Based on my limited study of post ice age civilization, a fresh water Black Sea fed by rapidly melting glaciers would be as perfect a breeding ground for early human pre-civilization as any place on earth. Plenty of fresh fish and game, the sea is large enough to prevent any one tribe from completely conquering all while the long circular shoreline allows plenty of interaction between bordering groups. The surrounding mountains allows attacked groups to retreat to safety only to merge back with the amalgamated shore group a generation later. Over 6,000 years, the many individual groups would benefit from any advances in technology any one group invented and all the groups would adapt a similar language. A sudden saltwater flood at 5600BC would not only not only permanently cover their villages but would kill the local food supply forcing the population to disperse in different directions.
"A sudden saltwater flood at 5600BC would not only not only permanently cover their villages but would kill the local food supply forcing the population to disperse in different directions." I've read extensively about this flood. Ryan & Pittman, in the book: Noah's Flood, explain that the whole region around the Black Sea (at that time) was very arid. The people crowded around the lake were fishers and farmers and even (probably) practiced irrigation farming. When the 'dam' broke, these people fled up the rivers (Danube, Don, Dnipier, etc) into europe taking their language (Indo-European) and farming with them. These are probably the 'invading' farmers from the 'Middle-East' that all these articles reference.
Now, having said all that, lol. I think a large number of these people (those crowded around the Black Sea) have their origins way east in the Gansu Province of China. (north of the Indus Valley). We would probably describe their appearance as Celtic. See my earlier thread titled: The Curse Of The Red-Headed Mummies.