Chapter 6

Genetics, Evolution, and Personality

Modified: 2022-06-29 11:08 am

The Human Genome Project along with Sociobiology and Evolutionary Psychology stimulated a revival of the genetic approach to personality. Its use of twin studies and recently developed direct methods for evaluating genetic information led to its application to the study of personality.

• Learning Objectives:
  • 6.1 Describe the procedures of twin studies and adoption studies
  • 6.2 Identify some of the personality qualities that are genetically influenced
  • 6.3 Identify two issues in behavioral genetics that complicate the process of drawing conclusions from findings
  • 6.4 Examine the kind of work done in the field of molecular genetics and genomics
  • 6.5 Examine four ways in which psychologists suggest that former evolutionary processes shaped present-day human behavior
  • 6.6 Analyze how the assessment from the genetic viewpoint and the trait viewpoint differ
  • 6.7 Outline two ways in which researchers have found evidence of genetic influence on problems in behavior
  • 6.8 Identify two criticisms of using evolutionary ideas to understand personality
• 6.1 Determining Genetic Influence on Personality (p. 67)
  • Hippocrates and Galen hypothesized physical body types and mechanisms for them. Does physical embodiment affect personality?
  • Behavioral genetics is the study of genetic influences on behavior, including personality
    • 6.1.1 Twin Study Method
      • Examines monozygotic twins (identical twins, MZ)
        • One egg splits in two
        • Genetically identical
      • Dizygotic twins (fraternal twins DZ)
        • Sperm fertilize two eggs
        • Share 50% of their genes
      • Determination of type is vital to research
  • Heretability estimate gives a measure of inheritance units (See Figure 6.1 below)

• 6.1.2 Adoption Research
  • Adoption studies examine how much adopted children resemble their parents
    • That resemblance would be environmentally based
  • MZ twins reared apart
    • If heredity is important MZ twins should be more similar than DZ twins
• Box 6.1 Early Biological Views: Physique and Personality (p.68)
• Kretschmer and Sheldon examined the relationship of body type and behavior
  • Sheldon defined three body types (see graphic below)
    • Endomorphs: plump, soft and round
    • Mesomorphs: muscular, hard and strong
    • Ectomorphs: thin, delicate and frail
  • He proposed three temperaments
    • Viscerotonia: calm, tolerant, sociable, loves comfort, easygoing
    • Somatotonia: bold, assertive, adventurous, active
    • Cerebrotonia: solitary, sensitive to pain, apprehensive
  • Social expectations may be the mechanism for associating the first list with the second

• 6.2 What Personality Qualities Are Genetically Influenced? (p. 69)
• 6.2.1 Temperaments
  • Temperament is an inherited personality trait present in early childhood
    • Activity level
      • vigor: behavioral intensity
      • tempo: behavioral speed
    • Sociability
      • prefer being with people
      • social responsiveness and stimulation
    • Emotionality
      • Ease of becoming emotionally upset
• 6.2.2 More Recent Views of Temperament
  • Approach-Avoidance
    • Resembles emotionality
  • Effortful Control
    • Attention management
    • Suppress approach
    • High levels associated with ewer problems with antisocial behavior as adults
• 6.2.3 Inheritance of Traits
  • The Five-Factor model shows consistent genetic influence
  • May suggest common genetic heritage of the factors
• 6.2.4 Temperaments and the Five-Factor Model
  • Big Five supertraits are similar to temperaments
    • Emotionality and neuroticism
    • Approach and Extraversion
    • Sociability and Agreeableness
    • Effortful Control and Conscientiousness
    • Intelligence and Openness to Experience
  • Not a perfect fit
• 6.2.5 How Distinct Are the Genetics of Other Qualities?
  • Genetics accounts for many personality phenomena:
    • Risk of divorce
    • Having adverse life events
    • Particular attitudes
  • Jang et al. 1998 argue:
    • The five supertraits are heritable
    • The facet traits, too, are heritable
• 6.2.6 Environmental Influences
  • The enviroment makes twins more different: nonshared environmental effect
  • Siblings vary in their friends
    • So, peer effects may not be shared
  • Family roles may be complementary, so different things are learned
  • Parents may favor one over the other
  • Research methods may obscure these differences
• 6.3 Complications in Behavioral Genetics (p. 72)
  • 6.3.1 Heritability Varies with the Environment
    • Figure 6.2 (below) shows effects of genetics and environment as a function of parental education
    • Note that for parents with little or no education genetics had hardly any effect
    • But for parents who were highly educated the genetic effect was large
    • Thus, parent's educational level must be controlled before inferring from sample data

• 6.3.2Correlations between Genetic and Environmental Influences
  • Genetics and Environment are correlated
    • Examples:
      • High IQ people seek out environments that promote learning
      • Slightly introverted people may seek out solitary pursuits (and become more introverted)
      • Slightly extroverted people may become involved in group activities (and become more extroverted
    • This is an issue when any genetic propensity meets a different or unusual environment
      • Parents, for example, (outsider's genes) may set up such an environment
      • Children (own genes) may seek out such environments
      • People may induce others to act in particular ways
• 6.4 Molecular Genetics and Genomics (p. 73)
  • Genome
    • The Human Genome Project discovered that humans had about 30,000 genes
    • That project transformed the study of genetics and made it possible to directly assess gene effects. In the past, those effects had to inferred indirectly
  • Alleles are DNA codes that appear at particular locations
  • Genotype: The genotype is the actual DNA sequence each individual possesses. Identical twins (see below) have the same DNA sequences.
    • The odds of any two unrelated humans having the exact same DNA code is one in 70 trillion
  • Polymorphism: Most of the information coded by DNA comes from multiple alleles
    • Only a very small number of alleles code for a particular structure of behavior singly
  • Phenotype: The phenotype is the physical expression of the genotype in structure or behavior in conjunction with the environment.
    • Example: If LeBron James had been born during a war and had been severely malnourished he would not have achieved his 6/9" height
  • Quantitative Genetics: is used in research with identical twins to confirm that they are, in fact, identical
  • Molecular Genetics (Genomics): is the now possible practice of "reading" an individual's DNA code
    • (FYI: don't accept the cup of water given you at the police station. They may be collecting your genome)
  • Candidate Gene Strategy: this is an older, simpler method of assessing the genome by selecting gene locations thought to be linked to behavior or personality
  • Particular Genes: Here are some genes of interest to psychologists
    • DRD4: in its long allelle form it correlates with novelty seeking, risky decisions, and inability to delay behavior
    • DRD2 (now ANKK1): linked to fun seeking
    • Both of the genes above are involved in the dopamine pathway
    • 5HTTLPR: in its short allelle variant it is associated with neuroticism and low agreeableness scores. It is part of the serotonin pathway
  • Genome-wide association studies (GWAS): this new technique allows the entire genome to be analyzed. But it is expensive and time consuming
    
• 6.4.1 Gene-by-Environment Interactions
  • Today, it is obvious that many genes interact with the environment
  • Common examples involve stressful environments
    • Sometimes the stressful environment will cause one genotype to react negatively in terms of the individual's behavior while another genotype will not
    • Some beneficial environment will not "turn on" a gene that in a stressful environment might activate and cause problems
• 6.4.2 Environmental Effects on Gene Expression
  • Gene expression is when a gene creates a protein
  • Gene expression varies throughout the body
    • Methylation, the addition of a methyl group to a gene's promoter region can affect gene expression
    • The more methylation, the less expression
    • This is an epigenetic effect
    • Diet and stress can cause methylation
  • Much of the research on genetic effects has been conducted on animals but human research is also done
  • Epigenetic changes can be passed on to subsequent generations greatly complicating the gene by environment interaction
• Box 6.2 Theoretical Issue: Universal Adaptations and Why There Are Individual Differences (p. 75)
  • Different biologically based characteristics imply different alleles for those characteristics
  • Selection can take several forms
    • Evolutionary selection is related to reproductive success (RS)
      • In the long run characteristics leading to RS will become more numerous within a species
    • In directional selection RS pushes a given characteristic toward an extreme
      • Example: the peppered moth (Biston betularia) in England
        • In the 19th century soot from industry smokestacks made the dark version of the moth have higher RS
        • In the 20th century green practices made the light version of the moth have higher RS
    • In stabilizing selection RS is greatest for characteristics near the middle forms of a characteristic
      • Example: clutch size (the number of eggs laid) is subject to stabilizing selection
        • Birds that lay to few or too many eggs will have lower RS
      • In humans, agreeableness is likely subject to stabilizing selection
    • In disruptive selection the environment may favor two opposite form of a characteristic
      • There, RS depends on the environment
      • Example: Brown or Green variants of a grasshopper
        • The brown variant has higher RS when hidden in dead vegetation
        • The green variant has higher RS when hidden in living vegetation
        • In both cases RS comes from avoiding predation by birds
• 6.5 Evolution and Human Behavior (p. 75)
  • Has evolution affected personality?
  • This is the focus of sociobiology and evolutionary psychology
    
    • 6.5.1 Sociobiology and Evolutionary Psychology
      • Sociobiology focused on the biological basis for social behavior in social species
        • FYI, most species are asocial or only show sociality in limited contexts
      • Altruism was explained on the basis of kin selection
        • Older explanations saw altruistic behavior as leading to lowered RS
        • The concept of shared genes among related individuals is the basis for kin selection.
        • Haldane once said, “I would lay down my life for two brothers or eight cousins”
        • His logic being that two brothers or eight cousins would be population genetic equivalent of his genes
      • Sociobiology has also suggested mechanisms for revenge and forgiveness
        
    • 6.5.2 Genetic Similarity and Attraction
      • Rushton proposed that perceived genetic similarity (e.g., phenotype) affects a number of phenomena. He called his notion: genetic similarity theory
        • Married couples share 50% of genetic markers
        • Married couples with children share 52% of genetic markers
        • Heterosexual male friends share 54% of genetic markers
      • Facial and body features and possibly body odor may be the signals for such relationships
    • 6.5.3 Avoidance of Incest
      • Inbreeding leads to bad genetic outcomes (decreased cognitive abilities, reduced height, and poor lung function)
      • The Incest Taboo is seen in all human groups
        • In other words, humans avoid mating with close relatives
        • Lieberman et al. (2011) used phone calls by college women to their fathers and mothers when the women were near or far from their period of maximum fertility
        • Results were clear, women called their fathers less when they were maximally fertile (See Figure 6.3 below)

• 6.5.4 Mate Selection and Competition for Mates
  • Human personality and genetics meet a the junction of mate selection
  • Because of reproductive mechanism differences, males and females have different short term and long term strategies regarding mating and sending their genes into the next generation
  • Females
    • Invest more in their offspring (one egg, nine month pregnancy, years of childcare)
    • Are choosier about mating and mating partners
    • Look for ideal male: one with good genes, who will provide parental care, and support mother and children
    • Stress youth and beauty in themselves
    • Look for resources, dominance, high status, kindness, and intelligence
    • Sexual intercourse during ovulation may overwhelm their usual mate requirements
    • Prefer slightly older men
    • More interested in romantic media
    • Look at males as success objects
  • Males
    • Invest less in their offspring (millions of sperm cells)
    • Maximize sexual opportunities
    • Stress status, dominance, and wealth
    • Look for reproductive capacity in women
    • Look for attractiveness, kindness, and intelligence
    • Prefer younger women
    • More interested in casual sex
    • More interested in sexual variety
    • More interested in visual erotica
    • Look at females as sex objects
• Jealousy
  • Males more concerned about paternity
    • So jealousy is maximal over sexual infidelity
    • Men are more jealous when a potential rival is dominant
  • Females more concerned about long-term support
    • So jealousy is maximal over emotional infidelity
    • Women are more jealous when a potential rival is attractive
      • FYI: warning to males, never tell your partner, "Your friend Gloria understands me so much better than you."
• Table 6.1 (below) Summarizes this section

• 6.5.5 Mate Retention and Other Issues
  • Getting a mate is the first problem
  • Keeping a mate is next
  • Men
    • Spend money and give into mate's desires
    • Work harder to keep their mate when she is physically attractive
    • Communication is:
      • individualistic, dominance-oriented, and focused on problem solving
  • Women
    • Make themselves attractive
    • Let other women know their mate is already taken
    • Women look harder to keep their mate when he has a high income
    • Communication is:
      • inclusive, focused on sharing, has a communal approach
• FYI: here's another tip for men:
  • When your mate says something like, "I hate my boss and my job." Don't say, "Let me call the bastard." Instead, say "I know how you feel."
• Similarities between men and women
  • Good humor
  • Pleasing personality
  • Agreeable
  • Emotionally stable
  • Intelligent
  • Symmetrical faces (symmetry is a sign of good genes)
    
• 6.5.6 Aggression and the Young Male Syndrome
  • Do ancient evolutionary pressures still act today?
    • Male posturing is common
    • Failure to secure reproduction may be a cause (especially when unemployed)
  • Homicide
    • Males more likely to kill than females
      • FYI: Females main motive for killing men is self-defense
    • Adolescent and young males have the highest propensity for killing (in other words, during their age of maximal potential RS)
    • Males kill more males that they kill females
    • Guns in USA make killing easier
    • Status attacks predict killing
    • Mating motivation increases in the presence of other males
    • Killing of children is rare, but more likely by stepparents of younger children
  • Other Aspects of Mate Retention
    • Some are coercive
      • controlling behavior
      • physical abuse
    • Title IX efforts today include making such aspects known to males
• 6.6 Assessment from the Genetic and Evolutionary Perspective (p. 81)
  • Similar to assessment in the trait perspective
  • Adds genetic "traits" to the assessment equation
  • Direct gene assessment unlikely any time soon because of polymorphism
    • FYI: for a dystopian view of genetic assessment in the future see the movie Gattaca (trailer)
• Box 6.3 Living in a Postgenomic World (p. 81)
  • Mapping the human genome has led to many benefits and potential problems:
    • Benefits
      • Identifying and curing single gene problems
        • Tay-Sachs, sickle cell anemia
      • Genetic therapies
      • Preventive medicine
    • Problems
      • Designer babies
        • Parents who insist upon adding specific genes to their unborn child
      • Discrimination against people identied as genetically challenged
      • Identifying people as potentially prone to antisocial behavior or criminal tendencies
      • Securing insurance for genetic issues
• 6.7 Problems in Behavior, and Behavior Change from the Genetic and Evolutionary Perspective (p. 81)
  • The genetic approach has revealed problems in behavior but, at present, too many genes are involved for the possibility of analyzing, predicting, and solving those problems
    
    • 6.7.1 Schizophrenia and Bipolar Disorder
      • Schizophrenic symptoms include:
        • disorientation
        • confusion
        • cognitive disturbances
        • separation from reality
      • The concordence rate for identical twins each developing schizophrenia is 50% and 9% for fraternal twins
      • Although there is a strong heritable component to schizophrenia context plays a role
        • The diathesis-stress view may be at work here (a Gene by Environment Interaction)
      • Bipolar symptoms include:
        • Mania
          • Episodes of frenetic, hyperactive, grandiose, talkative behavior accompanied by a rush of ideas
          • May be accompanied by positive or angry emotions
        • Depression
          • Episodes of worthlessness, lengthy sleep, loss of spark, and possible suicide
        • Onset of bipolar disorder can be sudden
        • Lack of sleep or experiencing success in goals can trigger symptoms, another Gene by Environment Interaction)
          
    • 6.7.2 Substance Use and Antisocial Behavior
      • Alcohol and other drug abuse have genetic components
        • MZ twins are more likely to be concordant for alcohol abuse
        • The DRD4 gene in its long allele form is linked to craving for alcohol and to heroin addiction
        • The ANKK1 gene has been linked to attention deficit disorder
        • Both of these genes are in the dopamine pathway
      • Antisocial behavior
        • Related to the approach temperament
        • Higher concordance rates for MZ twins and adult crime
        • Also in the dopamine pathway
      • Newer approaches stress looking for avoiding interaction opportunities
        
  • 6.7.3 Evolution and Problems in Behavior
    • Are humans prisoners of their biological evolution
    • Barash argued that humans are also subject to cultural evolution, the rapidly changing ways of the world (think of the internet, cell phones, and social media)
    • Human biological evolution cannot keep up with the rapid pace of cultural evolution
      
  • 6.7.4 How Much Behavior Change Is Possible?
    • It is currently unclear how much biological qualities can be therapeutically altered.
    • But, the role of the environment in the context of interaction can also be of therapeutic benefit
• 6.8 Problems and Prospects for the Genetic and Evolutionary Perspective (p. 83)
  • The genetic perspective is ancient but has been modernized
  • Many aspects of personality have a genetic basis
  • Molecular genetics provides direct access to genetic information and coding
  • What is the role of temperaments in personality theory?
    • Are they:
      • the entirety of personality
      • a part of personality
      • or the bedrock of personality
  • How many traits are genetically influenced?
  • What are traits, exactly?
  • Given that the evolutionaly approach is theoretically neutral, where will theory come from?
  • Sociobiology and Evolutionary Psychology
    • At first sociobiology was roundly criticized and was controversial
    • Today, it and evolutionary psychology are the source of new, sophisticated ideas about personality and genetics
    • Concerns
      • evolutionary theory remains ambiguous
      • sociobiology and evolutionary theory have controversial political and social overtones
      • some view them as racist and sexist
    • Responses
      • evolution only depends on RS
      • evolution does not specify equality
      • the slowness of evolutionary change may mean it applies more to our past than our present
      • societies will have to deal with the issues raised by evolution
• Summary (p. 84)
  • Personality and biology are closely linked
  • Genes are important to behavior
  • Twin studies, a kind of natural experiment, have yield much information about the role of genetics in personality and behavior
  • Molecular genetics is a strongly emerging field that may soon provide intimate access to the human genome
  • Evolution has much to say about human behavior as sociobiologists and evolutionary psychologists have argued
  • Mate selection is a specific issue related to genetics and personality
  • The genetic approach says little about assessment.
  • Schizophrenia, bipolar disorder, substance abuse, and antisocial behavior have strong genetic components
  • The genetic approach to personality has a long and fruitful road ahead
• Points to Remember
  • The approach to personality rooted in inheritance and evolution has two facets.
  • One emphasizes that your personality is tied to the biological body you inherit. This idea goes far back in history, but today’s version of the idea is quite different, emphasizing the role of genes.
  • Behavior genetics provides ways to find out whether personality differences are inherited.
  • In twin studies, correlations among identical twins are compared with correlations among fraternal twins; in adoption studies, children are compared with their biological and adoptive families. Studies of identical twins raised apart provide yet a different look at the effects of inheritance and environment.
  • Twin research has been used to look at genetic contributions to a variety of dispositions, starting
    with temperaments: broad, inherited traits that appear early in life. Early evidence supported genetic influences on activity level, emotionality, and sociability.
  • Other views of temperaments have also been suggested, including temperaments for approach, avoidance, and effortful control. There’s also evidence of genetic influence in the “big five” supertraits and other variables. It’s unclear whether the “big five” derive from (or duplicate) the temperaments studied under other names. It’s also unclear whether the influence of heredity on other variables depends on associations between the other variables and a temperament.
  • Recent developments in molecular genetics provide a new tool in the search for genetic influences on personality. Now, there’s evidence of specific genes playing roles in traits, including novelty seeking, neuroticism, and perhaps effortful control or impulsivity. This has been an active area of
    research in recent years.
  • The idea that dispositions are genetically influenced can be extended to suggest that many aspects of human social behavior are products of evolution.
  • This idea is behind an area of work termed sociobiology or evolutionary psychology.
  • Sociobiologists propose ways to account for various aspects of human behavior—even behavior that, on the face of it, seems not to provide an evolutionary advantage.
  • Altruism, for example, is understood as people acting for the benefit of their family groups, so that the family’s genes are more likely to be continued (kin selection). This idea has been extended to the notion that people are attracted to other people who share their genetic makeup.
  • The evolutionary view also has implications concerning mate selection, including the idea that males and females use different strategies.
  • The male strategy is to mate whenever possible, and males are drawn to signs of reproductive capability.
  • The female strategy is to seek the best male available, and females are drawn to signs of resources.
  • People use the relevant strategies and act in ways that make them seem better candidates as mates.
  • Mating pressures also may lead to aggression among young men.
  • Theory suggests that violence is most likely among men of reproductive age who are in poor reproductive circumstances. Evidence seems to bear this out, along with the idea that much violence concerns conflicts over status.
  • The genetic approach to personality says little about assessment except to suggest what dispositions are particularly important to assess—those that have biological links.
  • Assessment directly from genes will not likely occur soon, due to the probable involvement of many genes in any given trait.
  • With regard to problems in behavior, there is substantial evidence that schizophrenia and manic–depressive disorder are affected by heredity, as are tendencies toward substance abuse and antisocial behavior.
  • Like other topics, the study of disorder is beginning to use the tools of molecular biology to search for genetic influences.
  • With regard to therapeutic behavior change, this approach raises a question on the basis of studies of temperament: How much can people be expected to change, even with therapy, in directions that deviate from their biological makeup?

KEY TERMS

• Adoption study: A study of resemblances between children and their adoptive and biological parents.
• Allele: Some version of a particular gene.
• Approach temperament: Temperamental tendency to approach rewards.
• Assortative mating: Mating based on choice of specific characteristics rather than random.
• Avoidance temperament: Temperamental tendency to avoid threats.
• Behavioral genetics: The study of inheritance of behavioral qualities.
• Candidate gene strategy: Testing specific genes because evidence links them to particular biological processes and theory links those processes to personality.
• Concordance: Agreement on some characteristic between a twin and a co-twin.
• Directional selection: Evolution in which one extreme of a dimension is more adaptive than the other.
• Dizygotic (DZ) twins: Fraternal twins (overlapping genetically 50%, on average).
• Ectomorphy: A tendency toward frail thinness.
• Effortful control: A tendency to be focused, restrained, and planful.
• Endomorphy: A tendency toward obesity.
• Epigenetic: An effect that is not on DNA but affects DNA functioning and can be inherited.
• Gene expression: Activity in which the gene engages in the processes that create a protein.
• Genetic similarity theory: The idea that people work toward reproducing genes similar to their own.
• Genome: The sequence of the genes contained in the full complement of chromosomes.
• Genomics: See molecular genetics.
• Genome-wide association study (GWAS): Study in which all genes are tested at once.
• Genotype: The particular version of a gene that a given person or group has.
• GxE: Gene by environment interaction, in which the environment produces different outcomes depending on genetic composition.
• Heritability: An estimate of how much variance of some characteristic is accounted for by inheritance.
• Inclusive fitness: The passing on of genes through the survival of relatives.
• Mesomorphy: A tendency toward muscularity.
• Methylation: The attachment of methyl chemical groups to a gene or surrounding material.
• Molecular genetics: The study of how alleles of specific genes relate to other observed differences.
• Monozygotic (MZ) twins: Identical twins (overlapping genetically 100%).
• Nonshared environment effect: Effect of the environment that makes twins differ.
• Polymorphism: The characteristic of having more than one allele for a given gene.
• Quantitative genetics: The study of how much variance in a characteristic is attributable to genetics versus environment.
• Reciprocal altruism: Helping others with the expectation the help will be returned.
• Siblings: Brothers and sisters.
• Sociobiology: The study of the evolutionary basis for social behavior.
• Stabilizing selection: Evolution in which intermediate values of a dimension are most adaptive.
• Temperaments: Inherited traits that appear early in life.
• Twin study: A study comparing similarity between MZ twins against similarity between DZ twins.
  

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