Hecetaeus of Miletos

[Gaius Sempronius Gracchus]

...and a Celto-Germanic group, an Italo-Germanic group, a Hispano-Celtic group etc. :p

I think Koch hints at something very important when he says that what we describe as Celtic may be a much deeper root within 'Indo-European'. What he is really saying, it seems to me, is that what we define as Celtic is a much older rooting within European languages; that explains why we can make all those connections. If there were anything like proto languages we should expect to find them as isolated; ie without areal interjection. The only time this is likely is within the ice age refuges. That leaves about 15,000 years of language development before our first written languages. The idea that one language group was born of another, and so on in a linear fashion is nothing short of ludicrous. Further, these language groups are indelibly linked (within the model they derive from) with groups/peoples. There is an inherent genealogical aspect built into the model itself. In these terms ethnicity becomes genealogical.

I have no problem with your conception of ethnicity, I see that you are intelligent and don't have any (particularly nationalist) axe to grind. Unfortunately that is not the only version of ethnicity, and the model upon which we hang our ideas of ethnicity is inescapably genealogical - and that is how the term is used, and how related terms (Celtic/Germanic etc.) come to be abused.

I think what you raise with regards to shared concepts etc. is interesting, but such questions need to be structured; what is it we are looking for? If we look for a wide demographic similarity that is probably what we will find. If we look for differences, likely we will find them. What we need to do, though, is avoid over-simplifying for the sake of narratives.

You say things are forgotten, I think some things are outright forgotten and some things become mythologised, and these often have implications for how people describe their own ethnicity. I'm rambling a bit at the moment so I'll return to this a little later. Thanks for the discussion though, as it helps to refine the argument.