Origin of Proto-Germanic

Greetings all,

I've been trying to gather all that I can about the origin of Proto-
Germanic, and am hoping someone may be able to shed some light on the
questions below.

I'm sure you are all very familiar with this but I'll go into detail
simply for the sake of thoroughness.
Mallory (pgs 18-21) reviews a few theories. August Schleicher (1861)
believed Proto-Gmc shared a common intermediate ancestor with the
Balto-Slavic tongues, that was seperate from the intermediate branch
of Italo-Celtic tongues.
A copy of his linguistic family tree can be found at the bottom of
www.utexas.edu/cola/centers/lrc/books/read08.html

According to what I can gather, Gamkrelidze and Ivanov (1985) seem to
have espoused a similar view where there was a shared intermediate
branch of Proto-Germano-Balto-Slavic.

Of course these two similar models have the problem of addressing the
issue that the Balto-Slavic tongues are Satem while Germanic is
Centum.


I have also seen mention of a theory that Proto-Gmc is a hybrid
tongue formed by an interaction between Centum and Satem languages.
I do not know what the current evidence is for this theory (any info
would be fantastic).
However, if we imagine the Balto-Slavic Satem languages interacting
with the neighboring Italo-Celtic Centum tongues, I suppose this
might explain such a hybridization.

Furthermore, the runes are believed to have derived from a North
Italic script, (similar to Venetic?) and so could be an example of
just such cross-breeding.


Of course my knowledge and understanding are horribly limited as I
consider myself an amateur mythologist (rather than a philologist).
I am hoping you more knowledgable folks might clue me in as to
whether any of these theories has been proven or disproven in the
last decade or two - and whether there is anything you can think of
that might help clarify these matters.

Sincerely,
Aydan