At the moment the question is rather whether Baltic and Slavic are coordinate members of Balto-Slavic or whether Slavic is genetically nested within Baltic. The Proto-Baltic and Proto-Balto-Slavic reconstructions are practically indistinguishable, while Proto-Slavic can be derived from them rather easily.
Evidence? First of all, shared phonological innovations including such idiosyncratic stuff as the treatment of syllabic liquids and nasals (*R. > *iR/*uR), laryngeal "special effects" (*VRHC > *V:RC, where R is a nasal, liquid or glide) and Winter's Law (lengthening before the *d series). Very similar morphological processes, especially in the area of derivation (especially the distribution of secondary vowel grades, which represent common innovations and not IE archaisms). There are also a large number of exact morphological and lexical correspondences that might support a genetic relationship but which might also be due to diffusion, so I attach less importance to them.
----- Original Message -----
From: "P&G" <petegray@...>
To: <cybalist@yahoogroups.com>
Sent: Monday, March 17, 2003 9:08 PM
Subject: Re: [tied] How should Nostratic be viewed?
> >>Hasn't the world moved on?
> > It has, but Balto-Slavic has withstood the changes.
>
> Ooh, there's an interesting debate! Trying to think with you, rather than
> anything else, what evidence would point to original unity, rather than
> contact, or close relationship?
> I note in passing Lehmann's comment, that "individual scholars maintain
> strong views on both sides of the question."
>
> Peter