With reference to relevant research studies,
to what extent does genetic inheritance
influence behaviour?
Behavior Geneticists study our differences
and weigh the relative effects of heredity and
environment.
2
Chromosomes containing DNA (deoxyribonucleic
acid) are situated in the nucleus of a cell.
3
Segments within DNA consist of genes that make proteins to determine
our development.
4
Genome is the set of complete
instructions for making an organism,
containing all the genes in that
organism. Thus, the human genome
makes us human, and the genome for
drosophila makes it a common house fly.
5
 If
it were possible, would you want to take
a genetic test telling you which diseases
you are likely to suffer from later in life?
 If you or your spouse were pregnant,
would you want the unborn child tested
for genetic defects?
 Do you think it should be legal for
employers to use genetic tests in
deciding whom to hire?
6
Studying the effects of heredity and environment on
two sets of twins, identical and fraternal, has come in
handy.
7
Behavior geneticists’ effects of shared and unique
environments on total or partial genetic makeup.
8
A number of studies compared identical twins raised
separately from birth, or close thereafter, and found
numerous similarities.
Separated Twins
Personality, Intelligence
Abilities, Attitudes
Interests, Fears
Brain Waves, Heart Rate
9
Critics of separated twin studies note that such
similarities can be found between strangers.
Researchers point out that differences between
fraternal twins are greater than identical twins.
Bob Sacha
10
Adoption studies, as opposed to twin studies, suggest
that adoptees (who may be biologically unrelated)
tend to be different from their adoptive parents and
siblings.
11
Adoptive studies strongly point to the simple fact that
biologically related children turn out to be different in
a family. So investigators ask:
Do siblings have differing experiences?
Do siblings, despite sharing half of their genes, have
different combinations of the other half of their genes?
Ultimate question: Does parenting have an effect?
12
Parenting does have an effect on biologically related
and unrelated children.
Parenting Influences
children’s
Attitudes, Values
Manners, Beliefs
Faith, Politics
13
Temperament refers to a person’s stable emotional
reactivity and intensity. Identical twins express similar
temperaments, suggesting heredity predisposes
temperament.
BUT – Does the environment play a role as well?
14

1)
2)
3)
4)
5)
6)
Scientific American Frontiers 2nd ed (Clip #23/9:40)
What two personality styles have been identified in Rhesus
monkeys?
How do these styles relate to a monkey’s
relationship/attachment style with the mother?
How did Steve Sumi and his team investigate the origins of
these personality styles?
What were their major findings?
Provide evidence that: a) the environment has an impact on
temperament; b) biological programming has an impact on
temperament
What value do animal studies have on contributing to our
understanding of human development?
15

1)
2)
3)
4)
5)
6)
Go to www.preventiveoz.org and summarize
the findings under these headings:
Importance of temperament
Origins/history of temperament
Major temperament areas
Appearance of temperament
Gender differences
Impact of birth order
16
Heritability refers to the extent to which the
differences among people are attributable to
genes.
17
If genetic influences help explain individual diversity
in traits, can the same be said about group
differences?
Not necessarily. Individual differences in weight and
height are heritable and yet nutritional influences
have made westerners heavier and taller than their
ancestors were a century ago.
18
Some human traits are fixed, such as having two eyes.
However, most psychological traits are liable to
change with environmental experience.
Genes provide choices for the organism to change its
form or traits when environmental variables change.
Therefore, genes are pliable or self-regulating.
19
Genes can influence traits which affect
responses, and environment can affect gene
activity.
A genetic predisposition that makes a child
restless and hyperactive evokes an angry
response from his parents. A stressful
environment can trigger genes to manufacture
neurotransmitters leading to depression.
20
Genes and environment affect our traits individually,
but more important are their interactive effects.
Alessia Pierdomenico/Reuters/Corbis
Rex Features
People respond differently to
Rowan Atkinson (Mr. Bean) than Orlando bloom.
21

1)
2)
3)
The Mind, clip #29/ 11:40
Describe the brain deficits from which
alcoholics suffer.
What evidence has been offered for a
genetic/hereditary factor in
alcoholism?
How does the environment interact with
these hereditary factors to produce
alcohol addiction?
22
Molecular genetics is a branch extension of behavior genetics that asks
the question, “Do genes influence behavior?”
23
Molecular geneticists are trying to identify genes that
put people at risk for disorders. With this kind of
knowledge, parents can decide to abort pregnancies
in which the fetus is suspected of having such
disorders.
However, this opens up a real concern regarding
ethical issues involving such choices.
24
 MZ
(identical twins) share 100% genes
vs. DZ (fraternal) share approx 50%
genes
 Siblings share 50% genes
 Concordance rate calculated – likelihood
that if one individual has a trait, the other
will also have it (helps determine degree
to which a trait is inherited)
25
 One
twin acts as control for another
 Bouchard’s study only calculated
concordance rates and did not look at
environmental factors (equal
environment assumption)
 MZ twins are compared to DZ twins – if
high rates in MZ vs. DZ, then trait is
assumed to be linked to genetics
26
 Longitudinal
study; self-selected sample
of MZT and MZA to look at concordance
rates
 IQ (measured by WAIS) had a
concordance rate of 69% for MZA and
88% for MZT
 Environmental factors play a role but
intelligence is largely inherited (approx
70% of variation attributed to genetics)
27
 Sample
was primarily white, middle class
in industrialized nation)
 IQ can be increased (envir’l influence)
 BUT
• Correlational data does not create cause-effect
• Rates were far below 100% so relative influence
of genes is difficult to calculate
• No control for environmetal variables
• Difficult to generalize (self-selected sample)
28
 Course
Companion (pgs. 55-56)
 Outline the following:
• Criticisms of Bouchard’s study
• Scarr & Weingberg (1977) and Horn et al (1979)
•
•
•
•
on IQ scores
Wahlsten (1977) contributions
Hainer et al & less effort hypothesis
Plomin & Petrill (1997)
The Flynn effect
29
Natural selection is an evolutionary process through which adaptive
traits are passed on to ongoing generations because these traits help
animals survive and reproduce.
30
Biologists like Belyaev and Trut (1999) were able to artificially rear and
domesticate wild foxes, selecting them for friendly traits.
L.N. Trur, American Scientist (1999) 87: 160-169
Any trait that is favored naturally or artificially
spreads to future generations.
31
A number of human traits have been identified as a result of pressures
afforded by natural selection.
Why do infants fear strangers when they become
mobile?
Why are most parents so passionately devoted to their
children?
Why do people fear spiders and snakes and not
electricity and guns?
32
Gender Differences in Sexuality
Males and females, to a large extent, behave and think similarly.
Differences in sexes arise in regards to reproductive behaviors.
Question (summarized)
Male
Female
Casual sex
60%
35%
Sex for affection
25%
48%
Think about sex everyday
54%
19%
33
Natural selection has caused males to send their genes into the future by
mating with multiple females since males have lower costs involved.
However, females select one mature and caring male because of the
higher costs involved with pregnancy and nursing.
34