On Fri, 28 Apr 2017 16:02:41 -0700, Gage Amonette <[log in to unmask]> wrote:

>I'm currently working on the history of the Gagish language, and I
>encountered a problem: I want Classical Gagish to mark for the plural via
>reduplication of the first syllable of the root, but I want Proto-Gagish to
>have a plural and a dual number. Is it naturalistic for a language to just
>develop a reduplicative process like that?

An accepted theory of the origins of reduplication is something we still don't have (Niepokuj notwithstanding: she even says in her thesis that it's more of a first foray).  But to your question the answer is yes: reduplication can, from a historical linguist's point of view, just show up.  I think when it does it usually has more expressive (and iconic) semantics, at least at first.  But that's no problem for you.  Maybe in an intermediate stage the inherited plural can contrast with the reduplication, the latter having an intensive meaning more like 'Ns all over the place'.  Then the reduplicated plural ousts the original plural, maybe because the earlier inflection wore away through sound change or something.  

See for more.