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