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
- 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 - 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
