Introduction

The Rift Valley area of central and northern Tanzania is of considerable interest for the study of language contact, since it is unique in being the only area in Africa where members of all four language families are, and have been, in contact for a long time, having had linguistic interaction of various intensity at various points in time, which is reflected by convergence in parts of their grammatical structures (see map 6.1). The modern languages that took part in this linguistic contact are the West Rift languages of Southern Cushitic (Iraqw, Gorwaa, Alagwa, and Burunge), the Datooga dialects of Southern Nilotic, some Bantu languages of the F zone (Nyaturu, Rangi, Mbugwe, and maybe Nilyamba, Isanzu, and Kimbu), and Sandawe and Hadza, the Khoisan languages of eastern Africa. Actually, in the absence of any unambiguous indication that Hadza is genetically linked to Khoisan, it is better to be considered a linguistic isolate; see Sands (1998). The fact that the languages involved come from different, genetically unrelated families makes this area very promising for the study of language contact in that similarities between languages have five possible explanations: (i) universal properties, (ii) chance, (iii) borrowing or diffusion, (iv) retention, or (v) parallel development (Aikhenvald & Dixon 2001).