IQ

Who are the key figures in the historical development of genetics?

• Pythagoras (father supplies the characteristics, mother supplies the building)

• Aristotle (children were made from purified blood and menstrual blood)

• Darwin (theory of evolution)

• Mendel (laws of Mendelian inheritance)

• Galton (twin studies)

• Fisher (united Mendelian and biometric approaches)

What were the laws of Mendelian inheritance?

• Law of dominance (some alleles are dominant over others, and an organism with at least one dominant allele will display the dominant trait)

• Law of segregation (during gamete formation, the alleles for each gene separate from each other so that each gamete carries only one allele for each gene)

• Law of independent assortment (genes of different traits can segregate independently during the formation of gametes)

What are identical and fraternal twins?

Identical = single egg fertilized by a single sperm, which then splits into two (share 100% of their genes)

Fraternal = separate eggs fertilized by separate sperms (share 50% of their genes)

What is heritability?

The proportion of variation that is associated with genetic factors in a specific environment.

What do twin studies entail?

Compare similarities between identical (monozygotic) and fraternal (dizygotic) twins.

What do adoption studies entail?

Comparing adopted children to their adopted and biological families.

What are the limitations with both of these types of studies?

They may produce overestimate the role of genetics in certain traits due to gene-environment correlation (genes can influence the environments people end up in).

What kind of gene-environment correlations?

• Identical twins may create more similar environments for themselves

• Adopted children may seek out environments similar to their biological parents

The strength of genetic influence can vary?

• Between different populations

• Across different environments

• Over time

How does heritability change with age?

(Plomin, 2015)

• It increases form ~20% in infancy to ~80% in adulthood

What is true about effect sizes in cognitive traits?

They vary widely

Can heritability change over time?

(Rimfeld, 2018)

• They found that after Estonia transitioned from communism to capitalism, genetic factors played a bigger role in determining education and job status

• This suggests that in more merit-based societies, genetics (like talent and ability) have more influence on success

• This shows that genetic influences on social outcomes can change in response to a major social transformation

How might heritability also remain constant over time?

(Jelenkovic, 2016)

• Although genetic variance in height tended to increase across birth-year cohorts, heritability estimates did not show any clear pattern of change over time

• Over time, differences in height between people (due to genetics) got bigger, but the proportion of those differences explained by genetics (heritability) didn’t consistently increase or decrease

What are some misconceptions about heritability?

• Heritability does not imply causality (genes do not directly ‘cause’ something)

• If something is highly heritable it does not mean that it cannot be modified

• Heritability tells us nothing about the mean/average of a trait

What are the three models of gene-environment correlation?

• Passive

• Reactive

• Active

What is a passive correlation?

Parents provide both genes and environment (e.g. highly educated parents pass on their genes and create a cognitively stimulating home environment).

What is a reactive correlation?

A child's natural cognitive abilities trigger specific reactions from their environment (e.g. a child with high verbal ability may elicit more complex language from adults, further enhancing their linguistic skills).

What is an active correlation?

Individuals seek out environments that align with their genetic predispositions (e.g. a student with a genetic predisposition for high cognitive ability may choose more challenging courses, further developing their intellectual capacities).

What research shows an active correlation?

(Abdellaoui, 2019)

• People with genetic variants associated with higher educational achievement were more likely to move out of areas with fewer educational and economic opportunities

• Those who were born in coal mining areas but moved away had significantly higher education-related genetic scores than those who stayed

How did Galton attempt to measure intelligence?

He tried to show that there is a genetic basis to intelligence, his argument being that eminence runs in families.

What was Galton’s theory of intelligence?

The more a person is able to distinguish between subtle differences in things, the higher their level of intelligence is considered to be.

How did Binet attempt to measure intelligence?

He developed tests of mental ability for children based on what an average child of a particular age could solve.

What was the issue with this method^?

There is no increase in mental age during adulthood.

How did Wechsler attempt to measure intelligence?

Deviation IQ tells you how far a particular score deviates from the average score for a particular test.

What is an IQ score?

A measure of how far an adult’s score deviates from the population mean.

What is the main modern IQ test?

The Wechsler Intelligence Scale for Adults - Revised (WAIS-R), which consists of 11 subtests - six verbal and five performance subtests.

Why did Wechsler include such a wide range of tests?

A person’s intelligence could be manifest in a variety of ways; thus, the wider the range of subtests the better.

What did Wechsler realise?

If one subtest is considered to be a test of intelligence then all other subtests should correlate with it – they should have convergent validity.

What is the Raven’s Matrices?

It’s comprised of abstract reasoning problems and it correlates well with the WAIS.

What are the required criteria for any IQ test?

• Construct validity (scores on IQ tests should correlate with some independent measure of someone’s ability, such as educational achievement)

• Reliability (the consistency of scores which that test yields for an individual each time the individual is tested)

What kind of environmental effects affect IQ score?

• Parent’s income

• Occupational status

• Neighbourhood

• Type of accomodation

• Birth order

• Number of other children in family

What is Spearman’s g?

A single factor of general intelligence (the overall correlation between diverse IQ tests and IQ subtests proves that IQ tests measure this).

What might we suggest because of the fact that they do not correlate perfectly?

That intelligence consists of a set of largely independent abilities and it is this that IQ tests measure.

What is factor analysis?

A statistical method used to identify underlying relationships between variables by grouping them into factors based on their shared variance.

What does factor analysis tell us about this?

• Different subtests on the WAIS are correlated with one another, showing a general pattern of positive relationships across all subtests (positive manifold)

• Some subtests are more strongly related to each other than to others, suggesting the presence of specific factors (verbal factor and performance factor)

What are some other factors?

• Gc (crystallized intelligence)

• Gv (visuo-spatial intelligence)

• Gf (fluid intelligence)

What is the ‘purest’ test for measuring Spearman’s g?

The Raven’s Matrices

On which subtest of the WAIS do females outperform males?

Wechsler digit symbol substitution subtest

What is the ‘main’ determinant of intelligence?

Heritability

What does it mean if a characteristic has high heritability?

It is not affected very much by current environmental variables.

What suggests that IQ has substantial heritability?

• Adoption studies, which ask whether the IQ of an adopted child is closer to that of their biological or adoptive parent

• The concordance rate between MZ twins separated at birth and adopted into different families

What is the criticism of these studies^?

They did not control for shared environmental factors (environmental influences that are experienced similarly by individuals growing up in the same family or household).

How else can we estimate heritability of IQ?

Classical twin studies, which use very large numbers of MZ and DZ twin pairs who have been raised together and compare the concordance rate on a trait between the MZ twins to the concordance rate on that trait between DZ twins (heritability estimates have been substantial – roughly between 57% and 86%).

What is the criticism with this type of study?

The equal environments assumption

What is true about the genetical variation within and between races?

It is greater within a race than between two races (and evidence of IQ heritability within a group provides no evidence of genetic differences between groups).

Why is there not much evidence for genetic causes?

• There’s no single gene for cognitive abilities

• It would be hard to conduct such experiment (would have to raise children from birth in strict environments)

Who investigated these genetic causes and what did they find?

(Moore, 1986)

• Compares the IQ performance and response styles of 23 Black children adopted by middle-class White families and 23 Black children adopted by middle-class Black families

• Transracially adopted children scored nearly one standard deviation higher on the Wechsler Intelligence Scale for Children (WISC)

• Difference in scores was linked to distinct response styles, with White adoptive mothers engaging in more positive and supportive behaviors, while Black adoptive mothers displayed more neutral or negative reactions

• Concludes that the ethnicity of the rearing environment influences children's responses to intelligence tests and their test performance

What are some other environmental effects that may explain this result^?

• Poverty and lower socio-economic status

• Systematic and institutionalised racism

• Stereotype threat

• Poor self-esteem

If societal conditions for ethnic minorities have improved over the past few years, how have IQ test scores changed?

• (Dickens & Flynn, 2006) showed that between 1972 and 2002, black Americans gained 4 to 7 IQ points relative to whites

How does heritability of intelligence change with socio-economic background?

• (Tucker-Drob, 2015) showed that intelligence heritability is lower among poor children raised in the US compared to those from wealthier families

• This is not true for Europe where social policies more uniformly ensure access to education

What is the Flynn effect?

The observed rise in average IQ scores across generations, likely due to improved nutrition, education, and cognitive demands of modern society.

X Who conducted a meta-analysis on the Flynn effect?

(Pietschnig & Voracek, 2015)

Do Eas-Asians have an IQ advantage over Whites?

(Hsin, 2014)

• The superior academic achievement of Asian Americans is largely due to greater academic effort rather than cognitive abilities or socio-demographic factors

• Compares Asian-American and white students' educational trajectories from kindergarten to high school found that Asian-American students' advantage in academic performance is primarily driven by higher levels of effort

What is the teacher-expectancy effect?

When a teacher's expectations about a student's abilities influence the student's performance.

How can an IQ test be biased?

• Uper class english vocabulary

• Tests were designed by white (males) having other white people in mind

• Examiners are typically white

• Tests reflect white values and culture

What’s an example of a biased IQ test?

• (Wicherts & Dolan, 2010) showed that a Dutch IQ test for children were biased against ethnic minority students

How might we overcome these biases?

Use ‘culture-free’ IQ tests (even though theses can still be biased).

Are IQ tests fair (give an example)?

(Gonthier, 2022)

• Reviews evidence showing that the perception and manipulation of visuo-spatial information varies significantly across cultures, affecting how individuals solve problems on tests like Raven's matrices

• Concludes that visuo-spatial reasoning tests are not culture-fair

Are there sex differences in IQ performance?

• (Neisser, 1996) states that sex differences are non-existent or very small

• But, moderate differences are present on specific subtests

• Likely due to environmental and biological causes

What is the male-variability hypothesis?

Males exhibit greater variability in traits, including intelligence, with more males found at both the high and low ends of the distribution compared to females.