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Chapter 6: Genetics and Personality
Terms in this set (41)
The Human Genome
- Genome refers to the complete set of genes that an organism possesses
Human genome contains 30,000—80,000 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
- But identifying sequence of DNA molecules does not mean identifying the function of each molecule
- 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
Buss & Plomin Temperament
described something as a temperament if it had the following characteristics:
1. genetically influenced
2. its effects on behavior are broad, manifest early in life, and continue throughout life span.
An inherited personality trait present in early childhood - further studies indicate that
3 dimensions of individual differences
in personality deserve t be called temperaments:
- activity level
a person's overall output of energy or behavior
- shows moderate heritability
2 highly corrrelated aspects
- vigor (the intensity of behavior)
- tempo (speed)
tendency to prefer being with other people rather than being alone; a desire for sharing activities, along w/ the responsiveness and stimulation that are part of interaction.
To be sociable is to value intrinsically the process of interacting w/ others.
tendency to become emotionally aroused - easily & intensely - in upsetting situations.
Study on temperaments
Early evidence that the 3 dimensions of individual differences (emotionality, sociability, activity level) are inherited came from twin studies in which parents rated their children.
- Correlations b/w parents rating of activity, emotionality and sociability were strong for MZ twins; for DZ twins, they were practically inexistant
- Adoption research also indicated genetic influences.
study of psychopathic personality traits
All traits subsumed under psychopathic show moderate to high heritability
The heritability of these traits, which predispose individuals to criminal activity, may be the key reason why a massive study of more than a million people in sweden showed te heritiability of violent crime to be roughly 50%
heritability of personality in other species
in a study of Chimpanzees, WEiss King and Enns, explored the heritability of dominance and well being, as indexed by trained observer judgments.
Individual differences in chimpanzee well-being showed a moderate heritability of .40 whereas dominance showed an even stronger heritability of .66
This study suggest that personality heritability does in fact carry over to other species
Controversy About Genes and Personality
Behavioral geneticists attempt to determine the degree to which individual differences in personality (for example) are caused by genetic and environmental differences
- Ideological concerns: could be misused for political agendas
- Concerns about renewed interest in eugenics
Modern behavioral geneticists who study personality are typically very careful about addressing implications of work and are sensitive to ideological concerns
Knowledge is better than ignorance
In addition, finding that a personality trait has a genetic component does not mean the environment is powerless to modify trait
Goals of Behavioral 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 to which children are exposed
observed individual differences like height weight or personality
individual differences in the total collection of genes possessed by each person.
What is heritability
Proportion of observed variance in group of individuals that can be explained or accounted for by genetic variance, OR
Proportion of phenotypic variance that is attributable to genetic variance
Environmentality = proportion of observed variance in group of individuals attributable to environmental variance
Misconceptions About Heritability
Heritability CANNOT be applied to single individual, only refers to a sample or population
Heritability is NOT constant or immutable
Heritability is NOT a precise statistic its more of an estimate of the percentage of phenotypic differences due to genetic differences.
Nature-Nurture Debate Clarified
No such debate at the individual level
- genes and specific individuals are like flour and eggs for cake - both ingrediants are necessary but we cannot logically disentangle them to see which one is more important
Influence of genes and of environment is only relevant for the discussion of group-level variation
Selective Breeding—Studies of Humans' Best Friend
Occurs by identifying the dogs that possess the desired characteristic and having them mate only with other dogs that also possess the characteristic.
- some of these qualities are physical traits, observable characteristics like size, ear length, wrinkled skin, and coat of hair while others are more behavioral and can be considered personality traits
the fact that selected breeding has been so successful with dogs tells us that heredity must be a factor in the personality traits
Cannot be ethically conducted with humans
Correlates the degree of genetic overlap among family members with the degree of similarity in personality trait - capitalizes on the fact that there are known degrees of genetic relatedness among family members
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
Problem: Members of a family who share the same genes also usually share the same environment—confounds genetic with environmental influences
violates equal environments assumption
Thus, family studies are never definitive
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)
Two assumptions of the twins method
- Equal environments assumption
- Representativeness assumption
Equal Environments Assumption
The environments experienced by identical twins are no more similar to each other than are the environments experienced by fraternal twins
- if they turn out to be more similar, then the greater similarity of the identical twins could be due to the fact that they experience more similar environments rather than the fact that they have more genes in common.
- one way to deal with this is to examine twins who have been misdiagnosed as identical or fraternal
Behavioral Genetics and Mental Toughness
Researchers from the University of Western Ontario examined the heritability of toughness in 219 pairs of adult MZ and DZ twins from North America.
- they performed a self-report questionnaire to measure mental toughness and then the NEO-PI-R to understand the role of primary trait factors.
The results suggested that genes account for 54% of the variance in individual differences in mental toughness.
in descending order of the 4 subscales: control, challenge, confidence, commitment
Regarding the big 5:
h^2 ranged from .46 (conscientiousness) to .65 (openness)
Overall, the researcher Horsburgh (2009) was able to confirm that mental toughness was significantly correlated with all of the big 5 except for neuroticism which showed a negative neuroticism. These were attributable to common genetic effects meaning that significant correlations were observed between mental toughness and the big 5 due to some of the same genetic factors. This reflects the theory that one-to-one relationships between genes and personality traits are rare.
Pros and Cons of Selective bReeding Studies
Pro: Can infer heritability if selective breeding works
Con: are unethical to conduct on humans
Pros and Cons of Family Studis
Pro: provide heritability estimates
Con: Violate equal environments assumption
Pros and Cons of Twin Studies
Pro: Provide both heritability and environmentality estimates
Con: Sometimes violate equal environments assumption
Pros and Cons of Adoption
Pro: Provides both heritability and environmentality estimates; get around the problem of equal environments assumption
Con: Adopted kids might not be representative of the population; problem of selective placement.
Positive correlations on traits between adopted children and adoptive parents provide evidence of environmental influence
Positive correlations between adopted children and genetic parents provide evidence of genetic influence
Adoption studies are powerful because they get around the equal environments assumption—genetic and environmental causes are unconfounded
Assumption that adopted children and their adoptive and genetic parents are representative of the general population—questionable, but can be directly tested, and has been confirmed that representativeness holds for cognitive abilities, personality, education level, and even socioeconomic status.
Problem of selective placement of adopted children
Design that combines strengths of twin and adoption studies = twins reared apart
if adopted children are placed with adoptive parents who are similar to their birth parents, then this may inflate the correlations between the adopted children and their adoptive parents.
What Personality Qualities are Genetically influenced?
- emotionality (according to Buss & PLomin)
Major Findings: Personality Traits
Summaries of behavioral genetic data yield heritability estimates for major personality traits (
, agreeableness, conscientiousness,
, openness to experience) of about 20-45 percent
- extraversion and neuroticism are traits that are approximately half due to genetics.
- Controversial and developing area
- Current evidence suggests that genes provide modest and indirect influence (via childhood gender nonconformity) on adult sexual orientation
Major Findings: Attitudes and Preferences
Stable attitudes are generally regarded to be a part of personality: they show wide individual differences; they are stable over time, and are sometimes linked with actual behavior.
Minnesota Twin study and Colorado Adoption Project showed that some attitudes (e.g., traditionalism) show high heritability (about .60), whereas others show low or no heritability (e.g., beliefs in God, attitudes toward racial integration)
Not clear why only some attitudes appear to be heritable but a UWO study (Olson 2011) found that it for some attitudes, it was the heritability of personality traits that mediated the heritibability of related. attitudes
Occupation and Genetics
Occupational preferences such as desire for competition and wealth can lead to choosing occupations in which more status and income are actually achieved. The jobs in which we spend a large portion of our lives and the prestige and income that comes from those jobs are at least partly influenced by genes we inherit from our parents.
- in a study, 14 job aspects of an individual were correlated with seven measures of parental social status which showed that 71% of correlations were statistically significant for the genetic children while only 3 % were significant for adopted children.
Major Findings: Drinking and Smoking
Behavioral manifestations of personality traits such as sensation seeking, extraversion, neuroticism
Drinking alcohol and smoking cigarettes are stable over time
Both show evidence of heritability
- in anAustralian study of twins, individual differences in drinking and smoking habits showed that a MZ twin who smoked was roughly 16x more likely than a MZ twin who didn't smokee to have a twin who smoked. For DZ twins it was 7x.
- Heritabiltiy studies for alcohol drinking are more mixed, where some studies find heritability for only boys, or in reverse, for only girl. Although in general, most studies show moderate heritability for both genders.
- Heritability studies for alcoholism show even stronger heritabilities, where in almost every study it was greater than .50. It also appears that there is a genetic linkage between alcoholism and conduct disorder.
Major Findings: Marriage
A study revealed that genes can even influence the propensity to marry or stay single (Johnson et al 2004) with a heritability of 68%
- this could be because of personality characteristics
Married men, compared to single men scored higher on social potency and achievement which also happen to be highly valued by women in selecting marriage partners.
Genes also play a role in marital satisfaction:
- individual differences in women's marital satisfaction are about .50 heritable
- the personality characteristics of wives, (dispositional optimism, warmth, low agressiveness) accounted for both their own marital satisfaction and their partners.
Shared Versus Nonshared Environmental Influences
Same studies that suggest moderate heritability also provide good evidence of the importance of environmental influences
Personality characteristics show heritabilities in 30—50 percent range; hence, showing substantial degree of environmentality—50—70 percent
For most personality traits, the general environment has major influence, but we're not completely sure ff influence is primarily in the form of nonshared or non shared variables
- For most personality traits, the shared environment has little or no impact. Instead it appears that it's the unique nonshared experiences that influence personality.
Must distinguish between "objective" and "perceived" environments—siblings can be exposed to the same "objective" environment, but perceive it very differently (e.g., parental curfew)-
Shared Environmental Influences
In family environment, features of the environment shared by siblings (e.g., number of books in home)
Nonshared Environmental Influences
In family environment, features of the environment that differ across siblings (e.g., different friends, different teachers)
We do not know which nonshared experiences have a key impact on personality
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
- Another example: children with a genotype that produced low levels of the neurotransmitter MAOA frequently developed conduct disorders in abusive homes, while kids in the same abusive environment who produced higher levels were less prone to developing aggressive antisocial personalities.
Differential exposure of individuals with different genotypes to different environments. i.e. individuals with different genotypes are exposed to different environments.
Plomin, Defries, and Loehlin (1977) described 3 different kinds:
These correlations can be positive or negative where the environment can encourage or discourage the expression of the disposition. e.g. adolescents with positive personalities tend to evoke higher levels of helpful and afirmative attitudes from their parents. or vice versa.
Molecular Behavior Genetics
D4DR—gene located on the short arm of chromosome 11, codes for dopamine receptor
- Most frequently examined association between D4DR gene and a personality trait involves "novelty seeking"
- Individuals with the "long repeat" version of D4DR gene are higher on novelty seeking than individuals with the "short repeat" version of gene
- But several failures to replicate association and, when replicated, association is weak
Three types of genotype-environment correlations
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
Reactive: Parents (or others) respond to children differently depending on the child's genotype
- Baby's liking for cuddling and the mother's cuddling behavior
Active: Person with particular genotype seeks out a particular environment
- High sensation seekers expose themselves to risky environments
Genotype-environment correlations can be positive or negative
Behavior Genetics, Science, Politics, and Values
Findings that some personality traits are heritable seemed to violate prevailing environmentalist view that personality is determined by socialization practices, such as parenting style
People also worried about political and ideological misuse of behavioral genetics findings
Much controversy surrounding individual differences in intelligence
In past decade, attitudes shifted somewhat so that behavioral genetics are fairly mainstream (recent exception is sexual orientation studies)
Because scientific research can be misused for political and ideological goals, scientists bear special responsibility, but
Science can be separate from values
Knowledge is better than operating in ignorance
A closer look: Sexual Orientation
Refers to the object of a person's sexual and romantic desires, whether the person is sexually and/or romantically attracted to the same or opposite sex.
Debatable, but personality psychs think that sexual orientation is part of personality.
Early research by LeVay (1991) showed that gay and straight men differed in the size of their
medial preoptic region
in the *hypothalamus. (Gay men's were 3x smaller.) Problem is the sample size was too small and no one has replicated it yet.
Then Dean Hamer claimed that it is influence by a gene on the X chromose (1994) but this study has also yet to be replicated.
Main issue in sexual orientation studies: older studies neglect the correlates of sexual orientation like
chillhood non-gender conformity
Researcher Bailey (2000) conducted one of the largest twin studies of sexual orientation w/ n=25000 and 2000 MZ and DZ.
Results found that women are more likely to have slight homosexual feelings w/o being exclusively homosexual, whereas men tended to be exclusively hetero or homosexual.
- Also found that there was a ~20 concordance rate for identical twins (probability that if ones gay so is the other) this is significantly lower than previously predicted due to the fact that older studies selected participants by advertising in gay and lesbian magazines (Causing selection bias)
in the end genetic contribution to sexual orientation is lower than previously thought although, nonconformity did show significant heritability for both genders.
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