1. Nature & Nurture in Psychology

2. Nature and Nurture?
Nature – genetics
Nurture – environment

3. Heritability
percentage of trait variation in a group/population that can be attributed to genetic differences

4. Identical twins are GENETICALLY identical
Heritability
Sara is very outgoing and agreeable
Suzy is timid and non-conforming
If this pair of IDENTICAL twins is my population, what percent of their personality differences is attributed to genetic differences?
Heritability is 0%
Identical twins are GENETICALLY identical

5. Heritability Heritability is 100%
Joe and Hank are not related. At birth, both were placed in identical environments that were maintained identical until they were 10 years old.
At 10, Joe is withdrawn & shy.
At 10, Hank is outgoing & friendly.
What percentage of their personality difference is attributable to genes?
Heritability is 100%

6. How is heritability determined?
Twin Studies & Adoption Studies

7. Twin Studies v. same genes, different genes,
Identical Twins Fraternal Twins
same genes, different genes,
same environment same environment v.
Greater differences between the two groups indicate greater heritability (“nature”). The trait might have a large genetic component.

8. Twin Studies Criticisms:
(Don’t write this, just think about it)
Do fraternal twins really have equally similar environments to identical twins? Differences in looks or inborn temperament may cause people to treat you differently.
Identical twins may share a placenta but fraternal twins do not. Thus, we can’t eliminate prenatal environments as the cause of the differences between the two groups.

9. Identical Twins Raised Together
Twin Studies
Identical Twins Raised Apart
same genes,
different environments
Identical Twins Raised Together
same genes,
same environment v.
Greater difference between these two groups indicates greater role of the environment (“nurture”).

10. Twin Studies Criticisms:
(Don’t write this, just think about it)
Adoption agencies try to place twins in similar families so the variation in environment may be small
There is a very limited sample.

11. Adoption Studies Is the child more like adoptive parents…
…or biological parents?
Biological Parents - Nature
Adoptive Parents - Nurture

12. Adoption Studies
Note: Two related siblings that grow up in the same family are strikingly different in personality.

13. Nature or Nurture? NATURE NURTURE Personality Divorce Risk Heart Rates
Brain Waves
Intelligence Levels
Values
Attitudes
Manners
Political Beliefs
Religious Beliefs
Involvement in charitable activities
Age of death (7% heritability)
Interests (50% heritability)
NATURE
NURTURE
Intelligence Levels – separated identical twins have similar intelligence levels, BUT adopted children score higher on intelligence tests than their biological parents

14. How heritable is that trait?
Trait Population Heritability
Creativity adolescents 25%
Extraversion adults %
Autism general %
Depression general %
Sleep quality general 35%
TV viewing year olds %
Religious beliefs general 0%
Divorce general 55%
Height women 92%
The Stanton Peele Addiction Website
Heritability of Intelligence – most researchers believe it to be between 60-80%

15. “Nature deals the hand; nurture plays the cards.”
- Charles Brewer