Nature vs Nurture Flashcards
Figuring it out - Comparing Relatives, MZ together
Share 100% of genes
Share 100% of environment
Figuring it out - Comparing Relatives, MZ apart
Share 100% of genes
Share 0% of environment
However, prenatal environment was shared so may impact heritability estimates
Figuring it out - Comparing Relatives, DZ together
Share 50% of genes
Share 100% of environment
Figuring it out - Comparing Relatives, DZ apart
Share 50% of genes
Share 0% of environment
Figuring it out - Comparing Relatives, Interclass Coefficient
The proportion of variance due to between-family differences
Figuring it out - Comparing Relatives, Heritability Estimate
h2 = 2 ( rMZ - rDZ )
Average proportion of variance for a gene trait due to geentic variation in the population
Figuring it out - Comparing Relatives, rMZ
= h2 + c2
Correlation between the traits of MZ twins
Figuring it out - Comparing Relatives, rDZ
= 1/2 h2 + c2
Correlation between the traits of DZ twins
Halved because DZ twins share only 50% of genes
Figuring it out - Comparing Relatives, c2
= rMZ - h2
Common environment influence
Figuring it out - Comparing Relatives, Environmental Influence
Unique + Common Environmental Influence
Figuring it out - Comparing Relatives, Environmental Influence, Common
If MZ < 2 x DZ = Effect of the Common environment
Determine effect by compaing the traits of non-related individuals living in the same household
Figuring it out - Comparing Relatives, Environmental Influences, Unique
Within-Family differences
Birth order, Parental Treatment, Peer Groups
Figuring it out - Comparing Relatives, Environmental Influences, Unique, Birth Order
Adler - First born children are insecure, last born children are spoiled, middle born children are inbetween due to competition for approval
Sulloway 1995 - Later born children show increased Agreeableness and Openness to Experience and decreased Conscientiousness
Kristensen & Bjerkedual 2007 - Second-borns bought up at first-borns (as a result of adoption or death) had IQs similar to that of first-borns who tend to be 3 points higher, emphasising effect of environment as opposed to genetics
Figuring it out - Comparing Relatives, Environmental Influences, Unique, Parental treatment
Loehan 1997 - Personality and Parenting correlate .15
Figuring it out - Comparing Relatives, Environmental Influences, Unique, Peer Groups
Bart et al 2009 - Children that were delinquent at 14 had more delinquent peers are 17, personality determines the peers you choose NOT peers determining personality
Figuring it out - Comparing Relatives, Genetic Influence, Additive
Genes will present characteristics without the need for interactions with other genes
No need for dominance or recession
Figuring it out - Comparing Relatives, Genetic Influence, Non-Additive
Genes show interactions with other genes
MZ will have the same combination
DZ show the same combination 1/4 of the time
May result in MZ > 2 DZ
Assumptions - Assortative mating
Genetic influence measures assume that mating is random and partners are no more similar to eachother than any other members of the population
If parents are more similar than random, genes may overlap and so heritability may be underestimated
Assumptions - Personalities are measured independently
Personality measures of twins often result in the comparison of twins
Assimilation effects result in individuals being compared to the general population, making twins more similar
Contrast effects result in individuals being compared to eachother, making twins more different
Assumptions - Early environment is separate
Twins and even family members will share the same womb, contributing to a shared environment that may impact personality but be ignored, overestimating heritability estimates
Assumptions - Adoptive households are different
Adoptive households go through testing and monitoring to ensure they are safe for the child resulting in most adoptive households having above average treatment
Selective placement could also make the environment more similar to those that are then compared, overestimating heritability by saying any commonality is due to genes
Assumption - Twins are treated the same
If the environment is 100% the same then the twins must be being treated the exact same
Tendency for MZ twins to be treated mores similarly that DZ twins
Scarri et al 1979 - Differences in treatment do not have significant effects on personality
Separating heritability and common environments - Gene-environment Interaction
Different effects of the environment for people with different genotypes
People with the same genetic stress-sensitivity may show different stress levels as a result of the different environmental stressors each are exposed to
Separating heritability and common environments - Gene-environment Correlation
Passive, Active / Selective or Reactive / Evocative
Separating heritability and common environments - Gene-environment Correlation, Passive
The child does not choose their environment, it is a result of the parents’ genetic tendencies which are then passed down
Parents may have the genetic tendency to play music and have instruments in their home so the children plays these, in line with their inherited tendency
Separating heritability and common environments - Gene-environment Correlation, Active / Selective
Genetic tendencies result in the selection of the environment
Child may have a genetic tendency to play instruments and so chooses to go to music club at lunchtime
Separating heritability and common environments - Gene-environment Correlation, Reactive / Evocative
The child selects their environment as a result of other’s reaction
A child may have a genetic tendency to play instruments so plays them in the home, their parents praise them and so the child decides to go to music school which further improves thier abilities
Trait heritability - Personality
Minnesota Twin Study - .54 correlation between traits
Riemann et al 1997 - 38% Openness to Experience, 72% Conscientiousness, 46% Agreeableness, 80% Neuroticism, 56% Extraversion, no effect of Common environment
Trait heritability - Religiosity
Abrahamson, Baker & Caspi 2002 - Adult MZ from .70 to .60, Adult DZ from .60 to .40, large effect of common environment
.12 heritability for adolscents
Trait heritability - Political Attitude
Eaves et al 1997 - MZ .50 to .60, DZ .50 to .40, effect of environment when young, effect of genetics with age
Trait heritability - Smoking
Li et al 2003 - Persistence .55 h2
Vink et al 2005 - Initiation .44 h2
Trait heritability - Drinking
Alcoholism .50 - .71 h2
Drinking .21 - .56 h2
Caspi et al 2003
Investigated the effect of the serotonin gene 5HTT, which has two alleles (long or short)
Caspi et al 2003 - Findings, Depression
No main effect of genes
Main effect of stressful life events
Interaction where stressful life events predict depressive episodes in individuals with the short gene
Caspi et al 2003 - Findings, Suicide
Interaction where stressful events predict suicide in individuals with short genes
Caspi et al 2003 - Findings, Major Depressive Disorder
No main effect of genes
Main effect of childhood maltreatment
Interaction where childhood maltreatment predicts adult major depressive disorder in individuals with the short genes
