1. Biological Theory of Personality

3. Nature v. Nurture Nature! Nurture! “They are born that way!”
Responsible for ~50% of personality
Nurture!
“It’s their experiences & how they were raised!”
Responsible for ~50% of personality

4. Biological Approach What percentage of personality is inherited?
“Heritability”
We are not sure BUT temperaments do seem to be stable from infants to old age.

5. Biological Approach Genes: units of heredity
DNA holds our chemical make-up
Affect personality because they affect our behaviors, especially on infants
Inferring the existence of relevant genes
Hope one day specific genes underlying temperaments and key traits will one day be discovered

6. Heritability & Temperaments
Temperaments: dispositions to respond to the environment in certain ways
Ex: reactivity, soothability, positive & negative emotionality
Studied in infants
May later form into personality traits

7. …what? Heritability & Traits
Heritability: statistical estimate of the proportion of the total variance in some trait that is attributable to genetic differences among individuals within a group.
…what?

8. Heritability & Traits
Simply put, heritability is how likely a trait is transmitted from parent to child
High heritability: trait probably passed through genes
Low heritability: probably not.
Even high heritable traits can be modified by the environment.

9. Studies
Adoptive children
Different genes, same environment

10. Studies Identical v. fraternal twins
Genetic influences would cause identical twins to be more similar than fraternal twins, despite growing up in same environment

11. Studies Identical twins separated at birth
Same genes, different environments
Studies: similar personality, even though raised apart
Demonstrates heritability!

12. Heritable Personality Traits
Gestures
Mannerisms
Moods
“Big Five” traits

13. Practice!
I hope you have a few quiz-taking genes.

14. Practice!
What three broad lines of research support the hypothesis that personality differences are due in part to genetic differences?
In behavioral-genetic studies, the heritability of personality traits, including the Big Five, is typically about…
0.50
0.90
0.10 to 0.20

15. Practice!
A newspaper headlines announces: “Couch Potatoes Born, Not Made: Kids’ TV Habits May Be Hereditary.” Why is this headline misleading? What other explanations of the finding are possible? What aspects of TV watching could have a hereditary component?

16. How’d You Do??
Research on animal personalities, human temperaments, and the heritability of traits
A = 0.50
The headline implies there is a “TV-watching gene,” but there obviously isn’t such a gene. The writer fails to consider other explanations. For example, perhaps some temperaments dispose people to be passive, and this disposition leads to a tendency to watch a lot of TV