Problem 7
Nature Or Nurture:
Environmentalist (Genetic) Approach
Case 1 Learning Goals:
1. To what extent do genes and environment shape our personality & behaviour?
Case 2 Learning Goals:
1. How can we study heritability of personality?
Key Words: Identical twins
Case 1:
In the past, the search for the biological bases of personality has focused on the kinds of
genes that different types of people might possess, and hunted for specific genes that might
underlie different personality types and characteristics.
The vast majority of human genes are the same for every human being, resulting in the
enormous similarities that people share - 10 toes, 10 fingers, 2 arms, etc. But a relatively
small minority of genes are different for different people, and these make each individual
genetically distinctive.
Studies compare the similarity in personality shown by the individuals who vary in the degree
to which they share the same genes and/or the environments. Therefore, the “genetic” and
“environmental” influences on personality discussed next, do NOT refer to the effects of
specific genes and specific environments.
Heritability → A statistic that refers to the proportion of observed variance in a group of
individuals that can be accounted for by genetic variance. (A statistical method used to
estimate the percentage of a trait due to genetics.)
Environmentality → A statistical method used to estimate the percentage of a trait due to the
environment (not due to heritability).
Variance → Percentage of trait that is due to either the environment or genetics (heritability).
Phenotype → The observed individual differences.
Genotype → Individual differences in the total collection of genes.
→ The phenotype are the traits that are on the surface; able to be observed by behaviour
and personality. The genotype influences the phenotype.
Genome → The complete set of genes an organism possesses.
, Criticisms to Inheritance:
- Can’t be applied to an individual.
- Only applied to a different group, not constant, if the environment changes, then the
heritability may change.
- Also not super precise, there sometimes may be sampling errors.
Heritability Coefficient → Measures the correlation between twin types.
Formula: r² = 2(r(MZ) - r(DZ)
R = Heritability MZ = Monozygotic twins DZ = Dizygotic Twins
Monozygotic Twins → (Identical twins) 100% same DNA, Egg splits into 2 after fertilisation.
Dizygotic Twins → (Fraternal twins) 50% same DNA, 2 eggs fertilised instead of one.
Methods Of Testing:
1. Selective Breeding:
a. Mating Similar characteristics together to get desired characteristic trait. (E.g.
Breeding two dogs with desired characteristics together to get the ideal dog.)
b. If the heritability is high, the selective breeding is then successful.
c. Tells us that genes influence traits.
Criticisms:
- Doesn’t always apply to humans (unethical)
- Used only for vegetables, fruits, and animals.
- Traits need to be genetic basis.
2. Adoption Studies:
a. Examines the relationship between adoptive parents and their adopted
children.
b. Adoption studies are the most powerful behavioural genetic method available
because since there are no heritable traits shared between adoptive children
and parents, this method studies the environmental influences on personality
development.
c. If the correlation is high, the environment has a big influence on the traits. -
If the correlation is low, then the genetics have a big influence on the traits.
Criticisms:
- Assumption Of Representativeness → Adopted children, birth parents, and adoptive
parent’s representative a general population.
- Selective Placement → If adopted kids are placed in a family that are similar to the
birth parents, then this has an influence, as it affects with measuring the genetics and
environmental influences.
3. Family Studies:
a. Tests correlate between genetic and personality similarity.
b. This study finds correlations among family members who share the same
gene pool.
Nature Or Nurture:
Environmentalist (Genetic) Approach
Case 1 Learning Goals:
1. To what extent do genes and environment shape our personality & behaviour?
Case 2 Learning Goals:
1. How can we study heritability of personality?
Key Words: Identical twins
Case 1:
In the past, the search for the biological bases of personality has focused on the kinds of
genes that different types of people might possess, and hunted for specific genes that might
underlie different personality types and characteristics.
The vast majority of human genes are the same for every human being, resulting in the
enormous similarities that people share - 10 toes, 10 fingers, 2 arms, etc. But a relatively
small minority of genes are different for different people, and these make each individual
genetically distinctive.
Studies compare the similarity in personality shown by the individuals who vary in the degree
to which they share the same genes and/or the environments. Therefore, the “genetic” and
“environmental” influences on personality discussed next, do NOT refer to the effects of
specific genes and specific environments.
Heritability → A statistic that refers to the proportion of observed variance in a group of
individuals that can be accounted for by genetic variance. (A statistical method used to
estimate the percentage of a trait due to genetics.)
Environmentality → A statistical method used to estimate the percentage of a trait due to the
environment (not due to heritability).
Variance → Percentage of trait that is due to either the environment or genetics (heritability).
Phenotype → The observed individual differences.
Genotype → Individual differences in the total collection of genes.
→ The phenotype are the traits that are on the surface; able to be observed by behaviour
and personality. The genotype influences the phenotype.
Genome → The complete set of genes an organism possesses.
, Criticisms to Inheritance:
- Can’t be applied to an individual.
- Only applied to a different group, not constant, if the environment changes, then the
heritability may change.
- Also not super precise, there sometimes may be sampling errors.
Heritability Coefficient → Measures the correlation between twin types.
Formula: r² = 2(r(MZ) - r(DZ)
R = Heritability MZ = Monozygotic twins DZ = Dizygotic Twins
Monozygotic Twins → (Identical twins) 100% same DNA, Egg splits into 2 after fertilisation.
Dizygotic Twins → (Fraternal twins) 50% same DNA, 2 eggs fertilised instead of one.
Methods Of Testing:
1. Selective Breeding:
a. Mating Similar characteristics together to get desired characteristic trait. (E.g.
Breeding two dogs with desired characteristics together to get the ideal dog.)
b. If the heritability is high, the selective breeding is then successful.
c. Tells us that genes influence traits.
Criticisms:
- Doesn’t always apply to humans (unethical)
- Used only for vegetables, fruits, and animals.
- Traits need to be genetic basis.
2. Adoption Studies:
a. Examines the relationship between adoptive parents and their adopted
children.
b. Adoption studies are the most powerful behavioural genetic method available
because since there are no heritable traits shared between adoptive children
and parents, this method studies the environmental influences on personality
development.
c. If the correlation is high, the environment has a big influence on the traits. -
If the correlation is low, then the genetics have a big influence on the traits.
Criticisms:
- Assumption Of Representativeness → Adopted children, birth parents, and adoptive
parent’s representative a general population.
- Selective Placement → If adopted kids are placed in a family that are similar to the
birth parents, then this has an influence, as it affects with measuring the genetics and
environmental influences.
3. Family Studies:
a. Tests correlate between genetic and personality similarity.
b. This study finds correlations among family members who share the same
gene pool.
