Lecture 3 Flashcards
Bouchard and McGue (1981) Averages
Monozygotic twins - 0.86 Dizygotic twins - 0.6 Siblings - 0.47 Parent-child - 0.42 Adoptive parent-adopted child - 0.19
Newman et al (1937) monozygotic twins correlation
r = 0.71
Shields (1962) monozygotic twin
r = 0.75
Juel-Nielson monozygotic twins
r = 0.69
Bouchard et al (1990) monozygotic twins
r = 0.75
Pedersen et al (1992) monozygotic twins
r = 0.78
Explanations for high correlation in twins
IQ has a genetic component, IQ is transmitted by nurture and high IQ parents transmit high IQ by the way they nurture their children, there is some environmental factor that determines variation in IQ that tends to be shared within families, or some combination of the above.
Scarr and Weinberg (1978) - adopted and bio children in the same family
Mother:
- 23 - Adopted
- 35 - Bio
Father:
- 15 - Adopted
- 39 - Bio
Average of parents:
- 25 - Adopted
- 51 - Bio
Turkheimer et al (2003)
Analysed intelligence scores between monozygotic and dizygotic twins. Among poor families about 60% of the variance in IQ scores was accounted for by shared environment and the contribution of genes was close to 0. In wealthier families the reverse was true.
How this relates to eugenics?
In the USA, African Americans score around 15 points lower on IQ scores than White Americans. As IQ is highly heritable it suggests black people are less intelligent than white people.
Haworth et al (2010) - Participants with correlation
4809 monozygotic pairs of twins (0.76 correlation)
5880 dizygotic pairs of twins (0.49 correlation)
USA (Ohio, Minnesota, Colorado), UK, Australia, Netherlands
Child samples (mean ages 5-18 years)
Haworth et al (2010) - Procedure
Web based cognitive tasks (UK)
Ravens Matrices
Weschler Intelligence Scale for children
Haworth et al (2010) - Conclusions
54% variance in IQ attribute to genetic variance
24% to non-shared environment ‘e’
22% to shared environment ‘c’
Haworth et al (2010) - Quote
“As children grow up, they increasingly select, modify and even create their own experiences in part based on their genetic propensities.”
Bouchard (2013) - Quote
“The results do not mean that environments are irrelevant or unimportant. The proximate causes of variance in IQ are the ‘cognitively stimulating experiences’ that the individual is provided with and seeks for him/herself. Early in life, those experiences are primarily imposed…”
Martin et al (1986) - Quote
“Humans are exploring organisms whose innate abilities and predispositions help them select what is relevant and adaptive from the range of opportunities and stimuli presented in the environment. The effects of mobility and learning, therefore, augment rather than eradicate the effects of the genotype on behaviour”
Multiplier effect definition
The genetic tendency that guides behaviour will also cause the environment to change, and that magnifies the original trait.
Deary, Penke and Johnson (2010)
- Genome-wide association studies have not found common variants that explain much of the genetic variance in IQ across normal range
- Only a few relevant genetic loci have been discovered
- ‘Problem of the heritability’
- GWAS studies suggest many mutations of small effect is most likely genetic architecture
Davies et al (2018)
Found 11,600 significant SNPs, but one SNP often relates having another SNP so they didn’t know how many were independent.
Found that there were 434 independent SNPs that occurred at 148 regions along the 22 chromosomes.
Found that 709 genes were associated with intelligence. 25% of IQ variation was due to variation in their genes.
Deary (2020) - Quote
“Intelligence is therefore a polygenic trait, that is, associated with a great many genetic variants in many genes, and in many DNA locations that are not genes”
Genes, intelligence and health
- Several of the genes were related to the development of nerve cells and the nervous system
- Some of the DNA SNP variations appear to also be related to health (ie to height, weight, BMI, lung cancer, Crohn’s disease, bipolar disorder, schizophrenia, autism, Parkinson’s disease and Alzheimer’s disease)
Positive correlations between intelligence and health:
- Hand grip strength (r=0.09)
- Lung function (r=0.19)
- Short sightedness (r=0.32)
- Birth weight (r=0.11)
- Age at menopause (r=0.13)
- Autism Spectrum Disorder (r=0.12)
- Brain volume (r=0.27)
- Longevity (r=0.17)
Negative correlations between intelligence and health
- Hypertension (r=-0.15)
- BMI (r=-0.13)
- Smoking (r=-0.2)
- Heart attack (r=-0.17)
- Lung cancer (r=-0.26)
- Osteroarthitis (r=-0.24)
- ADHD (r=-0.24)
- Alzheimer’s disease (r=-0.37)
- Schizophrenia (r=-0.23)
- Major Depressive Disorder (r=-0.3)
- Neuroticism (r=-0.16)
- Low health satisfaction (r=-0.26)
- Sleeplessness (r=-0.12)
- Long-sightedness (r=-0.21)
