Problem 5: Heredity and Environment Flashcards
Obtaining the relative influence of heredity and environment
- Researchers have to calculate how similar relatives tend to be on a given trait
- The researchers calculate how much variance there is altogether in the trait of interest, across all of the people being studied
- They calculate what proportion of that variance is within families and what proportion is between families
Intraclass correlation coefficient
x% of the variance among people in any trait is due to the variance among people in their genes of heredity
–> if relatives tend to be much more similar to each other than to unrelated persons, then the correlation will be high
–> if relatives tend only to be modestly more similar to each other than to unrelated persons, then the correlation will be low
Identical twins
- share 100% of their genes
- any extra similarity of identical twins, beyond that of fraternal twins, should be due to the additional genetic similarity of identical twins, beyond that of fraternal twins
Fraternal twins
- share 50% of their genes
Additive genetic effects
= the combined effects of two or more genes on personality are very simple, with each gene contributing separately to making one’s level of the trait a bit higher or lower
–> the traits are independent of each other
–> the combined effect of the genes can be estimated by simply adding together their separate effects
Nonadditive gene effects
= the combined effects of two or more genes are more complex, with the combined effects being different from what you would expect based on adding the separate effects of the genes
–> the traits depend on each other
–> when nonadditive genetic influences on a trait are important, identical twins will be considerably more than twice as similar as fraternal twins will be
Common/shared envrionment
= effects of the rearing environment that is shared by any twins who have been raised together
–> between-family environmental influences
Nonshared/unique environmental influences
= many different features of the environment that differ even for individuals from the same household
–> within-family environmental influences
Comparison of the similarities between identical and fraternal twins
–> about 50% of the variation in each characteristic was found to be due to genetic influences (up to 65%)
–> almost all of genetic variance was additive
–> the remaining variance is due to unique environmental influences
Contrast effect
= the tendency to emphasize differences between related persons
Assimilation effect
= the tendency to emphasize similarities between related persons
selective placement
= adoptive families may be selected in such a way as to be similar to the biological parents of the children who are to be adopted
–> there is little selective placement
equal environments assumptions
the greater similarity of identical twins is due to their greater genetic similarity, not due to any greater similarity of their environments
–> the similarity of identical twins is not due to similar treatment of those twins
Effects of the unique environment on personality
–> different treatments by parents
–> different friend groups
–> siblings having different birth order positions - first-born, middle-born, last-born, or only child - might develop different personalities
Genotype-Environment Interactions
= the same environment will influence people’s levels of a given characteristic in different ways, depending on their genetic characteristics (i.e., their genotype)
Genotype-Environment Correlations
= your genetic tendencies might actually cause you to be exposed to some kinds of environments more than other kinds, and the differences between those environments might then influence the development of your personality characteristics
- Passive genotype-environment correlation
–> children inherit this combination of genes and environment “passively,” not as a result of their own behavior - Reactive genotype-environment correlation
–> other people’s reactions to the child’s genetic tendencies end up influencing the environment that the child experiences - Active genotype-environment correlation
–> the child actively chooses environments as a function of his or her genetic predispositions
Fluctuating optimum
= the ideal level of the characteristic might differ depending on environmental conditions that change from one time and place to another
–> the variation in the characteristic would tend to be maintained even over very long periods of time
Frequency dependence/Frequency-dependent selection
= a rough balance in the population between people who have higher and lower levels of the characteristic
–> the variation in a characteristic would persist because there might never be a single ideal level of a characteristic, but rather an ideal balance of different levels of a characteristic
Two different ways in which frequency dependence and the fluctuating optimum preserve trait variation
- by favoring the reproductive success of individuals who have a genetic inclination to have a particular level of the trait
- by favoring the reproductive success of individuals whose genetic inclination is more flexible, allowing the development of either a high or a low level of the trait, depending on experiences early in life
Effects of Honesty-Humility, Agreeableness, and Emotionality
Honesty-Humility: reciprocal altruism (fairness)
Agreeableness: reciprocal altruism (tolerance)
Emotionality: kin altruism
Higher levels of these three dimensions are associated with the tendency to help other individuals (or to avoid harming them), as opposed to the tendency to harm other individuals (or to avoid helping them)
Effects of Extraversion, Conscientiousness, and Openness to Experience
Extraversion: engagement in social endeavors
Conscientiousness: engagement in task-related endeavors
Openness to Experience: engagement in idea-related endeavors
Higher levels of each of these three dimensions are associated with being, in some sense, more “activated”, or “involved”
quantitative genetics
= estimates the extent to which observed differences among individuals are due to genetic differences and to environmental differences without specifying the exact factors of influence
Adoption Studies
Adoption produces family members who share a family environment but are not genetically related
–> normal families and adoptive families can be compared
–> resemblance between relatives is accounted for by shared heredity rather than by shared envrionment
Twin Studies
–> often compare fraternal and identical twins
–> if genetics are important for a trait identical twins must be more similar than fraternal twins
Combination Studies
Combining twin and adoption studies leads to more experimental power
–> adoption-twin combination involves twins adopted apart and compares them with twins reared together
–> genetic factors contribute substantially to schizophrenia and cognitive ability
Heritability
= the proportion of phenotypic variance that can be accounted for by genetic differences among individuals
–> phenotypic differences not explained by genetic differences can be attributed to the environment
–> IQ correlations for identical and fraternal twins are 0.85 and 0.60, therefore the heritability estimate is around 50%
–> heritability of a physical trait that causes you to be treated differently brings about differences in your personality
Genetic and Environmental Transmission of Political Orientations
Openness to Experience –> liberal ideology
Conscientiousness –> conservative ideology
- The views held by citizens on contemporary
issues of the day are the product of
characteristics of the immediate political
environment and deep-seated predispositions - Political orientations and attitudes are
psychologically based constructs that reach
beyond the political domain (e.g., social life) - Genetics play at least some role in shaping
political attitudes
Genetic influence on personality
–> 40-50% heritability
–> mostly nonadditive genetic variance
Genetic influence on intelligence
–> increasing genetic influence on IQ with age
–> decreasing shared environmental influence
–> with age, decline in heritability of intelligence
Genetic influence on psychiatric illnesses
Schizophrenia - very high degree of genetic influence, mostly additive genetic influence, no shared environmental influence
Antisocial behavior - additive genetic influence, shared environmental influences decrease from childhood to adulthood
Genetic influence on social attitudes
Political - until around 19 only environmental influence, afterwards genetic influence manifests itself, nonadditive
Religious - only slightly heritable in teens, moderately heritable in adults, influenced by shared environment
Life History Theory (LHT)
Describes individual differences as reflective of a series of coordinated adaptive trade-offs that organisms must make to maximize their allocation of the limited resources that are available to them in their environment.
- somatic effort: related to growth and
maintenance - reproductive effort
(a) mating effort: seeking out a mate,
establishing pair bonds
(b) parental effort
Fast life history
organisms come to reproductive age earlier, have a shorter life span, and emphasize bearing many offspring with limited parental investment
–> favor resource allocation toward reproductive efforts
Slow life history
organisms come to reproductive age more slowly, have a longer life span, and have a greater parental investment in fewer offspring
–> toward a long-term goal
–> favor resource allocation towards continued growth and maintenance
Sex differences in personality
–> females incur more of the cost of reproductive investment, which includes having to wait a necessary period before having more offspring –> selected as the choosier sex
–> males are not limited in their reproductive capacity since the amount of reproductive effort can be as short as a few seconds –> more mating-focused strategy
Personality throughout the life span
–> a tendency to decline in the traits of Openness, Extraversion, and Neuroticism, and an increase in Agreeableness and Conscientiousness occurs over this period of development
–> changes in personality occur more at young ages, but less as individuals get older
–> early-life calibration sets the stage for one’s traits and behaviors
Evolutionary psychology
= a relatively new metatheoretical paradigm that synthesizes the modern principles of psychology with the core principles of evolutionary biology
Costly Signaling Theory
–> individuals compete with one another in sending signals to others about their quality as a mate, friend, and coalition member
–> those perceived as having the highest quality have an advantage in being chosen by the highest quality mates, friends, and coalitions
–> any form of deception creates a selection for adaptations in signal receivers to detect deception and discount dishonest signals
Balancing Selection
= occurs when genetic variation is maintained by selection, such that different levels on a trait dimension are favored, or are adaptive, in different environmental conditions to the same degree
