Behavior Genetics and
Evolutionary
Psychology
Module 6
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Behavior Genetics and Evolutionary
Psychology
Behavior genetics: Predicting
Individual Differences
 Genes: our Codes for Life
 Twin Studies
 Temperament Studies
 Heritability
 Gene-Environment Interaction
 The New Frontier: Molecular Genetics
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Behavior Genetics and Evolutionary
Psychology
Evolutionary Psychology:
Understanding Human
Nature
 Natural Selection
 An Evolutionary Explanation of
Human Sexuality
 Critiquing the Evolutionary
Perspective
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Nature, Nurture and Human
Diversity
Similarities
Differences
Genes: Same set of
chromosomes
Genes: Genetic anomalies
may make us different
Biology: The organs and
body function the same
Biology: May change
during development
Brain: Same brain
architecture
Brain: Asymmetry of brain
across genders
Behaviors: Speak language
Behavior: Speak different
languages
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Evolution
Natural Selection
• The evolutionary process by which some genes in a
population spread more than others do, causing species to
change over time.
• Principles of Natural Selection:
– Within a species, no two are alike.
– Individuals differ in their suitability to their
environment.
– Those better suited are more likely to survive and
reproduce.
– Reproduction perpetuates the genes of better suited
individuals.
Evolution
Natural Selection
• Adaptations
– Advantageous physical and psychological
traits that are inherited
• Mutations
– Random gene copying errors that can
spark evolution by natural selection
Behavior Genetics: Predicting
Individual Differences
Behavior Geneticists study our differences and
weigh the relative effects of heredity and
environment.
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Genes
What Genes Are and How They
Work
Genetic Building Blocks
Genome
Genome is the set of complete instructions for
making an organism Containing all the genes in
that organism. Thus human genome makes us
human and the genome for drosophila makes it a
common house fly.
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Genes
How Genes Affect Behavior
Genotype
The underlying DNA sequence that an
individual inherits
Phenotype
An organism’s observable properties,
physical and behavioral
Genes contribute more directly to physical traits
than to psychological characteristics.
The Nature-Nurture Debates
The Pursuit of Heritability
• Nature-Nurture Debate
– The debate over the extent to which
human behavior is determined by
genetics and the environment.
• Heritability
– A statistical estimate of the percentage of
the variability of a trait within a group that
is attributable to genetic factors.
Twin Biology
To study the effects of heredity and
environment two sets of twins, identical and
fraternal, have come in handy.
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Twin and Procedures
Behavior geneticists study the effects of shared
and unique environments on total or partial
genetic makeup.
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Separated Twins
A number of studies have looked at identical
twins raised separately from birth or close there
after and have found a number of similarities.
Separated Twins
Personality, Intelligence
Abilities, Attitudes
Interests, Fears
Brain Waves, Heart Rate
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Adoption Studies
Opposed to twin studies, adoption studies
suggest that adoptees (who may be biologically
unrelated) tend to be different from their
adoptive parents and siblings.
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Adoptive Studies
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 genes?
Ultimate question: Does parenting have an effect?
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Parenting
Parenting does have an effect on biologically
related and unrelated children.
Parenting Influences
children’s
Attitudes, Values
Manners, Beliefs
Faith, Politics
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Temperament Studies
Temperament refers to a person’s stable
emotional reactivity and intensity. Identical
twins express similar temperaments, suggesting
heredity predisposes temperament.
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The Nature-Nurture Debates
Genetic Influences
• Other studies of twins and adoptees show:
– Genetic factors account for some differences in
intelligence, verbal and spatial abilities, criminality,
vocational interests, and aggressiveness.
– There is a genetic component to psychological
disorders, such as alcoholism, depression, and
schizophrenia.
– And, there is evidence for a genetic link to
people’s attitudes toward issues and activities.
The Nature-Nurture Debates
Genetic Influences
Heritability of Various Human
Attributes
• The role of genetic
factors is shown by
the extent to which
identical twins are
more similar to each
other than are
fraternal twin pairs.
The Nature-Nurture Debates
Genetic Influences
Heritability of Attitudes
• This study involved
672 twins who rated
their attitudes on
various issues and
activities.
• The results show
some influence of
genetic factors.
Gene-Environment Interaction
Genes can influence traits which affect
responses, and environment can affect gene
activity.
A genetic predisposition that makes a child
restless and hyperactive, evokes angry
responses from his parents. A stressful
environment can trigger genes to manufacture
neurotransmitters leading to depression.
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Molecular Genetics:
Promises and Perils
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 where fetuses are suspected
of having such disorders
But this opens up a real concern about ethical
issues involving such choices.
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Evolutionary Psychology:
Understanding Human Nature
Molecular genetics studies why we as
organisms are distinct.
Evolutionary psychology studies why we as
humans are alike. In particular it studies the
evolution of behavior and mind using
principles of natural selection.
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Artificial Selection
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.
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Human Traits
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?
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Human Sexuality
Gender Differences in Sexuality
Males and females to a large extent behave and
think similarly. Differences in sexes arise with
regards to reproductive behaviors.
Question (summarized)
Male
Female
Casual sex
60%
35%
Sex for affection
25%
48%
Think about sex everyday
54%
19%
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Mating Preferences
Natural selection has pressurized males to send
their genes into the future by mating with
multiple females because of lower cost involved.
But females because of higher costs involved
with pregnancy and nursing select one mature
and caring male.
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Mating Preferences
In order for males to pass their genes into future
they look for youthful appearance in females.
Females on the other hand look for maturity,
dominance, affluence and boldness in males.
Data based on 37 cultures.
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Critiquing the Evolutionary
Perspective
Evolutionary psychologists take a behavior and work
backward to explain it in terms of natural selection.
Evolutionary psychology proposes genetic determinism
and undercuts morality in establishing society.
Where genders are unequal, gender preferences are
wide, but closely equal, preferences narrow down.
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Evolutionary Psychologists Reply
Evolutionary psychologists argue that we need to test
behaviors that expound evolutionary principles.
Evolutionary psychologists remind us how we have
adapted, but does not dictate how we ought to be.
Males and females are more alike than different, if we
study these differences we can establish their causes.
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