PSYCH 372 - Chapter 12: Intelligence and Personality

lectures from Dr. Kathleen Munley

What is eugenics?

The scientifically inaccurate theory that humans can be improved through selective breeding of populations

What are some historical examples of eugenics?

1. 19th century England (Sir Francis Galton) → “Selective breeding” can be used to improve intelligence of human race, gave rise to eugenics movement

2. 1920s-1970s, United States → forced sterilization of mental patients in some states to prevent conception of ‘genetically inferior’ children

3. 1930s and 1940s, Germany → Nazi eugenics (racial ideology, forced sterilization, murder)

What is IQ?

Intelligence quotient → standard measure of intelligence obtained using the Wechsler Adult Intelligence Scale (WAIS) or Wechsler Intelligence Scale for Children (WISC)

What are the components of the Weschler scales?

1. Memory tests

2. Vocabulary tests

3. Arithmetic tests

How are results of IQ tests reported?

As two forms of intelligence:

1. Verbal IQ

2. Performance/non-verbal IQ

How is intelligence generally used for genetic studies?

A single measure (overall test score) is commonly used: “g” for “general cognitive ability”

• Represents common factor present in all intelligence subtests (verbal, spatial, numerical, mechanical)

What does the IQ scoring curve look like?

IQ scores are normalized to a population reference, in which 100 is the mean and 15 is one standard deviation

What are the results of twin and family studies of intelligence?

• 1981 review: Average correlation for MZ twins = 0.86, DZ twins = 0.6

• 1997 meta-analysis: Heritability of IQ: 48%

  • Twin and adoption studies indicate substantial heritability for IQ

What are some lessons from twin and family studies of intelligence?

1. Environmental effects are important, even when genetic effects are at large

2. Heritability depends on age

3. Environmental effects on IQ are limited to making the IQ of twins different, rather than similar

4. Genetic effects on intelligence are correlated across different IQ tests

What proof do we have that environmental effects still affect intelligence even with a high heritability?

IQ has been increasing over time (higher IQs in people born in 1990s vs. 1940s)

How does heritability change with age?

Genetic contribution peaks between 60-70 years old and falls by age 80

• Most likely explanation: as we age, we restrict and choose our own environmental exposures, and these choices are partly genetically determined

  • Eg. bright individuals are more likely to select intellectually stimulating environments (reading books, going to museums), which feeds back to increase IQ

• Reflects active gene-environment correlation

What has been observed regarding how environmental effects influence IQ in twins?

MZ twins reared apart (MZA) have no shared environmental effects

• Differences in IQ due to environment, similarities due to genetics

• 2015 Swedish adoption study showed that adoption into improved socioeconomic circumstances results in modest increase of 2-5 IQ points

How have we observed that genetic effects on intelligence are correlated across different IQ tests?

• Genetic correlations among cognitive subtests are typically > 0.6

• Indicates that same genes are responsible for heritability of intelligence

  • There is a common set of genes involved in intelligence that has pleiotropic effects (one gene encode multiple unrelated traits)

What is another proxy for intelligence other than IQ used by researchers?

Educational attainment - total years of schooling

What was the 2018 social genomics consortium?

Used a sample of 1.1 million people and identified 1,271 independent loci that contribute to variation in educational attainment

What are the main findings of the 2018 social genomics consortium?

1. Peaks near genes enriched for expression in central nervous system

• Neurotransmitter secretion, ion channel activation, and synaptic plasticity

2. No enrichment of glial cells

What are some key implications from intelligence GWAS?

1. “g” is negatively correlated with attention deficit hyperactivity disorder (ADHD), depressive symptoms, Alzheimer’s disease, and schizophrenia

2. “g” is positively correlated with longevity

3. IQ genetic data have been used to relate intelligence to brain anatomy

How are intelligence and brain anatomy related based on GWAS findings?

• Overall brain volume is heritable, and some brain structures have heritable variation

• No genome-wide significant loci have been found that contribute to both IQ and brain volume

What is personality?

The stable part of an individual’s attitudes, behavioral patterns, and emotional responses

How is personality measured?

Short, self-report questionnaires:

• Answers treated as responses to a set of stimuli (questions) rather than truth

• Correlations between responses used to generate personality factors

  • 5 correlated responses (factors) can be extracted using factor analysis

What are the big five?

Five factors that have been agreed upon to describe human personality: OCEAN

1. Openness

2. Conscientiousness

3. Extraversion

4. Agreeableness

5. Neuroticism

• In a short questionnaire, participants may be asked 3 questions pertaining to each trait

What is the genetic epidemiology of personality?

• Review of twin and adoption studies suggests heritabilities for the big five range from 30-45%

• Study of twins and their relatives showed heritability for neuroticism is 41% in females and 35% in males

What is neuroticism?

The propensity (natural inclination) of individuals to experience negative or unpleasant emotions such as anxiety, worry, sadness, anger, and irritability

• One of the big 5

What is emphasized by genetic studies of personality?

Non-shared environment

• Non-shared environmental factors are difficult to determine (survey of studies found~3% of variation in behavioral outcomes is due to measured, non-shared variables)

What does personality look like in twins?

Twins have similar correlation coefficients for personality scores, regardless of whether they were raised apart or together

What is an inversion polymorphism?

A structural chromosomal variation in which a segment of DNA is rearranged in reverse order

What were the findings of the UK Biobank GWAS for personality?

Found 2 loci on chromosomes 8 and 17 that cause inversion polymorphism

• Showed that personality is highly polygenic, with each trait contributing a very small effect (0.02-0.04% of total variance)

• Personality traits and certain psychiatric disorders exist on a continuum

What is principal component analysis (PCA)?

Statistical method that examines relationships between personality traits and psychiatric disorders

• Personality traits and certain psychiatric disorders exist on a continuum

• Angles between arrows = correlations (< 90° is positive, > 90° is negative)

What are personality disorders?

Represent stable, typically dysfunctional features of a person, often reflecting problems in the structure of the self and/or patterns of interpersonal relationships

How does language about a personality disorder differ from other disorders?

They are about what you “are” instead of what you “have”

What are the forms/clusters of personality clusters form DSM-III?

1. Odd cluster

2. Dramatic cluster

3. Anxious cluster

What are some personality disorders in the odd cluster?

• Paranoid

• Schizoid

• Schizotypal

• Personality disorder

What are some personality disorders in the dramatic cluster?

• Antisocial

• Borderline

• Histrionic

• Narcissistic personality disorder

What are some personality disorders in the anxious cluster?

• Avoidants

• Dependent

• Obsessive compulsive personality disorder (NOT OCD)

What is schizotypal personality disorder (SPD)?

Personality disorder characterized by deficits in social and interpersonal skills, eccentric behavior, and cognitive or perceptual distortions

What have twin and family studies found about SPD?

SPD is more common in relatives of patients with schizophrenia (7-15%) vs. relatives of controls (1-2%)

• 26% heritability

• No large-scale molecular genetic studies of SPD

What is the schizophrenia spectrum?

The group of related mental disorders that includes schizophrenia and SPD

• 2014 schizophrenia spectrum study sed high density pedigrees: contained ≥ 2 SCZ cases and multiple individuals with other SCZ-like symptoms (e.g., SPD)

What is antisocial personality disorder (APD)?

Personality disorder characterized by pervasive disregard for and violation of the rights of others, including deceit and manipulation

What are the major findings of the 2002 meta-analysis on APD?

1. 41% heritability, 16% shared environment

2. Shared environment effects are dynamic: strongest in children and lowest in adults

3. More common in males than females

4. Stronger heritability within than across generations (45% vs. 31%)

What are Eric Turkheimer’s 3 laws of behvaioural genetics?

1. All human behavioral traits are heritable

2. The effect of being raised in the same family is smaller than the effect of genes

3. A substantial portion of the variation in complex human behavioral traits is not accounted for by the effects of genes or families

• In theory, with a large enough sample size, any behavioral trait can be mapped