1. Copyright © 2010 Pearson Education Canada3-1 Genes, Evolution, and Environment Chapter 3

2. Copyright © 2010 Pearson Education Canada3-2 Chapter 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

3. Where Do Differences Come From? Previously two perspectives:Previously two perspectives: –Nativists: emphasized genes & inborn characteristics (nature) –Empiricists: focused on learning & experience (nurture) Now studied broadly, including evolutionary psychology and behavioural geneticsNow studied broadly, including evolutionary psychology and behavioural genetics Copyright © 2010 Pearson Education Canada3-3

4. Unlocking the Secrets of Genes Genes are the basic units of heredity that are composed of DNA and located on chromosomesGenes are the basic units of heredity that are composed of DNA and located on chromosomes –Chromosomes: rod-shaped structures found in the nucleus of every cell (23 pairs) –DNA (deoxyribonucleic acid): chromosomal molecule that transfers genetic characteristics by way of coded instructions for the structure of proteins Copyright © 2010 Pearson Education Canada3-4

5. Unlocking the Secrets of Genes Within genes, four chemical elements of DNA “code” for protein synthesisWithin genes, four chemical elements of DNA “code” for protein synthesis –Adenine (A) –Thymine (T) –Cytosine (C) –Guanine (G) Genome – full set of genes in each cell of an organism (except sperm & egg cells)Genome – full set of genes in each cell of an organism (except sperm & egg cells) Copyright © 2010 Pearson Education Canada3-5

6. Studying Genetic Material Linkage studiesLinkage studies –Studies that look for patterns of inheritance of genetic markers in large families in which a particular condition is common Genetic markerGenetic marker –Segment of DNA that varies among individuals, has a known location on a chromosome, and can function as a genetic landmark for a gene Copyright © 2010 Pearson Education Canada3-6

7. Linking Genes & 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 pair (polygenic); from simple to complex traitsMost human traits are influenced by more than one gene pair (polygenic); from simple to complex traits Copyright © 2010 Pearson Education Canada3-7

8. The Genetics of Similarity Evolution is a change in gene frequencies within a population over many generationsEvolution is a change in gene frequencies within a population over many generations –Mechanism for change in the genetically influenced characteristics of a population –Changes may result from mutations (errors in copying of DNA sequences during division of cells that produce sperm & eggs) Copyright © 2010 Pearson Education Canada3-8

9. Natural Selection Evolutionary process formulated by DarwinEvolutionary process formulated by Darwin Individuals with genetically influenced traits that are adaptive in particular environments tend to survive & reproduce in greater numbers (“survival of the fittest”)Individuals with genetically influenced traits that are adaptive in particular environments tend to survive & reproduce in greater numbers (“survival of the fittest”) As a result, traits become more common in the populationAs a result, traits become more common in the population Copyright © 2010 Pearson Education Canada3-9

10. Sexual Selection Darwin also proposed that genes were determined by sexual selectionDarwin also proposed that genes were determined by sexual selection –Intersexual 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 sex Copyright © 2010 Pearson Education Canada3-10

11. Traits & Preferences Evolutionary biologists start with an observation about a characteristic and try to account for it in evolutionary termsEvolutionary biologists start with an observation about a characteristic and try to account for it in evolutionary terms Evolutionary psychologists ask what sorts of challenges humans might have faced and infer what behavioural tendencies may have been selected to overcome these challengesEvolutionary psychologists ask what sorts of challenges humans might have faced and infer what behavioural tendencies may have been selected to overcome these challenges Copyright © 2010 Pearson Education Canada3-11

12. Mental Modules One perspective is that mind reflects mental modules shaped through evolutionOne perspective is that mind reflects mental modules shaped through evolution –Mental modules: a collection of specialized and independent sections of the brain, developed to handle specific survival problems (e.g., location of food, finding a mate) Critics point out that not all traits are adaptive but may be by-products of other traits (not isolated)Critics point out that not all traits are adaptive but may be by-products of other traits (not isolated) Copyright © 2010 Pearson Education Canada3-12

13. Innate Human Characteristics Evolution has shaped human development through innate characteristics such as:Evolution has shaped human development through innate characteristics such as: 1.Infant reflexes 2.An interest in novelty 3.A desire to explore & manipulate objects 4.An impulse to play & fool around 5.Basic cognitive skills Copyright © 2010 Pearson Education Canada3-13

14. Phenotype Matching According to evolution, we should favour family members to promote survival of genetic materialAccording to evolution, we should favour family members to promote survival of genetic material –Phenotype matching: an individual’s ability to assess relatedness to another individual based on phenotype (expression of gene-environment interaction) E.g., DeBruine’s (2002) trust studyE.g., DeBruine’s (2002) trust study Copyright © 2010 Pearson Education Canada3-14

15. Our Human Heritage: Language LanguageLanguage –A system that combines meaningless elements such as sounds or gestures to form structured utterances that convey meaning –Surface structure: the way a sentence is spoken –Deep structure: how a sentence is to be understood Copyright © 2010 Pearson Education Canada3-15

16. Copyright © 2010 Pearson Education Canada3-16

17. Innate Capacity for Language Chomsky argued that we are born with a language acquisition device that guides the development of language with proper exposureChomsky argued that we are born with a language acquisition device that guides the development of language with proper exposure –To transform surface into deep structures, children must use syntax (which is not taught) –Reflects a universal grammar where brains are sensitive to core features common to all languages (e.g., nouns & verbs) Copyright © 2010 Pearson Education Canada3-17

18. Evidence Supporting Chomsky 1.Children in different cultures go through similar stages of linguistic development 2.Children combine words in ways that adults never would 3.Adults do not consistently correct their children’s syntax, yet children learn to speak correctly anyway 4.Children not exposed to adult language might invent a language of their own 5.Infants as young as 7 months can derive simple linguistic rules from a string of sounds Copyright © 2010 Pearson Education Canada3-18

19. Learning & Language Other scholars argue environment plays larger role in language (not all innate)Other scholars argue environment plays larger role in language (not all innate) –Computer neural networks: mathematical models of the brain that can “learn” some aspects of language –Other arguments: major differences in acquisition, parents recast sentences rather than corrections, children imitate recasts & expansions Copyright © 2010 Pearson Education Canada3-19

20. Our Human Heritage: Courtship & Mating SociobiologySociobiology –Interdisciplinary field that emphasizes evolutionary explanations of social behaviour in animals & humans –We have a tendency to act in ways that maximize chances of passing on genes as well as helping close biological relatives do the same Copyright © 2010 Pearson Education Canada3-20

21. Evolution & Sexual Strategies Differences in survival & mating problems have led to differences in aggression, dominance, & sexual strategies between sexesDifferences in survival & mating problems have led to differences in aggression, dominance, & sexual strategies between sexes –Males compete with other males to access females, inseminate as many as possible –Females have larger biological investment in pregnancy so choose dominant males with resources & status Copyright © 2010 Pearson Education Canada3-21

22. Differences in Sexual Strategies 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 Copyright © 2010 Pearson Education Canada3-22

23. Evolution & Preferences Cross-cultural studies have found consistent differences between males and femalesCross-cultural studies have found consistent differences between males and females Mating preferences such as age predict status & dominance in men and fertility in womenMating preferences such as age predict status & dominance in men and fertility in women Copyright © 2010 Pearson Education Canada3-23

24. Culture & the “Genetic Leash” Criticisms of evolutionary explanations of sex differences:Criticisms of evolutionary explanations of sex differences: –Explanations of infidelity & monogamy based on gender stereotypes –Sexual behaviour is varied and not solely for reproductive purposes –Ignores cultural influences on sexual behaviour –Available mates were much more limited than currently –Similarity & proximity among strongest predictors of mate choice Copyright © 2010 Pearson Education Canada3-24

25. The Genetics of Difference The meaning of heritability:The 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 (e.g.,.60 or 60/100), with maximum value of 1.0 –High heritability means greater genetic contribution to trait Copyright © 2010 Pearson Education Canada3-25

26. Facts about Heritability 1.Estimates of heritability apply only to a particular group living in a particular environment 2.Heritability estimates do not apply to individuals, only to variations within a group 3.Even highly heritable traits can be modified by the environment Copyright © 2010 Pearson Education Canada3-26

27. Computing Heritability Infer heritability by studying people whose genetic similarity is knownInfer heritability by studying people whose genetic similarity is known Separate role of genetics & environment by studying adopted childrenSeparate role of genetics & environment by studying adopted children Copyright © 2010 Pearson Education Canada3-27

28. Computing Heritability Another approach compares identical (monozygotic) with fraternal (dizygotic) twinsAnother approach compares identical (monozygotic) with fraternal (dizygotic) twins If identical more similar than fraternal twins, greater the genetic influenceIf identical more similar than fraternal twins, greater the genetic influence Also study twins separated early in life & raised apartAlso study twins separated early in life & raised apart Copyright © 2010 Pearson Education Canada3-28

29. Our Human Diversity: Intelligence Intellectual functioning usually measured by an intelligence quotient (IQ) scoreIntellectual functioning usually measured by an intelligence quotient (IQ) score –Originally computed by dividing a person’s mental age by chronological age and multiplying by 100; now derived from norms on standardized IQ tests –Kind of intelligence that produces high IQ scores highly heritable: Children & adolescents (.40-.50); adults (.60-.80)Children & adolescents (.40-.50); adults (.60-.80) Copyright © 2010 Pearson Education Canada3-29

30. Twins, Adoption, & Intelligence IQ scores of identical twins more highly correlated than those of fraternal twinsIQ scores of identical twins more highly correlated than those of fraternal twins Also, scores of adopted children are highly correlated with their biological parentsAlso, scores of adopted children are highly correlated with their biological parents Copyright © 2010 Pearson Education Canada3-30

31. Group Differences If genes influence individual differences, can they account for differences between groups?If genes influence individual differences, can they account for differences between groups? –Differences have been used to justify differential treatment of groups (e.g., ethnicity, gender) Example: Differences in IQ scores between African Americans and Caucasian AmericansExample: Differences in IQ scores between African Americans and Caucasian Americans Copyright © 2010 Pearson Education Canada3-31

32. Explaining Group Differences Genetic explanations have a fatal flawGenetic explanations have a fatal flaw –Heritability estimates rely on Caucasian samples to estimate role of heredity between groups Studies that overcome methodological flaws fail to reveal genetic differences in IQ scores as a function of ethnicity (e.g., Eyferth, 1961; Fagan, 1992)Studies that overcome methodological flaws fail to reveal genetic differences in IQ scores as a function of ethnicity (e.g., Eyferth, 1961; Fagan, 1992) –Differences within groups may have a genetic basis but that does not mean differences between groups are genetic Copyright © 2010 Pearson Education Canada3-32

33. Environment & Intelligence Environmental influences associated with reduced mental ability:Environmental influences associated with reduced mental ability: –Poor prenatal care –Malnutrition –Exposure to toxins –Stressful family circumstances Copyright © 2010 Pearson Education Canada3-33

34. Environment & Intelligence Environmental influences associated with enhanced mental abilities:Environmental influences associated with enhanced mental abilities: –Good health care & nutrition –Mental enrichment in home, child care, school –Parental interaction, discussion, & encouragement of mental processing Copyright © 2010 Pearson Education Canada3-34

35. 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 –E.g., variations in gene “expression” according to internal & external environments Psychological diversity is adaptivePsychological diversity is adaptive Copyright © 2010 Pearson Education Canada3-35

36. End of Chapter 3 Copyright © 2010 Pearson Education Canada3-36