Individual differences in executive functions are almost entirely genetic in origin.

582 individuals from 293 same-sex twin pairs (316 monozygotic, 266 dizygotic)

Colorado Longitudinal Twin Study; tested at about age 17 (mean 17.3, range 16.1 to 20.1).

Latent-variable twin modelling on a battery of objective laboratory executive-function tasks, decomposing a Common EF factor plus updating-specific and shifting-specific factors. The latent approach is what makes the estimate credible - it strips task-specific measurement error before decomposing variance.

Genetic variance in the Common EF factor is 99%. Updating-specific 56%, shifting-specific 42%. Shared environment is approximately zero at the latent level. The phenotypic latent correlations among the components were 0.74 (inhibiting-updating), 0.73 (inhibiting-shifting) and 0.40 (updating-shifting).

This IS the genetic evidence. Classical twin design with its equal-environments assumption.

Replicated in an independent younger cohort by Engelhardt et al. 2015 (Texas Twin Project, ages 8-15), which found Common EF A = 1.00 with shared environment at zero. Consolidated by Friedman and Miyake 2017, which reports Common EF 96% heritable and stable from age 17 to 23 with the same genetic influences operating.