Ellen Verhoefa b, Lucía de Hoyosa b, Fenja Schlaga b, Jeffrey van der Vena b, Mitchell Olislagersa b c d, Philip S. Dalee f g, Evan Kiddh i, Simon E. Fishera b j k, Beaté St Pourcaina b j k l m
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Background Mastering gross motor abilities in early infancy and culturally defined actions (e.g. self‐care routines) in late infancy can initiate cascading developmental changes that affect language learning. Here, we adopt a genetic perspective to investigate underlying processes, implicating either shared or “gateway” mechanisms, where the latter enable children to interact with their environment. Methods Selecting heritable traits ( h 2 , heritability), we studied infant gross motor (6 months) and self‐care/symbolic (15 months) skills as predictors of 10 language outcomes (15–38 months) in genotyped children from the Avon Longitudinal Study of Parents and Children ( N ≤ 7,017). Language measures were combined into three interrelated language factors (LF) using structural equation modeling (SEM), corresponding to largely different age windows (LF 15M , LF 24M , LF 38M , 51.3% total explained variance). Developmental genomic and non‐genomic relationships across measures were dissected with Cholesky decompositions using genetic‐relationship‐matrix structural equation modeling (GRM‐SEM) as part of a multivariate approach. Results Gross motor abilities at 6 months ( h 2 = 0.18 ( SE = .06)) and self‐care/symbolic actions at 15 months ( h 2 = 0.18 ( SE = .06)) were modestly heritable, as well as the three derived language factor scores (LFS 15M ‐ h 2 = 0.12 ( SE = .05), LFS 24M ‐ h 2 = 0.21 ( SE = .06), LFS 38M ‐ h 2 = 0.17 ( SE = .05)), enabling genetic analyses. Developmental genetic models (GRM‐SEM) showed that gross motor abilities (6 months) share genetic influences with self‐care/symbolic actions (15 months, factor loading λ ; λ = 0.22 ( SE = .09)), but not with language performance ( p ≥ .05). In contrast, genetic influences underlying self‐care/symbolic actions, independent of early gross motor skills, were related to all three language factors (LFS 15M ‐ λ = 0.26 ( SE = .09), LFS 24M ‐ λ = 0.28 ( SE = .10), LFS 38M ‐ λ = 0.30 ( SE = .10)). Multivariate models studying individual language outcomes provided consistent results, both for genomic and non‐genomic influences. Conclusions Genetically encoded processes linking gross motor behaviour in young infants to self‐care/symbolic actions in older infants are different from those linking self‐care/symbolic actions to emerging language abilities. These findings are consistent with a developmental cascade where motor control enables children to engage in novel social interactions, but children's social learning abilities foster language development.
