Psychology 1230: Psychology
of Adolescence
Don Hartmann
Fall 2005
Lecture 8b: Heredity &
Environment
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Quiz 1 Information
80% of the multiple choice items will
come from the study guides. The MC
portion of the quiz will contain 30-40
items from the following sources:
– 3-5 questions from each chapter,
– 1-2 items from each lecture, and
– 0-1 questions from each handout.
The essay portion will include 3-5 relatively
brief essay questions taken from the study
guides. You will have some choice over
which questions you can choose to answer
2
WEB Discussion Process
Group
Whippets
Hotties
4♀+1♂
GypsyMafia
JusticeLeague
Psyched
PithHelmets
MAJACS
#1 due
09/12
09/13
09/19
09/20
09/21
09/22
09/23
09/26
#2 due
#3 due
#4 due
#5 due
---------Note: Anyone can contribute to any WEB discussion; group members are responsible to
summarizing the discussion. The last day to contribute to any discussion is 3 days
before the due date.
3
Handout Summary
Handout
Date
14. HO-Completing a Film Review*
15. HO-Preparing a Book Review
16. Completed Class Locator
08/31
17. Lect. #4: Introduction to Theory
18. Lect. #5: Bandura
19. Supplemental Lecture: Termpaper
20. Lect. #6: Method I
21. Lect. #7: Method II
22. Lect. #8: Puberty
23. Lect. #8b: Heredity & Envir.
----*Indicates handouts discussed in class.
WEB
Date
08/14
08/14
09/02
09/02
09/06
09/07
09/09
09/13
09/16
4
Supplementary References
Plomin, R.,
DeFries, J. C.,
McClearn, G. E.,
& Rutter, M.
(1997). Behavioral genetics (3rd ed.).
New York: W. H. Freeman.
Scar, S. (1993).
Biological and
cultural diversity:
The legacy of
Darwin for development. Child
Development, 64, 859-865.
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Overview
Questions:
– Why is it difficult to assess the contributions of heredity &
environment on, say, the timing of puberty?
– What is a heritability coefficient, and why should we care?
– What are the contributions of shared & non-shared
environments to our behavior?
– What is a GEI, and why should we care?
Intersects with the material in our text on pp. 109-112 and
152
Topics
– Heritability Coefficients
– Shared & Non-shared Environments
– Genotypic-Environment Interactions
Next: Lecture #9 (Piaget)
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Heredity or Environment?
7
Comments on Behavioral Genetics
Definition: Behavioral genetics—that field that
seeks to discover the influence of heredity
and environment on individual differences
in human traits and development
Important methods
– Study of pedigrees: A simplified diagram of a
family's genealogy that shows family
members' relationships to each other and how
a particular trait or disease has been inherited.
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More on Methods: Adoption Studies
– Adoption studies—e.g., the similarity of
adopted children to their adopted parents and
to their biological parents.
If adopted children more closely resemble their
biological parents than their adopted parents, we
would conclude that the trait in question was at least
partly hereditary determined (assuming the study
was well done)
If adopted children more closely resemble their
adopted parents that their biological parents, we
would conclude that the trait in question was at least
partly environmentally determined (assuming…)
For example, in one large study, the biological
mother-adopted child correlation was 0.37 whereas
the adoptive mother-adopted child correlations was
0.22.
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More on Methods: Twin Studies
– Comparisons of trait resemblence in identical
& fraternal twins (kinship studies).
For example, in studies involving more than
10,000 pairs of twins, the average “IQ”
correlations are 0.85 for identical twins and
0.60 for same-sex fraternal twins.
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The World’s First Genetically Engineered Human
Hits Adolescence: ‘We buy you the best genes in
the world — for this?’ (Thinks Dad.)
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Summarizing Twin Studies
Heritability Coefficients:
Used to estimate the degree to which
a characteristic is inherited, say IQ or
shyness
Compares the correlation between
monosygotic twins (rMZ) and between
dizygoticl twins (rDZ)
If (rMZ) > (rDZ), heritability coefficient
>0
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More on the Hereditability
Coefficient
For example, if the rMZ = .85, and the rDZ =
.60, H = 2(.85-.6) = 2(.25) = .50. And
this value indicates at least a moderate
tendency for the characteristic in question
to be inherited
For those other weirdos who like formulas, the
formula for H is as follows (the rest of you close
your eyes):
H = 2[rMZ – rDZ]
Interpretation requires some important
assumptions.
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Environments—Shared & Nonshared
The contribution of non-shared environments:
NSE = 1 - rMZ
Some caveats regarding shared environments
(Hoffman)—as they may have anomalous effects:
– Can create differences as well as similarities (e.g., effect
of divorce on different age children)
– Non-identical twins may exaggerate differences
The effects of shared environments, obviously,
are strongest for dimension on which siblings are
treated alike (e.g., religion)
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Genetic Determinants of
Behavior
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Genotype/Environmental
Interactions (GEIs): 1
Further messes our understanding
of the contributions of nature and
nurture to our behavior (phenotype)
– In certain cases, genotypes and environments
interact in atypical manners to produce
phenotypes—e.g., your genotype might help
determine the environment to which you are
exposed!
– As a result these GEIs make it difficult to
distinguish genetic from environmental causes
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Genotype/Environmental
Interactions (GEIs): 2
Assume we wanted to apportion causes of a
behavior to one of two categories: Genetic (G)
and Environment (E). Where would we put the
following example in which the focus is on a kids
reading speed: Cause A (reading books) was E
but was caused by the child’s G (the child’s
hereditary predisposition to be smart). So do we
put reading books in the G category or in the E
category?
G
? Reading ?
Books
E
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Passive G/E Interactions
Parents contribute to their children by providing
them with genes and with an environment in
which they can grow—and the environment which
they provide is dependent on the parents' genes
Consider EXERCISE. Parents who are genetically
prone to exercise may provide an abundance of
exercise equipment and encouragement. The
equipment and encouragement are clearly
Environment (E), but are they at some deeper
level? Both may be functions of the parents’
Genes (G), right?
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Evocative G/E Interactions
Kids with different genes may evoke different
reactions from their environment . E.g.,
smiley babies are responded to differently
in their social environments than are
smileless babies. So the responses of
observers of the smiling child are
environmental facilitators of the child’s
increasing sociability. But the child “created”
this environment by his/her genetic
predisposition to be smiley. So are the
adults who promote the child’s sociability G
causes or E causes?
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Active G/E interactions (Niche
picking)
The environments children choose will be
dependent upon their genes—will be compatible
with their genetic predispositions.
E.g., smart kids chose to be in intellectually stimulating environments where
they become even smarter, whereas
not-so-smart kids chose less intellectually stimulating environments where
their intellectual growth will be decelerated.
So do these more and less intellectually
stimulating environments belong in the G
category or the E category? It is a puzzle, right?
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Summary of Puberty Lecture
Heritability coefficients
Shared & Non-shared
Environments
Genotype- Environmental
Interactions (GEIs)
Next: Lect. #9 (Piaget)
Go in Peace
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