PSYC10004 Lecture Notes - Lecture 21: Twin, Genitive Case, Orderliness
Week 2: Explaining Personality
Need to explain individual differences:
• Origins
• Underlying mechanisms & processes
Biological Approaches
• Explaining biological bases of personality differences
• Operate at several levels:
o Genetics
o Brain functioning
▪ Neural systems
▪ Neural structures
▪ Neurochemicals
o Hormonal factors
Genetics of Personality
• Is personality inherited?
• DNA a source of human similarities & differences
• To what extend do these genetic variations underpin variations in personality?
Research Designs
• Family studies
o Examine resemblance between family members as a function of genetic relatedness
o Greater resemblance for closer relations implies genetic contribution
o BUT genetic contributions are confounded with shared environmental contributions
• Twin Studies
o Monozygotic twins (100% related), Dizygotic twins (50%)
o Greater resemblance between MZ implies genetic contribution
o Environments are same for both kinds of twin so environmental factors are not
confounded
o BUT possibility of more similar environments for MZ twins, & perhaps twins are
unrepresentative
• Adoption studies
o Compare resemblance of adopted children to adoptive and biological parents
o Degree of resemblance to adopted and biological parents shows environmental &
genetic contributions
o BUT adoption must occur early; problem of selective placement; biological mother
provides prenatal environment as well as genes
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Heritability
• Behavioural genetic studies yield estimates of heritability = proportion of variance in the trait
accounted for by genes
• Most personality attributes show heritability from 0.3 to 0.5
• This is true for apparently purely learned attributes (eg. Death penalty attitudes)
Caveats re. Heritability
• Even if personality is substantially heritable
o This does not entail strong resemblance between parents and children on personality
traits
o Heritability relates to variation within a population: it says nothing about genetic
contribution to any individual's personality
o Heritability does not imply that personality is fixed
o Heritability is consistent with substantial environmental contributions to personality
The Role of the Environment
• One outcome of behavioural genetic research is awareness of the role of the envirionment
• Most environmental influences are not 'shared'
o e.g parental education, class, ethnicity, diet
• Most is 'non-shared' environment
o Eg. Illnesses, friends, different treatment by parents
• Environmental factors can themselves be genetically influenced
Specific Personality-related genes
• Heritability says nothing about specific genes or genetic mechanisms
• Assumption that most traits represent summation of many small genetic influences
• Several specific genes have been identified
o Novelty-seeking & dopamine sensitivity
o Neuroticism/shyness & serotenergic functioning: increases risk of depression in
response to life stress
Brain Functioning: System
• If reading 2nd edition of textbook skim this part
• Eysenck's Theory:
o Extraversion & Low Brain Arousal
▪ Leads to desire for stimulation
o Neuroticism & Limbic System Reactivity
▪ Leads to greater automatic NS arousal to threat & stress
• Gray's Theory:
o Impulsivity & "behavioural activation system" (BAS)
▪ Linked to sensitivity to reward & pleasure
o Anxiety & "behavioural inhibition system" (BIS)
▪ Linked to sensitivity, punishment & pain
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Brain Functioning: Structures
• Some links between Big 5 & brain structure volumes
o Extraversion with a region involved in processing reward information
o Neuroticism with regions associated with threat, punishment & negative emotion
o Agreeableness with regions that process information about other people's intentions
and mental states
o Conscientiousness with region involved in planning & voluntary control of behaviour
• Implies that personality has a neuronal basis, although no brain volume correlates of openness
Brain Functioning: Chemicals
• Personality factors may be associated with neurotransmitter concentrations in brain
• Extraversion & dopamine levels
o Linked to exploration, approach, incentive motivation
• Neuroticism & norepinephrine levels
o Linked to negative emotion, vigilance for threat, cautiousness
• Constraint & serotonin levels
o Linked to inhibition of emotional response, low impulsiveness; low serotonin linked to
aggression & emotional instability
Hormonal Factors
• Evidence that personality influenced by prenatal exposure to sex hormones
• Among men, lower 2D:4D ration correlates with:
o Physical aggression
o More masculine career interests (realistic & enterprising)
o Less feminine gender role
• In women, lower 2D:4D ratio correlates with:
o More indirect aggression (spreading rumours, malicious humour, excluding people)
o More "masculine" interests (enterprising, less social)
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