Problem 5: Heredity and Environment Flashcards
(39 cards)
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