The diffusion of Nilo-Saharan languages
The original expansion of the Nilo-Saharan family may have been associated with the Aquatic industry. This industry, which dates to the 8th millennium bce, is a conglomeration of cultures that exploited the food resources of lakes, rivers, and surrounding areas from Lake Rudolf in East Africa to the bend of the Niger River in West Africa during a long era of wetter climate and higher lake levels than prevail today. The subsequent deterioration of the Saharan environment in the 6th millennium bce may be the reason for the relative geographic and linguistic isolation of several groups, especially in the western and central zones—e.g., the geographic locations where the Songhai, Saharan, Fur, Maban, Taman, or Daju languages were situated at the end of the 20th century.
In recent times several Nilo-Saharan languages in these areas, such as Fur, Kanuri, and Songhai, became associated with centralized political units whose states formed important chains in trans-Saharan trade routes. The Songhai language, now spoken by more than a million people living along the Niger River in West Africa from Mali to Nigeria, developed into the lingua franca of the Songhai empire, which reached its peak in the 15th century. The Songhai speech community probably absorbed speakers from various other linguistic communities through a process of primary language shift. Other modern Nilo-Saharan languages with more than a million speakers are the Saharan language Kanuri (mainly in Nigeria), Nile Nubian, and the Nilotic languages Dinka (South Sudan), Kalenjin (Kenya), Luo (mainly in Kenya and Tanzania), and Teso (Uganda and Kenya). Of these, only Kanuri is a lingua franca in the proper sense.
Such processes of linguistic expansion, while presumably common in human history, sometimes result in the extinction of other languages as the domains of language use begin to overlap to the extent that one of them becomes obsolete. Although the situation was somewhat less dramatic than in some other parts of the world, a number of Nilo-Saharan languages were endangered at the beginning of the 21st century because their speakers shifted toward other primary languages for daily communication. Such shifts can be observed for a number of Nilo-Saharan languages spoken by ethnic groups that generally number fewer than 1,000 speakers—e.g., the Kuliak language Nyang’i (Uganda), the Surmic language Kwegu (Ethiopia), and the Nilotic language Okiek (Kenya). Gule (or Anej), a Komuz language of Sudan, is now extinct, and the people speak Arabic.
The Maban languages, including Masalit, in Chad also are under pressure from Arabic, an important lingua franca and a prestigious language of education in the area. These gradual shifts in language domains sometimes are accelerated by other factors. The construction of the Aswan High Dam in Egypt in the 1960s, for example, forced many speakers of the Nile Nubian variety of Kenuz and Fadicca to abandon their ancestral land along the Nile, between Aswān and the Sudanese border, and to relocate to “New Nubia,” north of Aswān. An increase in daily contact with speakers of Arabic and the higher prestige of this official language of Egypt have resulted in a decrease in Nubian language use and competence. Massive resettlement schemes in the 1980s and ’90s for Sudanese refugees in such neighbouring countries as Ethiopia, Kenya, Uganda, and the Democratic Republic of the Congo have led to new multilingual settings. Moreover, modern urbanization may turn out to have a catalytic effect on the diffusion of particular languages at the expense of others. The majority of the more than 100 Nilo-Saharan languages nevertheless thrive as oral, and sometimes as written, means of communication.
The considerable typological diversity that characterizes the Nilo-Saharan languages corresponds to their wide geographic spread. Structural properties—for example, with respect to sound systems and word order—often are shared with unrelated neighbouring language groups. Thus, rich and complex consonant systems with universally rare distinctions—such as voiceless ejective versus voiced implosive consonants—are found, for example, in Koma, a Komuz language of western Ethiopia; comparable consonant distinctions occur in such Omotic (Afro-Asiatic) languages as Maale (southwestern Ethiopia). Several Central Sudanic languages, most of which are situated along the southern fringe of the Nilo-Saharan zone, share the presence of complex consonant systems with neighbouring Adamawa-Ubangi (Niger-Congo) languages. On the other hand, southern representatives of Nilotic have relatively simple consonant systems, as are common in neighbouring Bantu languages (which belong to the Niger-Congo language family). Such areal diffusion of properties usually results from extensive historical contacts and mutual borrowing not only of lexical items but also of structural features in situations of long-term bilingualism.
Most Nilo-Saharan languages are tonal; i.e., they use relative pitch on a syllable or word to mark lexical or grammatical distinctions. A number of them—western varieties of Songhai or northern varieties of Nubian—border on nontonal languages and are themselves only marginally tonal. On the other hand, languages in central Africa, such as the western dialect of Lugbara (a Central Sudanic language spoken in the border area of the Democratic Republic of the Congo and Uganda and bordering on highly tonal Niger-Congo languages), sometimes distinguish between as many as four tonal levels.
An additional areal feature, prominent especially in the Central Sudanic and in the Nilotic and Surmic groups of Eastern Sudanic and shared by neighbouring Niger-Congo languages, is that of vowel harmony. This feature restricts the co-occurrence in any given word of vowels that belong to more than one of two harmonic sets. Each of these harmonic sets includes five vowels, one set being produced with an advanced tongue root and the other with a retracted tongue root. In such Western Nilotic languages as Dinka, this contrast has developed further into a contrast between breathy voice and creaky (or hard) voice. Dinka has developed another universally rare feature, namely a three-way length distinction for vowels.