Section 2.2 of my IB HL Psychology text book

1. Biological Level of Analysis
Genetics and Behavior

2. Behavioral Genetics
• Behavioral genetics deal with understanding
how both genetics and environment
contribute to behavior
• A single gene doesn’t determine complex
behaviors
– i.e. intelligence, criminal behavior, altruism

3. Behavioral Genetics
• Individual may have a genetic predisposition
towards a certain behavior
– Just needs the appropriate environmental stimuli for
it to manifest
– Without it, the behavior won’t be developed
• Diathesis-stress model: Depression results from
a “genetic vulnerability” and traumatic childhood
events
– Doesn’t apply to everyone
– Sometimes one sibling becomes depressed and the
other does not

4. Inheritance
• Genes and DNA is passed down to offspring
• Mapping of human genes can help to explain
human behavior and develop treatments
– James Watson’s Human Genome Project
• Role of genes in behavior is still a mystery

5. Correlational Studies
• Correlational study establishes that there is a
relationship between variables
• No cause and effect can be determined
• Genes research twins a lot to find correlations
between genes and behavior
– The correlation found in these studies is referred
to as the concordance rate

6. Family Studies
• More representative sample of the general
population
• Different degrees of related genetics
compared to their behavior
• Expected that as genetic relation increases,
similarities in behavior increase also

7. Adoption Studies
• Demonstrates effects of nature vs. nurture
– Biology vs. environment
– For example: Is the child’s IQ more similar to the IQs
of the adopted parents’ or the biological parents’?
• Criticisms:
– Children are not representative of population
– Adoption agencies tend to use selective placement to
find adoptive parents who are similar to biological
parents
– Hard to decipher whether nature or nurture caused
something

8. Intelligence
• The Bell Curve by Richard J. Herrnstein
• Claims: Debate about whether/how much
genes and the environment have to do with
ethnic differences remains unresolved
• Suggests there may be intergroup differences
in intelligence
• Obviously controversal

9. Intelligence
• Charles Spearman “g” factor
– Don’t test facts and subject knowledge
– Test spatial ability, reasoning, divergent thinking,
and verbal fluency
• Bouchand and McGue (1981) meta-analysis of
111 studies
• Found that the closer the kinship, the higher
the correlation for IQ

10. Minnesota Twin Study (Bouchard et
al. 1990)
• Identical twins raised together vs. identical
twins raised apart
• Concordance rates of intelligence tested
• Determined 70% of intelligence can be
attributed to genetic inheritance
• Other 30% may be attributed to other factors

11. Minnesota Twin Study (Bouchard et
al. 1990)
• Pros:
– Mean age was 41 years old (most twin studies are
about adolescents)
– Most cross-cultural study to date
• Cons:
– Ethical concerns in reunited twins
– Equal environment assumption (just because twins
lived together doesn’t mean they had the same
experiences growing up)
– Used media coverage to recruit participants
– Frequency of contact between twins prior to study
could not be controlled

12. Adoption Studies
• Scarr and Weinberg (1977) & Horn et al.
(1979)
• Studied parents with both biological and
adopted children
– Same upbringing and environment, but different
biology
– Parents were white and middle class
– Children were from lower-class with low-IQ
biological parents
• No significant difference in IQ correlations

13. Wahlstein (1997)
• Moving an infant from a low socio-economic
home to a high socio-economic home
improved childhood IQ scores by 12-16 points
• Suggests intelligence has a lot to do with
environment
• Enriched environment can raise IQ

14. Hainer et al. (1988)
• PET Scan
• Individuals with high IQ had a lower metabolic
rate when solving a reasoning problem
• No change in metabolic rate with a data recall
problem
• Higher IQs use less energy to think
• Called the less effort hypothesis

15. Heritability in IQ Levels
• Plomin and Petrill (1997)
• Correlations between parents and child IQs
change over time
• It is possible that our genetic disposition pushes
us towards environments that accentuate that
disposition, thus leading to increased
heritability throughout the lifespan
• Socio-economic class is an important
environmental factor (i.e. poverty)

16. The Flynn Effect
• The Flynn Effect: the rise of average scores on
intelligence tests
– in most parts of the world
– over the last century
• Average mean scores on standard IQ tests go
up by about 3 points every decade
• Real increase in intelligence? Better at
cracking the test? Better nutrition, schooling,
childhoods, technology?

17. Darwin’s Theory of Evolution
• The environment presents challenges to each
individual
• Those who adapt best to environment will
have a greater chance of surviving and passing
on genes to offspring

18. Theory of Natural Selection
• Species with characteristics best suited to
environment are more likely to breed
• They pass on these beneficial characteristics
• Explains how species acquire adaptive
characteristics to survive
– Or makes them more competitive in an
environment
• This is adaptation

19. Darwin’s Ideology
• Humans have behaviors in common with
other animals
– Mate selection
– Love of mother for offspring
– Self-preservation
• Evolution can be studied by looking at
primates
– Our closest relatives in the animal kingdom

20. Tetsuro Matsuzawa (2007)
• Aim: Examine spatial memory in young chimps
• Method: 3 pairs of chimps memorized numerals
1-9; had to memorize which numbers were
where when replaced with blank squares
• Results: Humans made many errors (especially
as speed of replacement increased)
Chimpanzees “showed remarkable memory”
(time shown made no difference)

21. Tetsuro Matsuzawa (2007) Cont.
• Chimps adapted this way to remember where
food resources and dangers are
• Not essential for human survival because of
agriculture
• Memory skills of both chimps and humans
have adapted to become best suitable for the
environments in which they live

22. Evolutionary Psychology
• As genes mutate, those that are advantageous
are passed down through natural selection
• Natural selection cannot select for a behavior;
only for mechanisms that produce behavior

23. Fessler (2006)
• The emotion of disgust allowed our ancestors to
survive long enough to produce
• These offspring in turn passed the same sensitivities
on to us
• A pregnant woman’s immune system lowers so it
doesn’t fight off the new foreign material in her
womb (AKA the fetus)
• Nausea response heightens to compensate for the
suppressed immune system

24. Fessler (2006) Cont.
• Natural selection may have helped
compensate for the increased susceptibility to
disease during pregnancy by increasing the
urge to be picky about food
• Sensitivity decreases as the risk of disease and
infection decreases
• Disgust = form of protection from disease

25. Curtis et al. (2004)
• Aim: Test patterns in people’s disgust
responses
• Method: Ranked level of disgust for 20 images
• Findings suggest that disgust reaction was
strongest for items that threaten immune
system
• Higher disgust in young people
• Higher disgust in women than men

26. When examining an evolutionary
argument remember:
• Confirmation bias (see what they expect to
see) because it’s hard to test empirically
• Little is known about early humans
– Statements of how humans “used to be” are
hypothetical
• Often underestimate role of culture in shaping
behavior

27. Human Genetics Research
• Aims to identify particular genes involved in
hereditary diseases
• Participants need to know their privacy will be
protected and must be fully aware of the study they
are participating in
• Can reveal potentially harmful information
– i.e. misattributed paternity, unrevealed adoptions
• Stress over possessing a gene that could link to a
disease
• Consent as a community should be attained