Personality and Individual Differences > TASK 5 - GENETIC + ENVIRONMENTAL INFLUENCES > Flashcards


family studies (similarities between relatives)

= studies that correlated degree of genetic relatedness among family members, with degree of personality similarity
- highly heritable: family members with greater genetic relatedness should be more similar to each other (parents more than cousins)
x families usually share same environment --> difficult to disentangle the influence of genes and environment


results of family studies

- different correlations have been found
- biological relatives tend to be similar in personality (identical twins being much more similar than other kinds of relatives)
- similarity does not depend on whether or not they have been raised together
- substantial role of heredity in personality variation, but little (if any) role of common/shared environment


adoption studies

- genetically related individuals who don’t share a common environment --> similarity estimates contribution of genetics to family resemblance
- family members who share an environment but aren’t genetically related --> similarity estimates contribution of a shared environment to family resemblance


adoption studies
- other relatives raised apart

- 50% of genes in common
- similarity between them, we see effect of only 50% of the genes
- doubling the similarity


twin studies

= compares identical twins (MZ) with fraternal twins (DZ)
- genetic cause for trait: identical twins more similar than fraternal ones
- twins raised apart (adoption studies)
- twins raised together (vs. fraternal twins)
x assumption of representativeness: twins are usually not really representative for whole population --> findings cannot be generalised
x twins often born 3-4 weeks prematurely (language develops slower)


results of twin/adoption studies
- twins raised apart

- 100% of genes in common = genetic influence
- similarities can be assumed to be due to genetics --> if separated right after birth
- .60: twins more similar to each other than to unrelated people in that trait --> 60% of variance among people can be explained by heredity


results of twin studies
- twins raised together

- 50% of variation due to genetic influences (self- / observer-reports)
- 65% of variation due to heritability (self- + observer-reports)
--> almost all of that genetic variation was additive, almost none was non-additive
- remaining variation: due to unique environment influences, due to common environment influences


additive vs. non-additive

additive effects = each gene separately contributes to personality (make level of trait a bit higher or lower)

non-additive effects = combined effects of genes are more complex (e.g. effect of one allele depends on presence of another)


shared environmental influences

= effects of environment shared by any twins who have been raised together; between-family (differ between families)
- same socio-economic status, religious attitude, parenting style


unique/non-shared environmental influences

= effects that differ even for individuals from the same household; within-family (differ within families)
- different friends, treated different by parents


assumption of heritability study
- personality is measured independently

WRONG: similarities between relatives are inflated/deflated; compare themselves/relatives not to general but to each other
1. contrast effect = emphasise difference between related persons
- larger effects in fraternal twins
2. assimilation effect = emphasise similarities between related persons
--> effects could influence people’s personalities: might really become more different/similar
overcome effects:
- reports from someone who knows one individual well, but not the other (cannot contrast/assimilate)
- direct observations: only observes one relative


assumption of heritability study
- there is little assertive mating

‘TRUE’ for some characteristics: parents are not similar in some personality characteristic (BUT in beliefs, attitudes)
- similarity would not cause any important distortion
- assortative mating would cause parents to sharing genes --> inherit genetic tendencies --> more similar (=overestimate heritability)


assumption of twin-based heritability studies
- twins' early environment is separate

TRUE: similarity between twins raised apart is not attributable to early time spent together
- similarities in womb environment: shared + non-shared environment
- common environment: consistent across pregnancies (smokes during all pregnancies)
- unique environment: features that change across pregnancies (eating a lot of meat in first pregnancy, being vegetarian in second)


assumption of twin-based heritability studies
- adoptive households are different

WRONG: reduced variability in adoption families (higher socioeconomic status, less antisocial behaviour); very little selective placement
- selective placement: families may be selected due to similarity to biological parents
x unlikely have important effects


assumption of twin-based heritability studies
- identical/fraternal twins receive same treatment

TRUE: similarity of identical twins is not due to similar treatment of those twin
- equal environments assumption = greater similarity of identical twins is due to greater genetic similarity, not due to greater similarity of environments


Reasons why/how variation persists

- selection would tend to eliminate all variation (single, ‘best’ solution)
WRONG: not a single ideal level of each trait
1. variation is unimportant: has no consequences for survival and reproduction
2. mutations cannot be eliminated quickly enough and reproduce in following generation
3. importance of variation against infections by parasites: variations make it more difficult for parasites to invade bodies successfully


balancing selection
- fluctuating optimum

= ideal levels of a characteristic vary across places and times = ideal level of same characteristic shifts according to changes in environment
- average level of trait gradually shifting up/down within given population --> amount of variation not reduced
- e.g. food abundant/shortage: many offspring = better reproductive success with abundant, few offspring = better with shortage (better parental care)


blinking selection
- frequency dependence

= the advantages of doing what others are not doing = nearly everyone had high level of characteristic, few people who had low level of characteristic would be more successful
- rough balance in population between people with higher and lower levels BECAUSE only advantage when they are few with low level
e.g. females are attracted to rare colours: many green males + lone blue male = better reproductive success of blue males --> more blue males in next generation = advantage of blue decreases --> green males become more favoured


how do fluctuating optimum + frequency dependence preserve variation

1. favour reproductive success of individuals who have genetic inclination to have particular level of the trait
a. either high or level of trait --> over long run produce equal levels of reproductive success of different levels
2. favour reproductive success of individuals whose genetic inclination is more flexible --> allowing the development of high or low level of trait
a. individuals adapt successfully; develop different levels of trait in response to cues of environment


life-history theory

= trade-offs in problems of life to which limited energy is allocated
- optimal trade-off depends on variables like own qualities, life expectancy & energy
- individual differences


costly signalling theory

- individuals compete with one another in sending signals to others about their quality
- deception
- costly signals tend to be honest as not everyone can afford it
- link to life-history (e.g. male can’t afford signal as short-term mate so might shift to life-history strategy of heavy investment in one long-term partnership)


balancing selection

= occurs when genetic variation is maintained by selection
- different levels on trait dimension are favoured/adaptive in different environmental conditions to same degree


mutation load

= we differ in mutation load
- heritability of some traits comes from differences in mutation load


contingent shifts

= situation-specific shifts = select species-typical psychological mechanisms that are flexibly responsive to changes in environmental conditions
- reactive heritability = contingent shift in response to one’s heritable phenotypic characteristics
- life history theory: become more risk averse after becoming a father
- costly signalling theory: when an environmentally contingent increase in mate value affords a greater ability to emit costly signals


copy number variants + segmental duplication

- segmental duplications = CNVs that have gone to fixation because selection favoured duplication
- selection may favour changes in that segment so its function becomes different than that of the original copy
- copy-paste-modify
- much of human evolution occurred through changes in SD-rich regions


difficulties in separating effects of heritability + environment

- genotype-environment interactions = same environment influences peoples characteristics in different ways, depending on their genotype
- makes relatives less similar to each other
- genotype-environment correlation = genetic tendencies cause you to be more exposed to a specific kind of environment
1) passive: inherit combination of genes + environment passively, not as result of own behaviour
2) reactive/evocative: other peoples’ reactions to kid’s genetic tendencies end up influencing the environment
3) active: child actively chooses environment as a function of genetic predisposition


what accounts for genetic variability in general? (GANGESTAD)

1. no selection: no meaningful selection on a trait; very unlikely
2. mutation-selection balance: without mutations, selection would eventually eliminate variability around intermediate optimum; mutations do not die out
3. variable selection: selection itself may be variable (spatially or temporally)
4. negative-frequency dependent selection: when variants are rare in population they tend to success
5. non-additivity: genetic variance non-additive is typically not removed by selection


adaptive trade-offs
- Honesty-Humility

- reciprocal altruism (fairness, sincerity, modesty)
benefits of high levels:
- gains from cooperation (mutual help, non-aggression (= altruism))
costs of high levels
- loss of potential gains that would result from exploitation of others


adaptive trade-offs
- Agreeableness

- reciprocal altruism (tolerance, forgiveness)
benefits of high levels:
- gains from cooperation (mutual help, non-aggression)
costs of high levels:
- losses due to being exploited by others (as they keep cooperating in spite of some unfairness)


adaptive trade-offs
- Emotionality

- kin altruism
benefits of high levels:
- survival of kin personal survival by avoiding harm
costs of high levels:
- could enjoy greater gains as a result of confronting dangers


adaptive trade-offs
- Extraversion

- engagement in social endeavours
benefits of high levels:
- social gains (friends, mates, allies)
costs of high levels:
- energy + time + risks from social environment


adaptive trade-offs
- Conscientiousness

- engagement in task-related endeavours
benefits of high levels:
- material gains (improved use of resources), reduced risks
costs of high levels:
- energy + time


adaptive trade-offs
- Openness to experience

- engagement in idea-related endeavours
benefits of high levels:
- material + social gains
costs of high levels:
- energy + time + risks from natural environment