Heritability of Functional Literacy: Evidence from a Classical Twin Design

Behavior Genetics. 2026. Vol. 56. No. 4. P. 153–168.

Kolachev N., Kovaleva G.

Functional literacy—the ability to apply reading, mathematical, and scientific knowledge in authentic contexts as operationalized by the PISA framework—is a key predictor of educational attainment, labour-market outcomes, and economic growth. Despite extensive behavioral-genetic research on cognitive ability, the heritability of competency-based literacy measures remains largely unexamined, particularly outside Western populations. The present study addresses this gap by providing the first twin-based heritability estimates for PISA-type functional literacy from Russia. Participants were 114 twin pairs (50 monozygotic [MZ], 64 dizygotic [DZ]; age 14–15) identified within a nationally representative sample of 33,050 eighth-grade students assessed on the Russian Electronic School platform. A bifactor item-response theory model derived scores for a general cognitive ability factor and three domain-specific factors (mathematical, reading, and scientific literacy). Classical twin structural-equation modelling decomposed phenotypic variance into additive genetic (A), shared environmental (C), and non-shared environmental (E) components. The AE model provided the best fit across all phenotypes. Heritability estimates were substantial: functional literacy = 0.76 [95% CI: 0.67–0.85], mathematical literacy = 0.72 [0.59–0.84], reading literacy = 0.69 [0.56–0.82], and scientific literacy = 0.71 [0.59–0.82]. Shared environmental contributions were negligible and non-significant in all models. The twin sample was broadly representative of the source population, with only small mean differences in functional and mathematical literacy. These findings extend the behavioral-genetic architecture of cognitive ability to competency-based assessments and demonstrate its robustness in a non-Western educational context. Limitations include modest sample size, photo-based zygosity assignment, and absence of molecular genetic data.

Keywords: intelligence, reading literacy, twin study, scientific literacy, functional literacy, mathematical literacy