1. The Nature-Nurture Debates
Introducing Psychology
4/4/2019
The Nature-Nurture Debates
Extreme biological position
Personality traits, physical characteristics, etc. are all programmed or “hard-wired”
Extreme environmental position
All traits and characteristics are shaped by life experience
So how do we study this???
©2001 Prentice Hall

2. Introducing Psychology
4/4/2019
Twin-Study Method
Comparison of pairs of identical and fraternal twins of the same sex
Identical Twins
Are genetic clones - genetically identical
Share DNA, but not fingerprints
Have identical brain wave patterns
Occur once every 254 births
Adoption Studies
Comparison of twins and other siblings reared together with those separated by adoption
©2001 Prentice Hall

3. Twin and Adoption Studies Identical Versus Fraternal Twins

4. Twin and Adoption Studies Identical Versus Fraternal Twins Monozygotic
Twin and Adoption Studies Identical Versus Fraternal Twins Monozygotic Dizygotic

5. Twin and Adoption Studies Identical Versus Fraternal Twins Monozygotic
Twin and Adoption Studies Identical Versus Fraternal Twins Monozygotic Dizygotic

6. Twin and Adoption Studies Identical Versus Fraternal Twins Monozygotic
Twin and Adoption Studies Identical Versus Fraternal Twins Monozygotic Dizygotic

7. Twin and Adoption Studies Identical Versus Fraternal Twins Monozygotic
Twin and Adoption Studies Identical Versus Fraternal Twins Monozygotic Dizygotic

8. Twin and Adoption Studies Identical Versus Fraternal Twins Monozygotic
Twin and Adoption Studies Identical Versus Fraternal Twins Monozygotic Dizygotic

9. Introducing Psychology Genetic influences
4/4/2019
Nature and Nurture
Genetic influences
Based on the Minnesota personality studies:
When raised together, monozygotic twins are more similar than dizygotic twins.
MZ Twins raised apart are almost as similar to each other as those living in the same home.
Prepared by Michael J. Renner, Ph.D.
These slides ©2001 Prentice Hall Psychology Publishing.
©2001 Prentice Hall

10. Where does this leave you?.
Where does this leave you?

11. The Nature-Nurture Debates
Introducing Psychology
4/4/2019
The Nature-Nurture Debates
Other studies of twins and adoptees show:
Genetic factors account for some differences in intelligence, verbal and spatial abilities, criminality, vocational interests, and aggressiveness.
There is a genetic component to psychological disorders, such as alcoholism, depression, and schizophrenia.
And, there is evidence for a genetic link to people’s attitudes toward issues and activities.
©2001 Prentice Hall

12. The Nature-Nurture Debates
This study involved 672 twins who rated their attitudes on various issues and activities.
The results show some influence of genetic factors.

13. The Nature-Nurture Debates
Introducing Psychology
4/4/2019
The Nature-Nurture Debates
Genetic differences typically account for less than 50 percent of the variation in personality.
Environmental factors account for the rest of the variation.
©2001 Prentice Hall

14. The Nature-Nurture Debates
A study of 5,542 three-year-olds found that
Children with older brothers had higher masculinity scores
Children with older sisters had higher femininity scores
These results support the nurture hypothesis.

15. How do we study and quantify nature vs. nurture?
Heritability
A statistical estimate of the percentage of the variability of a trait within a group that is attributable to genetic factors.

16. Heritability Intelligence (50%) Height (90%) O 1
What does it mean when we say something is heritable?
Intelligence (50%)
Height (90%) O 1
100 % down to genes
100 % down to environment

17. So 50% with respect to intelligence means that genetic influence explains 50% of the observed variation among people w.r.t. intelligence
In other words, we are looking at the extent to which difference among people are attributable to genes
Heritability means…

19. Each value only refers to the particular population studied and its unique range of genetic and environmental factors
The more an environment varies, the greater their opportunity to account for individual differences and the lower heritable estimates are likely to be
Heritability estimates are controversial because they can be misapplied and because their application is limited

20. The Nature-Nurture Debates The Interplay of Nature and Nurture
Introducing Psychology
4/4/2019
The Nature-Nurture Debates The Interplay of Nature and Nurture
Genetic and environmental influences are not independent.
Identical twins receive more similar treatment from their parents compared to fraternal twins.
People’s genetic makeup influences how they are treated by others, the environments in which they live, and the way they perceive and recall the details of that environment.
©2001 Prentice Hall

21. Your time to work on your debates.