1. Copyright © 2007 Pearson Education Canada1 Evolution, Genes, and Behaviour Chapter 3

2. Copyright © 2007 Pearson Education Canada2 Chapter 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: languageOur 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

3. Copyright © 2007 Pearson Education Canada3 Evolution & Psychology Evolutionary PsychologyEvolutionary Psychology –A field of psychology emphasizing evolutionary mechanisms that may help to explain human commonalities in cognition, development, emotion, social practices, and other areas of behaviour Behavioural GeneticsBehavioural Genetics –An interdisciplinary field of study concerned with the genetic bases of individual differences in behaviour and personality

4. Copyright © 2007 Pearson Education Canada4 Unlocking the Secrets of Genes Genes and how they operateGenes and how they operate –Genes –Chromosomes –DNA –Genome Studying genetic materialStudying genetic material –Linkage studies –Genetic markers –The link between genetics and behaviour

5. Copyright © 2007 Pearson Education Canada5 Unlocking the Secrets of Genes GenesGenes –functional units of heredity which are composed of DNA and specify the structure of proteins ChromosomesChromosomes –rod-shaped structures within cells that carry genes DNA (deoxyribonucleic acid)DNA (deoxyribonucleic acid) –transfers genetic characteristics by way of coded instructions for the structure of proteins

6. Copyright © 2007 Pearson Education Canada6 Genome Genome The full set of genes in each cell of an organism (with the exception of sperm and egg cells)Genome The full set of genes in each cell of an organism (with the exception of sperm and egg cells)

7. Copyright © 2007 Pearson Education Canada7 Studying Genetic Material Linkage studiesLinkage studies –Because genes lying close together on a chromosome may be inherited together across generations, researchers can look for genetic markers in families Genetic markersGenetic markers –A segment of DNA that varies among individuals, has a known location on a chromosome, and can function as a genetic landmark for a gene

8. Copyright © 2007 Pearson Education Canada8 The Link Between Genes and Behaviour Even when researchers locate a gene on a chromosome, they do not automatically know its role in physical or psychological functioningEven when researchers locate a gene on a chromosome, they do not automatically know its role in physical or psychological functioning Most human traits are influenced by more than one gene pairMost human traits are influenced by more than one gene pair –Examples include height and eye colour

9. Copyright © 2007 Pearson Education Canada9 The Genetics of Similarity EvolutionEvolution Natural selectionNatural selection Evolutionary biologists and psychologistsEvolutionary biologists and psychologists Innate human characteristicsInnate human characteristics

10. Copyright © 2007 Pearson Education Canada10 The Genetics of Similarity EvolutionEvolution –A change in gene frequencies within a population over many generations –A mechanism by which genetically influenced characteristics of a population may change –Changes may occur due to mutations or errors occurring during copying of original DNA sequence –Changes may occur due to natural selection

11. Copyright © 2007 Pearson Education Canada11 The Genetics of Similarity Natural SelectionNatural Selection –The evolutionary process in which individuals with genetically influenced traits that are adaptive in a particular environment tend to: survive; andsurvive; and reproduce in greater numbersreproduce in greater numbers –As a result, their traits become more common in the population

12. Copyright © 2007 Pearson Education Canada12 Evolutionary Biologists Start with an observation about a characteristic and try to account for it in evolutionary termsStart with an observation about a characteristic and try to account for it in evolutionary terms –Plumage differences in male and female peacocks

13. Copyright © 2007 Pearson Education Canada13 Evolutionary Psychologists Ask what sorts of challenges human beings might have faced and then infer which behavioural tendencies might have been selected to overcome these challengesAsk what sorts of challenges human beings might have faced and then infer which behavioural tendencies might have been selected to overcome these challenges –Avoiding poisonous food and an innate dislike for bitter tastes

14. Copyright © 2007 Pearson Education Canada14 Sexual selection Intersexual selection: a member of one sex chooses a mate from the other sex on the basis of certain characteristicsIntersexual selection: a member of one sex chooses a mate from the other sex on the basis of certain characteristics Intrasexual selection: members of the same sex compete for a partner of the other sexIntrasexual selection: members of the same sex compete for a partner of the other sex

15. Copyright © 2007 Pearson Education Canada15 Innate Human Characteristics Infant reflexesInfant reflexes Interest in noveltyInterest in novelty Desire to explore and manipulate objectsDesire to explore and manipulate objects Impulse to play and fool aroundImpulse to play and fool around Basic cognitive skillsBasic cognitive skills

16. Copyright © 2007 Pearson Education Canada16 Phenotype matching An individual’s ability to assess relatedness to another individual based on the phenotype, the expression of gene-environment interactionsAn individual’s ability to assess relatedness to another individual based on the phenotype, the expression of gene-environment interactions

17. Copyright © 2007 Pearson Education Canada17 Our Human Heritage: Courtship and Mating SociobiologySociobiology –Interdisciplinary field that emphasizes evolutionary explanations of social behaviour in animals, including humans –We behave in ways that maximize our chances of passing on our genes, and to help our close biological relatives, with whom we share genes, to do the same

18. Copyright © 2007 Pearson Education Canada18 Evolution and Sexual Strategies Due to different kinds of survival and mating problems, the sexes have evolved differently in the areas of aggressiveness, physical dominance, and sexual strategiesDue to different kinds of survival and mating problems, the sexes have evolved differently in the areas of aggressiveness, physical dominance, and sexual strategies –Males compete with other males for access to females, and try to inseminate as many females as possible –Females conceive and carry only a limited number of pregnancies so they choose fewer, more dominant males with good resources and high status

19. Copyright © 2007 Pearson Education Canada19 Males Want sex more oftenWant sex more often Are fickle and promiscuousAre fickle and promiscuous Drawn to sexual novelty and even rapeDrawn to sexual novelty and even rape Are undiscriminating in partner choiceAre undiscriminating in partner choice Concerned with competition and dominanceConcerned with competition and dominance Females Want sex less oftenWant sex less often Are devoted and faithfulAre devoted and faithful Drawn to stability and securityDrawn to stability and security Are cautious and choosy in partnersAre cautious and choosy in partners Less concerned with competition and dominanceLess concerned with competition and dominance Differences in Sexual Strategies

20. Copyright © 2007 Pearson Education Canada20 Evolutionary Psychologists and the Question of Gender Evolutionary psychologists consider such analogies of human and animal behaviours simplistic and misleadingEvolutionary psychologists consider such analogies of human and animal behaviours simplistic and misleading Focus more on commonalities of human mating and dating around the worldFocus more on commonalities of human mating and dating around the world

21. Copyright © 2007 Pearson Education Canada21 Culture and the “Genetic Leash” Criticisms of sociobiological and evolutionary explanations for sexual behaviour include:Criticisms of sociobiological and evolutionary explanations for sexual behaviour include: –Evolutionary explanations of infidelity and monogamy are based on stereotypes –Actual behaviour of humans and other animals fails to conform to images of promiscuous males and coy females –Human sexual behaviour is too varied to be explained solely from an evolutionary perspective –Historically, available mates for selection were much fewer than they are today

22. Copyright © 2007 Pearson Education Canada22 Our Human Heritage: Language The nature of languageThe nature of language The innate capacity for languageThe innate capacity for language Learning and learningLearning and learning

23. Copyright © 2007 Pearson Education Canada23 The Nature of Language LanguageLanguage –A system that combines meaningless elements such as sounds or gestures to form structured utterances that convey meaning

24. Copyright © 2007 Pearson Education Canada24 Innate Capacity for Language Language too complex to be learned bit by bit (Chomsky, 1957, 1980)Language too complex to be learned bit by bit (Chomsky, 1957, 1980) Sentences have surface and deep structures.Sentences have surface and deep structures. –Surface structure the way a sentence is spokenthe way a sentence is spoken –Deep structure how a sentence is to be understoodhow a sentence is to be understood To transform surface sentence structures into deep ones, children must apply rules of grammar (syntax)To transform surface sentence structures into deep ones, children must apply rules of grammar (syntax)

25. Copyright © 2007 Pearson Education Canada25 Surface and Deep Structures

26. Copyright © 2007 Pearson Education Canada26 Language Acquisition Device If we don’t teach syntax to toddlers, human brains must contain a language acquisition device (Chomsky, 1957;1980)If we don’t teach syntax to toddlers, human brains must contain a language acquisition device (Chomsky, 1957;1980) –An innate module that allows young children to develop language if they are exposed to an adequate sampling of conversation Children are born with universal grammar or a sensitivity to the core features common to all languagesChildren are born with universal grammar or a sensitivity to the core features common to all languages –Examples include nouns and verbs, subjects and objects, and negatives

27. Copyright © 2007 Pearson Education Canada27 Evidence Supporting the LAD Children:Children: –in different cultures go through similar stages of linguistic development –combine words in ways adults never would –learn to speak or sign correctly although adults do not correct syntax –If not exposed to adult language may invent a language of their own Infants as young as 7 months can derive simple linguistic rules from a string of soundsInfants as young as 7 months can derive simple linguistic rules from a string of sounds

28. Copyright © 2007 Pearson Education Canada28 Evidence for Learning and Language Computerized neural networks can “learn” aspects of languageComputerized neural networks can “learn” aspects of language Children learn the probability that any given word or syllable will follow anotherChildren learn the probability that any given word or syllable will follow another Although there are commonalities in language acquisition, there are also many differencesAlthough there are commonalities in language acquisition, there are also many differences Parents respond to children’s errors by restating or elaborating on the phraseParents respond to children’s errors by restating or elaborating on the phrase Children imitate these adult recasts and expansionsChildren imitate these adult recasts and expansions

29. Copyright © 2007 Pearson Education Canada29 The Genetics of Difference The meaning of heritabilityThe meaning of heritability –A statistical estimate of the proportion of the total variance in some trait that is attributable to genetic differences among individuals within a group –Expressed as proportion (.60 or 60/100) –Maximum value is 1.0 Some variables such as height are highly heritable, other variables such as musical ability are moderately heritableSome variables such as height are highly heritable, other variables such as musical ability are moderately heritable

30. Copyright © 2007 Pearson Education Canada30 Facts About Heritability An estimate of heritability applies only to a particular group living in a particular environmentAn estimate of heritability applies only to a particular group living in a particular environment Heritability estimates do not apply to individuals, only to variations within a groupHeritability estimates do not apply to individuals, only to variations within a group Even highly heritable traits can be modified by the environmentEven highly heritable traits can be modified by the environment

31. Copyright © 2007 Pearson Education Canada31 Computing Heritability Studying adopted children allows researchers to compare correlations between the traits of adopted children and those of their biological and adoptive relativesStudying adopted children allows researchers to compare correlations between the traits of adopted children and those of their biological and adoptive relatives Results are used to compute heritability estimateResults are used to compute heritability estimate

32. Copyright © 2007 Pearson Education Canada32 Computing Heritability If identical twins are more alike than fraternal twins, then the increased similarity must be due to genetic influencesIf identical twins are more alike than fraternal twins, then the increased similarity must be due to genetic influences

33. Copyright © 2007 Pearson Education Canada33 Computing Heritability Investigators have also studied identical twins who were separated early in life and reared apartInvestigators have also studied identical twins who were separated early in life and reared apart Any similarities in traits between them should be primarily genetic and should permit a direct estimate of heritabilityAny similarities in traits between them should be primarily genetic and should permit a direct estimate of heritability

34. Copyright © 2007 Pearson Education Canada34 Our Human Diversity: The 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

35. Copyright © 2007 Pearson Education Canada35 Our Human Diversity: The Case of Intelligence Genes and individual differencesGenes and individual differences –Intelligence Quotient (IQ) measure of intelligences originally computed by dividing a person’s mental age by his or her chronological age and multiplying result by 100measure of intelligences originally computed by dividing a person’s mental age by his or her chronological age and multiplying result by 100 now derived from norms provided for standard intelligence testsnow derived from norms provided for standard intelligence tests –The kind of intelligence that produces high IQ scores is highly heritable.50 for children and adolescents.50 for children and adolescents.60 -.80 for adults.60 -.80 for adults

36. Copyright © 2007 Pearson Education Canada36 Twins and Intelligence Intelligence scores of identical twins are always more highly correlated than those of fraternal twinsIntelligence scores of identical twins are always more highly correlated than those of fraternal twins

37. Copyright © 2007 Pearson Education Canada37 Adopted Children and Intelligence The scores of adopted children are highly correlated with their biological parentsThe scores of adopted children are highly correlated with their biological parents

38. Copyright © 2007 Pearson Education Canada38 The Question of Group Differences Genetics are used to explain differences between groupsGenetics are used to explain differences between groups These differences are used to justify differential treatment for these groupsThese differences are used to justify differential treatment for these groups –Example: Differences between average IQ scores for African Americans and Caucasian Americans Genetic explanations have a flawGenetic explanations have a flaw –They use heritability estimates based on white samples to estimate the role of heredity in group differences

39. Copyright © 2007 Pearson Education Canada39 The Question of Group Differences Those studies overcoming past methodological problems fail to reveal genetic differences between blacks and whites on IQThose studies overcoming past methodological problems fail to reveal genetic differences between blacks and whites on IQ Examples:Examples: –Children fathered by black and white American soldiers in Germany after WWII and reared in similar German communities did not differ significantly in IQ –Black and white infants perform equally well on tests for novelty

40. Copyright © 2007 Pearson Education Canada40 The Environment and Intelligence Experiences that hinderExperiences that hinder –Poor prenatal care –Malnutrition –Exposure to toxins –Stressful family circumstances Experiences that helpExperiences that help –Good health care and nutrition –Mental enrichment in home and child care or school

41. Copyright © 2007 Pearson Education Canada41 Beyond Nature Versus Nurture Heredity and environment always interact to produce the unique mixture of qualities that make a humanHeredity and environment always interact to produce the unique mixture of qualities that make a human Psychological diversity is adaptivePsychological diversity is adaptive