copyright © 2010 pearson education canada3-1 genes, evolution, and environment chapter 3

Copyright © 2010 Pearson Education Canada 3-1

Genes, Evolution,Genes, Evolution,and Environmentand Environment

Chapter 3Chapter 3


Chapter OutlineChapter Outline

• Unlocking the Secrets of GenesUnlocking the Secrets of Genes

• The Genetics of SimilarityThe Genetics of Similarity

• Our Human Heritage: LanguageOur Human Heritage: Language

• Our Human Heritage: Courtship & MatingOur Human Heritage: Courtship & Mating

• The Genetics of DifferenceThe Genetics of Difference

• Our Human Diversity: IntelligenceOur Human Diversity: Intelligence

• Beyond Nature versus NurtureBeyond Nature versus Nurture

Where Do Differences Where Do Differences Come From?Come From?

• Previously two perspectives:Previously two perspectives:

– NativistsNativists: emphasized genes & inborn : emphasized genes & inborn characteristics (nature)characteristics (nature)

– EmpiricistsEmpiricists: focused on learning & experience : focused on learning & experience (nurture)(nurture)

• Now studied broadly, including Now studied broadly, including evolutionaryevolutionary psychologypsychology and and behavioural geneticsbehavioural genetics


Unlocking the Secrets of GenesUnlocking the Secrets of Genes

• GenesGenes are the basic units of heredity that are the basic units of heredity that are composed of DNA and located on are composed of DNA and located on chromosomeschromosomes

– Chromosomes:Chromosomes: rod-shaped structures found in the rod-shaped structures found in the nucleus of every cell (23 pairs)nucleus of every cell (23 pairs)

– DNA (deoxyribonucleic acid): DNA (deoxyribonucleic acid): chromosomal molecule chromosomal molecule that transfers genetic characteristics by way of coded that transfers genetic characteristics by way of coded instructions for the structure of proteinsinstructions for the structure of proteins


Unlocking the Secrets of GenesUnlocking the Secrets of Genes

• Within genes, four chemical elements of DNA Within genes, four chemical elements of DNA “code” for protein synthesis“code” for protein synthesis

– Adenine (A)Adenine (A)– Thymine (T)Thymine (T)– Cytosine (C)Cytosine (C)– Guanine (G)Guanine (G)

• GenomeGenome – full set of genes in each cell of an – full set of genes in each cell of an organism (except sperm & egg cells)organism (except sperm & egg cells)


Studying Genetic MaterialStudying Genetic Material

• Linkage studiesLinkage studies– Studies that look for patterns of inheritance of Studies that look for patterns of inheritance of

genetic markers in large families in which a genetic markers in large families in which a particular condition is commonparticular condition is common

• Genetic markerGenetic marker– Segment of DNA that varies among individuals, Segment of DNA that varies among individuals,

has a known location on a chromosome, and has a known location on a chromosome, and can function as a genetic landmark for a genecan function as a genetic landmark for a gene


Linking Genes & BehaviourLinking Genes & Behaviour

• Even when researchers locate a gene on a Even when researchers locate a gene on a chromosome, they do not automatically chromosome, they do not automatically know its role in physical or psychological know its role in physical or psychological functioningfunctioning

• Most human traits are influenced by more Most human traits are influenced by more than one gene pair (polygenic); from simple than one gene pair (polygenic); from simple to complex traitsto complex traits


The Genetics of SimilarityThe Genetics of Similarity

• EvolutionEvolution is a change in gene frequencies is a change in gene frequencies within a population over many generationswithin a population over many generations

– Mechanism for change in the genetically Mechanism for change in the genetically influenced characteristics of a populationinfluenced characteristics of a population

– Changes may result from Changes may result from mutationsmutations (errors in (errors in copying of DNA sequences during division of copying of DNA sequences during division of cells that produce sperm & eggs)cells that produce sperm & eggs)


Natural SelectionNatural Selection

• Evolutionary process formulated by Evolutionary process formulated by DarwinDarwin

• Individuals with genetically influenced traits Individuals with genetically influenced traits that are adaptive in particular environments that are adaptive in particular environments tend to survive & reproduce in greater tend to survive & reproduce in greater numbers (“survival of the fittest”)numbers (“survival of the fittest”)

• As a result, traits become more common in As a result, traits become more common in the populationthe population


Sexual SelectionSexual Selection

• Darwin also proposed that genes were Darwin also proposed that genes were determined by sexual selectiondetermined by sexual selection

– Intersexual selection: Intersexual selection: a member of one sex a member of one sex chooses a mate from the other sex on the chooses a mate from the other sex on the basis of certain characteristicsbasis of certain characteristics

– Intrasexual selection: Intrasexual selection: members of the same members of the same sex compete for a partner of the other sexsex compete for a partner of the other sex


Traits & PreferencesTraits & Preferences

• Evolutionary biologistsEvolutionary biologists start with an start with an observation about a characteristic and try to observation about a characteristic and try to account for it in evolutionary termsaccount for it in evolutionary terms

• Evolutionary psychologistsEvolutionary psychologists ask what sorts of ask what sorts of challenges humans might have faced and challenges humans might have faced and infer what behavioural tendencies may have infer what behavioural tendencies may have been selected to overcome these challengesbeen selected to overcome these challenges


Mental ModulesMental Modules

• One perspective is that mind reflects mental One perspective is that mind reflects mental modules shaped through evolutionmodules shaped through evolution

– Mental modules:Mental modules: a collection of specialized and a collection of specialized and independent sections of the brain, developed to handle independent sections of the brain, developed to handle specific survival problems (e.g., location of food, finding specific survival problems (e.g., location of food, finding a mate)a mate)

• Critics point out that not all traits are adaptive but Critics point out that not all traits are adaptive but may be by-products of other traits (not isolated)may be by-products of other traits (not isolated)


Innate Human CharacteristicsInnate Human Characteristics

• Evolution has shaped human development Evolution has shaped human development through innate characteristics such as:through innate characteristics such as:

1.1. Infant reflexesInfant reflexes

2.2. An interest in noveltyAn interest in novelty

3.3. A desire to explore & manipulate objectsA desire to explore & manipulate objects

4.4. An impulse to play & fool aroundAn impulse to play & fool around

5.5. Basic cognitive skillsBasic cognitive skills


Phenotype MatchingPhenotype Matching

• According to evolution, we should favour According to evolution, we should favour family members to promote survival of family members to promote survival of genetic materialgenetic material

– Phenotype matching: Phenotype matching: an individual’s ability to an individual’s ability to assess relatedness to another individual based assess relatedness to another individual based on phenotype (expression of gene-environment on phenotype (expression of gene-environment interaction)interaction)

• E.g., DeBruine’s (2002) trust studyE.g., DeBruine’s (2002) trust study


Our Human Heritage: LanguageOur Human Heritage: Language

• LanguageLanguage– A system that combines meaningless elements A system that combines meaningless elements

such as sounds or gestures to form structured such as sounds or gestures to form structured utterances that convey meaningutterances that convey meaning

– Surface structure: Surface structure: the way a sentence is spokenthe way a sentence is spoken

– Deep structure: Deep structure: how a sentence is to be understoodhow a sentence is to be understood


Innate Capacity for LanguageInnate Capacity for Language

• Chomsky argued that we are born with a Chomsky argued that we are born with a language language acquisition device acquisition device that guides the development of that guides the development of language with proper exposurelanguage with proper exposure

– To transform surface into deep structures, children must To transform surface into deep structures, children must use use syntaxsyntax (which is not taught) (which is not taught)

– Reflects a Reflects a universal grammar universal grammar where brains are sensitive where brains are sensitive to core features common to all languages (e.g., nouns & to core features common to all languages (e.g., nouns & verbs)verbs)


Evidence Supporting Chomsky Evidence Supporting Chomsky

1.1. Children in different cultures go through similar stages of Children in different cultures go through similar stages of linguistic developmentlinguistic development

2.2. Children combine words in ways that adults never wouldChildren combine words in ways that adults never would

3.3. Adults do not consistently correct their children’s syntax, Adults do not consistently correct their children’s syntax, yet children learn to speak correctly anywayyet children learn to speak correctly anyway

4.4. Children not exposed to adult language might invent a Children not exposed to adult language might invent a language of their ownlanguage of their own

5.5. Infants as young as 7 months can derive simple linguistic Infants as young as 7 months can derive simple linguistic rules from a string of soundsrules from a string of sounds


Learning & LanguageLearning & Language

• Other scholars argue environment plays Other scholars argue environment plays larger role in language (not all innate)larger role in language (not all innate)

– Computer neural networks: Computer neural networks: mathematical models mathematical models of the brain that can “learn” some aspects of of the brain that can “learn” some aspects of languagelanguage

– Other arguments: major differences in acquisition, Other arguments: major differences in acquisition, parents recast sentences rather than corrections, parents recast sentences rather than corrections, children imitate recasts & expansionschildren imitate recasts & expansions


Our Human Heritage: Our Human Heritage: Courtship & MatingCourtship & Mating

• SociobiologySociobiology

– Interdisciplinary field that emphasizes Interdisciplinary field that emphasizes evolutionary explanations of social behaviour in evolutionary explanations of social behaviour in animals & humansanimals & humans

– We have a tendency to act in ways that We have a tendency to act in ways that maximize chances of passing on genes as well maximize chances of passing on genes as well as helping close biological relatives do the sameas helping close biological relatives do the same


Evolution & Sexual StrategiesEvolution & Sexual Strategies

• Differences in survival & mating problems Differences in survival & mating problems have led to differences in aggression, have led to differences in aggression, dominance, & sexual strategies between sexesdominance, & sexual strategies between sexes

– Males compete with other males to access females, Males compete with other males to access females, inseminate as many as possibleinseminate as many as possible

– Females have larger biological investment in pregnancy Females have larger biological investment in pregnancy so choose dominant males with resources & statusso choose dominant males with resources & status


Differences in Sexual StrategiesDifferences in Sexual Strategies

MalesMales

• Want sex more oftenWant sex more often• Are fickle and Are fickle and

promiscuouspromiscuous• Drawn to sexual novelty Drawn to sexual novelty

and even rapeand even rape• Are undiscriminating in Are undiscriminating in

partner choicepartner choice• Concerned with Concerned with

competition and competition and dominancedominance

FemalesFemales

• Want sex less oftenWant sex less often• Are devoted and faithfulAre devoted and faithful• Drawn to stability and Drawn to stability and

securitysecurity• Are cautious and choosy Are cautious and choosy

in partnersin partners• Less concerned with Less concerned with

competition and competition and dominancedominance


Evolution & PreferencesEvolution & Preferences

• Cross-cultural studies have found consistent Cross-cultural studies have found consistent differences between males and femalesdifferences between males and females

• Mating preferences Mating preferences such as age predict such as age predict status & dominance status & dominance in men and fertility in men and fertility in womenin women


Culture & the “Genetic Leash”Culture & the “Genetic Leash”

• Criticisms of evolutionary explanations of sex Criticisms of evolutionary explanations of sex differences:differences:

– Explanations of infidelity & monogamy based on gender Explanations of infidelity & monogamy based on gender stereotypesstereotypes

– Sexual behaviour is varied and not solely for reproductive Sexual behaviour is varied and not solely for reproductive purposespurposes

– Ignores cultural influences on sexual behaviour Ignores cultural influences on sexual behaviour – Available mates were much more limited than currentlyAvailable mates were much more limited than currently– Similarity & proximity among strongest predictors of mate Similarity & proximity among strongest predictors of mate

choicechoice


The Genetics of DifferenceThe Genetics of Difference

• The meaning of The meaning of heritabilityheritability::

– A statistical estimate of the proportion of the total A statistical estimate of the proportion of the total variance in some trait that is attributable to genetic variance in some trait that is attributable to genetic differences among individuals within a groupdifferences among individuals within a group

– Expressed as proportion (e.g., .60 or 60/100), with Expressed as proportion (e.g., .60 or 60/100), with maximum value of 1.0maximum value of 1.0

– High heritability means greater genetic contribution High heritability means greater genetic contribution to traitto trait


Facts about HeritabilityFacts about Heritability

1.1. Estimates of heritability Estimates of heritability apply only to a particular apply only to a particular group living in a particular group living in a particular environmentenvironment

2.2. Heritability estimates do not Heritability estimates do not apply to individuals, only to apply to individuals, only to variations within a groupvariations within a group

3.3. Even highly heritable traits Even highly heritable traits can be modified by the can be modified by the environmentenvironment


Computing HeritabilityComputing Heritability

• Infer heritability by studying people whose Infer heritability by studying people whose genetic similarity is knowngenetic similarity is known

• Separate role Separate role of genetics & of genetics & environment environment by studying by studying adopted adopted childrenchildren


Computing HeritabilityComputing Heritability

• Another approach compares Another approach compares identical identical (monozygotic)(monozygotic) with with fraternal (dizygotic) twinsfraternal (dizygotic) twins

• If identical more If identical more similar than similar than fraternal twins, fraternal twins, greater the genetic greater the genetic influenceinfluence

• Also study twins Also study twins separated early in separated early in life & raised apartlife & raised apart


Our Human Diversity: IntelligenceOur Human Diversity: Intelligence

• Intellectual functioning usually measured by Intellectual functioning usually measured by an an intelligence quotient (IQ) intelligence quotient (IQ) scorescore

– Originally computed by dividing a person’s mental Originally computed by dividing a person’s mental age by chronological age and multiplying by 100; age by chronological age and multiplying by 100; now derived from norms on standardized IQ testsnow derived from norms on standardized IQ tests

– Kind of intelligence that produces high IQ scores Kind of intelligence that produces high IQ scores highly heritable:highly heritable:

• Children & adolescents (.40-.50); adults (.60-.80)Children & adolescents (.40-.50); adults (.60-.80)


Twins, Adoption, & IntelligenceTwins, Adoption, & Intelligence

• IQ scores of identical twins more highly IQ scores of identical twins more highly correlated than those of fraternal twinscorrelated than those of fraternal twins

• Also, scores Also, scores of adopted of adopted children are children are highly highly correlated correlated with their with their biological biological parentsparents


Group DifferencesGroup Differences

• If genes influence individual differences, can If genes influence individual differences, can they account for differences between they account for differences between groups?groups?

– Differences have been used to justify differential Differences have been used to justify differential treatment of groups (e.g., ethnicity, gender)treatment of groups (e.g., ethnicity, gender)

• Example: Differences in IQ scores between African Example: Differences in IQ scores between African Americans and Caucasian Americans Americans and Caucasian Americans


Explaining Group DifferencesExplaining Group Differences

• Genetic explanations have a fatal flawGenetic explanations have a fatal flaw– Heritability estimates rely on Caucasian samples to Heritability estimates rely on Caucasian samples to

estimate role of heredity between groupsestimate role of heredity between groups

• Studies that overcome methodological flaws fail to Studies that overcome methodological flaws fail to reveal genetic differences in IQ scores as a reveal genetic differences in IQ scores as a function of ethnicity function of ethnicity (e.g., Eyferth, 1961; Fagan, 1992)(e.g., Eyferth, 1961; Fagan, 1992)

– Differences Differences withinwithin groups may have a genetic basis but groups may have a genetic basis but that does not mean differences that does not mean differences betweenbetween groups are groups are geneticgenetic


Environment & IntelligenceEnvironment & Intelligence

• Environmental influences associated with Environmental influences associated with reducedreduced mental ability: mental ability:

– Poor prenatal carePoor prenatal care– MalnutritionMalnutrition– Exposure to toxinsExposure to toxins– Stressful family circumstancesStressful family circumstances


Environment & IntelligenceEnvironment & Intelligence

• Environmental influences associated with Environmental influences associated with enhancedenhanced mental abilities: mental abilities:

– Good health care & nutritionGood health care & nutrition– Mental enrichment in home, child care, schoolMental enrichment in home, child care, school– Parental interaction, discussion, & Parental interaction, discussion, &

encouragement of mental processingencouragement of mental processing


Beyond Nature versus NurtureBeyond Nature versus Nurture

• Heredity and environment always interact to Heredity and environment always interact to produce the unique mixture of qualities that produce the unique mixture of qualities that make a humanmake a human

– E.g., variations in gene “expression” according to E.g., variations in gene “expression” according to internal & external environmentsinternal & external environments

• Psychological diversity is adaptivePsychological diversity is adaptive


End of Chapter 3End of Chapter 3


copyright © 2010 pearson education canada3-1 genes, evolution, and environment chapter 3

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