Avestan

Avestan (/əˈvɛstən/) is an umbrella term for two Old Iranian languages: Old Avestan (c. 1500 – c. 1000 BCE) and Younger Avestan (c. 1000 – c. 500 BCE). They are known only from their conjoined use as the scriptural language of Zoroastrianism, and the Avesta likewise serves as their namesake. Both are early Eastern Iranian languages within the Indo-Iranian language branch of the Indo-European language family.

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 * A keystone in the traditional short chronology for Indo‐European, for instance, is the perception that Avestan and Vedic are ‘so close’ that the divergence between them ‘must’ be but a matter of a few centuries. Sims‐Williams (1998: 126), for example, offers selected sentences that “may be transposed from the one language into the other merely by observing the appropriate phonological rules.” Much the same, though, can be said of selected phrases in Italian and Spanish, for instance: see Heggarty and Renfrew (2014: 545). Change and divergence have been minimal in no end of word pairs, such as Italian [liŋgwa] vs. Spanish [lɛŋgwa] tongue (from Latin [liŋgʷa]), [mɔndo]~[mundo] world, [θjelo]~[t͡ʃelo] sky, etc. Indeed, other cases show no real divergence at all: [kanto]~[kanto] I sing, [salta]~[salta] s/he jumps, and so on. Here too, simply applying phonological rules can straightforwardly transpose one language to the other, but that hardly proves a time‐depth of divergence of just a few centuries, as traditionally envisaged between Avestan and Vedic. For the net diver- gence between Italian and Spanish to arise, out of Latin, took the same two millennia that in French saw much more radical change.
 * Bayesian Phylolinguistics . SIMON J. GREENHILL,1 PAUL HEGGARTY,2 AND RUSSELL D. GRAY in, The Handbook of Historical Linguistics, Volume II