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Maltby 2022- chapter : 8 & 9
Myers Briggs personality indicator
vague, just overall unreliable and not based on empirical evidence
DNA:
chemical building blocks of our body, contains proteins, which control the structure and function of all cells that make up your body. contained in nucleus of cells.
chromosomes:
23 pairs, chunks of dna
nucleotide:
unit of DNA, basic building block, come in pairs
genome:
complete set of DNA of an organism
genetic variation:
dna sequence difference between people;
most of our dna is identical, but there are also differences between people
what is SNP (snip)
single nucleotide polymorphism, approx 4-5 million SNPs in a persons genome
monogenic traits
caused by variation in a single gene, tends to be very rare.
eg Huntington’s disease- starts about mid life
complex traits
cause by variation within multiple gene and their interaction with environmental factors
tend be more common in the population
lots of genes (each one has a small effect) that influence a persons personality
genotype
individuals genetic make-up. specific set of dna sequences
phenotype:
trait/characteristic that occurs as a results of the genotype
height, personality, intelligence
behavioural genetics
different family members share different % of their dna
it investigates whether individuals who share more of their dna are more similar to each other on a trait
!does not looks at specific dna differences!
types of behavioural genetic studies
family, twin and adoption studies
identify the role of genetics and environment (everything that is not genetic)
family studies
Compare family members on a trait
• Test whether family members who share more DNA are more
similar on a trait
• Inherit 50% of DNA from your mother, and 50% from your father
• Share, on average, 50% of our DNA with full (non-twin) siblings
• Share, on average, 25% of our DNA with half siblings, grandparents,
aunts/uncles, nieces/nephews
• Share, on average, 12.5% of your DNA with first cousins
• But they also share (some of) the same environment
• Same household
• Similarities might be due to genetics OR environment
twin studies - identical
Twin studies have shown that differences in our genetic make-up
contribute to differences in personality
• Different types of twins share a different proportion of their DNA with each other
1 sperm, 1 egg
• 1 zygote (fertilized egg)
• Monozygotic (MZ twins)
• Share 100% of their DNA
twin studies- fraternal
Twin studies have shown that differences in our genetic make-up
contribute to differences in personality
• Different types of twins share a different proportion of their DNA with each other
2 different sperm, 2 eggs
• 2 zygotes
• Dizygotic twins (DZ twins)
• Share 50% of their DNA
twin studies and environment
Criticism of twin studies: Identical and fraternal twins may not
have similar environments
• Identical twins may dress more similarly, may be treated more
similarly by parents/teachers/friends
• If identical twins have more similar environments than fraternal
twins
→ Over-estimate the genetic effect of a trait
adoption studies
Compare adopted children with:
• Adopted parents
• share 0% of their DNA
• Biological parents
• share 50% of their DNA
• Similar to adopted parents
→ Environmental component
• Similar to biological parents
→ Genetics component
twin reared apart
Compare identical and fraternal
twins reared apart
• Removes (most of the) effect of
environment
• If identical twins reared apart
are more similar on a trait than
fraternal twins reared apart
→ Genetic component
genetic heritability- additive assumption
Additive assumption: the combined effects of genetic and
environment are equal to the sum of their individual effects
• Genetic effects + Environmental effects = 100%
• If you know the genetic heritability, you can calculate the
environment influence of a trait
• 100 - Genetic Effects = Environmental effects
• Additive assumption now thought to be a simplification
• But often used as a starting point to determining the genetic
influences of a phenotype
heritability- population estimate
Heritability estimate of 50%
• 50% of the reason individuals in a given population differ from each other
on a specific trait is due to the genetic differences between them
• Across a population, the genetic heritability has been estimated to an
average of 50%
• Does not mean you personally inherited 50% of the trait from your genes
genetic influences
If traits are is highly heritable, it does not mean they are
deterministic
• Genes predispose you to a trait
→ increase your chances of scoring high on a trait
• Genes are only one part of the story
• Environment is important
• Genes and environment work together to influence a trait
genetic influences- examples
Height is highly heritable
• About 80% of the difference between people in height is due to genetics
• Does not mean the environment can’t impact height (e.g., malnutrition)
• Depression is heritable → an individual's genotype may predispose
them to depression
• Higher genetic risk for depression does not mean you will develop it
• Low genetic risk for depression does not mean you won’t develop it
• If something is highly heritable, it doesn’t mean we can’t use tools to
change the outcome (e.g., glasses for short-sightedness)
behavioural genetics: conclusion
Substantial genetic influence on personality
• On average, between 40-50% of the variance on tests of
personality is due to genetic differences
• I.e., personality traits are 40-50% heritable
• 50-60% of the variance in differences on tests of personality are
not due to genetic differences
• Environmental influences
heritability is
the degree of variation in a trait that is due to genetic differences between people in a given population
heritability equation
h2 = (MZ corr – DZ corr)*2
genome wide association studies (GWAS)
Identify specific genes and specific genetic
variants that are associated with a trait
• Single nucleotide polymorphisms (SNPs)
• Nucleotide: unit of DNA - basic building block
• Nucleotides can vary between people
• Common genetic variants: SNPs are the
most common type of genetic variation that
are present in at least 1% of a population
• Looks at every SNP along the genome
• Tests whether each SNP is associated with
the trait
GWAS of neuroticism- Luciano
GWAS of neuroticism
• Largest GWAS of personality traits to date
• N = 329,821 participants from UK Biobank
• Less variability than a meta-analysis
• Same personality scale
• Same genotyping technique
• Eysenck Personality Questionnaire - Revised Short-From
• 18,485,882 SNPs
luciano results
10,353 genetic variants (SNPs) were significantly associated with
neuroticism (p < 5*10-8)
• 116 significant independent genetic locations associated with
neuroticism
• SNPs found to be significant in other studies were also significant in
this study (replication)
• This study found a lot more significant SNPs than other studies
(because it was so large)
• 249 genes were associated with neuroticism
• Many of these genes associated with schizophrenia and depression
in other studies
• h2SNP = Proportion of variance explained by all SNPs
• h2SNP for neuroticism = 10.8% (SE = .005)
luciano summary
Many SNPs were associated with neuroticism
• Many genes were associated with neuroticism
• Each SNP/gene individually had only a very small effect
• SNP-based heritability for neuroticism was 10.8%
• 10.8% of the variance between participants in neuroticism was due to
common genetic variants
• There was genetic overlap between neuroticism and many
mental health-related trait
• The same genetic variants associated with neuroticism were also
associated with mental health traits
molecular genetics
directly link genetic differences to behavioural differences
molecular genetic studies criticism
Early, complex and controversial field
• Few studies because very large samples are needed
• Heritability estimates much lower than found with behavioural
genetic techniques
• Only testing “common” genetic variants
• Does not consider rare genetic variants
• Lower end of heritability estimate
• Despite the differences in estimates, molecular genetic and
behavioural genetic studies show that personality is heritable
molecular genetic studies of neuroticism revealed that
many genetic variants are associated with neuroticism; each
genetic variant has only a very small effect on individual
differences in neuroticism
heritability estimates for personality tend to be
smaller in molecular genetic studies than in behavioural
genetic studies
higher genetic correlation means
there is a large overlap in the genes or the genetic variants that were found to be found to be associated with another.
neurobiological influences of personality
Hans Eysenck (1967; 1990): Biological basis of personality
• Proposed the human brain had two sets of neural mechanisms
• Excitatory: keeping you alert, active and aroused
• Inhibitory: keeping you inactive and lethargic
• Aim to maintain a balance between these mechanisms
• Regulated by the ascending reticular activating
system (ARAS)
• Located in the brainstem
• Manages the amount of stimulation received by the brain
• Waking and sleeping
• Alert and active ex
ascending reticular activating system (ARAS): arousal
Arousal: Level of stimulation received by the brain
• Two circuits manage arousal:
1. Reticulo-cortical circuit: controls the cortical arousal
generated by incoming stimuli
2. Reticulo-limbic circuit: controls arousal to emotional
stimuli
• Eysenck linked extraversion and neuroticism to arousal
extraversion and arousal
extraversion and arousal Extraversion-introversion caused by variability in
cortical arousal (Eysenck, 1967)
• The ARAS of extraverts and introverts works
differently
• Different thresholds for cortical arousal
• Introverts: lower response threshold and are
more cortically aroused
• ARAS provides a lot of arousal
• Seek to avoid stimulation and excitement
• Extraverts: higher response thresholds and are
more cortically under-aroused
• ARAS does not provide a lot of arousal
• Seek stimulation and excitement
neuroticism and arousal
Neuroticism caused by variations in the level of
activity (arousal) in the limbic system (Eysenck, 1967)
• Neurotics more aroused because of
increased emotional stimulation in the
reticulo-limbic circuit
• Emotionally stable people, less activity in
limbic system, so less aroused
• Stressful situation: sitting exams
• Neurotic individual → more aroused by the
stress → more likely to worry
• Emotionally stable individual → not aroused by
the stress → worry less
brain structure
High extraversion associated with
• Size of the medial orbitofrontal cortex: cortical area involved in processing reward information
• Size of prefrontal cortex
• High neuroticism associated with
• Size of the dorsomedial prefrontal cortex and parts of the left medial
temporal lobe: areas associated with threat, punishment and negative affect
• Increased volume in cerebellum, and decreased volume in superior frontal
gyrus: linked to negative affect and
regulation of negative emotions
brain connectivity
High neuroticism associated with
• Loss of white matter connectivity in tracts that connect the prefrontal cortex to the amygdala (limbic): areas implicated in negative affect
• Widespread loss of connectivity across the brain, including
o Connections between orbitofrontal regions with limbic regions
o Connections between thalamic (limbic) and frontal regions
evaluation of arousal theory of personality
Identify and test biological mechanisms for individual
differences in personality
• Proposed the theory over 50 years ago, before brain imaging
techniques were invited
• Experimental and brain imaging evidence provide support for
Eysenck’s biological model of personality
• Brain imaging studies show support that extraversion and
neuroticism are related to structure and connectivity in cortical
and limbic regions of the brain
• Criticism: Effect sizes are small and do not always replicate
animal studies
• Gosling (2001)
• Compare personality across species
• How different species differ from each other in terms of personality
• Identify the origins and adaptations of specific traits
• Compare personality within species
• Individual differences within a species
• Help to identify adaptive nature of personality traits that allow
species to develop and evolve
• Are individual differences in personality unique to humans or
found in animals?
animal studies conclusion
Neuroticism and extraversion: basic dimensions of biological
and physiological functioning
• Evolved quite early and are found in many species
• Conscientiousness: advances in cognitive processes (following
rules, establishing norms, understanding values)
• Evolved relatively late and have only been reported in chimpanzees
• Criticisms
• Anthropomorphic projections: attributing human characteristics to animals
• May not actually be rating animal behaviours
animal studies- differences between species
openness identified in 7/12 species, but not consistent across
multiple studies of the same species
• Chimpanzees were the only species studied with a separate
conscientiousness factor
• Suggest conscientiousness may have appeared relatively recently in
evolution
• The lack of evidence for a personality factor does not mean it
does not exist
• Studies may not have included them
cultural differences in personality
Some evidence that personality traits do not predict behaviour
as well in collectivistic compared to individualistic cultures
(Church and Katigbak, 2000)
• Mixed evidence: only 40% of people in a particular culture embrace
either individualistic or collectivistic goal
personality and culture- lexical approach
De Raad et al (2010): examined whether personality factors were
replicable across many different languages
• 14 lexical datasets with descriptions on large number of trait
adjectives from 12 different languages
• English, Dutch, German, Italian, Hungarian, Polish, Czech, Filipino, Korean, French, Greek, Croatian
• Tested a 5 factor model of personality and compared the agreement between these factors across languages
• Only 3 of the Big Five are robustly replicable across 12 languages
• Substantial universality of the “Big Three”
• Conscientiousness
• Extraversion
• Agreeableness
personality and culture - critique
Mixed evidence for the universality of personality
• Using lexical techniques, de Raad et al. (2010) found that 3 of the Big Five replicated across 12 languages
• Schmitt et al. (2007) found:
• Evidence of good reliability for the Big Five (measured with BFI) across 10 geographic regions
• Evidence of good agreement in the factor structure of the Big Five across 10 geographic regions
• But reliability and agreement was lower in Africa and South/Southeast Asia (large % of world population!)
• Personality theories are almost always developed in Western cultures
• Develop models in Western cultures and test these for universality in
multiple cultures
• Western way of thinking → testing on the rest of the world
• Not developing personality theories in other cultures and testing the similarities
gender differences in personality
In general, women tend to score higher on all facets of
Neuroticism and Agreeableness, compared to men
• Extraversion:
• Women score higher on warmth, gregariousness, and positive emotion
• Men score higher on excitement seeking and assertiveness
• Openness
• Women score higher on scales of openness to feelings
• Men score higher on scales of openness to ideas
• No real differences for Conscientiousness.
explanations for gender differences
Gender differences tend to be small to medium in size and
distributions largely overlap
• Consistent with gender stereotypes
• Difficult to disentangle if gender differences are:
• Neurobiological (e.g., brain differences, hormone differences)
• Evolutionary (e.g., sexually selected differences in personality)
• Social-environmental (e.g., consistent with gender stereotypes)
gender differences (schmitt et al, 2008) procedure/ methods
• Samples from 55 nations including many African, Asian and
Middle Eastern samples (n = 17,637)
• Personality assessed with Big Five Inventory
• Gender differences:
• Women scored higher on neuroticism, extraversion, agreeableness,
and conscientiousness than men in most nations
• Overall magnitudes of gender differences (Cohen’s d) were small to moderate
• Neuroticism: 0.40 (0.55 in UK)
• Agreeableness: 0.15
• Conscientiousness: 0.12
• Extraversion: 0.10
• Gender differences in openness were mixed across culture
schmitt et al results
• Gender differences were not the same size across all nations or
cultures
• Smallest gender differences in Asian and African cultures
• Largest gender differences in European and American cultures
• Gender differences in personality traits often larger in
prosperous, healthy and egalitarian cultures in which
women have more opportunities to be equal with men
• Differences in men’s personality traits found to be the primary
cause of gender difference variation across cultures
theories of variation in gender differences schmitt
Mismatch perspective (evolutionary approach)
• Hunter-gatherers: men and women developed sexually selected
differences in personality
• Men: more risk taking and dominance seeking
• Women: more nurturing and cautious
• Less developed cultures: larger disparities in resource distribution
and relative gender inequality → personalities become constrained
and gender differences in personality may reduce
• More egalitarian cultures: more equal distribution of resources →
evolutionary gender differences show again
• Speculative!
• Reason unknown
continued
Different frame of reference used in difference cultures
• Compare self to people of same gender: no gender differences
• Compare self to everyone: gender differences
• Observed gender differences may be caused by differences in
measurement error across cultures
• We saw earlier that reliability and congruence was lower in Asian and
African cultures
• Personality theories developed in Western cultures
influences of personality - conclusions
1. There is behavioural genetic and molecular genetic evidence
that personality is heritable
2. There is behavioural and neuroimaging evidence that there
are distinct circuits in the brain linked to extraversion and
neuroticism
3. The evidence for the universality of personality is mixed →
some personality traits have been found to be more universal
than others
4. There are gender differences in personality and these
differences may vary by culture
Note
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