2.2 To what extent does genetics influence behavior?

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2.2 TO WHAT EXTENT DOES
GENETICS INFLUENCE
BEHAVIOR?
Back up your response with research
BEHAVIORAL GENETICS
Behavioral genetics deals with the
understanding of how both genetics and the
environment contribute to individual variations
in human behavior.
 Is a single gene responsible for complex
behaviors?
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NO, behaviors is brought about through a series of
building blocks (genes)
DIATHESIS STRESS
MODEL
Diathesis stress model argues that depression
may be the result of the interactions of a “genetic
vulnerability” and traumatic environmental
stimuli in early childhood.
 BUT…..do all siblings raised in the same
environment develop depression …..?

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There is no single cause and effect relationship
between genes and behavior.
GENETIC RESEARCH
GENETIC RESERCH
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Method of Study: Correlation
How different variable may co-vary
 No manipulation of the variables, thus no cause and
effect can be established.

TWIN STUDIES, FAMILY STUDIES &
ADOPTION STUDIES
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Twin Studies
Monozygotic (100%) vs dizygotic (50%)
 The higher the genetic relationship, the more similar
the individuals should be in the trait being inherited.
 Concordance rate = correlation found in twin studies.
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Family Studies
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More representative of the population
Adoption Studies
Allow the comparison of biological and environmental
influences
 Not representative of the population

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Criticized for selected placement
INTELLIGENCE (REFERENCE PG 54)
Is intelligence inherited or is it the result of the
environment?
 What is intelligence?
 How can it be measured?

BE A THINKER: ON THE INTERNET YOU WILL
FIND FREE IQ TEST. GO ONLINE AND TAKE AT
LEAST THREE DIFFERENT TESTS. EACH TEST
SHOULD GIVE YOU A SCORE.
1.
2.
3.
Do you think that these tests appropriately
evaluate your intelligence?
Do you feel that the tests were adequate? Why
or why not?
How would you change the tests to make them
reflect more accurately what you consider to be
your intelligence?
RESEARCH IN INTELLIGENCE

Meta-analysis: the statistical synthesis of the
data from a set of comparable studies of a
problem that yields a quantitative summary of a
pooled result.
Example: Bouchard and McGue (1981) reviewed 111
studies of IQ correlation between siblings from
research on intelligence from around the world.
 Results: the closer the kinship the higher the
correlation for IQ.

BOUCHARD (1990) MINNESOTA TWIN STUDY IS
A longitudinal study (1979) of MZ raised apart vs
MZ raised together.
 70% IQ attributed to genetic inheritance
 30% IQ to other factors
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Criticism of the study:
Self selected sampling. Bouchard relied on the media
to recruit participants
 Ethical concerns about reuniting the twins
 No adequate control to establish frequency of contact
between twins prior to study.
 Cannot assume twins raised in same environment
received identical treatment.

SCARR & WEINBERG (1977) AND HORN ET AL.,
(1979)
ADOPTION STUDIES
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Adoptive children and natural biological children
raised by the one biological parent should
demonstrate no difference in IQ if environment is
the contributing factor in intelligence.
Researchers found no significant difference in IQ
correlations
Adoptive parents were wealthy, white, middle class,
high IQ
 Adopted children were from poor, lower class
background, with lower IQ parents.

WAHLSTEN 1997
Transferring an infant from a low-socio-economic
status to a home where parents have a higher
socioeconomic status improved IQ by 12-16
points.
 Enriched environment?

CONCLUDING THOUGHT ON INTELLIGENCE
Is intelligence based on knowledge or the ability
to problem solve?
 Hainer et al. (1988)

“Less Effort Hypothesis”
 When problem solving (reasoning) individuals with
high IQ had lower metabolic rates than those with
low IQ
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Plomin and Petrill (1977)
Socio-economic class appears to be an important
environmental factor in developing intelligence.
 “Poverty - not genetic inferiority – is key to
understanding the differences in intelligence.”
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CONCLUDING THOUGHT ON INTELLIGENCE
CONT.,
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The Flynn Effect
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The rise in average scores of IQ tests in most parts of
the world over the last century.
Neisser, 1997 documented :
The average score increase by 3 points every 10 years
 Cause is unknown

Is it an increase in intelligence?
 Is it the ability to manipulate the test taking process?
 Does better nutrition , improved education, added
technology add to the effect?
 What effect does the highly visual environment have ?
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SOCRATIC SEMINAR : THE
NATURE OF INTELLIGENCE
IB Question: To what extent does genetic
inheritance influence behavior?
THE SEMINAR WILL FOCUS ON 3
QUESTIONS
1.
2.
3.
How do we define intelligence – and why does it
matter?
To what extent is intelligence biological? (what
are the strengths and limitations of a purely
biological argument?)
Can intelligence change over time? What are
the implications for schools if we find that
intelligence has a biological basis and cannot be
changed?
You will use the information gathered to create a
graphic organizer to answer the question: To what
extent does genetic inheritance influence behavior?
2.2 WHAT ROLE DOES
EVOLUTION HAVE IN BEHAVIOR?
DARWIN,(1871) “THE DESCENT OF MAN”
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Humans have a number of behaviors in common
with animals.
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Mate selection
Love of mother to offspring
Self-deprivation
Facial expressions humans share with primates.
Humans share many of the same feelings as animals
EVOLUTION AND SPATIAL MEMORY
TETSURO MATSUZAWA (2007)
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Do chimps have better spatial memory than
humans?
Read study
EVOLUTIONARY PSYCHOLOGY
As genes mutate, those that are advantageous
are passed down through natural selection.
 Evolutionary Psychologist attempt to explain
how certain human behaviors explain the
development of our species over time.
 Natural selection does not select the behavior – it
only selects the mechanisms that produces the
behavior.

Fessler (2006) – evolution of disgust. (pg. 58)
 Curtis et al., (2004) 
EXAMINING THE EVOLUTIONARY
ARGUMENT – THINGS TO CONSIDER
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Difficult to prove empirically
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susceptible to conformational bias - they see what
they expect.
Little is known about behavior of early Homo
sapiens
 Cultural differences are often overlooked as a
role in evolutionary differences.
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ETHICAL CONSIDERATIONS IN RESEARCH
INTO GENETIC INFLUENCES OF BEHAVIOR
How will the participants privacy be protected?
 What will happen to any of the genetic material
obtained from the study?
 Informed, written consent must be given, with
the full understanding of the aim of the research.
 Confidentiality and full anonymity
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Protect from insurance co., employers, police military
etc.
What do you do if the results show information
that can harm the participant?

Misidentified paternity, adoption, genetic disorders.

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