In addition, a number of grammatical features of Vedic Sanskrit not found in its sister Avestan language appear to have been borrowed from Dravidian languages. These include the gerund, which has the same function as in Dravidian. Some linguists explain this asymmetrical borrowing by arguing that Middle Indo-Aryan languages were built on a Dravidian substratum. These scholars argue that the most plausible explanation for the presence of Dravidian structural features in Indic is language shift, that is, native Dravidian speakers learning and adopting Indic languages due to elite dominance. Although each of the innovative traits in Indic could be accounted for by internal explanations, early Dravidian influence is the only explanation that can account for all of the innovations at once; moreover, it accounts for several of the innovative traits in Indic better than any internal explanation that has been proposed.