2. 63.1 – Discuss the evidence for a genetic influence on intelligence and explain what is meant by heritability.
Nature vs. Nurture and Intelligence
Early pioneers of intelligence…
Maintained the nature view of intelligence
Today’s nature theorists…
Assert that a child’s intelligence CANNOT be changed; genetic destiny
Many argue that this downplays the value of special education programs for underprivileged groups

3. 63.1 – Discuss the evidence for a genetic influence on intelligence and explain what is meant by heritability.
Nature vs. Nurture and Intelligence
Today’s nurture theorists…
Assert that traits with a strong genetic component are not necessarily unchangeable
Argue that even MORE funds be allocated for remedial programs, especially in lower-income areas

4. 63.1 – Discuss the evidence for a genetic influence on intelligence and explain what is meant by heritability.
Family Studies
Can determine only whether genetic influence on a trait is plausible
Twin Studies
The average correlation for identical twins is +0.86
The average correlation for fraternal twins is +0.60
Adoption Studies
Studies indicate that there is more than chance similarity between adopted children and their biological parents

5. 63.1 – Discuss the evidence for a genetic influence on intelligence and explain what is meant by heritability.
Heritability: the proportion of variation among individuals that we can attribute to genes. The heritability of a trait may vary, depending on the range of populations and environments studied.
Heritability Ratio
Can be estimated for any trait
90% for height
85% for weight
Intelligence?

6. 63.1 – Discuss the evidence for a genetic influence on intelligence and explain what is meant by heritability.
Heritability
Heritability estimates for intelligence vary considerably
High Estimate: 80%
20% of the variation in intelligence is attributable to environmental factors
Low Estimate: 40%
60% of the variation in intelligence is attributable to environmental factors

7. 63.1 – Discuss the evidence for a genetic influence on intelligence and explain what is meant by heritability.
Heritability
Limitations of heritability estimates
Heritability is a group statistic; CANNOT be meaningfully applied to individuals
A trait’s heritability may vary from one group to another
“There really is no single fixed value that represents any true, constant value for the heritability of IQ or anything else…”

8. 63.1 – Discuss the evidence for a genetic influence on intelligence and explain what is meant by heritability.
Genetic Influences
Studies of twins, family members, and adopted children support the idea that there is a significant genetic contribution to intelligence.

9. 63.2 – discuss the evidence for environmental influences on intelligence.
Twin Studies
The average correlation for identical twins raised together is +0.86
The average correlation for identical twins raised apart is +0.72
Adoption Studies
There is some resemblance between adoptive parents and their children
Siblings reared together are more similar in IQ than siblings reared apart (0.48, as opposed to 0.23)

10. 63.2 – discuss the evidence for environmental influences on intelligence.
Sandra Scarr (1991)
Reaction-Range Model
Heredity sets certain limits on intelligence and environmental factors determine where individuals fall within these limits
Genetic makeup places an upper limit on a person’s IQ
Cannot be exceeded; even when environment is ideal
Genetic makeup places a lower limit on a person’s IQ except in extreme cases

11. 63.2 – discuss the evidence for environmental influences on intelligence.
Malnutrition, sensory deprivation, and social isolation can retard normal brain development.
Schooling is an experience that pays dividends: increased schooling correlates with higher intelligence scores.
having a “growth mindset” results in a focus on learning and growing.