This is another neat website I've found in looking for linguistics-related stuff. I would like to point out that while Ruhlen does seem to have his head on straight (and know his stuff!), he overlooked the fact that Old English is the "parent" language of Modern English much the way that Latin is the parent language of Spanish, French, and Italian.
Oh, I know it's not entirely the same. Latin is the (dead) forebear of a whole family of languages (the Romance Languages), while Old English is the (dead) ancestor of just one Germanic Language, but I think it's a shame that he doesn't point out the fact that the Germanic (and Slavic, etc.) Languages do have ancestor languages, and we do have written documentation of some them, it's just that they don't all stem from the one parent language like the Romances do. I think that, since Old English was contemporary to at least some of the time period when Latin was spoken, he should point that out. I agree, though, that there must be some proto-Germanic and proto-Slavic tongues that gave rise to the various Germanic & Slavic languages we speak today. And more to the point, that there is likely some proto-everything language from which all of our tongues come.
Maybe it's proto-Babel.