A study of 473 sets of twins followed since birth found that compared to single-born children, 47 percent of 24-month-old identical twins had language delay compared to 31 percent of non-identical twins. Overall, twins had twice the rate of late language emergence of single-born children. None of the children had disabilities affecting language acquisition.
The results of the study were published in the Journal of Speech, Language, and Hearing Research.
University of Kansas Distinguished Professor Mabel Rice, lead author, said that all of the language traits analyzed in the study – vocabulary, combining words and grammar – were significantly heritable with genes accounting for about 43 percent of the overall twins’ deficit.
The “twinning effect” – a lower level of language performance for twins than single-born children – was expected to be comparable for both kinds of twins, but was greater for identical twins, said Rice, strengthening the case for the heritability of language development.
“This finding disputes hypotheses that attribute delays in early language acquisition of twins to mothers whose attention is reduced due to the demands of caring for two toddlers,” said Rice. “This should reassure busy parents who worry about giving sufficient individual attention to each child.”
Read the full, original story: Language delay likely due more to nature than nurture
