Genetic “General Intelligence,” Objectively Determined and Measured

Abstract

It has been known for 115 years that, in humans, diverse cognitive traits are positively intercorrelated; this forms the basis for the general factor of intelligence (g). We directly test for a genetic basis for g using data from seven different cognitive tests (N = 11,263 to N = 331,679) and genome-wide autosomal single nucleotide polymorphisms. A genetic g factor accounts for 58.4% (SE = 4.8%) of the genetic variance in the cognitive traits, with trait-specific genetic factors accounting for the remaining 41.6%. We distill genetic loci broadly relevant for many cognitive traits (g) from loci associated with only individual cognitive traits. These results elucidate the etiological basis for a long-known yet poorly-understood phenomenon, revealing a fundamental dimension of genetic sharing across diverse cognitive traits.Genetic General Intelligence (g) Genetic "General Intelligence," Objectively Determined and Measured § § The title adds the word Genetic to the start of Spearman's 1904 title that discovered phenotypic general intelligence, which he abbreviated as g Scores on psychometric tests of cognitive abilities (intelligence) robustly predict educational performance, socio-economic attainments, everyday functioning, health, and longevity (1-3). In 1904, Charles Spearman identified a positive manifold of intercorrelations among school test results and estimates of intelligence, leading him to propose that they arise from a single general dimension of variation, which he termed general intelligence (and which he denoted as g) (4). He theorized that most of the remaining variance in each cognitive test was accounted for by a factor specific to that test, which he called s. Thus, some variance in each cognitive test is shared with all other cognitive tests (g), and some is specific to that test (its s). Hundreds of studies have since replicated the finding that, when several or many diverse cognitive tests are administered to a sizeable sample of people, a g factor is found that accounts for about 40% of the total test variance (5,6). Considerable efforts over the past century have been placed on identifying the biological bases of g, spanning levels of analysis from molecular, to neuroanatomical, to cognitive (7-11).Psychometrically, a hierarchical structure of cognitive abilities is commonly agreed, with cognitive tests' variance accounted for by three different strata of variation (Fig. S1), representing each test's specific variance (s), broad domains of cognitive function (e.g. reasoning, processing speed, memory), and g (5). Most twin studies that examine the heritability of human intelligence differences use test scores that mix g and s; relatively few have applied the twin method to the hierarchy of cognitive test score variance (12). The twin-based studies that have separated g variance from s variance indicate a strong heritable basis for g, suggesting that cognitive traits are positively correlated substantially because of strongly overlapping genetic architecture (13-17). These findings are consist...

Investigating the genetic architecture of noncognitive skills using GWAS-by-subtraction

“…The ability to control statistically for any variable, genetic or otherwise, depends on how well and comprehensively that variable is measured 91 . The tests of cognitive performance included in the Cog GWAS likely do not capture all genetic influences on all forms of cognitive ability across the lifespan 92 , 93 . Despite these limitations, our simplified and incomplete statistical separation of NonCog from Cog allowed us to test whether heritable traits other than cognitive ability influenced educational attainment and to explore what those traits might be.…”

Cognitive Ability in Everyday Life: The Utility of Open-Source Measures

“…Psychological and physical differences can be highly heritable but also highly malleable by the environment (e.g., height). Furthermore, in the United States, heritability-of-ability estimates vary as a function of social class (Giangrande et al, 2019), but this effect is not observed in Europe or Australia, which may be taken as a sign of greater socioeconomic inequality in the United States (Tucker-Drob & Bates, 2016).…”

“…Early research on intelligence also contributed to advances in measurement and theory. While still a graduate student, Charles Spearman (1904) published a fundamentally important article establishing the tradition of measuring general intelligence ( g ) that continues to this day (de la Fuente, Davies, Grotzinger, Tucker-Drob, & Deary, 2019). Spearman correlated psychophysical sensitivity to pitch, weight, and light with teacher ratings of “common sense” and cleverness in 24 village children and with school performance in the classics, French, English, and mathematics in the upper class of a preparatory school ( N = 22).…”

Multifactorial structure of cognitive assessment tests in the UK Biobank: A combined exploratory factor and structural equation modeling analyses

“…Some have used a single test, such as a Verbal Numerical Reasoning (Fluid Intelligence, FI) score or a reaction time (RT) score (Davies et al, 2016;Sniekers et al, 2017;Kievit et al, 2018;Lee et al, 2018;Savage et al, 2018). Others have extracted a 'g-factor' of general cognitive ability by aggregating several variables using Principal Component Analysis (PCA) or Confirmatory Factor Analysis (CFA; Lyall et al, 2016;Navrady et al, 2017;Cox et al, 2019;de la Fuente et al, 2021;Hepsomali and Groeger, 2021). However, this inconsistency in the definition of cognitive domains across different studies is a potential threat to replicability of the findings.…”