Week 4: Intelligence

Question 1

Galton - Eugenics

Answer 1

Eugenics is the scientifically erroneous and immoral theory of “racial improvement” and “planned breeding”

believe inheritance is purely inherited

Question 2

Fluid intelligence (Cattell)

Answer 2

Primary reasoning ability that is free from cultural influences

Question 3

Pattern of cognitive aging and intelligence

Answer 3

Both increase steeply in childhood

• Crystallised abilities continue to rise for many years (env influence)
• From the mid-twenties, fluid intelligence declines

Question 4

Deary et al. (2013): stability of intelligence

Answer 4

r = .54 between IQ measured at age 11 and age 90

	➢ One of the most stable behavioural traits 

	➢ One of the biggest predictors of being smarter in old age is being smart at a young age 

➢ Correlation is not 1 (not a perfect predictor)

Question 5

Estimates of heritability

Answer 5

A heritability of 50% means that genes explain 50% of the variation in intelligence in the population

Question 6

Methods to study heritability

Answer 6

• Family studies – Assess resemblances between family members on characteristics of interest as a function of their degree of relatedness
  • Twin studies – Behaviours are compared across monozygotic (MZ) and dizygotic (DZ) twins as a naturally occurring manipulation of shared genetic makeup
  • Adoption studies – Comparisons drawn between biological parents, adoptive parents and adopted children

Question 7

Plomin et al 2004 findings, twin study and adoption study

Answer 7

As genetic similarity decreases, so do correlations with intelligence = are genetic factors to intelligence

When twins/sibling raised apart, the levels of IQ similarity are reduced = there are environmental influences

Question 8

Plomin et al estimate of intelligence

Answer 8

simultaneous analysis of all family, adoption, and twin data showed a heritability estimate of about 50%

Question 9

Heritability of intelligence across the lifespan: Haworth et al, 2010

Answer 9

The heritability of intelligence is not the same at different ages.

Gene-environment interaction

From childhood to young adulthood, moved from more nurture to nature!

= Intelligence is one of the most heritable behavioural traits

Question 10

Issues with heritability of intelligence

Answer 10

Representativeness

Complexity of genetic influence

Assortative mating

Question 11

Representativeness

Answer 11

– Adoption and twin studies make up a large proportion of the literature in this area
– Are these families atypical from the norm?
– E.g., adoption families tend to be of higher SES (criteria for adoption)
– E.g., identical twins tend to have more similar environments than dizygotic twins

Question 12

Complexity of genetic influence

Answer 12

– We don’t know how genes produce intelligence yet; clearly not a single gene predicts intelligence
Complexity of intelligence

Question 13

Assortative mating: Watson et al. (2004)

Answer 13

= tendency to mate with those who are similar to ourselves

	– Studied the similarity of 291 newlywed couples 
	– Measured, e.g., age, religious/political beliefs, education, intelligence 
* Correlations of couples’ IQs were around r = .40 
* Caused by the initial selection of a mate (assortment) rather than by couples becoming more similar to each other after living together (convergence)

Question 14

Why is assortative mating a problem for heritability estimates?

Answer 14

➢ Leads to a non-random distribution of the genetic variants important for a trait as spouses will be more similar genetically than expected by chance
➢ Assortative mating increases additive genetic variance (offspring differ more from the average than they would if mating were random)
➢ Since two highly intelligent partners are more likely to produce a child who is also highly intelligent, and similarly for low intelligence, assortative mating could inflate observed similarity of intelligence in a family.
➢ May lead to biased estimates of the relative magnitude of genetic and environmental factors (e.g., Vinkhuyzen et al., 2012)

Question 15

The brain and intelligence:

Answer 15

Intelligence associated with both structural and functional differences in the brain

Question 16

Structural differences

Answer 16

Grey and white matter density & number of connections are structural differences

	– Brain volume 
	– Cortical thickness  – White matter connectivity

Question 17

Functional differences

Answer 17

Functional differences are the activation when doing tasks

More efficient processing of information, in a wide network including frontal and parietal lobe

Question 18

Do more intelligent people have bigger brains? Evolutionary pov:

Answer 18

Potts (2011)

	* Skull size (and thus brain size) increased substantially over time 
	* Larger brain = better cognition: more brain cells allow for more complex mental processing 
	* Complexity and organisation of our brains changed as well

Steepest increase in the last 1 million years

Question 19

Do intelligent people have bigger brains? McDaniel (2005)

Answer 19

• McDaniel (2005)
  – Meta-analysis of 37 studies, over 1,500 individuals
  – Positive correlation between brain volume & intelligence of r = .33

Question 20

Do intelligent people have bigger brains? pietschnig et al. (2015)

Answer 20

– Meta-analysis of 88 studies, over 8,000 individuals
– Reported a significant, slightly smaller correlation of r = .24

Question 21

Do intelligent people have a thicker cortex?

Answer 21

Cortical thickness shows initial increase at earlier ages, followed by sustained thinning around puberty

Question 22

Shaw et al. (2006): cortical thickness and children

Answer 22

– Cortical thickness develops differently in high- compared to average-IQ children
– Cortex thickens for longer in high-IQ children, particularly in frontal areas

	➢ Intelligence is related to the pattern of cortical growth during childhood and adolescence, rather than cortical thickness itself

Question 23

Do intelligent people have better neural highways?

Answer 23

• Areas involved heavily depend on the particular task that is used to measure intelligence
• Intelligence suggested to be particularly dependent on a brain network that links the frontal to the parietal lobes (P-FIT: Parieto-Frontal Integration Theory; Jung & Haier, 2007)
  • Intelligence can’t be located in isolated brain areas
    – a complex network involving the whole brain is involved

Question 24

(Penke et al., 2012) better neural highways? White matter connectivity and IQ

Answer 24

White matter connectivity is correlated with IQ

Age-related deterioration of white matter tracks is correlated with age-related cognitive decline in IQ (Lövdén et al., 2014)

Question 25

Brains of higher IQ show less or more activity when completing a task?

Answer 25

Brains of higher-IQ individuals tend to show less, rather than more activity when completing a task - > more efficient processing?

Question 26

Environmental influences of intelligence

Answer 26

➢ The Flynn effect ➢ Environmental influences

Question 27

The Flynn effect

Answer 27

= the substantial and sustained increase in intelligence scores over time. 73 studies using Wechsler and Simon-Binet tests (~7,500 participants) from white Americans’ – IQ scores rose between 1932 and 1978 - from 20 countries - IQ scores rised yearly across nation * Nonverbal tests: average increase of ~ 15 points per generation (30 years) * Verbal tests: average increase of ~ 9 points per generation

Question 28

The Flynn effect: Further evidence Pietschnig & Voracek (2015), meta-analysis

Answer 28

* 271 independent samples, almost 4 million participants * 31 countries ➢ worldwide IQ gains across 1909–2013 IQ gains vary with domain: – Full-scale IQ: 0.28 points annually – Fluid IQ: 0.41 points annually – Crystallized IQ: 0.21 points annually – Spatial IQ: 0.30 points annually

Question 29

Flynn effect: recent years

Answer 29

IQ gains seem to have flattened or even reversed (e.g., Flynn & Shayer, 2018) ➢Has humanity reached ‘peak intelligence’?

Question 30

2 opposing hypotheses for explaining flynn effect

Answer 30

– Nutrition hypothesis – Cognitive stimulation hypothesis

Question 31

nutrition hypothesis

Answer 31

Increased intelligence is part of a nurturing environment that includes increased height and lifespan, improved health, decreased rate of infant disease, better vitamin and mineral nutrition

Question 32

Cognitive stimulation hypothesis

Answer 32

Increased intelligence driven by, e.g., improved visual analysis skills, improved schooling, changes in parental rearing styles, better-educated parents, smaller families, greater availability of educational toys

Question 33

WEIRD (Henrich, Heine, & Norenzayan, 2010)

Answer 33

* WEIRD: Western, Educated, Industrialized, Rich, and Democratic * A substantial part of the evidence base - including what we know about intelligence – is based on data from WEIRD countries * However: there is substantial variability in experimental results across populations and WEIRD subjects are particularly unusual compared with the rest of the species – frequent outliers * Generalisability of findings?

Question 34

Environmental influences on intelligence Neisser et al. (1996) identified four main areas

Answer 34

1. Biological environment (e.g., prenatal environment, nutrition) 2. Family environment 3. School & education 4. Culture

Question 35

Prenatal environment - Substance abuse

Answer 35

* Mortensen et al. (2005; see also review by Clifford et al. 2012): Smoking – Mothers who smoked 20+ cigarettes daily late in their pregnancy were likely to have children who performed less well on IQ tests at age 18/19 * Mattson & Riley (1998): Alcohol – Children prenatally exposed to alcohol may exhibit a variety of problems with memory and attention – Fetal Alcohol Syndrome (FAS): deficits in, e.g., abstract thinking, planning and organizing information (Kodituwakku et al., 1995)

Question 36

Nutrition: Breastfeeding

Answer 36

* Oddy et al. (2003) – Children (age 8) breastfed for more than 6 months scored 3-6 IQ points higher on a vocabulary IQ test than did children who were never breastfed * However, maternal intelligence is positively correlated with the likelihood of breastfeeding (Der et al., 2006) * When controlling for parental IQ or genetics, the effect is much smaller if at all present (review by Walfisch et al., 2013)

Question 37

Socio-economic status of the family

Answer 37

SES captures income, parental education level, parental occupation and status in the community – SES is significantly correlated with intelligence with r = 0.3 - 0.4 (e.g., Stumm & Plomin, 2015) – SES is related to growth in intelligence (Stumm & Plomin, 2015) – Improving SES can improve intelligence Better access to education?

Question 38

Family size and birth order Belmont and Marolla (1973)

Answer 38

* Children from larger families had a lower IQ (controlled for SES) * First-born child always had a better IQ; scores decline with rising birth order

Question 39

Birth order criticism (Kanazawa 2012)

Answer 39

However, effects of birth order are suggested to be a methodological artefact – less intelligent parents are more likely to have more children and – higher birth-order children necessarily come from larger families, whereas children from smaller families have greater representation among lower birth-order children – e.g., 4th-borns necessarily come from families with 4 (or more) children, whereas 1st - borns can come either from families with 1 or 2 children or families with 5 or 6 children - So more likely that children of smaller families have higher rank in order and IQ

Question 40

Group socialisation Judith Harris (1995)

Answer 40

Non-shared factors outside the family may be more important in developing people’s intelligence * As children get older, they become more influenced by their life outside the family * Children may identify with several social groups based on age, gender, ethnicity, abilities, interests, personality etc.; and share norms with and be influenced by these groups * Positions within in-group and rejection of out-groups influence behaviours, personality, and intelligence

Question 41

Education

Answer 41

* Governments across the globe do the one thing that is most likely to raise IQ: send children to school * Ceci (1991), meta-analysis – Children attending school more regularly showed higher IQ scores – Students’ IQ scores decrease over the long summer holidays – Each year of schooling is associated with a rise of 2.7 IQ points * Cause and effect: Intelligence is likely to influence school attendance, length of schooling, and the quality of school attended (Neisser et al., 1996)

Question 42

Culture and intelligence

Answer 42

Different cultures have different conceptions (~implicit theories) of what intelligence is * Cocodia (2014) compared cultural perceptions of intelligence in Asia, Africa, and Western cultures * For instance, the Luo people’s (East Africa) notion of intelligence consists of 4 main concepts: – Rieko: similar to the Western idea of academic intelligence – Paro: practical thinking – Luoro: social attributes (respect, responsibility, consideration) – Winjo: comprehending instructions * Western and Asian cultures emphasise academic ability, rural African cultures perceive practical ability as more important * Some Western concepts (e.g., speed when completing tasks) are unfamiliar in African cultures ➢ Cultural differences may affect equal access to the skills and knowledge required by IQ tests ➢ Can we really compare IQ (test results) across cultures?

Question 43

Is IQ culturally biased?

Answer 43

* Raven’s Progressive Matrices are often described as a culture fair or culture reduced test, as it consists of nonverbal items thereby reducing the language loading of the test * However, language loading is not the same as cultural loading – E.g., Raven’s matrices require a specific type of abstract reasoning, which may not be entirely culture fair

Question 44

Summary

Answer 44

* Global changes in intelligence across generations * Several different environmental aspects can – positively or negatively – impact intelligence * Intelligence is malleable, intelligence is not fixed ➢Gen-environment interaction ➢Nature with nurture