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Biological Bases of Personality.pdf

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McMaster University
Jennifer Ostovich

Biological Bases of Personality - interested in quantitatively in describing biological bases - what are the biological factors and howmuch of an impactdo they have on personality o nature vs. nurture (relative importance) - many of the previous theories had some component of genetics (built in  id, trait theory etc.) - certain characteristics tend to run in families - similarity however, does not indicate the existence or strength of biological bases of personality - characteristics can be shared in families for other reasons o given their interest, their personality  parents provide environment so that their kids will develop similar interests o children’s genes themselves, regardless of how similar theyare, leads parents to treat them in a way that is similar to their personality o children have a tendency to put themselves in situations which lead them to have similar experiences than their parents have Factors involved in personality - genetics: undoubtly inherit genes from parents that do in some way shape our personalities o major shape for trait theorists - shared environment: there are things that individual raised in the same family share (e.g. house, meals, parenting, parents take them on trips so they share similar experiences)  tend to make familymembers moresimilar o on a larger scale, books, country etc. - non-shared environment: experiences that people have that they do not share with anyone else. Makes them more different. o Even in a family, children may have different teachers, treated differently by parents, other after school activities  non-shared environment experiences becomes even greater siblings move away for school - Can we quantify? How big of the pie do each of these consist of? Phenotype and genotype - phenotype: any measurable characteristic of that individual (e.g. height, IQ) o personality is phenotypic of individual (you can measure and assess) o not necessarily visible/ measurable, observable - genotype: genes that you inherit from your parents - to what extent is your phenotype determined by your genotype Monozygotic & Dizygotic - compare similarities phenotypically in people that differe in a known way in their genotypic similarity o compare personality in people who’s genotypic similarity is known o e.g. in twins - monozygotic: zygote splits into two and they develop individually (share the same genes since they came from the same zygote)  100% identical in genotype (does not mean they are 100% identical genetically though) - Dizygotic (fraternal, non-identical): developed separately from 2 eggs. Share roughly 50% of their genome in common o No more similar genetically than any siblings are - Their genetic similarity is “known”, use this to asses impactof genetics/environment - Compare MZ twins who are raised together vs. twins who were raised apart - E.g. look at IQ o When you compare similarities, use correlation coefficient r (0-1, +/-)  as number goes from 0 to 1, indicates stronger relationship between the two variables  indicates extent of whether we can predict one from another (e.g. 1.00  knowing value of one, allows us to know perfectly the value of the other) o If correlation between twins raised together was 0  knowing IQ of one twin does not help has make any predictions about the other twin o If there was a phenotypic characteristics which was 100% determined by genotype (resemblance assuming 100% genetic determination), then r=1.00 all the time  always be able to predict phenotypic characteristic of one twin from the other o Would be true whether they were raised together or not o Has never been found  nothing/no phenotype is 100% genetically determined o MZ reared together is higher than MZ twins raised apart  extent to this difference is the importance of genes o Compare MZ raised apart/together and compare it to correlation of DZ raised together/apart o If we have phenotypic chracteristics which was 100% determined, correlation between MZ twins would always be 1.00, and correlation between DZ would always be 0.5 (this is assuming 100% genetic determination)  never get that because nothing is 100% genetic determination o MZ reared together/apart, DZ reared together/apart o Use these comparisons to estimate relative importance of genetics vs. environment in whatever phenotypic chracteristics you are assessing Family studies - don’t have to use twins - parents/children share roughly 50% genes (kid gets roughly50% from dad, other from dad)  50% similar to siblings, 25% similar to grandparents, uncle - use information to compare similarity between one and their family members (use correlation to estimate relative contribution that genetics makes to phenotype) Adoption studies - look at phenotypic similarities between their parents and adopted children, and children + their biological parents - if genes were important,there would be higher correlationbetween children and biological parents than children and their adopted parents  estimate importance of genes - can combine studies (e.g. twins who were adopted) Problems with Studies - twins studies has been one of the most commonly used - but in order to use them effectively, have tomake assumptions which in many cases are not true - DZ twins confused as MZ (only underestimate) o some pairs of DZ twins are same sex, born the same time, look very alike o misclassify them as MZ o will reduce estimate of importance of genes o only recently have kids been made sure that they are MZ or DZ before assigned to study group - Selectiveplacement: correlated environments in adopted twins o When comparing similarities when twins are reared apart o Assuming that they are raised in un-related environments (i.e. knowing environment of which first twin is being reared is not predictive of environment of 2 twin) o However, when twins are separted for adoption purposes, one of the things that every adoption place tries to do is to put twins in families which are similar to which their original familiy was like..prettymuch try to ensure that the environments of which the two twins are raised in are correlated o Assuming un-correlated environments, and saying that difference is due to genes  but if they were raised in correlated environments, then phenotypic similarity is going to be due to environmental similarities o Will cause us to overestimate importance of genes (attributing genetic similarity when it’s due to environmental similarity) - Differences between MZ and DZ twins in environmental similarity o MZ vs. DZ reared together in same family o Assumption: environmental similar is same for MZ and DZ  if we know environment for one MZ twin, then we have certain ability to predict environment for the other MZ twin o Environment shared is the same o MZ parents deliberately emphasize similarity of twins  share highly similar environment which is engineered by parents o DZ parents very often emphasize the dissimilarities/uniquness of each twin  try to make environment as different as they can make it o Will cause us to over-estimate importance of genes - Assortive mating: greater parent-child similarity o In formulas we use to compare similarities in families, we are assuming random mating (there is no strong correlation between genotype of one parent and genotypeof the other- orthogonal) o But for a number of things (e.g. personality), this may not be true o E.g. If we knowIQ ofmom, assumption is that it doesn’t tell us anything about IQ of dad (assuming 0 correlation)  However, this is not true. Can predict with some accuracy the IQ of the other  We tend to be attracted to people who have similarIQs o Individuals with similar genotypes marry each other married someone with similar IQ, meaning that we share some similar genes o Random mating  Mom has 6 genes, dad has 6 genes (assuming they are all for IQ)  no similarities between two sets of genes  Child gets half genes from mom, half from dad  Assuming random mating, child is 50% identical to mom/dad in genotype o Assortive mating  SimilarIQ, thus parents share some similar genes (for IQ)  Child gets 2,3,4 from mom, 5,6,10 from dad  2,3,4,5,6 is identical to whatmom has (she’s 80% similar to mom)- she got from dad some of the genes that mom also shares  Assertive mating leads childrenmore similar to parents than in random mating  If we assume random mating, we’re underestimating genetic similarity if assoritve mating does exist o Not sure howmuch personality is inrandom/assortive mating, but its quite likely since people tend to put themselves in situations because of their personality o Individuals with similar personalities willmeet and have kids o The extent that this happens in respect to personality  we will have assoritve mating  higher levels of similarity between parents and children  messes up estimate of (overestimate) importance of genetics vs. environment Distributions and variance - we cannot determine how much of IQ is determined by genes or environment  we can only ask how much of the variability of some phenotype can be attributed to genetic differences in the population or environmental differences (contribution to variability) - variance: sum of squared deviations from themean/ number of scores (measure of variability) - total variance (Vt): due to the fact that you have differencegenes (Vg) and difference experiences (VE) - what proportion of total variance (VT) is contributed by Vg 2 - heritabilitycoefficienth = Vg/Vt (ratio of variance) - can get from correlation to H2 - h = r mza o correlation coefficient for MZ reared apart mza  then you have calculation/estimate of H2 for that phenotypical characteristic o should be the highest estimate of all formulas (in theory) 2 - h = 2r dza o DZ reared apart o Double the number because DZ are only half as similar as MZ twins o Both of these require that either MZ or DZ were reared apart  if they were reared together, confusing two sources of similarity o For them reared apart, assuming only similarity is genetic (un-correlated environments)  to the extent that they are similar, it has to be due to genetics o If you rear them together, there are two contributions to their variance: genetics and shared environment  cannot tease that apart - h = 2(r mz -2r dz o take MZ correlation and subtract DZ correlation o both twins have to be raised in same condition: both (MZ and DZ) either have to be raised together or raised apart - e.g. 0.3, 0.5  0.3-0.5 x 2 - because MZ are twice as similar as DZ, the correlation coefficient between MZ should never be more than twice the correlation for DZ twins (vice versa, should not be more than half) o will not see this if assumptions are violated Heritabilitycoefficient - applies only to groups, not individuals o Heritability coefficient does not talk about the contributionof genes to any single individual  its about groups. What proportion of variance from GROUP SCORES can be attributed to genetic/environmental factors - Varies from population to population, and over time - Valid only if measures used to calculate it are valid o Only get valid estimates if you have valid data - Ve in this case is smaller than Vg  hertiabilty estimate: - 2 one: Ve gotten smllar, Vg remained the same  same Vg over slightly smaller total, so Vg will look bigger. The amount that it has contributed has not change, but by reducing the environmental contribution, it seems like genetics made a bigger contribution o Variance from environment used to be greater (education system, health care)  how much one was educated, how much health care they got variedlots o Over the years, reduced variance (health care available to all, education up to grade 12 is mandatory)  many which were variables that contributed to environmental differences is gone now o Increase heritability coefficient because denominator is smaller (hertitability coefficient has thus gone up) o Does not mean that genes now contributes more to IQ, but about the proportion of variation which comes from genes/environment  reduce environmental variance, as long as genetic variability about the same - But genetics has actually also changed  probably gone up in this case in Canada (e.g immigration) o Hertitability coefficient increase again due to bigger variation in genetics - Environmental stay the same, just variety in gene pool o Environmental variations not so big, coefficient low in places like Haiti - Coefficient assesses how much variability is due to genetics/environment  genetics may contribute, but if all the people have same genetics, then it will be 0 Recap - coefficient is not about any individual (i.e. how much anindividual’s x is due to heritability?)  meaningless question - it characterizes the proportion of variability in some phenotypic characteristic which can be attributed to genetic variability  value is different from time to time, varies in different places - heritability is a variable, something that may be constantly changing  about the characteristics of a population Where is the biological basis of personality located? What is the nature of human nature? What is it that we inherit from parents that shapes our personality - Temperament: hard to define what it is, definition varies. General activity levels, emotional reactivity to stimuli. o It is what we think most likely to strongly determinate our genetic substrate Thomas, Chess & Birch (1970) - Looked at infants (~less than a year old)  looking to assess dimension of behaviour that constitute aspects of their temperament - Rated their behaviour as high, medium or low on each of the dimensions - Some of the dimensions they looked at (6/9 they looked at): o level of motor activity: howmuch they move (e.g. constantly kicking) o positive response to new object: introduced toy/stuffed animal to infant and watch its response  was it happy?- strong positive response or did it get distressed/turn away- low positiveresponse to novel object o regularity in biological functions: there are babies who seem to do everything on a schedule (sleep/wake up at same time etc.), others get hungry at any time/sleep any time  degree of variability o friendliness or good mood: those who smile/giggle often vs. those who aremore grumpy, cry a lot o adapts to changes in environment: characteristics of human is that we dislike change, prefer predictability (~Maslow’s safety needs). There are kids who are fine no matter who’s holding them vs. those who get disturbed/upset in any alterations o usual degree of energy in responding: different from level of motor activity  can have lot of activity but low energy vs. low activity but very energetic (it is the amount of energy put into activity, not the amount of activity) - looked at intercorrelations between the ratings. Identified three basic groups: o Easy infants:  Tend to be very predictable/regular in biological rhythms (eating, sleeping etc.)  Generally in good mood most of the time  Tend to be tolerant to novelty  Adapt well to change: nomatter where you bring them etc.  Low/moderate level of energy response: laid back o Difficult infants:  Irregular rhythms: not sure when they want to wake up/eatetc.  More oftenin poor mood, displeased  Dislikes novelty: prefer the old predictable, new stuff makes them grumpy/cry  Adapts poorly to change: change in schedule/environment is not welcomed  High levels of energy: not necessarily high motor activity, but high energy whenever there is motor activity o Slow to warm up (not focus)  Same as difficult infants, but they havelow levels of energy to responding o The two categories had about 10-20% of the infants - So what if we can discriminate these babies? Maybe these infants were just caught on a good/bad day o Need to show that it’s a consistent behaviour of responding o Proven: had them come back 6 months, 1 year etc. , these kids are in the same categories (not every infant is true, butmost are)  6.7, high correlation between ratings– relatively unchanging o Not just a good day/bad day thing  something consistent about these infants - So why do we care? o Does itmake a difference in their lives? Yes. o Followed infants until early adolescence o Proportion of easy vs. difficult infants who during their regular school years were referred for some kind of psychological difficulties  70% of difficult infants were referred vs. less than 20% of the easy infants were referred o Difficult infants are over represented in the clinical population (people who seek professional health after they leave school): 25% of people in clinical population would have been classified as difficult infants. When you consider population as a whole, only 10% of infants are classified as difficult- they are 2.5 times over- represented in clinical population compared to prevalence in population as whole o This is something that’s consistent across their lives and it has an impact since status of difficult infant is related to school year and beyond psychological difficulties o Want to identify these kids as early as possible  perhaps there’s something we can do to amoelerioate the problems that may be associated with infants with difficulties o Given that it shows up so early, we are assuming that it may be geneticrelated - Furthermore, pre-term/early birth babies aremore likely tohave difficult temperaments than are full-term babies/those born on time o Study inmid-80s in Canada, reported that pre-term infantsmorelikely to be classified as difficult- followed them for a year or two and assessed their temperament o Kids were at same temperament at both times (if they wereeasy a few months after birth, they were easy after a year) o However, there were kids who shifted: there were easy infants who were classified as difficult a year or two later (vice versa) o Those who shifted from difficult to easy  this is the groupthat researchers focused on. How do you get from difficult to easy when we know that being difficult is a problem? - Looked at everything about the kids who shifted from difficult to easy o One things that seemed to best discriminate those who shifted from difficult to easy was mothering (sensitive, patient, tolerant mothering) o Environmental impact which affected temperament - Did not use heritability coefficients- were not trying to explain howmuch variability of these aspects could be explained by genetics/environment - But other studies did Plomin & Rowe (1979) - Plomin: big name in behavioural genetics - Looked at social development of twins because sociability is thought to be one of the underlying characteristics/parts of temperament - Studied social development of male and female twin pairs, MZ and DZ - Looked at infants who were about 2 years of age, rated them on a number of different social characteristics (how closely they approached stranger, how long they looked at them etc.) - How similar were these twins to each other in each of theseareas of social development? o Looking at stranger: correlation for MZ was 0.7, o Approaching stranger: 0.4 (MZ), 0.1 (DZ) o Nearness to stranger (how close they get to them): ~0.4 (MZ), 0 (DZ) o Vocalizing to stranger: ~0.4 (MZ), 0 o Can’t use these by correlations themselves as estimates of heritability coefficients because they are MZ reared together (can use if they were reared apart, first formula- correlation for MZ reared apart) rd o Because they had DZ, can use 3 formula (correlation between MZ-DZ and doubleresults because MZ and DZ are assumed to be half as similar to each other- 50% identity for DZ, 100% for MZ) o Correlations for MZ and DZ twins, one issue: should never see correlation for MZ which is more than double correlation for DZ  we should never see DZ which is less than half the correlation for MZ (because they are 50% similar)  but clearly these results violate the assumption (0.7 for MZ, then should be ~0.35 for DZ) - How can DZ not be similar? If genes were important, which is suggested by MZ, we should be seeing some correlation for DZ! o But we’re not seeing these correlations  something wrong with the data o MZ:0.7 – 0.1 = 0.6 x 2 = 1.2 (120% variability due to genes? Not possible) o Described it as a CONTRAST EFFECT (too big of a contrast between correlations for MZ and DZ) o Problem appears to be that correlation for DZis way too low o But it was not explained Buss & Plomin (1984) - looking at a particular measure of temperament: EAS (survey/test for temperament) - saw temperament as involving 3 basically inherited characteristics - Emotionality: roughly equivelnt to neuroticism/emotional stability- tendency to show negative rather than positive emotions - Activity level: how active are you in general (running around vs. sitting around) - Sociability: how well do they get along with other people, who much do they like being with others (~extroversion/introversion) - Developed a 20 item survey called the EAS survey, had 6 or7 rating scales for each of these aspects  filled by parents most often (e.g. statement: is easily frightened, which characterizes the chid: makes friends easily etc.) – rate on 5 point Likert scale - Looked at MZ and DZ twins and their ratings on these characteristics o Emotionality: 0.6 (MZ), 0.1 (DZ) o Activity: 0.5 (MZ), 0 (DZ) o Sociability: 0.35 (MZ), 0 (DZ) o Contrast effect again! Weird correlations between MZ andDZ o Using heritability correlation formula, come up with values greater than 1, which is impossible (you cannot explainmore variance that what exists) o Same results again, can’t just let it go - A few things that we should be aware of when doing calculations: - Distinction between additive and non-additive genetic variance o The only distinction made was environment vs. genetics, but no distinctions made within each category o Additive: if you have a gene, and it’s active regardless of what other genes you have  that gene has an additive effect (if it’s in your genome, it is active) o Non-additive:  Dominant-recessive effect: some genes which are active only if the other gene pair is passive (dominant vs. recessive)  E.g. if you have a brown gene from mom, blue eyed gene from dad  you don’t get brownish-blue eyes, the blueis recessive and if its present with a brown allele, you see the brown  Unless you have two blue alleles, you won’t get blue eyes  Genes activity is not automatically present  Epistatic effects: activity of gene does not depend on partner, but depends on some other gene in the genome  Gene A is only active if B is present, somewhere else on chromosome  Genes active/inactive depending on whether other genes are present in the genome  Another non-additive genetic variability - We care because the difference between additive and non-additive makes a difference in how similar twins are o Identical MZ have all the same genes, thus they share 100%of additive genetic effects and 100% non-additive effects (any dominant-recessive effects which occur in onewill occur in the other etc.) o Different for DZ: share 50% of all additive genetic effects (since they have 50% of genes in common) – this is what we’ve been assuming so far when doing the calculations o They DO NOT SHARE 50% of non-additive effects of genetics  E.g. have dominant-recessive situation: 50% chance that twin will have original dominant gene shared, other 50% it will have the other same allele (50 x 50 = 25% chance that both twins will have the same dominant-recessive pairing, 25% for dominant-recessive/non-additive effects  Same for epistatic effect; 50% they will share first gene in common, 50% chance they will share 2nd gene in common  25% chance that they will share both genes in common and have same epi-static effect,  So overall DZ share 50% of additive genetic variance, but only 25% of their non-additive genetic variance in common - Overall, DZ are not 50% genetically similar, they are somewhere between 25 and 50% genetically similar - If all genetic effects were additive, they would be 50% similar, but depending on what proportion of genetic effects were non-additive, then its different (e.g. if all genetic effects were non-additive, then they would only be 25% similar) - How does this affect our formula? The reason we subtract one from other and then double is because difference represents 50% genetic similarity (100% for MZ, 50% for DZ) - If MZ are 100% genetically identical, but DZ are only 40% simi
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