Having such understanding about the languages formation of the European inhabitans someone could  rise the question - where did lived the Baltic and Slavic predecessors and what kind of language they used. The level of their technologies proofs that they really could comunicate using some speach. The relicts of the first fishing nets found in the layers of 20 thousand and more years old and some bone art carvings  belonging to glacial time confirms this idea. So, scientific models presented in the literature have "stealed" at least 22 thousand years of Baltic and Slavic history - the fog period, i.e. the period from the first IX group inhabitants reached the Europe till agriculture spreading.  including  German, Celtic, Italico-Greece ethnic predeccesors too. 

The map presents Europe at the moment of maximal glaciation.

According to the nature situation presented in this map it is reasonable to suppose, that at the iceland bottom near the Karpat forest there lived preBaltic people, and by the Danube river pre-Slavic and preGreek people, becouse the Finno-Ugric people homeland is supposed to be Asia or Ural mountain area. Probably, the reason of preBaltic and preSlavic separation from the preGermanic and preCeltic people was the narrowness of the usefull tundra stepe land among the Scandinavian and Alpic.  So, the comunication and changes among the people was mainly the vertical, not horizontal and this caused the lots of simmilarities among the the Baltic and Slavic language groups.

The Slavic language uses the name for the hard oak tree DUB (like doob in russ.) - different from Lithuanian, but the Baltic has the name for the bear - LOKIS (in lith.) different from the slavic. These facts alow to predict, that differences among both language group existed at the mesolithic time of hunters and fishmen, but Lithuanian name of the oak - Аюuolas(like azhuolas) it is possible to derive from the oakcorn Russian name -zhelud, and Lithuanian word for the bear - LOKIS possibly was derived using the Lithuanian name of the bow - LANKAS which is simmilar to the russian bow - LUK.  This fits to the hypothesis about Baltic homeland existance more to the north and Slavic - more to the southern oak spreading zone confirming close relations among preBaltic and preSlavic speaking people. The word TINKLAS for the fishing net was used in Lithuanian language and this is related to the russian TENNETO - the net for the birds, but the fish in Lithuanian is ЮUVIS (like zhuvis) and in Russian - RYBA. So, at the moment of mesolithic spreading of preBaltic people to the coast of the Baltic sea, those two language were separated enough, stressing ethnic differencies. The Druid order to which I belong, Ord Na Darach Gile — the Order of the White Oak — honors this tree above all others, so lithuanian the oakcorn - gile is very close to Celtic one. 

 The reality of such a model could be confirmed using the analysis of the pine tree name, too. The Karpatian pine in the Lithuanian is called PUРIS (like pushis), that is closely conected to the old German and the Greek names for the pine tree but not so close to the Slavic one. The Lithuanian word - the name of the oak derived from the Slavic one, consists the idea of oak forest artificial planting and growing learned at the southern neighbours, when the idea of the Slavic one possibly gives characteristics to the hardness of the oak. This leads to the idea about Slavic homeland full of natural growing oak trees before or  the time of maximal glaciation of the Europe. The Armenian language supports the idea about possible simmilarity of the oak and oak corn names too. The distinct Baltic southern tribe language - Prussian gives some more facts about neighbouring Baltic and Slavic people from the premesolithic forestification time. Their language when living in the Poland and Kaliningrad area used the names of gut and hair close to the Slavic oak and pine, so prePrussian homeland was very close to the Slavic one at the moment of maximal glaciation.