1. Unit 6: Testing & Individual Differences
Module 33: Genetic & Environmental Influences on Intelligence

2. Genetic Influences
Do people with the same genes share comparable mental abilities?
Answer: YES!
IQ’s of identical twins are similar to those of the same person taking the same test twice.
Fraternal twins (share ½ of their genes) are much less similar.
Identical twins raised separately also have similar scores.

3. Genetic Influences
Fraternal twins tend to score more alike than other non-twin siblings.
Intelligence scores of adopted children are more like those of their biological parents.
So…genetics seem to play a large role in IQ.

4. Genetic Influences

5. Genetic Influences

6. Genetic Influences

7. Genetic Influences

8. Genetic Influences

9. Environmental Influences
Environmental influences effect children of less-educated parents more.
Children in poor families have more similar intelligence scores.
Meaning that poor environmental conditions can override genetic differences.
Extreme poverty trumps genetics!

10. Environmental Influences
Can intelligence be improved with practice or education?
Head Start Program: Government funded preschool program.
Targeted children below poverty level. Over 900,000 children.
Quality programs increase school readiness, but results fade over time
Small intelligence boost, but experiences after Head Start is important.

11. Environmental Influences
Of course…schooling and intelligence is correlated.
IQ scores rise during school year, but drop during summer.
Flynn Effect: worldwide rise in IQ scores since the 1920s due to increasing years of schooling.
More school = more intelligence.

12. Racial & Ethnic Differences
Racial groups differ in average scores on IQ tests.
Bell curve:
Whites: Average – 100
Blacks: Average – 85
Hispanics: Average in between whites and blacks.
Similar results appear on aptitude tests like SAT, although gap is getting smaller.

13. Racial & Ethnic Differences
Environmental factors in racial gap:
Skin color does not differentiate people.
Race is no longer easy to define with more mixed race people.
Asians outperform North Americans on math and aptitude tests. (They also spend 30% more time in school.)

14. Racial & Ethnic Differences
IQ scores of today’s better-fed, better-educated population exceeds those of the 1930s. (Flynn Effect)
White and black infants score equally well on infant intelligence measures.
Each ethnic group had their glory years: Greeks, Egyptians, Romans, Aztecs, Arabs, etc.

15. Gender Differences Boys vs. Girls:
Spelling: Girls are better spellers.
Verbal: Girls are more verbally fluent and remember words better.
Memory: Girls are better at locating objects.
Sensation: Girls are more sensitive to touch, taste, and odor.

16. Boys vs. Girls Continued:
Gender Differences
Boys vs. Girls Continued:
Emotion Detection: Girls!
Underachievement: More boys are at the low extremes of intelligence.
Math and Spatial Intelligence: Girls are better at computation, but boys are better at problem solving. Also more boys at the highest extremes in math.

17. Bias
Bias: Differences in performances caused by cultural experiences detected on tests.
Most psychologists believe that the major aptitude tests (ACT, SAT, IQ tests) are not biased.
Their predictions applies to both genders and all ethnic and economic groups.

18. Bias
Stereotype Threat: A self- confirming concern that one will be evaluated based on a negative stereotype.
When one feels that they won’t succeed based on negative stereotypes, they usually perform poorly.
This may account for lower test scores of blacks and women.