Week 4: Intelligence 2

What did Francis Galton suggest in relation to nature and nurture?

• First to differentiate between influences of nature and nurture

• Observed that eminence seems to run in families

• 'Nature over nurture'

What are eugenics?

• The scientifically erroneous and immoral theory of 'racial improvement' and 'planned breeding'

• Galton suggested that humanity may be improved through artificial selection

• Based on:

• Inaccurate understanding of genetics claiming that: intelligence is simply and purely inherited

• Scientifically inaccurate theory that humans can be improved through selective breeding of populations

How does fluid and crystallised intelligence change when aging?

• Steep increase in both fluid and crystallised intelligence in childhood

Clear distinction in what happens next:

• Crystallised abilities continue to rise for many years

• From the mid-twenties, fluid intelligence declines

Describe the Stability of Intelligence (Deary et al. 2013)

Intelligence shows high stability across the lifespan; Deary et al. (2013) found an IQ correlation of r = .54 between ages 11 and 90.

How can heritability explain intelligence?

Heritability of 50% means genes explain 50% of the variation in intelligence within a population.

What did Plomin et al. (2004) discover about heritability and intelligence?

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

What can occur during the interplay of genes and the environment?

• Genes influence the environments we experience

• Gen-environment correlation

• Genetic differences can influence the environments people experience, elicit or choose

• The effect of genes depends on the environment

• Gen-environment interaction

• The influence of genes on a trait differs across environments

What did Haworth et al. (2010) propose about heritability and intelligence?

The heritability of intelligence is not the same at different ages

• Gen-environment correlation

• Transition from (more) nurture to (more) nature

• Intelligence is one of the most heritable behavioural traits

What is the Gene-Environment Interaction? What is the difference between low and high SES families? (Turkheimer et al., 2003)

In low-SES families, the environment accounts for much IQ variation.

In high-SES families, genetic influences are substantially larger.

What are some issues regarding heritability of intelligence?

• Representativeness: adoption and twin studies make up a large proportion of the literature in this area

• Complexity of genetic influence: we don't know how genes produce intelligence yet; clearly not a single gene predicts intelligence

• Assortative mating

What is assortative mating?

The tendency to mate with those similar to ourselves, which can inflate observed genetic similarity and bias heritability estimates.

What did Watson et al. (2004) study about assortative mating?

• 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)

 

Name some problems for heritability estimates

•  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 the amount of inherited variation underlying individual differences in the trait (assortative mating increases additive genetic variance)

• 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.

• May lead to biased estimates of the relative magnitude of genetic and environmental factors (e.g., Vinkhuyzen et al., 2012)

Outline the neurobiological perspective of intelligence

• Intelligence is associated with both structural and functional differences in the brain

• Both genes and the environment can have an effect on brain structure and/or function

How can evolutionary explanations explain the relationship between brain size and intelligence?

• 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

Outline two studies showing support for the relationship between brain volume and intelligence?

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

• Pietschnig et al. (2015)– Meta-analysis of 88 studies, over 8,000 individuals – Reported a significant, slightly smaller correlation of r = .24

What did Shaw et al. (2006) discover about the relationship between Cortical Thickness and Intelligence?

Shaw et al. (2006) found that intelligence is related to the pattern of cortical growth—specifically, the cortex thickens for longer in high-IQ children.

What is meant by ‘the Flynn Effect’?

The substantial and sustained increase in global intelligence scores over time

Outline the Flynn effect - Flynn (1984) study

• Flynn (1984): 73 studies, ~7,500 participants; IQ scores rose between 1932–1978.

• Flynn (1987, 1994): Data from 20 countries showed yearly increases in IQ.

• Nonverbal tests: Average increase of 15 IQ points per generation (30 years).

• Verbal tests: Average increase of 9 IQ points per generation.

What did Pietschnig & Voracek (2015) find about the Flynn Effect?

• Meta-analysis: 271 independent samples, almost 4 million participants across 31 countries.

• Worldwide IQ gains: Observed between 1909–2013.

• Annual IQ increases:

  • Full-scale IQ: +0.28 points

  • Fluid IQ: +0.41 points

  • Crystallized IQ: +0.21 points

  • Spatial IQ: +0.30 points

• Key finding: IQ gains have decreased in more recent decades.

Name some limitations of the Flynn effect

• Must be due to multiple environmental factors rather than a genetic shift

• Opposing hypotheses:

• Nutrition hypothesis

• Cognitive stimulation hypothesis

What is meant by the nutrition hypothesis in regards to intelligence?

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

What is meant by the cognitive stimulation hypothesis in regards to intelligence?

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

What are the four main environmental areas of influence on intelligence? Neisser et al. (1996)

1. Biological environment (e.g., prenatal environment, nutrition)

2. Family environment

3. School & education

4. Culture

How has substance abuse been shown to affect intelligence? (Prenatal environment)

• 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)

How has breastfeeding been shown to affect intelligence? (Nutrition)

• 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)

How does socio-economic status of the family affect intelligence?

Socio-Economic Status (SES) and IQ

SES (capturing income, education, and occupation) is significantly correlated with intelligence with r = 0.3 - 0.4.

Education and IQ (Ceci, 1991)

Children attending school more regularly showed higher IQ scores, with each year of schooling associated with an average rise of 2.7 IQ points.

Luo People's Concept of Intelligence (Cocodia, 2014)

Consists of four concepts: Rieko (academic intelligence), Paro (practical thinking), Luoro (social attributes), and Winjo (comprehending instructions).

Social Constructionism

Views intelligence not as a fixed, innate trait, but as a social and cultural product constructed through language and social interactions.