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Nature, Nature, Nurture, and Nurture, and

Human Human DiversityDiversity

Chapter 3Chapter 3

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Behavior Genetics: Behavior Genetics: Predicting Individual Predicting Individual

DifferencesDifferencesBehavior GeneticistsBehavior Geneticists study our study our

differences and weigh the relative effects differences and weigh the relative effects of heredity and environment.of heredity and environment.

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Genes: Our Codes for LifeGenes: Our Codes for Life

ChromosomesChromosomes containing DNA containing DNA ((deoxyribonucleic aciddeoxyribonucleic acid) are situated in ) are situated in

the nucleus of a cell.the nucleus of a cell.

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Methods for studying Methods for studying Nature Vs. NurtureNature Vs. Nurture

Twin StudiesTwin Studies Adoption StudiesAdoption Studies

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Twin BiologyTwin Biology

Studying the effects of heredity and Studying the effects of heredity and environment on two sets of twins, identical environment on two sets of twins, identical

and fraternal, has come in handy.and fraternal, has come in handy.

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Twins and ProceduresTwins and Procedures

..

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Separated TwinsSeparated Twins

A number of studies compared identical A number of studies compared identical twins raised separately from birth, or close twins raised separately from birth, or close thereafter, and found numerous similarities.thereafter, and found numerous similarities.

Separated TwinsSeparated Twins

Personality, Personality, IntelligenceIntelligence

Abilities, AttitudesAbilities, Attitudes

Interests, FearsInterests, Fears

Brain Waves, Heart Brain Waves, Heart RateRate

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Separated TwinsSeparated Twins

Critics of separated twin studies note Critics of separated twin studies note that such similarities can be found that such similarities can be found

between strangers. Researchers point out between strangers. Researchers point out that differences between fraternal twins that differences between fraternal twins

are greater than identical twins.are greater than identical twins.

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Adoption StudiesAdoption Studies

Adoption studies, as opposed to twin Adoption studies, as opposed to twin studies, suggest that adoptees (who may be studies, suggest that adoptees (who may be biologically unrelated) tend to be different biologically unrelated) tend to be different from their adoptive parents and siblings.from their adoptive parents and siblings.

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Adoptive StudiesAdoptive Studies

Adoptive studies strongly point to the simple Adoptive studies strongly point to the simple fact that biologically related children turn out fact that biologically related children turn out

to be different in a family. So investigators to be different in a family. So investigators ask:ask:

Do siblings have differing experiences?

Do siblings, despite sharing half of their genes, have different combinations of the other half of their genes?

Ultimate question: Does parenting have an effect?

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ParentingParenting

Parenting does have an effect on biologically Parenting does have an effect on biologically related and unrelated children.related and unrelated children.

Parenting Influences Parenting Influences children’schildren’s

Attitudes, ValuesAttitudes, Values

Manners, BeliefsManners, Beliefs

Faith, PoliticsFaith, Politics

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Temperament StudiesTemperament Studies

Temperament refers to a person’s stable Temperament refers to a person’s stable emotional reactivity and intensity. Identical emotional reactivity and intensity. Identical

twins express similar temperaments, twins express similar temperaments, suggesting heredity predisposes temperament.suggesting heredity predisposes temperament.

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Gene-Environment Gene-Environment InteractionInteraction

Genes can influence traits which affect Genes can influence traits which affect responses, and environment can affect responses, and environment can affect

gene activity.gene activity.

A genetic predisposition that makes a child A genetic predisposition that makes a child restless and hyperactive evokes an angry restless and hyperactive evokes an angry

response from his parents. A stressful response from his parents. A stressful environment can trigger genes to environment can trigger genes to

manufacture neurotransmitters leading to manufacture neurotransmitters leading to depression.depression.

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Gene-Environment Gene-Environment InteractionInteraction

Genes and environment affect our traits Genes and environment affect our traits individually, but more important are their individually, but more important are their

interactive effects.interactive effects.

People respond differently toRowan Atkinson (Mr. Bean) than Orlando bloom.

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