Abstract
The heritability of language and literacy skills increases during development. The underlying mechanisms are little understood, and may involve (i) the amplification of early genetic influences and/or (ii) the emergence of novel genetic factors (innovation). Here, we use multivariate structural equation models to quantify these processes, as captured by genome-wide genetic markers. Studying expressive and receptive vocabulary at 38 months and subsequent language, literacy and cognitive skills (7-13 years) in unrelated children (ALSPAC: N≤6,092), we found little support for genetic innovation during mid-childhood and adolescence. Instead, genetic factors for early vocabulary, especially those unique to receptive skills, were amplified. Explaining as little as 3.9%(SE=1.8%) variation in early language, the same genetic influences accounted for 25.7%(SE=6.4%) to 45.1%(SE=7.6%) variation in verbal intelligence and literacy skills, but also performance intelligence, capturing the majority of SNP-heritability (≤99%). This suggests that complex verbal and non-verbal cognitive skills originate developmentaly in early receptive language.