1. Nature vs. Nurture in IQ
Are differences between people due to environmental or genetic differences?
Misunderstanding the question
“Is a person’s intelligence due more to genes or to environment?”
no genes = no intelligence
both genes & intelligence crucial for any trait
Clearly, IQ is not the only psychological construct for which this debate applies, and instructors may wish to take a moment to name the other areas (i.e., personality, mental disorders, etc.) for which heritability is hotly debated.

2. Nature vs. Nurture in IQ Rectangle analogy
is a rectangle’s area due more to its width or its length?
are differences in area among rectangles due more to differences in their length or in their width?
Group A
Group B
Length
Width
Clearly, IQ is not the only psychological construct for which this debate applies, and instructors may wish to take a moment to name the other areas (i.e., personality, mental disorders, etc.) for which heritability is hotly debated.

3. Heritability & Environmentality
degree to which variation in trait stems from genetic, rather than environmental, differences among individuals
Environmentality
degree to which variation is due to environmental rather than genetic differences

4. The Heritability Coefficient
Single number, ranging from 0 to 1.0
Represents amount of trait due to genetic differences
0 means no variance due to genetics
1 means all variance due to genetics
.30 means 30% is due to genetic differences, 70% due to environmental

5. Twin Studies & Family Influence
If trait genetic:
closely related more similar than less closely related
Many close relatives share environments too
Types of studies to separate effects
monozygotic twins reared together
monozygotic twins reared apart
siblings/dizygotic reared together
siblings/dizygotic reared apart
adoptive siblings reared together
figure taken from CD-ROM, Myers text, pg. 353, figure 11.7
Discussion here about the higher correlation between identical twins’ IQ scores than fraternal twins’ and whether siblings were reared together or apart and the genetic role then in intelligence

6. Family Influence on IQ
Transient influence of family in which you are raised
adoptive siblings as children and adults
identical vs. fraternal twins reared together
Fraternal twins
Identical twins
figure scanned in from Gray's text, pg. 370, figure 10.7

7. IQ Differences among Racial/Cultural Groups
Find differences among racial & cultural groups on IQ
American Blacks score about 15 points lower than Whites
WHY?
genetics?
Witty & Jenkins (1935)
No support for genetic differences
environment?
Gray discusses the Witty & Jenkins study of high-IQ Black children in Chicago on page it makes a good discussion topic

8. IQ Differences among Racial/Cultural Groups
Each wheat field planted from same package of genetically diverse seeds
One field is quite fertile, the other is not
Within each field, differences due to genetics
Between each field, differences due to environment (fertility)
figure taken from CD-ROM, Gray's text, pg. 373, figure 10.8

9. Why differences between Blacks & Whites?
Social designation influences
autonomous minorities
deliberately separate themselves
immigrant minorities
came to country to better lives
see selves as better than those left behind
involuntary minorities
did not choose minority status
routinely judged as inferior by dominant majority
cross-cultural findings on IQ scores
Gray reports that involuntary minorities consistently score lower on IQ tests than the dominant majority

10. Historical increase in IQ
Improved performance on IQ tests over the years
Big increases in tests assessing fluid intelligence, smallest in factual knowledge
Increased schooling only accounts for small portion of this increase
Due to changes in the culture?
Year IQ
Scores
figure taken from CD-ROM, Myers text, pg. 345, figure 11.5

11. Summary Nature vs. nurture debate Racial & cultural differences in IQ
heritability vs. environmentality
studies of twins & family influence
Racial & cultural differences in IQ
why we can’t interpret differences as due to genetics
what we can attribute the differences to
Historical increase in IQ scores