Chapter 9:THE INHERITANCE OF PERSONALITY: Behavioral Genetics and
1. Behavioral genetics: attempts to explain how individual differences in
behavior—personality traits—are passed from parent to child and shared by
2. Evolutionary psychology: attempts to explain how patterns of behavior that
characterize all humans originated in the survival value these characteristics
provided over the history of the species.
3. Behavioral genetics
1) Personality trait: A pattern of behavior relevant to more than one
a. Eugenics: the belief that humanity could be improved through
b. Cloning: it might be technologically possible to produce a
complete duplicate—psychological as well as physical—of a
c. Either eugenics or cloning turns out to be very feasible.
Because personality is the result of a complex interaction
between an individual’s genes and the environment
3) Calculating heritability
a. Basic research: to compare similarities in personality between
individuals who are and are not genetically related and are related
to each other to different degrees
b. Basic questions: the degrees to which variation in the phenotype
can be attributed to variation in the genotype
c. Look at twins
d. Concentrates on the less than 1 percent of the human genome
e. Heritability coefficient: Conclusion: Heritability = 40%.
f. The figures are average, doesn’t describe any of a particular pair:
This point underlines the fact that behavioral genetic analyses and
the statistics they produce refer to groups or populations, not
g. As a result, in terms of genetic expression, fraternal siblings will
be less than one-fourth as similar to each other, on average, as
identical twins instead of half as similar.
4) What heritabilities tell you
a. Genes matter. Not all of personality comes form experience, some
of it comes form genes b. Insight into etiology: severe mental retardation is not heritable.
c. Insight into environment: it provides a window into how the early
environment does—or does not—operate in shaping personality
5) Does family matter?
A recent major meta-analysis that summarized the results of
many studies concluded that the shared family environment
was important in the development of many forms of
psychopathology between childhood and adolescence,
including conduct disorder, rebelliousness, anxiety, and
depression. The only exception was attention deficit
hyperactivity disorder (ADHD), for which the shared family
environment did not seem to matter—this outcome might be
more directly under the control of genes.
6) Nature and Nurture
a. The less a trait varies across individuals, the lower its
heritability is likely to be.
b. If a given trait has a high heritability, two situations are
possible: The trait might vary greatly across individuals, or it
might be a trait that is determined largely by genes.
7) How genes affect personality
a. Molecular genetics.
- Association method: tries to determine whether
differences in a trait correlate with differences in a
particular gene across individuals.
- Examples: The genetic basis of homosexuality in males: X
chromosomes they shared
- Traits associated with behavioral and emotional control
and a gene called DRD4, which affects the development of
• Dopamine is part of the brain system that responds
• Different forms of the DRD4 gene are associated
with variations in sensation seeking, and so
concluded that this gene might be a basis of
sensation seeking via its effect on dopaminergic
- A shortage of serotonin has been blamed for a wide variety
of emotional disorders ranging from depression to anxiety
and social phobia, and that drugs (such as SSRIs) that
increase the level of serotonin in the brain effectively treat
these disorders, at least sometimes. The 5-HTT gene,
associated with a serotonin transporter protein, has two
variants, or alleles.
• People with the short allele score higher on
measures of neuroticism • The amygdala in people with the short allele also
shows stronger responses to viewing fearful and
unpleasant stimuli such as pictures of frightened-
looking faces, accident victims, mutilated bodies,
and polluted scenery
• The prevalence of the short allele of the 5-HTT gene
may vary across cultural groups.
• Some writers have speculated that it may be one
reason why Asian cultures emphasize cooperation
and avoiding conflict over the kind of individualistic
striving said to be characteristic of Western cultures
- They do not apply to everybody
b. Gene-environment interaction
- Basic principle: genes influence the development of
behavior only in people who live in some kind of
- Genes affect personality (shorter and was teased)
- People choose their environment due to genes
- The same environment can affect individuals in different
- Epigenetics: how experience, especially early in life, can
determine how or even whether a gene is expressed during
8) The future of behavioral genetics
a. The genome-wide association (GWA) study: require exploring
for the genes that are associated with personality using
b. This is very difficult and expensive technique
4. Evolutionary personality psychology
1) Evolutionary theory is the foundation of modern biology.
2) One landmark book, E. O. Wilson’s Sociobiology: The New Synthesis
(1975), applied evolutionary theory to psychology and sociology.
3) Evolution and behavior
a. The more a behavioral tendency helps an individual to survive
and reproduce, the more likely the tendency will appear in
b. The approach is to is to identify a common behavior pattern
and then ask how it might have been adaptive (beneficial to
survival and reproduction) for the human species across the
c. Aggression and altruism
- A tendency to be aggressive can help a person to protect
territory, property, and mates, and also lead to dominance
in the social group and higher status.
- A tendency to aid and protect other people, especially close relatives, might help ensure the survival of one’s own genes
into succeeding generations, an outcome called inclusive
- all of us—are the descendants of people who cared deeply
what other people thought about them.
- crying may often be a useful way of seeking social support,
and that fatigue and pessimism can prevent one from
wasting energy and resources on fruitless endeavors.
f. Mating behavior
- Differences between mate selection (attraction), and
• Definition: the willingness to engage in sexual
relations in the absence of a serious relationship
• Men score higher
• Both men and women who score high are interested
in the physical attractiveness and social visibility of
potential partners, those score lower foucs more on
personal qualities and their potential to be good
• Men- not the biologically father
• Women- the man is not emotional bonded with her
• “sexy son” theory
5. Individual differences
1) The mechanism of evolution requires individual differences to be
maintained. For a species to remain viable, it must include diversity
2) Evolutionary psychology accounts for individual differences in three
a. Behavioral patterns evolve as reactions to particular
b. People have several behavioral strategies, but they use the one