Large twin study suggests that language delay due more to nature than nurture

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 June 2014 Journal of Speech, Language, and Hearing Research.

http://www.eurekalert.org/pub_releases/2014-07/uok-lts071814.php