The Nature and Nurture of Personality & Environmental Effects "Who am I?"
CHAPTER 9
Genetics and Evolution: The Inheritance of Personality
The Personality Puzzle, Eighth Edition
© 2019 W. W. Norton & Company
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Objectives
Discuss two biologically based approaches to how personality might be inherited.
Discuss how these approaches can be combined with each other and with other approaches.
Discuss two biologically based approaches to how personality might be inherited: behavioral genetics and evolutionary psychology.
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Behavioral Genetics
Addresses how personality traits that differ among individuals are passed from parent to child and shared by biological relatives
Examines how genes influence broad patterns of behavior
Controversy from associations with eugenics and cloning
Modern research is not concerned with these issues.
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Personality traits that differ among individuals: not concerned with traits that are the same for everyone (e.g., need for food and water), but only in traits that vary across individuals
Examines how genes influence broad patterns of behavior (i.e., personality traits)
Eugenics: idea that humanity could be improved through selective breeding
Modern research is not concerned with these issues: Eugenics and cloning are not feasible; personality is determined by more than just genetics.
Activity: The Island
Calculating Heritability (1)
To examine how phenotypes may be attributed to variation in genotypes
Compare similarity in personality between people who are and are not related and people who are related to different degrees
Monozygotic (MZ) versus dizygotic (DZ) twins
Assumption
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Phenotype: observable traits
Genotype: genetic structure
Assumption: Traits and behaviors influenced by genes should be more similar among more closely related people.
| Identical (MZ) | Fraternal (DZ) | |||
| Score of First Twin | Score of Second Twin | Score of First Twin | Score of Second Twin | |
| Pair 1 | 54 | 53 | 52 | 49 |
| Pair 2 | 41 | 40 | 41 | 53 |
| Pair 3 | 49 | 51 | 49 | 52 |
| … | … | … | … | … |
| … | … | … | … | … |
Calculating Heritability (2)
Heritability coefficient
Heritability coefficient definition: percentage of the variance of a trait in the population that can be attributed to variance in genes
These are the average correlations across many traits when age and gender are controlled.
Table 9.1 CALCULATING HERITABILITY
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Calculating Heritability (3)
Heritability coefficients from twin studies ≈ .40
Heritability coefficients from non-twin studies ≈ .20
Difference suggests that the effects of genes are interactive and multiplicative
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What Heritability Tells You (1)
Genes matter.
Insight into the effects of the environment on personality development
Shared family environment does not seem to matter very much
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Genes matter: Not all of personality comes from experience.
Shared family environment does not seem to matter very much: The average correlation of personality for adopted siblings is only .05.
What Heritability Tells You (2)
No or very little
Extreme conclusion
Behavioral genetics studies on the effect of shared family environment
Research with self-reports
Yes
Developmental psychology and shared family environment
Behavioral observation
Does the family matter?
Shared family environment definition: developmental outcomes are affected by growing up in the same household; affects juvenile delinquency, aggression, love styles, and the development of psychopathology
Effects of parent training: influences behavior and emotional control
Behavioral observation: when research is based on direct observation instead of self-reports, most traits are influenced by shared environment.
Activity: Identical Twins, Raised Apart
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What Heritability Can’t Tell You
Nature versus nurture
Traits with little variation will have heritabilities close to zero.
You can’t use heritability to determine what percent of a trait is determined by genetics and by the environment.
How genes affect personality
Create propensities to behave in certain ways
Discussion Question: Twin studies are prevalent in research on genetics, but what are some issues with twin studies in research on the inheritance of personality?
Discussion Question: What are some issues with assigning a percentage to heritability of personality (or anything)?
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Molecular Genetics
Uses the methods of molecular biology
DRD4 affects dopamine receptors.
5-HTT gene affects serotonin.
Alleles and cultural differences
Limitations: not applicable to everyone
Molecular genetics definition: determine whether differences in traits are correlated with differences in a particular gene
Alleles: variants of a gene; different alleles can be associated with different outcomes (anxiety, reaction to stress, amygdala response to fearful and unpleasant stimuli); prevalence may vary across cultural groups, but many genes are involved in complex traits.
Cultural difference: The allele that is related to neurotic responding is more common in some cultures (Japanese) than others (Caucasian).
Limitations: Many genes are involved in complex traits.
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Gene-Environment Interactions
Genes are not causal.
There must be an environment in order for there to be behavior.
Environments can affect heritabilities.
Genetic expression and social environment
Choice of environments (niche picking)
People can react differently to the same environment.
But lots of findings have not replicated
Genes are not causal; they only provide the design.
Environments can affect heritabilities: Nutrition and height (heritability will be higher when all children have the same level of nutrition, but lower when nutrition differs and therefore contributes differently to height); likewise for the relationship between intellectual stimulation and educational opportunities and IQ
Genetic expression and social environment: height and teasing
Choice of environments: People tend to select or create environments compatible with genetically influenced tendencies.
People can react differently to the same environment: People with a short allele for the 5-HTT gene were more likely to have depression after a stressful experience than those with the long allele, but there was no difference in depression for those who didn’t have a stressful experience; however, this is not found in every study.
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Genome-Wide Association Studies and Epigenetics
GWA studies
Progress has been slow.
The ultimate picture will be complicated.
Epigenetics: Experience affects biology.
May be possible to help people find environments that will lead to good outcomes
Genome-wide association (GWA) studies: look for associations between hundreds of thousands of genes or patterns of genes and personality in large samples; relationships will capitalize on chance, so look for relationships that are found in different samples.
Epigenetics definition: nongenetic influences on a gene’s expression (stress, nutrition); experience, especially early in life, can influence how or whether a gene is expressed during development; most research has been with rats (stress response differs as a function of early maternal care).
Activity: Behavioral Epigenetics and Personality
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The Future of Behavior Genetics
Focus on how genes and the environment interact
Genes have important influences on personality but are not predestination.
Understanding genetic predispositions could possibly be used to help people find environments likely to lead to good outcomes.
The big picture will be complicated because traits will be associated with many genes, with effects that depend both on other genes and on the environment.
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Evolutionary Personality Psychology
Addresses how patterns of behavior that characterize all humans may have originated in the survival value of these characteristics
Evolution and behavior
Assumption
Evolutionary mismatch
Aggression and altruism
Inclusive fitness
Self-esteem: “sociometer theory”
Depression
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Apply evolutionary theory to human behavior
Assumption: Behavioral patterns developed because they were necessary for survival in evolutionary history; characteristics with more survival value are more likely to appear in subsequent generations.
Evolutionary mismatch: The modern environment does not match human history; “natural” tendencies can be harmful or dangerous.
Aggression: increase protection, can lead to dominance in a social group and higher status; but also has negative outcomes such as fighting and war
Altruism: may increase inclusive fitness by helping and protecting others
Inclusive fitness definition: tendency to aid and protect other people, especially close relatives, to ensure survival of one’s own genes into succeeding generations
Self-esteem: reflection of degree of acceptance by others
Sociometer theory definition: feelings of self-esteem evolved to monitor the degree to which a person is accepted by others
Depression: pain signals something is wrong and must be fixed; crying may be a way of seeking social support; fatigue and pessimism may prevent wasting resources.
Discussion question: Ask students to name a few prevalent “maladaptive” behaviors. Discuss what the benefit or adaptive nature might be of one or two of these behaviors in terms of evolution. What would make them adaptive? What would make the opposite behavior maladaptive to evolution?
Evolutionary Personality Psychology: Individual Differences
Focus has been on general human nature
Adaptation
Diversity is necessary for adaptation.
Life history: Animals generally exhibit one of two approaches to reproduction, fast or slow.
Diversity is necessary for viability: Different traits and behaviors are adaptive in different situations .
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Accounting for Individual Differences
Behavioral patterns evolved as reactions to particular environmental experiences.
Several possible behavioral strategies evolved.
Some behaviors may be frequency dependent.
Human nature is flexible.
Behavioral patterns evolve as reactions to particular environmental experiences, so different environments will result in different behavioral patterns (traits).
Several possible behavioral strategies may have evolved: Each individual uses the strategy that makes the most sense given her other characteristics.
Some behaviors may be frequency dependent: They adjust according to how common they are (some behaviors are adaptive as long as only a few people do them; examples include psychopaths and con artists).
Human nature is flexible: This undermines the idea of evolution, which makes evolutionary theory controversial.
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Five Stress Tests for Evolutionary Psychology (1)
Methodology: Backward speculation is difficult to test empirically.
Responses
Reproductive instinct
Response
Conservative bias
Responses
Methodology: It doesn’t really make sense to think of an instinctual basis for rare behaviors (rape, stepchild abuse). It is probably not wise to think that every trait or behavior pattern has an adaptive advantage; some may be side effects of other adaptive behaviors.
Responses: Alternative explanations are always possible in any area; specific predictions can be tested.
Reproductive instinct: Not everyone wants as many children as possible.
Response: People do not have to consciously try to do what is evolutionarily adaptive.
Conservative bias: implies that the current behavioral order was inevitable and is unchangeable and appropriate (including male promiscuity and aggressive tendencies)
Responses: This is scientifically irrelevant; just because something is natural does not mean it is good.
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Five Stress Tests for Evolutionary Psychology (2)
Human flexibility
Response
Biological determinism or social structure?
Aspects of social structure
Theoretical importance
Practical importance
Human flexibility: People are more flexible than evolution and genetically determined behavior account for.
Response: acknowledges that we are evolved to behave flexibly and we can overcome innate urges
Biological determinism or social structure: Sex differences may be caused by social structure.
Aspects of social structure: Men tend to be warriors, rulers, and controllers of economic resources; women tend to stay near the home (to bear and raise children); this can be used to explain differences in mate preferences.
Theoretical importance: how much human nature is determined by evolution and biology versus the effects of society
Practical importance: The world is changing, and therefore sex differences may also change. Some change has already occurred.
Activity: Be an Evolutionary Psychologist
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| Share of husbands whose wives’ income top theirs in 1970 | Share of husbands whose wives’ income top theirs in 2007 |
| 4% | 22% |
Changes in Educational and Income Differences Between Husbands and Wives
Figure 9.5 Changes in Educational and Income Differences Between Husbands and Wives Increasingly often, married women have more education and make more money than their husbands. What does this fact imply for the future of marriage and traditional social roles?
Source: Taylor et al. (2010), p. 1.
Credit: Figure from Fry, Richard and D’Vera Cohn in Taylor, et. al., “Women, Men and the New Economics of Marriage,” Pew Research Center, Washington, D.C. (January 19, 2010). http://www.pewsocialtrends.org/2010/01/19/women-men-and-the-new-economics-of-marriage/.Reprinted with permission.
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Inheritance Is the Beginning, Not the End
How a person uses what was inherited depends on many things.
Genes determine where you start.
How a person uses what was inherited depends on many things: society and how one is raised
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Will Biology Replace Psychology?
Implication that personality is rooted in biology
Biological reductionism
We do not know enough about biology.
Biology leaves out most of psychology and does not ask many important psychological questions.
Biological reductionism definition: Everything about the mind can be reduced to biology
Important psychological questions: What are people thinking? How are people influenced by the environment, including other people?
Activity: Identity Shift
Discussion Question: If the study of psychology was replaced by biology at some point, what would that look like in terms of academia and research? What would be the implications in everyday life?
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Clicker Question 1
Genes affect behavior
directly, by being able to control certain behaviors.
because genes and behavior have a one-to-one correspondence.
by influencing the propensities or tendencies toward certain behaviors.
much more than does the environment.
Correct answer: c
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Clicker Question 1: Answer
Genes affect behavior
directly, by being able to control certain behaviors.
because genes and behavior have a one-to-one correspondence.
by influencing the propensities or tendencies toward certain behaviors. (correct answer)
much more than does the environment.
Correct answer: c
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Clicker Question 2
According to evolutionary personality psychology,
one way to explain personality and behavior is to look at how behaviors might have been adaptive for our ancestors.
personality is entirely determined by genetics.
everyone should have the same personality, and those who differ are maladaptive.
evolutionary theory can only be used to explain a few human behaviors.
Correct answer: a
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Clicker Question 2: Answer
According to evolutionary personality psychology,
one way to explain personality and behavior is to look at how behaviors might have been adaptive for our ancestors. (correct answer)
personality is entirely determined by genetics.
everyone should have the same personality, and those who differ are maladaptive.
evolutionary theory can only be used to explain a few human behaviors.
Correct answer: a
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Clicker Question 3
One criticism of evolutionary personality theory is that it
attempts to explain only a narrow range of behavioral patterns.
is too easy to find evidence against the theory.
places too much emphasis on how social structure influences behavior.
does not explain how people living now decide to behave.
Correct answer: d
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Clicker Question 3: Answer
One criticism of evolutionary personality theory is that it
attempts to explain only a narrow range of behavioral patterns.
is too easy to find evidence against the theory.
places too much emphasis on how social structure influences behavior.
does not explain how people living now decide to behave. (correct answer)
Correct answer: d
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Credits
This concludes the Lecture PowerPoint presentation for Chapter 9 of The Personality Puzzle.
For more resources, please visit https://digital.wwnorton.com/puzzle8.
Copyright © 2019 W. W. Norton & Company
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