Problem 7: Nature vs Nurture

Question 1

family studies
focus
limitation
sibling contrast
split parent identification

Answer 1

focus: correlating the degree of genetic relatedness among family members with degree of personality similarity

rest: notes

Question 2

how do twin studies shed light on genetic factors in personality? 2 types of twins

Answer 2

the twin method:
– compares the degree of similarity on measures of personality obtained for genetically identical twins (from the same egg – monozygotic (MZ)) opposed to fraternal twins (from a dif fertilized egg – dizygotic (DZ)).
monozygotic: 100% equal
dizygotic: 50 % equal
conclusion: identical twins must be more similar than fraternal twins with regard to that characteristic.

Question 3

What do twin studies find regarding the degree of resemblance in personality as compared with other characteristics? (twin study on 800 pairs of twins)

Answer 3

800 pairs of adolescent twins
measuring dozens of personality traits
resemblance with identical twin pairs
conclusion:
identical twins are much more alike than fraternal twins
for personality..
MZ → 50%
DZ → 25%
nearly all personality traits measured by self-report questionnaire show moderate genetic influence

Question 4

What can we interpret about the big 5

Answer 4

MZ twins show a moderate genetic influence on personality (extraversion (.51) and neuroticism (.50) have been extensively studied, the same results are expected for the other 3 factors). Activity level showed a heritability of .40

Question 5

types of temperaments
how are they measured (for children and for adults)
In twin studies, how strongly do genetic factors seem to influence temperament? Why are these results difficult to interpret?

Answer 5

• traits that are visible in early childhood adn seem especially relevant to the individual’s emotional life
• Emotionality, Sociability, Activity
• temperaments are asssed through…
  –> in children: parental reports about their children (rating scales)
  –> in adults: self-report measures
• Emotionality (emotional reactivity):
  tendency to become aroused easily physiologically (by ready activation of the autonomic nervous system) and especially to experience frequent and intense negative emotions such as fear, ander and distress

Sociability:
degree to which the person seeks to interact with others and be with others (introversion – extraversion)

Activity:
intensity and speed of responses. (hyperactivity – inactivity)

conclusions:
– on emotionality: identical twins are rated much more similar by their mothers than fraternal twins.
– MZ twins are rated as much more alike than DZ twins. But, may be because MZ twins are treated more similarly, or ratings may be influenced by expectations/preconceptions for MZ vs DZ twins
– ⅓ to ½ of individual differences in temperamental traits can be attributed to genetic variation among children.
– Observational studies for MZ twins show genetic influences for fearfulness, activity level, shyness/inhibition and empathy. (valuable because they go beyond self-report measures)

Question 6

drinking and smoking habits between twins

Answer 6

MZ twins also show large similarities in their drinking and smoking habits.

Question 7

How strongly are attitudes influenced by genetic factors? Which attitudes seem most strongly influenced?

Answer 7

Genetics plays a role in individual differences in beliefs and attitudes.
from a number of twin studies (including twins who were adopted and reared apart) – genetic influence was found in traditionalism (as opposed to liberal), and many other attitudes also seem to show genetic influence.

Attitudes that are more heritable may differ from those that are less heritable systematically.

Study:
Researchers separated specific attitudes into 2 sets:
one contained attitudes that twin studies have shown very heritable (attitudes about death penalty and jazz)
the other contained those shown less heritable (truth of the Bible and straightjackets)
Then set up experimental situations to change these attitudes on college students
Found:
The more heritable attitudes were harder to influence and also more important in determining the person’s judgements of interpersonal attraction.

Question 8

what are the findings about aggressive and altruistic tendencies?

Answer 8

Study:
self-reports on aggressiveness/altruism questionnaires from a large number of twin pairs in England
For MZ twins the correlation was higher than expected by chance, whereas by DZ twins, the correlation was merely at chance level.
researchers estimate genetics accounteed for around 50% of the individual differences in answers.

Question 9

what are the findings for romantic love and marriage?

Answer 9

Romantic love seems to be beyond DNA.
Study:
890 adult twins and 172 spouses married for around a dozen years
Six dif love styles were measured in adult twins and their spouses: passion, excitement, intimacy, self-disclosure and ‘being in love from the start’ and one that values a relationship that is affectionate and reliable and has companionship and friendship.
Findings: How people love is almost completely due to the environment and unaffected by genes. Family environment is important!! Love styles are not heritable, BUT the tendency to get married is.

Question 10

What is the special value of comparing twins raised together and apart?

Answer 10

To try to separate the role of genetics and environment, it is especially informative to assess identical twins who have been reared apart in different families.

Question 11

what does the study on twins reared apart indicate? What is the conclusion on the role of genes vs environment in personality?

Answer 11

To try to separate the role of genetics and environment, it is especially informative to assess identical twins who have been reared apart in different families.

Study:
MZ twins who were reared apart early in life. (<2 months)
They grew up in different families (mostly English-speaking), and had not seen each other for an average of 30 years.
Comparisons were made of twins who were reared together and grew up in Minnesota.
There were instances of dramatic psychological similarities even when they grew up apart from each other: shared distinctive mannerisms, postures, attitudes, interests.
(ex: posing alike for photos). some turned out to have same: height; weight; n. marriages and children; drinking and smoking habits; mannerisms, clothes, food and jewelry preferences, physical symptoms and smiliar scores on peronality tests
Many also felt a close intimate relationship with each other even after years apart.
the similarity of the similarity was almost as high for the monozygotic twins who grew up in different homes as it was for those raised within the same family

Conclusion:
70% of individual differences in intelligence can be attributed to genes
50% effect of genes in personality + effects of family environm. are trivial
Big 5 factor similarity is influenced more by genes than by environment

monozygotic more similar to dyzigotic even when reared apart

Question 12

what is heritability?

Answer 12

statistic that refers to the proportion of observed variance in a group of individuals
describes the degree to which genetic differences between individuals cause differences in an observed property

the proportion of phenotypic variance that is attributed to genotypic variance

provides useful information for identifying the genetic and environmental determinants of personality

Question 13

2 types of variance

Answer 13

phenotype variance: observed individual differences (height, weight, personality)
genotype variance: individual differences in the total collection of genes possessed by each person

Question 14

heritability index: what is, how to compute

Answer 14

Heritability index: correlations used to estimate the percent of the variation in scores measuring individual differences that is attributable to genetic factors

To compute: measure correlations of MZ (r(mz)) and DZ (r(dz)) twins. Then subtracting the latter from the former and multiplying the result by 2 gives the heritability index.

heritability^2= 2 (r(mz) - r(dz))

It is an estimate of the role of genes in the measures variable. Twin studies are a good measure for the role of genes

Question 15

the heritability indexes have to be interpreted cautiously because:

Answer 15

1. heritability index reflects characteristics of a population, rather than of an individual.
   If there is a genetic variation that reduces the fitness of an individual, the heritability index will be close to 0. Because all individuals are similar on that gene, and a mutation of that gene is due to the environment.
2. When identical twins are reared apart, similarities on personality measures are not necessarily due to genes for personality itself. E.g. shared interest in becoming a fashion model is due to heritability of an attractive face, not due to heritability of personality.
3. Many studies rely mostly on self-report measures, but here the answers can be the same because they identify closely with each other, or might be treated the same by environment.
4. High heritability coefficients do not imply that the particular characteristic cannot be changed significantly. Even though genes influences traits, environment can shape these traits too.
5. Heritability index itself does not know how genes influence the mechanisms on personality etc.

Question 16

environmentality

Answer 16

the percentage of observed variance in a group of individuals that can be attributed to nongenetic differences

Question 17

relationship between heritability and environmentality

Answer 17

larger heritability smaller environmentality

Question 18

shared environment

Answer 18

Shared nevironemnt: Same circumstances (e.g. parents, friends), making for a similar personality.

correlation of personality variables between adopted siblings who share a lot of environment but share no genes in only 0.05

smoking and drinking is related to shared environment

Identical twins are more likely to have a shared environment.
E.g. Doing the same things when together.

Question 19

non shared environment

Answer 19

nonshared environment: Difference in environment in twins, causing twins to be more different.
Fraternal twins are more likely to be a non-shared environment.
E.g. Different friend groups.

They think family members are alike because of shared genes, and that the environment accounts for the differences.
So, nonshared environment has the impact, based on 2 findings:
Twins reared apart are still very much alike (compared to those that lived together)
Adopted children who grew up in the same environment are not very alike – even though they shared the same environment

Question 20

Selective breeding:

Answer 20

Selecting a desired trait in an animal to see if said trait will be inherited -> find out if/to what extent a trait is heritable (with the end goal to apply it to human traits).

Question 21

non shared environment
within and outside the family

Answer 21

nonshared environment: Difference in environment in twins, causing twins to be more different.
Fraternal twins are more likely to be a non-shared environment.
E.g. Different friend groups.

They think family members are alike because of shared genes, and that the environment accounts for the differences.
So, nonshared environment has the impact, based on 2 findings:
Twins reared apart are still very much alike (compared to those that lived together)
Adopted children who grew up in the same environment are not very alike – even though they shared the same environment

within the Family:
nonshared unique environment affects each person in many ways:
beginning in prenatal development and birth order effects
biological events (illness, nutrition)
psychosocial events like interpersonal experiences (w/ parents, peers, romantic partners, …)
children are born in a slightly different family, psychologically and structurally because parents treat siblings differently and siblings treat each other differently. Children also experience events differently (e.g. divorce).
Links between experiences in childhood and life outcomes: negative aspects of parenting (e.g. conflict) lead to antisocial behaviour later on. Also, differences in parental negativity towards MZ twins lead to differences in depression and antisocial behaviour between those twins. Weaker correlations have been found between positive aspects of parenting and positive outcomes.
Chicken and egg matter → Because, maybe, differential treatment is due to genetically influenced differences between siblings, like personality.

→ outside the Family:
Some of the most important nonshared environments are experiences outside the family as they interact with their expanding world
such as school etc.
Also relationships, illnesses and jobs cause significant differences in siblings
Events can be minor, but snowball into big differences in later life outcomes.

Question 22

Genotype-environment interaction:

Answer 22

Genotype-environment interaction: Genetics causing a different response in individuals to the same environment.
Environment might affect expression of genotype in phenotype.
E.g. Someone with a tall genotype might not actually become tall due to environmental factors like malnutrition.
E.g. Introverts perform better while the is silence, extraverts aren’t affected as much (but likely prefer silence as well).
E.g. low amount of MAOA gene: predi sposition to violence -> low MAOA gene + abusive environment -> more likely to develop antisocial traits

Question 23

Genotype-environment correlation: (3 types, negative vs positive)

Answer 23

Genotype-environment correlation: Genetics causing for a different environment to be provided.
- Reactive: Parents respond differently to child’s genotype -> personality is formed in accordance.
E.g. Baby reacts more positively to cuddling -> Mother cuddles baby that responds more positively more than baby that doesn’t respond as positively.

• Passive: Parents provide environment + genotype -> personality is formed in accordance.
  E.g. Parents have a good verbal ability + provides child with books -> Child also has good verbal ability skills
  !! Child does nothing to form personality trait themselves.
• Active: Child with genotype -> seeks out environment reinforcing personality.
  E.g. Child has a thrill seeking genotype -> child goes skydiving to seek a sensation.

Negative correlation: environment discourages expressing disposition -> going against genotype
Positive correlation: environment encourages expressing disposition.

Question 24

.interaction vs correlation:

Answer 24

.interaction vs correlation:
correlation: dif exposure due to dif genes
interaction: dif responses to the same environment due to genetic make up

Question 25

adoption studies
focus
strength and limitations

Answer 25

notes

Question 26

temperaments

Answer 26

Temperaments: inherited personality traits, observable from the baby stage of development -> observing heritability in twin studies
In general there is a 50% percent of heritability in temperaments.
Temperaments are stable (genetics) and affect a large range of responses, personality develops and can change overtime (environment).

• Emotionality (emotional reactivity): tendency to express emotional arousal (anger, fear, stress) in upsetting situations.
  E.g. Seeing a bear -> more likely to express a bigger amount of fear.
• Sociability: desire of others attention and being with others
  - Tied together with extraversion
  E.g. Child who is always plays outside with their friends.
• Activity: energy of behaviour
  - Tempo: speed of behaviour
  - Vigor: energy of behaviour
  E.g. Child who participates in a lot of different sports.