"According to the Gamkrelidze and Ivanov model, this protolanguage initially contains two major dialect groupings, which they call A and B. Group A consists of Anatolian, Tocharian, and Italic-Celtic, group B, of Indo-Aryan, Greek, Armenian, Balto-Slavic, and Germanic. Anatolian, which is held to have uniquely preserved some very archaic language features as I have discussed, is the first to break away from the home-land, leaving the rest of group A and group B together for a period during which they develop some common isoglosses not visible in Anatolian. Many scholars hold that Tocharian was the next to break off. After the initial departure of Anatolian, and Tocharian group A my parts company with group B and eventually subdivides into the Celtic and Italic language groups that enter into protohistory. After being separated from group A, several isoglosses in group B require that Indo-Iranian, Greek, Germanic, and Balto-Slavic all coexisted in some degree of proximity. Subsequently this group also subdivides into Balto-Slavic-Germanic and Indo-Iranian-Greek-Armenian, but in such a way that Indo-Iranian maintains a central position for a period. This centrality allows it to share isoglosses with Slavic, on the one hand, and Germanic, on the other, even while remaining more closely affiliated with Greek and Armenian. Balto-Slavic-Germanic also goes its separate way in time, and the remainder of group B, having developed some common features among its members, also eventually breaks down into the individual Indo-lranian, Greek, and Armenian groups that ultimately manifest in the historical record. These morphological isoglosses separating the various groups are further reinforced by phonemic and lexical isoglosses, which are "unambiguous evidence for the historical reality of the dialect areas of Indo-European" (Gamkrelidze and Ivanov 1995, 364)."