Transcript Nature v. Nurture

Behavior typical of every culture
 Communicate both verbally and nonverbally, enforce rules of
etiquette, and show favoritism toward groups member,
including preference for kin over non-kin.
 They avoid incest, fear snakes, and exchange gifts.
 Demonstrate modesty in sexual behavior and bodily
functions (even when clothes are non worn).
 Labor is divided by age and by gender
 People form beliefs about death and disease
 Men are more aggressive and women provide child care.
 ALL cultures have taboos, sanctions against society, and
mechanisms to deal with theft, murder, and rape.
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People everywhere recognize marriage
People mimic, flirt, envy, empathize, joke, tease, and dance
and make music.
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What is the difference
between behavior
genetics and evolutionary
psychology?
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What do we mean by
nature and nurture?
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http://www.youtube.com/
watch?v=8mvZ4EbPbME
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Behavior Genetics: the study of the relative effects of genes
and environment on behavior.
Behavior Geneticists study our differences and weigh the
relative effects of heredity and environment.
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Genes – biochemical units of heredity that make up a
chromosome
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Chromosome – Threadlike structures made of DNA
molecules that contain genes (46 total, 23 from each parent)
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DNA (deoxyribonucleic acid) – complex molecule that
contains genetic information that makes up chromosomes
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Cell -> Nucleus -> Chromosomes -> DNA -> Genes
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Chromosomes containing DNA (deoxyribonucleic acid)
are situated in the nucleus of cells.
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In humans, each cell normally
contains 23 pairs of
chromosomes, for a total of 46.
Twenty-two of these pairs,
called autosomes, look the same
in both males and females.
The 23rd pair, the sex
chromosomes, differ between
males and females.
Females have two copies of the
X chromosome, while males
have one X and one Y
chromosome.
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Segments within DNA consist of genes that make
proteins to determine our development
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Genes made up of nucleotides
(A,T,C, or G)
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Genome – complete instructions
for making an organism
consisting of all genetic material
in its chromosomes
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Humans have about 30,000
different genes
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Does anyone know the animal
humans are most genetically
related to?
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All organisms have many genes
corresponding to various
biological traits, some of which
are immediately visible, such as
eye color or number of limbs,
and some of which are not, such
as blood type, increased risk for
specific diseases, or the
thousands of basic biochemical
processes that comprise life.
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Genome the set of complete
instructions for making an
organism. It contains all genes in
that organism. The human
genome makes us human, and the
genome for drosophila makes it a
common house fly.
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Genes are responsible for predisposing our appearance and
behavior, not concretely determining either.
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Predisposition – a situation that allows something else to
occur but doesn’t necessarily cause it to occur; “Her genetic
makeup left her with a predisposition to develop
Alzheimer's.”
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Mutations – random error in gene replication that lead to a
change in genetic code
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Natural selection – the
idea that , among the
inherited trait variations,
those contributing to
survival will most likely be
passed on to future
generations.
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Adaptation – species
changing genetically to
better survive in their
environment.
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Identical twins – twins that develop from a single
fertilized egg and then split in half; are genetically
identical.
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Fraternal twins – twins that develop from separate
eggs; no more related genetically than normal
siblings.
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Twin studies have discovered that identical twins
are strikingly similar is intelligence, attitude and
even brain waves!
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 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
 The New Frontier: Molecular Genetics – Specific
genes for specific behaviors and disorders
 Epigenetics changes in gene expression caused by
environmental factors, not by changes in the
underlying DNA
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Studying the effects of heredity and environment on two
sets of twins, identical and fraternal, has been valuable
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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”)
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Herit – comes from the word inherit.
 To inherit means to process something that someone else has given
you
 We inherit traits and qualities from our parents.
 -ability – means “capable.”
 If a trait is genetically passed from one generation to the next, then it
is capable of showing up in the offspring of parents who possess the
genes for that trait.
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The percentage of trait variation
within a group that can be
attributed to genetic differences
(v. environmental).
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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…)
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Sara is very
outgoing and
agreeable
Suzy is timid
and nonconforming
If this pair of IDENTICAL twins is the population, the
percent of the personality differences attributable to
genetic differences between them is??
The heritability is 0%.
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Joe and Hank are
not related. At
birth, both were
placed in identical
environments that
remained identical
until they were 10
years old
At 10, Joe is outgoing
and friendly
At 10, Hank is withdrawn and shy
In this (very small) population, what is the heritability of their
personality traits? In other words, what percentage of the difference
is attributable to genes? Heritability is 100%
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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, but nutritional influences have made
westerners heavier and taller than their ancestors were
a century ago, or others in the developing world.
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Average risk of schizophrenia among biological relatives of people with
schizophrenia.
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Similarity of IQ Test Scores in Twins
Correlation
0.9
0.8
0.7
Criticisms:
1) Adoption agencies try to
place twins in similar
families so the variation
in environment may be
small.
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0.5
Identical twins reared
together
Identical twins reared
apart
2)
There is a very limited
sample
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Studies of adopted children
show that they exhibit similar
personality traits of their
biological parents.
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However, adopted children tend
to be smarter, more productive
and more successful than their
biological parents.
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Nurture is back in the game!
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Similarity of Temperament Between Adopted
Children and their Parents
0.5
0.4
0.3
0.2
0.1
0
Biological parents
Adoptive parents
Correlation Coefficient
Correlation Coefficient
Similarity of Values Between Adopted
Children and their Parents
0.6
0.5
0.4
0.3
0.2
0.1
0
Biological parents
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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).
A number of studies compared identical twins raised
separately from birth, or close thereafter, and found
numerous similarities.
Separated Twins
Personality, Intelligence
Abilities, Attitudes
Interests, Fears
Brain Waves, Heart Rate
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Is child more
like adoptive
parents…
Adoptive Parents - Nurture
…or biological
parents?
Biological Parents - Nature
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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
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Kagan The Temperamentalist
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http://www.boston.com/news/globe/i
deas/articles/2004/08/29/the_temper
amentalist?pg=full
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Are parents to blame for
success/failure of children?
Studies say “not really”.
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Siblings raised together
tend to be as different
personality-wise as two
random people on the
street.
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What do we mean by environment?
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Prenatal experiences, early childhood experience,
parental and peer influence, culture
 Early experience – Rosenzweig’s and Greenough’s
enriched environment studies, developmental
plasticity, synaptic pruning, Bronfenbrenner’s proximal
processes theory, and epigenetics research
 Does peer influence exceed parental? Judith Harris
 Cultural influences, e.g., collective v. individualistic
societies, cross-cultural research notes similarities and
variations across culture and some of their sources
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Prenatal experiences, early childhood
experience, parental and peer influence,
culture.
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Early experience – Rosenzweig’s and Greenough’s
enriched environment studies, developmental
plasticity, synaptic pruning, Bronfenbrenner’s
proximal processes theory, and epigenetics research
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Does peer influence exceed parental? Judith
Harris
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She challenges the idea that the personality of adults is determined chiefly by the way
they were raised by their parents.
 She looks at studies which claim to show the influence of the parental environment and
claims that most fail to control for genetic influences.
▪ For example, if aggressive parents are more likely to have aggressive children, this is
not necessarily evidence of parental example; it may also be that aggressiveness has
been passed down through the genes.
▪ Harris argues that children identify with their classmates and playmates rather than
their parents, modify their behavior to fit with the peer group, and this ultimately
helps to form the character of the individual.
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Cultural influences, e.g., collective v. individualistic societies,
cross-cultural research notes similarities and variations
across culture and some of their sources
 The individualistic countries tend to put rights and privacy first. People in
these societies tend to overvalue their own skills and overestimate their own
importance to any group effort. People in collective societies tend to value
harmony and duty. They tend to underestimate their own skills and are more
self-effacing when describing their contributions to group efforts.
 Collectivist societies tend to pop up in parts of the world, especially around
the equator, with plenty of disease-causing microbes. In such an environment,
you'd want to shun outsiders, who might bring strange diseases, and enforce
a certain conformity over eating rituals and social behavior.
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Identical twins who share the same placenta are more
alike than those who do not, suggesting prenatal
influences on psychological traits
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For our brains to reach their
developmental potential, early
experience is CRITICAL.
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Children raised in abusive homes
tend to be less intelligent that
children raised in loving
environments.
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Score one for nurture!
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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
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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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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
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Discover Article
1.
Describe Jirtle and Waterland’s experiment and its significance
Explain how epigenetics is related to, but different than, genetics
How does epigenetics change the “genes as fate” mentality?
Describe Meaney’s research and the challenges it offers to the
traditional nature-nurture debate regarding behaviors. What are the
social and political implications of this research?
Briefly describe Pembrey and Bygren’s work in the area of human
epigenetics
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3.
4.
5.
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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?
http://www.youtube.com/watch?v=lP1cCjBk
WZU
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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
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Peers hold a heavy influence on the behaviors of individuals
(i.e. smoking, drinking, promiscuity )
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Bandwagon phenomenon
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“Fitting In”
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Parents influence behaviors of children by supplying them
the environment from which they have to work within (i.e.
parents “choose” which neighborhood to live in)
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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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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
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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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 Ethology (Lorenz) – science of animal behavior. Fixed
action patterns- A fixed action pattern (FAP) is an
instinctive behavioral response triggered by a very specific
stimulus. Once triggered, the FAP behavior can’t be
stopped ‘midstream’, but must play out to completion.
Yawning is one example.
 Sociobiology – Species-wide social behavior i.e, aggression
and reciprocal altruism, kin selection
 Are humans subject to behavioral similarities and
tendencies that allow us to pass on our genes? Are
behaviors based in natural selection, i.e., reproductive
success
 Evolved psychological mechanisms (EPM) e.g., sexual
behavior, mating preferences, parental investment, kin
selection, incest taboos, fear of strangers, heights, snakes.
Do you think these are inborn?
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Gender Differences in Sexuality
Question (summarized)
Male
Female
Casual sex
60%
35%
Sex for affection
25%
48%
Think about sex everyday
54%
19%
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Males look for youthful appearing females in
order to pass their genes into the future. 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
 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
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