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Modules 11, 12, 13
Nature, Nurture,
and Human
Diversity
Behavior Genetics: Predicting Individual Differences
The topics in the text:1. genes2. twin and adoption studies 3. temperament and heredity4. molecular genetics5. heritability6. 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")
"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 are parts of DNA molecules, which are found in chromosomes in the nuclei of cells.
DNA (Deoxyribonucleic Acid)
GENES:The Building Blocks of Heredity and Development
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.
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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)
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 VariationGenetic Variation• Alleles
Variation in some nucleotide sequences in a gene
• Genetic variationPresence of alleles in a population
• Gene poolTotal variety of alleles in the population
• Population GeneticsStudy of distributions of alleles and their
effects
• AllelesVariation 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
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
GenotypeThe underlying DNA sequence that an
individual inherits
PhenotypeAn organism’s observable properties,
physical and behavioral
Polygenic Involving many genes
GenotypeThe underlying DNA sequence that an
individual inherits
PhenotypeAn 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
Selective Breeding
Behavioural Genetics Methods
Belyaev (1969)
Belyaev (1969)
Domestication / tameness ● Occurs quickly● Changes are wide ranging
Appearance: Ears, tail, coat color Temperament: Friendliness, CuddlinessMore social --> Easily trainable
HPA reactivity ↓ (Hypothalamic-Pituitary Axis)
Serotonin ↑
Family StudiesGenetic overlap is known
Siblings share how many genes? (50%)Cousins share how many genes? (12.5%)
Measure similarity in traits.Between siblingsBetween parents and offspringBetween 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
Twin and Adoption StudiesTo 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
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 StudiesHow 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).
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.
What proportion of human variation in any major personality trait is due
to genetic variation at birth?
A) 8 %
B) 18 %
C) 40 %
D) 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 ofOhio (1979)
Typical Heritability Findings
IQ 50-80%
Personality 30-50 %
Attitudes 20-30 %
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.
Criticisms
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…
Error20%
Genetic40%
Non-sharedEnvironment
35%
Shared Environment
5%
Despite the strong impact of genetics on personality, parenting does has an influence on:
religious beliefs values manners attitudes politics habits
Parenting Does Matter
The typical correlation between parents and children for political party preferences…
.10 .20 .40 .70
= .70r
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”
TemperamentTemperament
def= early appearing differences• What categories?• Are temperaments stable?• What causes diff.
temperaments?
def= early appearing differences• What categories?• Are temperaments stable?• What causes diff.
temperaments?
Thomas & Chess (1977)Thomas & Chess (1977)
Temperamental ClustersTemperamental Clusters
Easy: 40%, happy and easy to care for
Slow to warm up: 15%, “shy” personality
Difficult: 10%, tough on caretakers
Undifferentiated: 25%
Easy: 40%, happy and easy to care for
Slow to warm up: 15%, “shy” personality
Difficult: 10%, tough on caretakers
Undifferentiated: 25%
TemperamentTemperament
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
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
Video (7 mins)
"Bringing Up Monkey"
Is innate temperamentfixed or changeable?
Video (7 mins)
"Bringing Up Monkey"
Is innate temperamentfixed or changeable?
Cross-fostering studiesCross-fostering studies
Harlow and Suomi (1974)
• Nervous s babies• Placed with calm moms.
Q: Can mothering style alter baby temperament?
Harlow and Suomi (1974)
• Nervous s babies• Placed with calm moms.
Q: Can mothering style alter baby temperament?
Cross-fostering studiesCross-fostering studies
Video (7 mins)
"Bringing Up Monkey"
Is innate temperamentfixed or changeable?
Video (7 mins)
"Bringing Up Monkey"
Is innate temperamentfixed 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 Behavior 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 Behavior Genetics
Specific genes behavior, e.g., personality traits, psychological disorders
e.g., Dopamine Receptor Gene Allele of D4DR (the “long repeat” version”)
is associated with novelty seeking
Molecular Behavior Genetics
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
Self-regulation: genes turn each other on and off in response to environmental conditions
Epigenetics: the environment acts on the surface of genes to alter their activity
How does the interaction of genes and environment work?
Example of self-regulation in animals: shortened daylight triggers animals to change fur color or to hibernate
Example of self-regulation in humans: obesity in adults can turn off weight regulation genes in offspring
EvolutionEvolution