Abstract
Related to intelligence is IQ, the heritability of which is 45% for children, and rises to 75% for late adolescents and adults. IQ is related to g-factor, which includes subsets of mental abilities related to fluid intelligence (Gf), crystallized intelligence (Gc), visuospatial processing (Gv), working memory (Gwm), and quantitative reasoning (Gq). A detailed meta-analysis of intelligence involving 78,308 individuals, looking for associations between intelligence and specific genes identified 336 associated SNPs in 18 genomic loci, of which 15 were new. It confirmed 40 novel genes for intelligence. The identified genes were predominantly found in brain tissue. Overall the SNPs accounted for a non-negligible 5.0% difference in intelligence.
Man’s yesterday may ne’er be like his morrow; Nought may endure buy mutability!—Frankenstein—Mary W. Shelly
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Notes
- 1.
IQ scores have a normal distribution with a mean of 100 and a standard deviation of 15; 50% of individuals score above 100, and 50% score below 100. The average IQ is 85–114, and 68% fall into this range. Only 16% have scores of 85 or lower, and 14% of have scores of 115–129. The top 2% of individuals have IQ scores of 130–145; these scores are higher than 98% of the population. IQ scores over 145 indicate the top 0.1%.
- 2.
For example, a person may have a high level of musical intelligence, but a low level of logical/mathematical intelligence. Gardner identified eight intelligences: linguistic, logical-mathematical, musical, spatial, bodily/kinesthetic, interpersonal, intrapersonal, and naturalistic.
- 3.
The g-factor can be thought of as a subset of IQ, which in turn is a subset of intelligence, which in turn is a subset of the entirety of mental abilities.
- 4.
I list five of ten broad categories of g, which can be subdivided into seventy more narrow abilities.
- 5.
The Colorado Adoption Project is an ongoing genetically-informative longitudinal study of behavioral development that began in the mid-1970s. The experiment accumulated data from both parent-offspring and related- versus unrelated- sibling comparisons to estimate the importance of genetic and shared environmental influences for resemblance among family members.
- 6.
Monozygotic, or identical twin, studies combined with imaging of brain structures and features, consistently confirm a genetic basis for particular forms of intelligence. Until recently, because identical twins develop from a single fertilized egg, they were thought to have the identical genome. But this has been revised. Any differences between twins may be due to, as previously understood, their environments, but a new discovery has shown that twins from the same embryo can differ in phenotype, which of course is genetic. Part of the answer is that specific changes identified are found where a gene exists in multiple copies, or a set of coding letters where DNA is missing. Researchers are not sure if these changes in identical twins occur at the embryonic level, as the twins age or both. See, O’Connormarch, A. (2008). “The Claim: Identical Twins Have Identical DNA,” New York Times. https://www.nytimes.com/2008/03/11/health/11real.html.
- 7.
Variance is a measure of how dispersed or spread-out data are in a statistical distribution, calculated as square of the standard deviation from the mean.
- 8.
H.K. Kim, The Creativity—Post Does Science Say Smart People Are Creative? See, https://www.creativitypost.com/article/does_science_say_smartest_people_are_creative (Last visited 5/23/2019).
- 9.
SHANK3, DIXDC1, DISC1, C4, are gene candidates for autism, schizophrenia, and GRIN1, can lessen its gene expression and impair learning in children. A variation in the gene COMT can increase dopamine levels by four-fold in the frontal cortex, which can increase concentration.
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Carvalko Jr., J.R. (2020). Revising the Bell Curve. In: Conserving Humanity at the Dawn of Posthuman Technology. Palgrave Macmillan, Cham. https://doi.org/10.1007/978-3-030-26407-9_11
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DOI: https://doi.org/10.1007/978-3-030-26407-9_11
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