copyright © 2007 pearson education canada1 evolution, genes, and behaviour chapter 3

Copyright © 2007 Pearson Education Canada

1

Evolution, Genes, and Evolution, Genes, and BehaviourBehaviour

Chapter 3Chapter 3

Copyright © 2007 Pearson Education Canada 2

Chapter OutlineChapter Outline

• Unlocking the secrets of genesUnlocking the secrets of genes• The genetics of similarityThe genetics of similarity• Our human heritage: courtship and matingOur human heritage: courtship and mating• Our human heritage: language Our human heritage: language • The genetics of differenceThe genetics of difference• Our human diversity: the case of intelligenceOur human diversity: the case of intelligence• Beyond nature versus nurtureBeyond nature versus nurture


Evolution & PsychologyEvolution & Psychology

• Evolutionary PsychologyEvolutionary Psychology– A field of psychology emphasizing evolutionary A field of psychology emphasizing evolutionary

mechanisms that may help to explain human mechanisms that may help to explain human commonalities in cognition, development, emotion, commonalities in cognition, development, emotion, social practices, and other areas of behavioursocial practices, and other areas of behaviour

• Behavioural Genetics Behavioural Genetics – An interdisciplinary field of study concerned with An interdisciplinary field of study concerned with

the genetic bases of individual differences in the genetic bases of individual differences in behaviour and personalitybehaviour and personality


Unlocking the Secrets of Unlocking the Secrets of GenesGenes

• Genes and how they operateGenes and how they operate– GenesGenes– ChromosomesChromosomes– DNADNA– GenomeGenome

• Studying genetic materialStudying genetic material– Linkage studiesLinkage studies– Genetic markersGenetic markers– The link between genetics and behaviourThe link between genetics and behaviour


Unlocking the Secrets of GenesUnlocking the Secrets of Genes• Genes Genes

– functional units of heredity functional units of heredity which are composed of DNA which are composed of DNA and specify the structure of and specify the structure of proteinsproteins

• Chromosomes Chromosomes – rod-shaped structures within rod-shaped structures within

cells that carry genescells that carry genes

• DNA (deoxyribonucleic acid) DNA (deoxyribonucleic acid) – transfers genetic transfers genetic

characteristics by way of characteristics by way of coded instructions for the coded instructions for the structure of proteinsstructure of proteins


GenomeGenome• GenomeGenome

The full set of genes in each cell of an The full set of genes in each cell of an organism (with the exception of sperm and egg cells)organism (with the exception of sperm and egg cells)


Studying Genetic MaterialStudying Genetic Material

• Linkage studiesLinkage studies– Because genes lying close together on a Because genes lying close together on a

chromosome may be inherited together chromosome may be inherited together across generations, researchers can look for across generations, researchers can look for genetic markers in familiesgenetic markers in families

• Genetic markersGenetic markers– A segment of DNA that varies among A segment of DNA that varies among

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


The Link Between Genes and The Link Between Genes and BehaviourBehaviour

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

• Most human traits are influenced by Most human traits are influenced by more than one gene pairmore than one gene pair– Examples include height and eye colourExamples include height and eye colour


The Genetics of SimilarityThe Genetics of Similarity• Evolution Evolution

• Natural selectionNatural selection

• Evolutionary biologists and Evolutionary biologists and psychologistspsychologists

• Innate human characteristicsInnate human characteristics


The Genetics of SimilarityThe Genetics of Similarity

• EvolutionEvolution– A change in gene frequencies within a A change in gene frequencies within a

population over many generationspopulation over many generations– A mechanism by which genetically influenced A mechanism by which genetically influenced

characteristics of a population may changecharacteristics of a population may change– Changes may occur due to mutations or errors Changes may occur due to mutations or errors

occurring during copying of original DNA occurring during copying of original DNA sequencesequence

– Changes may occur due to natural selectionChanges may occur due to natural selection


The Genetics of SimilarityThe Genetics of Similarity

• Natural SelectionNatural Selection– The evolutionary process in which The evolutionary process in which

individuals with genetically influenced traits individuals with genetically influenced traits that are adaptive in a particular that are adaptive in a particular environment tend to: environment tend to: • survive; andsurvive; and• reproduce in greater numbersreproduce in greater numbers

– As a result, their traits become more As a result, their traits become more common in the populationcommon in the population


Evolutionary BiologistsEvolutionary Biologists

• Start with an observation about a Start with an observation about a characteristic and try to account for it in characteristic and try to account for it in evolutionary termsevolutionary terms– Plumage differences in male and female Plumage differences in male and female

peacockspeacocks


Evolutionary PsychologistsEvolutionary Psychologists

• Ask what sorts of challenges human beings Ask what sorts of challenges human beings might have faced and then infer which might have faced and then infer which behavioural tendencies might have been behavioural tendencies might have been selected to overcome these challengesselected to overcome these challenges– Avoiding poisonous food and an innate dislike for Avoiding poisonous food and an innate dislike for

bitter tastesbitter tastes


Sexual selectionSexual selection

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

• Intrasexual selection: members of the Intrasexual selection: members of the same sex compete for a partner of the same sex compete for a partner of the other sexother sex


Innate Human CharacteristicsInnate Human Characteristics

• Infant reflexesInfant reflexes

• Interest in noveltyInterest in novelty

• Desire to explore and manipulate Desire to explore and manipulate objectsobjects

• Impulse to play and fool aroundImpulse to play and fool around

• Basic cognitive skillsBasic cognitive skills


Phenotype matchingPhenotype matching

• An individual’s ability to assess An individual’s ability to assess relatedness to another individual based relatedness to another individual based on the phenotype, the expression of on the phenotype, the expression of gene-environment interactionsgene-environment interactions


Our Human Heritage: Our Human Heritage: Courtship and MatingCourtship and Mating

• SociobiologySociobiology– Interdisciplinary field that emphasizes Interdisciplinary field that emphasizes

evolutionary explanations of social evolutionary explanations of social behaviour in animals, including humansbehaviour in animals, including humans

– We behave in ways that maximize our We behave in ways that maximize our chances of passing on our genes, and to chances of passing on our genes, and to help our close biological relatives, with help our close biological relatives, with whom we share genes, to do the samewhom we share genes, to do the same


Evolution and Sexual StrategiesEvolution and Sexual Strategies

• Due to different kinds of survival and mating Due to different kinds of survival and mating problems, the sexes have evolved differently problems, the sexes have evolved differently in the areas of aggressiveness, physical in the areas of aggressiveness, physical dominance, and sexual strategiesdominance, and sexual strategies– Males compete with other males for access to Males compete with other males for access to

females, and try to inseminate as many females females, and try to inseminate as many females as possibleas possible

– Females conceive and carry only a limited number Females conceive and carry only a limited number of pregnancies so they choose fewer, more of pregnancies so they choose fewer, more dominant males with good resources and high dominant males with good resources and high statusstatus


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

promiscuouspromiscuous• Drawn to sexual Drawn to sexual

novelty and even rapenovelty and 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 Are devoted and

faithfulfaithful• Drawn to stability Drawn to stability

and securityand security• Are cautious and Are cautious and

choosy in partnerschoosy in partners• Less concerned with Less concerned with

competition and competition and dominancedominance

Differences in Sexual StrategiesDifferences in Sexual Strategies


Evolutionary Psychologists and Evolutionary Psychologists and the Question of Genderthe Question of Gender

• Evolutionary psychologists consider such analogies Evolutionary psychologists consider such analogies of human and animal behaviours simplistic and of human and animal behaviours simplistic and misleadingmisleading

• Focus more on commonalities of human mating and Focus more on commonalities of human mating and dating around the worlddating around the world


Culture and the “Genetic Leash”Culture and the “Genetic Leash”• Criticisms of sociobiological and evolutionary Criticisms of sociobiological and evolutionary

explanations for sexual behaviour include:explanations for sexual behaviour include:– Evolutionary explanations of infidelity and Evolutionary explanations of infidelity and

monogamy are based on stereotypesmonogamy are based on stereotypes– Actual behaviour of humans and other animals Actual behaviour of humans and other animals

fails to conform to images of promiscuous males fails to conform to images of promiscuous males and coy femalesand coy females

– Human sexual behaviour is too varied to be Human sexual behaviour is too varied to be explained solely from an evolutionary perspectiveexplained solely from an evolutionary perspective

– Historically, available mates for selection were Historically, available mates for selection were much fewer than they are todaymuch fewer than they are today


Our Human Heritage: LanguageOur Human Heritage: Language

• The nature of languageThe nature of language

• The innate capacity for languageThe innate capacity for language

• Learning and learningLearning and learning


The Nature of LanguageThe Nature of Language

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

elements such as sounds or gestures to elements such as sounds or gestures to form structured utterances that convey form structured utterances that convey meaningmeaning


Innate Capacity for LanguageInnate Capacity for Language• Language too complex to be learned bit by bit Language too complex to be learned bit by bit

(Chomsky, 1957, 1980)(Chomsky, 1957, 1980)• Sentences have surface and deep structures.Sentences have surface and deep structures.

– Surface structureSurface structure• the way a sentence is spokenthe way a sentence is spoken

– Deep structureDeep structure• how a sentence is to be understoodhow a sentence is to be understood

• To transform surface sentence structures into To transform surface sentence structures into deep ones, children must apply rules of deep ones, children must apply rules of grammar (syntax)grammar (syntax)


Surface and Deep StructuresSurface and Deep Structures


Language Acquisition DeviceLanguage Acquisition Device

• If we don’t teach syntax to toddlers, human If we don’t teach syntax to toddlers, human brains must contain a language acquisition brains must contain a language acquisition device (Chomsky, 1957;1980)device (Chomsky, 1957;1980)– An innate module that allows young children to An innate module that allows young children to

develop language if they are exposed to an adequate develop language if they are exposed to an adequate sampling of conversationsampling of conversation

• Children are born with universal grammar or a Children are born with universal grammar or a sensitivity to the core features common to all sensitivity to the core features common to all languageslanguages– Examples include nouns and verbs, subjects and Examples include nouns and verbs, subjects and

objects, and negativesobjects, and negatives


Evidence Supporting the LADEvidence Supporting the LAD

• Children:Children:– in different cultures go through similar stages of in different cultures go through similar stages of

linguistic developmentlinguistic development– combine words in ways adults never wouldcombine words in ways adults never would– learn to speak or sign correctly although adults do learn to speak or sign correctly although adults do

not correct syntaxnot correct syntax– If not exposed to adult language may invent a If not exposed to adult language may invent a

language of their ownlanguage of their own

• Infants as young as 7 months can derive Infants as young as 7 months can derive simple linguistic rules from a string of soundssimple linguistic rules from a string of sounds


Evidence for Learning and LanguageEvidence for Learning and Language

• Computerized neural networks can “learn” Computerized neural networks can “learn” aspects of languageaspects of language

• Children learn the probability that any given word Children learn the probability that any given word or syllable will follow anotheror syllable will follow another

• Although there are commonalities in language Although there are commonalities in language acquisition, there are also many differencesacquisition, there are also many differences

• Parents respond to children’s errors by restating Parents respond to children’s errors by restating or elaborating on the phraseor elaborating on the phrase

• Children imitate these adult recasts and Children imitate these adult recasts and expansionsexpansions


The Genetics of DifferenceThe Genetics of Difference

• The meaning of heritabilityThe meaning of heritability– 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 (.60 or 60/100)Expressed as proportion (.60 or 60/100)– Maximum value is 1.0Maximum value is 1.0

• Some variables such as height are highly Some variables such as height are highly heritable, other variables such as musical heritable, other variables such as musical ability are moderately heritableability are moderately heritable


Facts About HeritabilityFacts About Heritability

• An estimate of heritability An estimate of heritability applies only to a particular applies only to a particular group living in a particular group living in a particular environmentenvironment

• 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

• Even highly heritable traits Even highly heritable traits can be modified by the can be modified by the environmentenvironment


Computing HeritabilityComputing Heritability• Studying adopted children allows researchers to Studying adopted children allows researchers to

compare correlations between the traits of compare correlations between the traits of adopted children and those of their biological adopted children and those of their biological and adoptive relativesand adoptive relatives

• Results are used to compute heritability Results are used to compute heritability estimateestimate


Computing HeritabilityComputing Heritability

• If identical twins are If identical twins are more alike than more alike than fraternal twins, then fraternal twins, then the increased the increased similarity must be similarity must be due to genetic due to genetic influencesinfluences


Computing HeritabilityComputing Heritability

• Investigators have also studied identical Investigators have also studied identical twins who were separated early in life twins who were separated early in life and reared apartand reared apart

• Any similarities in traits between them Any similarities in traits between them should be primarily genetic and should should be primarily genetic and should permit a direct estimate of heritabilitypermit a direct estimate of heritability


Our Human Diversity: Our Human Diversity: The Case of IntelligenceThe Case of Intelligence

• Genes and individual differencesGenes and individual differences• The question of group differencesThe question of group differences• The environment and intelligenceThe environment and intelligence


Our Human Diversity: Our Human Diversity: The Case of IntelligenceThe Case of Intelligence

• Genes and individual differencesGenes and individual differences– Intelligence Quotient (IQ)Intelligence Quotient (IQ)

• measure of intelligences originally computed by dividing measure of intelligences originally computed by dividing a person’s mental age by his or her chronological age a person’s mental age by his or her chronological age and multiplying result by 100and multiplying result by 100

• now derived from norms provided for standard now derived from norms provided for standard intelligence testsintelligence tests

– The kind of intelligence that produces high IQ The kind of intelligence that produces high IQ scores is highly heritablescores is highly heritable

• .50 for children and adolescents.50 for children and adolescents• .60 -.80 for adults.60 -.80 for adults


Twins and IntelligenceTwins and Intelligence

• Intelligence scores of identical twins are always more Intelligence scores of identical twins are always more highly correlated than those of fraternal twinshighly correlated than those of fraternal twins


Adopted Children and IntelligenceAdopted Children and Intelligence

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


The Question of Group DifferencesThe Question of Group Differences

• Genetics are used to explain differences between Genetics are used to explain differences between groupsgroups

• These differences are used to justify differential These differences are used to justify differential treatment for these groupstreatment for these groups– Example: Differences between average IQ scores for Example: Differences between average IQ scores for

African Americans and Caucasian AmericansAfrican Americans and Caucasian Americans

• Genetic explanations have a flawGenetic explanations have a flaw– They use heritability estimates based on white samples They use heritability estimates based on white samples

to estimate the role of heredity in group differencesto estimate the role of heredity in group differences


The Question of Group DifferencesThe Question of Group Differences

• Those studies overcoming past methodological Those studies overcoming past methodological problems fail to reveal genetic differences problems fail to reveal genetic differences between blacks and whites on IQbetween blacks and whites on IQ

• Examples:Examples:– Children fathered by black and white American Children fathered by black and white American

soldiers in Germany after WWII and reared in similar soldiers in Germany after WWII and reared in similar German communities did not differ significantly in IQGerman communities did not differ significantly in IQ

– Black and white infants perform equally well on tests Black and white infants perform equally well on tests for noveltyfor novelty


The Environment and IntelligenceThe Environment and Intelligence

• Experiences that hinder Experiences that hinder – Poor prenatal carePoor prenatal care– MalnutritionMalnutrition– Exposure to toxinsExposure to toxins– Stressful family circumstancesStressful family circumstances

• Experiences that help Experiences that help – Good health care and nutritionGood health care and nutrition– Mental enrichment in home and child care or schoolMental enrichment in home and child care or school


Beyond Nature Versus NurtureBeyond Nature Versus Nurture

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

• Psychological diversity is adaptivePsychological diversity is adaptive

copyright © 2007 pearson education canada1 evolution, genes, and behaviour chapter 3

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