = a measure of Big 5 traits • Less often, exp’tl laboratory studies are done • Then, a correlation coefficient , particularly the intraclass correlation coefficient is used • Basic assumption = if a trait is mostly influenced by genes, then MZ twins corr coeff > DZ • Furthermore, closer relatives (siblings) should be more similar than distant (cousins) • Heritability coeff can be calc’d to reflect this inference o for twins: ~ =MZr- DZ)*2 o across many traits, the avg corr for MZ = 0.60 and for DZ = 0.40 o thus, according to twin studies, the avg ~ = 0.40. therefore, the avg proportion of phenotypic (behv’l) variance that can be explained by gen variance is 40% • big 5 trait values, when both self and peer reports, can even increase to a range of 0.65- 0.79 • other studies are of children vs. adopted children (kids share 50% of their genes w/ each parent) • full siblings share about 50%, half-siblings share 25%, first cousins share 12.5% • all of these %’s are averages though (i.e. it is possible, tho unlikely, that siblings could share 0%) • thus, behv gen is about group differences (kinds of relatives) not individual differences • for non-twin studies, the avg ~ = 20% (i.e. half of that for twin studies) • this might mean that the effects of genes are interactive and multiplicative (and not additive) o though MZ twins share 50% of genes, they share only 25% of the two-way interactions among those genes, even fewer of the three-way interactions, and so on o so, for DZ twins, they will share less than 25% of interactions (i.e. genetic expression) • Human Genome Project in 2003 concluded that humans have about 25,000 genes o Fruit flies have between 13,000 - 14,000 o Roundworm has only 959 cells but over 19,000 genes • Thus, another good reason to conclude that genes interact w/ each other is that: The vast diff btwn humans and other species cannot be accounted for simply by adding genetic effects. However, complex interactions w/ gene-gene and gene-enviro do. Three Things Heritabilities Tell You • 1) Genes Matter • For years, P psy’ists presumed that all of P was enviro-determined (i.e. early exp’s, parental practices) • Heritability estimates >0 challenge this. And virtually everything is >0. To the point that it st has been suggested the the “1 law” of behv gen be that everything is heritable to some degree • This imp realization is relatively new to psy and not accepted by all • 2) Insight Into Etiology • Heritabilities can show how much certain illnesses are part of normal range or are pathologically distinctive or extremes on the normal range of variation • Severe mental retardation (= IQ <50) is not heritable (a rare violation of “1 law”) • But moderate retardation does seem to run in families • This implies that severe comes from something other than inheritance of a low IQ. i.e. mother had infection during pregnancy, or birth trauma/head injury, etc. • Traits and psychopathological tendencies seem to be heritable to some degree • 3) Insight Into Effects of the Enviro • One of the major findings of behv gen = growing up together in the same home does not tend to make children similar to each other • Only 5% of the var in P of adoptive siblings is explained by their common family enviro • More important than common family enviro through life is early enviro that siblings don’t share • i.e. effect of birth order: degree to which firstborns are treated diff from those born later • or what sort of friends each sibling has • though, the research does not tell us which aspects of a child’s early enviro are most imp Does the Family Matter?  • psy’ist Judith Rich Harris tried to answer ~ and wrote a best-selling book arguing that it does not matter at all really. That parents do not have any imp long-term effects on the dev of child’s P • this is radical, though not such a big step away from the finding that growing up in same home does not make siblings have similar P’s • Harris’s work implies that many dev psy findings are wrong and that it doesn’t matter if parents are amazing parents or abusive ones... • It must be admitted though that research on how parent styles affect children has been confounded (by the fact that parents and children are genetically related) o So, some of the effect may be bc genes not enviro • Exp’t showing that when parents are taught to be better parents, their children behave better and control their E’s more effectively o This might be bc good parents adjust their own behv to child’s needs rather than treating their children the same o This would not show up in analyses of shared effect, but would still be bc enviro • Adoptive parents are often screened and so it has been argued that adoptive parent enviros might actually be more similar to each other than that of family enviros of general pop’n • Also, a lot of families in heritability studies are from the same culture o To the extent that families in these studies are similar, the result for the effect that family enviro has on P will be an underestimate o Because range has been restricted on the family enviro variable, lowering its chance of demonstrating an effect on any other variable o In fact, when studies are corrected to account for this, up to 50% of the var in individ diffs is accounted for by shared family enviro • The most imp response to Harris’ hypoth = the studies she references aren’t actually that strong • many studies show the opposite result and meta-analyses have concluded that it does matter • these opposite results may be largely due to using diff methods • i.e. B data may make similarities more apparent than S data (aggression has been show to be partly bc of family enviro, especially when direct observation methods are used) • ADHD seems to be completely bc genes though • Extraversion was found in Borkenau’s study to be the only trait not influenced by shared enviro o But every other trait measured was influenced • Borkenau said there were two important implications of their results: o 1) the widely advertised conclusion that family does not matter was assumed too quickly, on the basis of limited data (because mostly S data was used) o 2) Conclusions based on only one kind of data are at risk. Consistent results across several kinds of data are more likely to be valuable • Overwhelming scientific evidence is that family enviro does matter. But genes also influence. Nature and Nurture • For a long time, ppl have looked for a simple formula to find the amount of var due to nature and the amount of var due to nurture • Heritability coeff seemed to be the sol’n • But, one issue is that if there is no variation across individuals (i.e. virtually everyone is born with two arms), then the heritability formula will approach zero (i.e. # of arms is entirely determined by enviro) • less individ diffs (i.e. variance btwn ppl for a trait)  lower heritability (by heritability coeff) • also, we can conclude that a high heritability coeff could actually mean either that: o largely determined by genes o or, there’s just a looooot of individ variance • also, traits measured with better reliability will tend to have higher heritabilities for same reason • thus, the heritability formula didn’t actually “go wrong”. Bc almost always, the reason why someone will not have two arms is bc of some kind of enviro event (accient). Therefore, the difference between people w/ 1 arm vs 2 arms (i.e. the variation in that trait) is produced by enviro, not genes • So, a high heritability coeff does not mean that a trait within a person is determined by genes. Rather, the variation in that trait between people is determined by genes How Genes Affect Personality?  • to a statistically sig degree, television watching is heritable. • Bc of some related propensity that has not been researched yet (maybe sensation seeking , lethargy, etc.) that would have a gen component • And this component interacting w/ bio dev + early life exp can cause lots of television watching • Divorce is heritable in a similar fashion. (even if you’ve never met your divorced relatives) o i.e. one or more gen traits are relevant to divorce • Turkheimer says “just about everything is heritable” o i.e. if every personality trait related to divorce is heritable, divorce will turn out to be indirectly heritable as well. But there is not a “divorce gene” Molecular Genetics • change to field of behv gen recently bc of new molec bio methods • association method: tries to determine whether diffs in a trait corr w/ diffs in a particular gene across individs • study on gen basis of homosexuality in males: o identified a gene on the X chromosome that most (but not all) of the ppl they studied shared, but that was not found in their hetero siblings • other studies have tried to show a relationship btwn behv+emotional control and the DRD4 gene (which affects the dev of Dopamine receptors) o theory is that shortage of dopamine/inability to respond to dopamine will cause people to crave extra stimulation (i.e. risky behvs) • DRD4 gene has thus been theorized to be the basis of sensation seeking o variations in this gene corr w/ pt’s scores on a test of novelty seeking • DRD4 is also associated w/ risk for ADHD bc dopamine also involved in brain reg of cog + behv • The 5-HTT gene, assoc’d w/ a serotonin transporter protein, has two alleles ( = variants) o Called short and long bc of their chromosomal structure • Short  neuroticism (anxiety, overreaction to stress, amygdala actually shows stronger responses to viewing fearful stimuli like mutilated bodies) o Amygdala also responds strongly when ppl w/ social phobia have to give a public speech • * Interesting * 5-HTT also reg’s the deg to which the amygdala and prefrontal work together (which may be an important clue to the brain structure of depression) • Prevalence of short allele of 5-HTT may actually vary across cultures o Over 75% of Japanese (which is double the prevalence in Caucasians) o Some have speculated that this is 1 reason why Asian cultures emphasise cooperation and try to avoid conflict (i.e. collectivist) o Bc since neuroticism = emotional sensitivity, Asians mmay find interpersonal conflict more aversive than Westerners and try extra hard to avoid • but have to be careful with all these sorts of studies. • A frequently cited limitation is that these findings do not apply to everyone • Also, the effect size for 5-HTT on P and behv is rather small and can’t always be replicated • As well, inheritance of P goes beyond the effects of single genes (interactions with gene- gene, gene-enviro. And also, always multiple genes will be involved) • 10-500 genes may be involved in complex traits like sensation seeking, anxious-prone • Until the year 2000, nearly everything we knew about genetics vs P came from twin studies • Since, there’s been a spike in new research thanks to molec bio • COMT(catechol-O-methyltransferase)  prefrontal dopamine, extraversion, reasoning ability o Thus, a gene is connected to a neuro trans to a trait + aspect of intelligence Gene-Enviro Interactions • Behv gen began w/ the study of main effects (how particular genes/patterns of genes are associated w/ particular behv/P outcomes • But ultimately, genes only determine genotype (blueprints), which only indirectly affects phenol • Gene-enviro interaction can be more precisely labelled as the phenotype-enviro interaction • Basic principle = genes influence dev of behv only in ppl who live in some kind of enviro o W/o an enviro, there would be no behv. Regardless of genes. o But also, w/o genes, no behv can occur. Regardless of enviro. o So, to emphasize, genes and enviro interact. Either one alone is insufficient. • Enviro can even affect heritability itself (i.e. in an enviro where everyone receives adequate nutrition, height will vary bc genes only. But, if food is scarce, enviro is more a factor than genes) • As the intellectual enviro improves, heritability of IQ goes up too. In richer families, the variance in IQ will be more bc of genes than for impoverished families, who don’t have access to edu • Being shorter, as a guy, could lead to more teasing, which could have long-term effects on P (which is another way genes and enviro interact and could only influence behv together) • Also, ppl choose their enviros o i.e. hanging out with criminals  being a criminal too o this could still be due to an inherited trait of sensation seeking but still requires interaction w/enviro • attempts to find genes associated w/ extraversion have been very unsuccessful o but, it is related to being attractive and strong. Probably bc this makes interactions w/ other ppl more likely to be successful and rewarding (i.e. interaction) • this finding shoes that if one wants to find genes responsible for P, it may actually be easier to study the bases of social attributes like attractiveness and strength • most important way genes and enviro interact is that the same enviro can affect diff individs in diff ways (i.e. predisposition + stress  mental illness. But nonpredisposed  still healthy) • the stressful enviro may not even be perceived as stressful to some people • this variation in exp leads to variation in behvs ppl express which over time affects P dev • molec gen is only recently beginning to acknowledge for the complex interactions possible • Caspi + Moffitt are two psy’ists who are pioneers in this field • They did a major longitudinal study on children in New Zealand o Tried to relate life difficulties + genes  depression o Found that short 5-HTTLPR + life exp were more likely o But, there was no difference in outcomes for long vs short if zero stressors o Therefore this is a perfect example of a gene-enviro interaction • They did another study on whether child abuse + genes  criminality o Gene on X chromosome that affects the enzyme MAOA (monoamine oxidase A). This enzyme affects norepinephrine, serotonin, dopamine o An earlier study showed that if this gene is turned off (neutralized) in mice, they become aggressive. Therefore, related to aggression regulation o The low MAOA gene seemed to double risk of antisocial behv if mistreated as kids • However, there have been issues replicating both of these studies and some have even felt that studying gene-enviro interactions is pointless • * Interesting * Recent work on epigenetics has found that early life exp can actually alter how or weven whether a gene is expressed during dev! o Found by study where rats vary in stress response bc of how much attention from mom • The term interaction does not capture the complexity of th
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