Transcript Memory

Nature and Nurture
• What is the difference
between behavior genetics
molecular genetics and
evolutionary psychology?
• What do we mean by
nature and nurture?
1
Behavior Genetics:
Predicting Individual Differences
Behavior Geneticists study our differences and weigh the
relative effects of heredity and environment
2
Behavior Genetics: Types of Research
 Minnesota Twin Studies - Monozygotic (mz) and
dizygotic (dz) twins separated at birth
 Adoption studies Comparisons of adopted
children and their biological and adoptive parents
 Temperament studies findings. Role of heredity,
predispositions and stability
3
Minnesota Twin Studies
Studying the effects of heredity and environment on two
sets of twins, identical and fraternal, has been valuable
4
MZ Twin Studies
Identical Twins Reared Together v.
Identical Twins Reared Apart
Same genes,
Same environment
Same genes
Different environment
Greater difference between these two groups indicates greater
role of the environment (“nurture”)
5
Separated MZ Twins and Similarities
A number of studies compared identical twins raised
separately from birth, or close thereafter, and found
numerous similarities. Exploring the Traits of Twins
NG Twins
Separated Twins
Personality, Intelligence
Abilities, Attitudes
Interests, Fears
Brain Waves, Heart Rate
6
Twin Studies
Similarity of IQ Test Scores in Twins
Correlation
0.9
0.8
0.7
0.6
0.5
Identical twins reared Identical twins reared
together
apart
Criticisms:
1) Adoption agencies try
to place twins in similar
families so the variation
in environment may be
small, and
2) There is a very limited
sample
Heritability (Coefficient)
• The percentage of trait variation within a group that can be attributed
to genetic differences (v. environmental). For example, assume you all
were raised in identical, enriched environments – all differences in I.Q.
are then due to genetic difference (100% heritability)
• Determined by comparing MZ twins separated at birth. Remember,
heritability estimates are NOT measures of the importance of genes in
the production of a trait (e.g., I inherit 65% of my intelligence from…)
8
Group Differences
If genetic influences help explain individual diversity in
traits, can the same be said about group differences?
No. Individual differences in weight and height are
heritable (within a group), but nutritional influences
have made westerners heavier and taller than their
ancestors were a century ago, or others in the
developing world. The notion of maximal expression
9
Adoption Studies
Is child
more like
adoptive
parents…
…or biological
parents?
Adoption Studies
0.5
0.4
0.3
0.2
0.1
0
Biological parents
•
Similarity of Temperament Between Adopted
Children and their Parents
Correlation Coefficient
Correlation Coefficient
Similarity of Values Between Adopted
Children and their Parents
Adoptive parents
0.6
0.5
0.4
0.3
0.2
0.1
0
Biological parents
Adoptive parents
Note: Two related siblings that grow up in the same family are strikingly different in
personality (as I’m sure many of you can attest to).
Temperament Studies
Temperament refers to a person’s stable emotional
reactivity and intensity. Identical twins research and
that of Jerome Kagan (reactivity studies) suggest that
temperament is fixed or stable, and under some genetic
influence. Environmentalists vehemently disagree
Kagan The Temperamentalist
12
Nature and Nurture Dynamic
While some traits are fixed (ear lobes, tongue curl, PTC)
most behavioral traits are modified by or under the
influence of environmental experience. Our previous
understanding of Nature versus Nurture turned out to
be a false dichotomy
Genes can influence traits which affect responses. And
so, environment can affect gene activity. In such
circumstances genes are allowed to be expressed (e.g., a
genetic predisposition to restlessness evokes an angry
response from a parent which, in turn, results in fuller
expression of the genetic tendency.
Related notion of maximal expression
13
Role of Environment
• What do we mean by environment?
• Prenatal experiences, early childhood experience,
parental and peer influence, culture…
– Early experience – Rosenzweig’s and Greenough’s
enriched environment studies, issue of
developmental plasticity, synaptic pruning, and
epigenetics research
– Peer influence over parental? Judith Harris
– Cultural influences, e.g., collective v.
individualistic societies, cross-cultural research
notes similarities and variations across culture
14
Prenatal Environment
Identical twins who share the same placenta are more
alike than those who do not, suggesting prenatal
influences on psychological traits
15
Experience and Brain Development
Early postnatal experiences affect brain development.
Rosenzweig et al., showed that rats raised in enriched
environments developed thicker cortices than those in
impoverished environments. Subsequent work by
Greenough
16
The Role of Parenting? Peer Influence?
While biological inputs are significant, parenting does
have a considerable effect on both biologically related
and unrelated children
Parenting Influences
children’s
Attitudes, Values
Manners, Beliefs
Faith, Politics
17
The Role of Peer Influence
Peers are influential in such areas as learning
to cooperate with others, gaining popularity,
and developing interactions
Judith Rich Harris’ Do Parents Matter?
18
Cultural Influences on Behavior
Cultures differ. Each culture develops norms – rules for
accepted and expected behavior. Men holding hands in
Saudi Arabia is the norm. Norms are behavioral
expectations; what is allowed to be by the group
19
Epigenetics and Gene Expression
• Epigenetics refers to changes in gene expression caused by
environmental factors, not by changes in the underlying
DNA sequence. Changes may remain for the remainder of
the cell's life and may last for multiple generations.
However, there is no change in the underlying DNA
sequence of the organism, instead, environmental factors
cause the organism's genes to behave (or "express
themselves") differently
• ScienceNow Epigenetics
• BBC Article
20
Reflections on Nature and Nurture:
Bio-PsychoSocial Influences
21
Molecular Genetics: Promises and Perils
Molecular geneticists are
currently seeking to identify
genes that put people at risk
for specific disorders
This raises ethical issues
involving choices to abort or
even alter genes related to
genetic predispositions Mental illness, Addiction?
Criminality? Homosexuality?
22
Evolutionary Psychology
Evolutionary
psychology studies
why we as humans are
alike. In particular, it
studies the evolution of
behavior and mind
using principles of
natural selection
23
Human Sexuality
Gender Differences in Sexuality
Question (summarized)
Male
Female
Casual sex
60%
35%
Sex for affection
25%
48%
Think about sex everyday
54%
19%
24
Evolutionary Psychology
 Critiquing the Evolutionary Perspective
 The central premise is impossible to prove.
Predictive power is null.
 It’s hindsight bias, reductionist and dangerous.
Potential justification for harmful behaviors and
attitudes
 EPs respond
 EP does not imply genetic determinism, in fact
adaptation is premised in environmental
influence
 EP instructs us to change our destructive
evolutionary behaviors
25