Genetics and Personality - Chapter 6 PDF

Genetics and Personality Chapter 6 Dr. Linden-Andersen PSY 206 © 2023 McGraw Hill Limited 1 Learning Objectives 1. Discuss the history and current state of the scientific study of genes and personality, noting concerns and controversies. 2. Define heritability and describe primary goals...

Genetics and Personality Chapter 6 Dr. Linden-Andersen PSY 206 © 2023 McGraw Hill Limited 1 Learning Objectives 1. Discuss the history and current state of the scientific study of genes and personality, noting concerns and controversies. 2. Define heritability and describe primary goals and research methods of behavioural genetics. 3. Describe the major findings from behavioural genetics research. 4. Explain the difference between shared and nonshared environmental influences, citing key findings. 5. Summarize the insights gained from molecular genetics. 6. Identify and explain how genetic and environmental factors interact. © 2023 McGraw Hill Limited 2 The Biological Domain A record of the past is written in the Genetic Blueprint © 2023 McGraw Hill Limited 3 Genes and Personality Genome refers to the complete set of genes that an organism possesses Human genome contains 20,000–30,000 genes on 23 pairs of chromosomes Human Genome Project is designed to sequence the entire human genome—i.e., identify the particular sequence of DNA molecules in human species Identifying sequence of DNA molecules does not mean identifying the function of each molecule © 2023 McGraw Hill Limited 4 Genes and Personality 2 Most genes in a human genome are the same for all humans Small number of genes are different for different individuals, including genes that indirectly code for physical traits and for personality traits © 2023 McGraw Hill Limited 5 Controversy About Genes and Personality Behavioural geneticists attempt to determine the degree to which individual differences in personality (for example) are caused by genetic and environmental differences Highly controversial Ideological concerns Concerns about renewed interest in eugenics © 2023 McGraw Hill Limited 6 Controversy About Genes and Personality 2 Modern behavioural geneticists who study personality are Typically very careful about addressing implications of work Are sensitive to ideological concerns Knowledge is better than ignorance Finding that a personality trait has a genetic component does not mean the environment is powerless to modify the trait © 2023 McGraw Hill Limited 7 Sorting Science, Politics, and Values Environmentalist view Personality was determined by socialization practices Controversy centred around studies of intelligence Links between science and politics, and between knowledge and values, are complex but need to be confronted Scientific method is self-correcting © 2023 McGraw Hill Limited 8 Behavioural Genetics Determine the percentage of individual differences in a trait that can be attributed to genetic differences and percentage that can be attributed to environmental differences Determine the ways in which genes and environment interact and correlate with each other to produce individual differences Determine precisely where in the “environment” environmental effects exist—e.g., parental socialization, different teachers © 2023 McGraw Hill Limited 9  Behavioural Genetics 2 Height Genetic research confirmed: Environmental and genetic factors are important Roughly 90 percent due to genetics Environment is 10 percent @David Keeler/Getty Images The actor Danny DeVito (left) is about 60 centimetres shorter than basketball player Lebron James (right) © 2023 McGraw Hill Limited 10  Behavioural Genetics 3 Methods used by behavioural geneticists can be applied to any individual variable Height and weight Differences in intelligence Differences in personality traits Differences in attitudes Percentage of Variance Individuals vary, or are different from each other, and this variability can be partitioned into percentages that are due to different causes © 2023 McGraw Hill Limited 11  What Is Heritability? Heritability: A statistic that refers to the proportion of observed variance in a group of individuals that can be accounted for by genetic variance Phenotypic variance: Refers to observed individual differences, such as in height, weight, or personality © 2023 McGraw Hill Limited 12  What Is Heritability? 2 Genotypic variance: Refers to individual differences in the total collection of genes possessed by each person Environmentality: Proportion of observed variance in group of individuals attributable to environmental variance © 2023 McGraw Hill Limited 13 Misconceptions About Heritability Heritability CANNOT be applied to single individual Heritability is NOT constant or immutable Heritability is NOT a precise statistic © 2023 McGraw Hill Limited 14 Nature-Nurture Debate Clarified Arguments about whether genes or the environment in more determinant of personality No such debate at the individual level Influence of genes and of environment is only relevant for the discussion of group-level variation © 2023 McGraw Hill Limited 15 Research Methods in Behavioural Genetics Selective Breeding—Studies of Our Canine Friends Family Studies Twin Studies Adoption Studies © 2023 McGraw Hill Limited 16  Selective Breeding Can only occur if a desired trait is heritable Selective breeding studies of dogs Select @Comstock Images/Alamy Randy J. Larsen desirable The Labrador retrievers (left) and qualities the Chesapeake Bay retriever Cannot be (right) have been selectively bred ethically for certain characteristics. conducted with Their webbed feet make them humans strong swimmers and excellent water retrievers. © 2023 McGraw Hill Limited 17 Family Studies Correlates the degree of genetic overlap among family members with the degree of similarity in personality trait If a trait is highly heritable Family members with greater genetic relatedness should be more similar to one another on the trait than family members who are less closely genetically related © 2023 McGraw Hill Limited 18 Family Studies Problem: Members of a family who share the same genes also usually share the same environment—confounds genetic with environmental influences Thus, family studies are never definitive © 2023 McGraw Hill Limited 19 Twin Studies Estimates heritability by gauging whether identical (monozygotic or MZ) twins, who share 100 percent of genes, are more similar than fraternal (dizygotic or DZ) twins, who share only 50 percent of genes If MZ twins are more similar than DZ twins, this provides evidence of heritability Calculating heritability—many formulas, simple one: Two times difference between correlation (“r”) for MZ twins and DZ twins, or 2 (rmz – rdz) © 2023 McGraw Hill Limited 20 Twin Studies 2 Two assumptions of the twins method Equal environments assumption Assumes that the environments experienced by identical twins are no more similar to each other than the environments experienced by fraternal twins Monozygotic Twins Dizygotic Twins © 2023 McGraw Hill Limited 21 Adoption Studies Positive correlations on Traits between adopted children and adoptive parents provide evidence of environmental influence Between adopted children and genetic parents provide evidence of genetic influence Adoption studies are powerful because they get around the equal environments assumption Assumption that adopted children and their adoptive and genetic parents are representative of the general population—questionable © 2023 McGraw Hill Limited 22 Adoption Studies 2 Problem of selective placement of adopted children Most powerful research design that combines strengths of twin and adoption studies is studying twins reared apart © 2023 McGraw Hill Limited 23  Major Findings from Behavioural Genetic Research Personality Traits Attitudes and Preferences Drinking and @Shutterstock/Kzenon Smoking The trait of activity level—how vigorous and energetic a person is—shows a moderate degree of heritability © 2023 McGraw Hill Limited 24 Personality Traits Most commonly studied personality traits in behavioural genetic designs are extraversion and neuroticism Lower heritabilities Summaries of behavioural genetic data yield heritability estimates for major personality traits of about 50% Extraversion, agreeableness, conscientiousness, neuroticism, openness to experience © 2023 McGraw Hill Limited 25 Attitudes and Preferences Wide variance in heritability of attitudes Some attitudes (e.g., traditionalism) show high heritability (about.60) Whereas others show low or no heritability e.g., beliefs in God Not clear why only some attitudes appear to be heritable Sexual orientation Developing area Current evidence suggests that genes provide modest and indirect influence (via childhood gender nonconformity) on adult sexual orientation © 2023 McGraw Hill Limited 26 Drinking and Smoking Behavioural manifestations of personality traits such as sensation seeking, extraversion, neuroticism Drinking alcohol and smoking cigarettes are stable over time Both show evidence of heritability © 2023 McGraw Hill Limited 27 Marriage Genes can influence the propensity to marry or stay single 68% Genes also play a role in marital satisfactions Roughly 50% heritable for women Disposition optimism, warmth, and low aggressiveness accounted for marital satisfaction and husband’s marital satisfaction © 2023 McGraw Hill Limited 28 Shared Versus Nonshared Environmental Influences: A Riddle Same studies that suggest moderate heritability also provide good evidence of the importance of environmental influences Personality characteristics show heritabilities in 40-60 percent range; hence, showing substantial degree of environmentality © 2023 McGraw Hill Limited 29 Shared Versus Nonshared Environmental Influences: A Riddle 2 Two key types of environmental influences Shared: In family environment, features of the environment shared by siblings e.g., number of books in home Nonshared: In family environment, features of the environment that differ across siblings e.g., different friends, different teachers © 2023 McGraw Hill Limited 30  Molecular Genetics Techniques designed to identify specific genes associated with personality traits D4DR— Gene located on the short arm of chromosome 11, Codes for dopamine receptor Men with DRD4 7R+ allele invest more money in a financial risk game. © 2023 McGraw Hill Limited 31 Molecular Genetics 2 D4DR Gene Most frequently examined association between D4DR gene and a personality trait involves “novelty seeking” Individuals with the “long repeat” version of D4DR gene Higher on novelty seeking than individuals with the “short repeat” version of gene Several failures to replicate association and, when replicated, association is weak, however Genome-wide association studies (GWAS) © 2023 McGraw Hill Limited 32 Genes and the Environment Genotype-Environment Interaction Genotype-Environment Correlation © 2023 McGraw Hill Limited 33 Genotype-Environment Interaction Differential response of individuals with different genotypes to the same environments For example, task performance of introverts versus extraverts in loud versus noisy conditions Individual differences interact with environment to affect performance © 2023 McGraw Hill Limited 34 Genotype-Environment Correlation Differential exposure of individuals with different genotypes to different environments Genotype-environment correlations can be positive or negative Three types of genotype-environment correlations 1. Passive 2. Reactive 3. Active © 2023 McGraw Hill Limited 35 Genotype-Environment Correlation 2 Passive: Parents provide both genes and environment to children, yet children do nothing to obtain that environment Child’s verbal ability and the number of books in home © 2023 McGraw Hill Limited 36 Genotype-Environment Correlation 3 Reactive: Parents (or others) respond to children differently depending on the child’s genotype Baby’s liking for cuddling and the mother’s cuddling behaviour © 2023 McGraw Hill Limited 37 Genotype-Environment Correlation 4 Active: Person with particular genotype seeks out a particular environment High sensation seekers expose themselves to risky environments © 2023 McGraw Hill Limited 38 Epigenetics The study of how experience (i.e., environmental influences) can determine how or whether a gene is expressed in an organism Common mechanisms include chemical processes like DNA methylation and histone modification Derived from animal research May play a role in anxiety and stress reactivity Epigenetic changes can change in childhood and adulthood © 2023 McGraw Hill Limited 39 Summary and Evaluation Empirical evidence on heritability has become stronger and stronger through the use of behavioural genetic methods: selective breeding, family studies, twin studies, and adoption studies Much of the environmental influence is due to nonshared variables— experiences unique to siblings Heritability versus environmentality © 2023 McGraw Hill Limited 40 Summary and Evaluation 2 Genotype-environment interaction and correlations, as well as the new field of molecular behaviour genetic analysis and epigenetics, are promising areas for future work © 2023 McGraw Hill Limited 41