Nature and Nurture

1
Nature and Nurture

• What is the difference between behavior genetics
  molecular genetics and evolutionary psychology?
• What do we mean by nature and nurture?

2
Behavior Genetics Predicting Individual
Differences
Behavior Geneticists study our differences and
weigh the relative effects of heredity and
environment
3
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

4
Minnesota Twin Studies
Studying the effects of heredity and environment
on two sets of twins, identical and fraternal,
has been valuable
5
MZ Twin Studies

• Identical Twins Reared Together v.
• Identical Twins Reared Apart
• Same genes, Same genes
• Same environment Different environment

Greater difference between these two groups
indicates greater role of the environment
(nurture)
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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
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Twin Studies

• Criticisms
• Adoption agencies try to place twins in similar
  families so the variation in environment may be
  small, and
• There is a very limited sample

8
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)

9
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
10
Adoption Studies
Is child more like adoptive parents
or biological parents?
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Adoption Studies

• Note Two related siblings that grow up in the
  same family are strikingly different in
  personality (as Im sure many of you can attest
  to).

12
Temperament Studies
Temperament refers to a persons 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
13
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
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Role of Environment

• What do we mean by environment?
• Prenatal experiences, early childhood experience,
  parental and peer influence, culture
• Early experience Rosenzweigs and Greenoughs
  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

15
Prenatal Environment
Identical twins who share the same placenta are
more alike than those who do not, suggesting
prenatal influences on psychological traits
16
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
17
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 childrens
Attitudes, Values
Manners, Beliefs
Faith, Politics
18
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?

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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
20
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

21
Reflections on Nature and Nurture
Bio-PsychoSocial Influences
22
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?
23
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
24
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
25
Evolutionary Psychology

• Critiquing the Evolutionary Perspective
• The central premise is impossible to prove.
  Predictive power is null.
• Its 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