from each other in a significant way. Some Ukrainian features were recognizable in the southern dialects of Old East Slavic as far back as the language can be documented. Ukrainian linguist Stepan Smal-Stotsky denies the existence of a common Old East Slavic language at any time in the past. Similar points of view were shared by Yevhen Tymchenko, Vsevolod Hantsov, Olena Kurylo, Ivan Ohienko and others. According to this theory, the dialects of East Slavic tribes evolved gradually from the common Proto-Slavic language without any intermediate stages during the 6th through 9th centuries. The Ukrainian language was formed by convergence of tribal dialects, mostly due to an intensive migration of the population within the territory of today's Ukraine in later historical periods. This point of view was also supported by George Shevelov's phonological studies. Origins and developments during medieval times As a result of close Slavic contacts with the remnants of the Scythian and Sarmatian population north of the Black Sea, lasting into the early Middle Ages, the appearance of the voiced fricative γ/г (romanized "h"), in modern Ukrainian and some southern Russian dialects is explained by the assumption that it initially emerged in Scythian and related eastern Iranian dialects, from earlier common Proto-Indo-European *g and *gʰ. During the 13th century, when German settlers were invited to Ukraine by the princes of the Kingdom of Ruthenia, German words began to appear in the language spoken in Ukraine. Their influence would continue under Poland not only through German colonists but also through the Yiddish-speaking Jews. Often such words involve trade or handicrafts. Examples of words of German or Yiddish origin spoken in Ukraine include dakh (roof), rura (pipe), rynok (market), kushnir (furrier), and majster (master or craftsman). Developments under Poland and Lithuania In the 13th century, eastern parts of Rus (including Moscow) came under Tatar rule until their unification under the Tsardom of Muscovy, whereas the south-western areas (including Kyiv) were incorporated into the Grand Duchy of Lithuania. For the following four centuries, the languages of the two regions evolved in relative isolation from each other. Direct written evidence of the existence of the Ukrainian language dates to the late 16th century. By the 16th century, a peculiar official language formed: a mixture of the liturgical standardised language of Old Church Slavonic, Ruthenian and Polish. The influence of the latter gradually increased relative to the former two, as the nobility and