3. Heritability

What did Francis Galton contribute to the beginnings of the heritability debate?

• first popularised the distinction between nature and nurture

• interested in intelligence, personality, physical traits

• proposed that abilities are inherited in the same way physical traits are

What methods did Francis Galton use which informed his contributions?

• looking at obituaries in The Times newspaper for familial relations and their connection to ‘eminence’ and found that close relatives of eminent people were far more likely to be eminent than distant relatives

• also surveyed 190 royal society fellow, asked about birth order, parents details to determine if scientific prowess was due to nature or environment

• acknowledged there was an overlap - need to look at similarities and differences between people with different levels of shared genes

What is the degree of relationship?

How much genetic information is shared

• first-degree relatives share 50% e.g. parents and siblings

• second-degree relatives share 25% e.g. grand-parents

• third-degree relatives share 12.5% of genes e.g. great-grandparents, first cousins

What is genotype and phenotype?

genotype - individual genetic makeup of a person

phenotype - how that genetic makeup is expressed through observable traits

What is shared variability?

• how much of the difference between two people can be explained by genes - expressed as a percentage

How do we explain shared variability is parent and child are quite difference?

• high variability/ proportion of shared variance is low

How do we explain shared variability is parent and child are very similar?

• low variability/ proportion of shared variance is high

What are the two broad techniques for determining heritability estimates?

• behavioural approaches

• DNA/physiological approaches

What is the procedure of family studies? (a behavioural approach)

• parents and children share 50% genes

• measure intelligence, then compare performance

• If similar can assume genetic influence on intelligence

What are strengths and limitations of family studies?

• easy to get samples

• but difficult to separate out genes and environment

What is the logic and procedure of twin studies? (a behavioural approach)

• MZ share 100% of DNA. DZ share 50%

• compare phenotype between MZ and DZ to examine relative influence of genetics

• children have the same environments → natural comparison between genetic similarity (MZ V DZ) so can assume impact of genes

What are key strengths and limitations of twin studies?

• natural control over gene similarity

• however, MZ twins may be treated more similarly than DZ

• and twins might not represent the whole population

What is the logic/procedure of adoption studies?

• same genes, different environments

• ideal is to study adopted twins

What are strengths of adoption studies?

• study both genes and environment separately. nearest to ideal design

• tease out genes/environment

What are limitations of adoption studies?

• families are matched deliberately - not random

• adopted families are not always representative (higher SE)

• contact with birth parents can blur the line

• prenatal environment may have impact

What were the key findings of Ridley 1999 regarding heritability of intelligence based on behavioural/family studies?

• variability decreases from identical twins reared together (86%) and identical twins reared apart (76%) suggesting that the environment must play some part but genetics have large role

• shared variability is 0% for adopted children living together. Same environment but different biology. No correlation suggests genetics must play some part

What were the heritability estimates for intelligence made by eysenck and the Bell curve book and what might be a limitation?

estimated heritability of intelligence is quite high

• 69% Eysenck (1979)

• 74% Bell Curve book (Herrnstein and Murray 1994)

• But all evidence so far uses behaviour methods - making assumptions about physiology/DNA

What is a Genome-Wide Association Study?

considers the entire set of genetic material of a large group of people - searching for genetic variations

What is a Single Nucleotide Polymorphism (SNP or ‘Snips’)

• The small variations that are being searched for in a genome-wide associations study

• scientists want to identify SNPs that occur more frequently in people with, for example, high or low intelligence

How did Davies et al (2011) use DNA to directly explore intelligence?

• directly considered heritability of intelligence using genome-wide data looking for SNPs and phenotype data (measures of cognitive traits associated with intelligence)

• compared 3511 unrelated, middle/older adults

What did Davies et al (2011) find using DNA to directly explore intelligence?

• found that 40-50% of variation in intelligence is associated common SNPs

• supports genetic heritability in intelligence

How did Deary et al. (2012) investivate the genetic contribution to the stability of intelligence across the life span?

• noticed people who score high on intelligence tests as children tend to score similarly as adults or older adults

• measure intelligence at 11 then again at 65, 70, 79 (2000) unrelated individuals

• combined this is DNA analysis

• examined more than 500,000 genetic markers (SNPs) to see how genetically similar these individuals were despite not being related

What did Deary et al. (2012) find regarding the genetic contribution to the stability of intelligence across the life span?

People who were more genetically similar:

• had more similar childhood IQ

• had more similar older-age IQ

• and showed more similar stability

suggests there is a genetic contribution to the stability of intelligence across the life span. However it’s estimated to only be 38%

Is there a single intelligence gene?

• there is no single gene that dictates intelligence

• intelligence is polygenic

• thousand of genetic variants each contribute tiny effects

• a single SNP might explain 0.002% of variation in intelligence

• genes do influences broader process which might influence intelligence e.g. synaptic development

What are 4 environmental influences on intelligence?

• biological (not genetic)

• family environment

• school and education

• culture

What is involved in the biological environmental influence on intelligence?

• nutrition

• prenatal factors (e.g. drinking and smoking)

What might be involved in the family environment influence on intelligence?

• shared and non-share environments

• SES (large influences - estimated IQ variation of 45 points

• birth order (first born has highest IQ then decreases)

• family size (larger family - lower IQ)

What is the nature of the school and education influence on intelligence?

• it is bidirectional

• education ←> intelligence

What is involved in the culture influence on intelligence?

• linked to implicit ideas of intelligence

• contributes to what kinds of intelligence develops

What are the two different ways genes/ environment interact to produce the phenotype?

What are the 4 different considerations for genetic heritability?

• genetic potential

• gene-environment correlation

• differential susceptibility

• moderating factors

What is the genetic potential consideration for genetic heritability?

• child may have the genes for high intelligence: whether it’s realised is dependent on the environment

• with stimulating school/ home environment they may be able to reach their potential

• the environment changes the size of genetic impact

What is the gene-environment correlation consideration for genetic heritability?

• those that have the genes might undertake behaviours which will lead to higher intelligence e.g. choosing harder books to read, joining clubs

• genes shape the environment they’re in which is then shping their outcome in terms of intelligence

What is the differential susceptibility consideration for genetic heritability?

• some genetic profiles make a child more sensitive to their environment

• genetic profile will make them more malleable to whatever is going on

• if positive environment - will flourish more

What are moderating factors as a consideration for genetic heritability?

other things that affect the strength of the interaction

What are 5 considerations of the GxE interaction?

• estimates only tell us about groups/society - not individuals

• intelligence is an abstract concept - not a concrete definition/ biological basis

• genetic variation depends on dominance

• assortative mating: pair up with similar others

• twin/adoption studies

What is The Bell Curve (1994) what were the main general things reported

• book published containing same/similar negative ideas around intelligence

• reported how intelligence is genetic

• focus on the rise of the “cognitive elite”

• increased intelligence → increased chance of success

• intellectual inferiority of some cultural groups

What were the 6 main arguments of the bell curve?

1. There is such a thing as a general factor of intelligence upon which humans differ

2. IQ tests are designed to measure ‘g’ and are mostly accurate

3. IQ scores match implicit theories of intelligence

4. IQ score are stable, although not perfectly so

5. properly administered IQ tests are not biased against social, ethnic, economic or racial groups

6. cognitive ability is substantially heritable 40-80%

What was involved in the Bell Curve’s main theme of the cognitive elite?

Intelligence is more important than social class/wealth in uni admissions

• allow intelligent people to get certain jobs

• cognitive elite distinct because of separation through education and jobs

• intelligence is the basis of the class system

What was involved in the Bell Curve’s main theme of the socioeconomic variables and IQ?

Suggest than an individual’s intelligence is more important than SES for predicting economic and social welfare

What was involved in the Bell Curve’s main theme of the relationship between race and intelligence?

described evidence for the higher IQ of asian-americans and lower IQ of African-American in comparison to white Americans

What was involved in the Bell Curve’s main theme of the ideas implications for social policy?

Women with a lower IQ tend to have more children, so the population of those with lower IQ is increasing

• immigrants contribute towards this

• this will increase societal problems associated with low IQ (e.g., crime)

implicit in these stated arguments then is that groups of people in America with lower intelligence (e.g., immigrants and African-Americans) are potentially part of this social problems.

What did Herrnstein and Murray argue that the best way to tackle the ‘problems’ outline in the Bell curve book?

• not to use affirmative action (support) as measures such as these have led to a decrease in intelligence within education and the workplace

• its failed in the past and if intelligence genetic then it won’t help anyway

• also argue that resources should be shifted from supporting underprivileged population to supporting the ‘cognitive elite’. society will improve because the workforce will improve

What were the consequences of the bell curve book?

• initially quite positive response but prompted the APA to put together a taskforce headed by ulric neisser

• taskforce to represent wide range of views and opinions on intelligence

What was one of the conclusions of the taskforce put together after the Bell Curve book?

While the average IQ scores between African American and White Americans may differ, there is no definite evidence to suggest this is due to genetics. It is more likely to be cultural

What is the flaw with the Bell Curve 1 assumption that G exists and differs?

• more empirical evidence of this now, but research not as clear back then

• no expert consensus yet

What is the flaw with the Bell Curve 1 assumption that IQ tests measure g and are accurate?

• can be some debate over this, given the context around the origins of g and around its testing and development

What is the flaw with the Bell Curve 1 assumption that IQ scores match implicit theories of intelligence?

• maybe western ideas, but there are some differences across cultures and sub-cultures

• even within one culture our ideas can shift and change

What is the flaw with the Bell Curve 1 assumption that IQ scores are stable?

• quite but not perfectly (e.g. deary 2000 said around 60)

• and consider ideas around malleable and fixed intelligence

What is the flaw with the Bell Curve 1 assumption that IQ tests are not biased?

• tests themselves may not be biased, but the theories behind them could be

What is the flaw with the Bell Curve 1 assumption that cognitive ability is substantially heritable?

• based on less robust research methods that were available at the time

• large estimate range (40-80), and difficult to use to explain group differences

What are 3 issues with the stats and evidence used in The Bell Curve?

• Correlations between SES and intelligence are not causations. SES can be bound up with multiple confounding factors

• Measure validity: studies using self-report measures for SES with children and no additional checks

• Problematic research studies: over-reliance of certain academics and cherry-picking results