Transcript Psychology 10th Edition David Myers

Nature,
Nurture,
and
Human
Diversity
Modules
11, 12, 13
Behavior Genetics:
Predicting Individual Differences
The topics in the text:
1. genes
2. twin and adoption studies
3. temperament and heredity
4. molecular genetics
5. heritability
6. gene/environment interaction
"A devil, a born devil, on whose
nature Nurture can never stick;
on whom my pains Humanely
taken, all, all lost, quite lost."
William Shakespeare
(Spoken to Calaban by Prospero
in "The Tempest")
Behavior genetics
have always been
controversial . . .
American Eugenics movement
● Alexander Graham Bell, 1881
– Island (Martha's Vineyard) deaf population
– Genetic cause
– Supported more restrictive immigration
● Proposed controlling immigration
Immigration Restriction Act 1924
● Compulsory Sterilization Policies
● 1930s rise of German Nazi party
Nazi Eugenics policies
Influenced by
American, Swedish,
and British Eugenics
movements
Eugenics
See flags of other
countries on 1936
Nazi poster
American laws
against interracial
marriage not
overturned until
1967
Cdn sterilization
laws exist up to
1970
=Politically sensitive topic
 “…Are group differences due to
biological differences…?”
 Beh Genetics has dangerous potential
for political abuse
Essentialism
Dehumanization
 Researchers today respect the need
for extreme cautiousness in genetic
explanations of behavior
Overview:
Nature/Nurture/Diversity Questions
 How do we explain traits that all humans may
have in common?
 How do we explain the origins of diversity,
the source of differences in the traits:
• between genders?
• among cultures?
• among individuals?
 But first, how do we investigate these issues?
GENES:
The Building Blocks of
Heredity and
Development
Genes are
parts of DNA
molecules,
which are
found in
chromosomes
in the nuclei of
cells.
DNA
(Deoxyribonucleic Acid)
DNA
• Watson and Crick (1953)
• Identified the molecule’s structure
– Double helix
– 4-letter alphabet code: A,G,T,C= 4 Nucleotides
– Mechanism of replication discovered
– DNA = an amazing little replicator
• Nobel Prize (1962)
"for their discoveries concerning the molecular
structure of nucleic acids and its significance for
information transfer in living material"
Chromosomes are made of DNA,
which are made of genes.
Chromosome:
threadlike structure
made largely of DNA
molecules
DNA:
a spiraling, complex
molecule containing
genes
}
Chromosomes and Inheritance
 The human genome includes 46
chromosomes in 23 sets
matched sets; each
chromosome has the same
gene locations.
 This includes the X and Y
chromosomes, not a matched
set in males, who are missing
some genes on the Y.
 A biological parent donates half
his/her set of chromosomes to
his/her offspring.
 We received half a set of
chromosomes from each
biological parent.
Genome
• The genetic blueprint for making a complete
human being
• Sequence is 99.9% the same among human beings
• .1% accounts for human diversity
Human Genome Project
• 2001
• Find all the genes along the DNA strand in each
chromosome
• Much lower number of genes than expected (many
guessed 100,000, but were only 25,000)
Human vs Bonobo: 3% difference
Bonobo vs Cm. Chimp: 1% diff
The Human Genome:
20,000 to 25,000 Genes
 Human genomes are so nearly
identical that we can speak of one
universal human genome.
 Yet tiny genetic differences make a
difference. If there is a:
 .001 percent difference in
genome, your DNA would not
match the crime scene/you are
not the baby’s father.
 0.5 to 4 percent difference in
genome, you may be a
chimpanzee.
 50 percent difference in
genome, you may be a banana.
The genome: an
organism’s entire
collection of genes
Genetic Variation
• Alleles
Variation in some nucleotide sequences in
a gene
• Genetic variation
Presence of alleles in a population
• Gene pool
Total variety of alleles in the population
• Population Genetics
Study of distributions of alleles and their
effects
Genetics
• Branch of biology that deals with the
mechanisms of heredity.
Heredity
• Transmission of genetic information from
one generation to the next
Behavior Genetics
• Study of how variation in genes affects
variation in behavior
Genotype
The underlying DNA sequence that an
individual inherits
Phenotype
An organism’s observable properties,
physical and behavioral
Polygenic
Involving many genes
Behavior Genetics
3 Goals of Behaviour Genetics
1. Determine % variation due to genetic
variation, and % due to
environmental influences
2. Determining how genes interact with
environment
3. Type of environmental influences that
are most important
Behaviour Genetics Methods
Selective Breeding
Family Studies
Twin Studies
Adoption Studies
Behavioural Genetics Methods
Selective Breeding
Belyaev (1969)
Belyaev (1969)
Domestication / tameness
● Occurs quickly
● Changes are wide ranging
Appearance:
Ears, tail, coat color
Temperament: Friendliness, Cuddliness
More social --> Easily trainable
HPA reactivity ↓
Serotonin ↑
(Hypothalamic-Pituitary Axis)
Family Studies
Genetic overlap is known
Siblings share how many genes? (50%)
Cousins share how many genes? (12.5%)
Measure similarity in traits.
Between siblings
Between parents and offspring
Between cousins . . . etc.
Problem?
Nature & Nurture are confounded.
Twin Method
(MZ) Monozygote (identical)
● similar prenatal environment
● similar rearing environment
● 100% shared genes
(DZ) Dizygote (fraternal)
● similar prenatal environment
● similar rearing environment
● 50% shared genes
Fraternal and Identical Twins
Fraternal “twins” from separate
eggs are not any more genetically
alike than other siblings.
Identical twin: Same sex only
Fraternal twin: Same or opposite sex
Twin and
Adoption Studies
To assess the
impact of nature
and nurture, how
do we examine
how genes make a
difference within
the same
environment?
 study traits of
siblings vs.
identical twins
 see if the
siblings vary
more than
twins
Identical vs. Fraternal Twins
Studies of twins in adulthood
show that identical twins are
more alike than fraternal twins in:
 personality traits such as
extraversion (sociability) and
neuroticism (emotional
instability).
 behaviors/outcomes such as
the rate of divorce.
 abilities such as overall
Intelligence test scores.
Twin and
Adoption Studies
How do we find
out how the same
genes express
themselves in
different
environments?
We can study the
traits of identical
twins as they grow
up, or if they were
raised separately
(e.g., the
Minnesota Twin
Family Study).
What proportion of human variation in
any major personality trait is due
to genetic variation at birth?
A)
B)
C)
D)
8%
18 %
40 %
70 %
Twin+Adoption Method
Minnesota Study of Twins
Reared Apart
● 2 Jim's from Ohio
● separated at birth
● met at age 39
● U Minnesota calls them up
● located 57 more MZ-Raised Apart twins
Twin+Adoption Method
Minnesota Study of Twins
Reared Apart
● 2 Jim's of
Ohio (1979)
Typical Heritability Findings
IQ
50-80%
Personality
30-50 %
Attitudes
20-30 %
Criticisms
1. Didn’t test them before them met and chatted.
2. Small sample size (< 60 pairs).
3. Coincidences do happen; randomly chosen pairs
sometimes have very similar traits, including
even spouses, children, and dogs with identical
names.
4. Environments might be unusually similar, e.g.,
adoptive families tend to be more similar than
randomly selected families.
BUT: Above doesn’t explain why MZ > DZ
in similarity
Environmental Influences
Q: Which environmental influence has
more impact on personalilty?
Shared?
Presence of a TV, number of books…
Non-Shared?
Different friends, hobbies…
Shared
Environment
5%
Error
20%
Non-shared
Environment
Genetic
40%
35%
Parenting Does Matter
Despite the strong impact of
genetics on personality,
parenting does has an
influence on:
 religious beliefs
 values
 manners
 attitudes
 politics
 habits
The typical correlation between parents and
children for political party preferences…
.10
.20
.40
.70
r = .70
If parenting has an influence,
why are siblings so different?
 Siblings only share
half their genes.
 Genetic differences
become amplified as
people react to them
differently.
 Siblings are raised in
slightly different
families; the youngest
has more older
siblings and has older
(wiser? more tired?)
parents.
Temperament is another difference
not caused by parenting.
 From infancy into adulthood,
most people do not seem to
change temperament (defined
as a person’s general level and
style of emotional reactivity).
 According to some researchers,
three general types of
temperament appear in infancy:
• “easy”
• “difficult”
• “slow to warm up”
Temperament
def= early appearing differences
• What categories?
• Are temperaments stable?
• What causes diff.
temperaments?
Thomas & Chess (1977)
Temperamental Clusters
Easy: 40%, happy and easy to care for
Slow to warm up: 15%, “shy” personality
Difficult: 10%, tough on caretakers
Undifferentiated: 25%
Temperament
Jerome Kagan (1984)
• book: "Galen's Prophecy"
• 2 really clear baby types
uninhibited (bold)
inhibited (shy)
• only .40 corr, age 2-age11
• limbic system differences
reactivity to novelty, stress
Cross-fostering studies
Harlow and Suomi (1974)
• Nervous s babies
• Placed with calm moms.
Q: Can mothering style
alter baby temperament?
Cross-fostering studies
Video (7 mins)
"Bringing Up Monkey"
Is innate temperament
fixed or changeable?
Molecular Genetics
 Molecular genetics = study of the molecular
structure and function of genes.
 Molecular genetics might help us see exactly
how specific genes have an influence on
behavior.
 Genetic tests can reveal which people are at risk
for many physical diseases, and may soon
identify people at risk of mental health
disorders.
 Ethical issues: should people use genetic tests
to select sperm, eggs, and even embryos?
Molecular
BehaviorGenetics
Genetics
Molecular Behavior
Specific genes
- personality traits
- psychological disorders
Dopamine Receptor Gene
The “long repeat” version”
is associated with noveltyseeking and excitementseeking
e.g., Serotonin Transporter
Genes and the Environment
Genotype-Environment Correlation
Genotype-Environment Interaction
Genotype-Envir Correlation
Different Genotypes may
systematically experience
different environments
Genotype-Enviro Interaction
Low MAO
x
DeliqPeers = DELIQUENCY
How does the interaction of genes and environment work?
 Self-regulation: genes
turn each other on and
off in response to
environmental
conditions
Example of selfregulation in
animals:
shortened daylight
triggers animals to
change fur color or
to hibernate
 Epigenetics: the
environment acts on the
surface of genes to alter
their activity
Example of selfregulation in
humans:
obesity in adults
can turn off
weight regulation
genes in offspring
Evolution