Proto-Bantu is the reconstructed common ancestor of the 550 or so Bantu languages which are spread across Central and Southern Africa. It is thought to have originally been spoken in West/Central Africa in the area of what is now Cameroon. Approximately 3000–4000 years ago, it split off from other Niger–Congo languages when the Bantu expansion began to the south and east. Two theories have been put forward about the way the languages expanded: one is that the Bantu-speaking people moved first to the Congo region and then a branch split off and moved to East Africa; the other (more likely) is that the two groups split from the beginning, one moving to the Congo region, and the other to East Africa.
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Like other proto-languages, there is no record of Proto-Bantu. Its words and pronunciation have been reconstructed by linguists. From the common vocabulary which has been reconstructed on the basis of present-day Bantu languages, it appears that agriculture, fishing, and the use of boats were already known to the Bantu people before their expansion began, but iron-working was still unknown. This places the date of the start of the expansion somewhere between 3000 BC and 800 BC.
Doubts continue to be raised as to whether Proto-Bantu, as a unified language, actually existed in the time before the Bantu expansion, or whether, if we were to go back in time to that period we would find not a single language but a group of related dialects. One scholar, Roger Blench, writes: "The argument from comparative linguistics which links the highly diverse languages of zone A to a genuine reconstruction is non-existent. Most claimed proto-Bantu is either confined to particular subgroups, or is widely attested outside Bantu proper."
Phonology
Proto-Bantu is generally reconstructed to have a relatively small set of sounds of 11 consonants and 7 vowels.
Consonants
The above phonemes exhibited considerable allophony, and the exact realisation of many of them is unclear.
Consonants could not occur at the end of a syllable, only at its beginning. Thus, the syllable structure was generally V or CV, and there were only open syllables.
Consonant clusters did not occur except for the "pre-nasalised" consonants.
The so-called "pre-nasalised" consonants were sequences of a nasal and a following obstruent. They could occur anywhere a single consonant was permitted, including word-initially. Pre-nasalised voiceless consonants were rare, as most were voiced. The nasal's articulation adapted to the articulation of the following consonant so the nasal can be considered a single unspecified nasal phoneme (indicated as *N) which had four possible allophones. Conventionally, the labial pre-nasal is written *m while the others are written *n.
The earlier velar nasal phoneme /ŋ/, which was present in the Bantoid languages, had been lost in Proto-Bantu. It still occurred phonetically in pre-nasalised consonants but not as a phoneme.
Vowels
The representation of the vowels may differ in particular with respect to the two "middle" levels of closedness. Most linguists write the "less closed" set as *ɪ and *ʊ. However, some prefer to denote them as *e and *o, with the more open set represented as *ɛ and *ɔ. Regardless of its representation, the third level (*e and *o in the table) was open-mid [ɛ] and [ɔ].
Syllables always ended in a vowel but could also begin with one. Vowels could also occasionally appear in a sequence but did not form diphthongs; two adjacent vowels were separate syllables. If two of the same vowel occurred together, that created a long vowel, but that was rare.
Tones
Proto-Bantu distinguished two tones, low and high. Each syllable had either a low or a high tone. A high tone is conventionally indicated with an acute accent (´), and a low tone is either indicated with a grave accent (`) or not marked at all.
Noun classes
Proto-Bantu, like its descendants, had an elaborate system of noun classes. Noun stems were prefixed with a noun prefix to specify their meaning. Other words that related or referred to that noun, such as adjectives and verbs, also received a prefix that matched the class of the noun ("agreement" or "concord").
The following table gives a reconstruction of the system of nominal classes. Spellings have been normalised to use the ɪ and ʊ notations.
Vocabulary
During the last hundred years, beginning with Carl Meinhof and his students, great efforts have been made to examine the vocabulary of the approximately 550 present day Bantu languages and to try to reconstruct the proto-forms from which they presumably came. Among other recent works is that by Bastin, Coupez, and Mann, which assembled comparative examples of 92 different words from all the 16 language zones established by Guthrie.
Although some words are found only in certain of the Guthrie zones, others are found in every zone. These include for example *mbʊa [HL] 'dog', *-lia 'eat', *ma-béele 'breasts', *i-kúpa 'bone', *i-jína 'name', *-genda 'walk', *mʊ-kíla 'tail', *njɪla 'path', and so on. (The asterisks show that these are reconstructed forms, indicating how the words are presumed to have been pronounced before the Bantu expansion began.)
Other vocabulary items tend to be found in either one or the other of the two main Bantu dialect groups, the Western group (mainly covering Guthrie zones A, B, C, H, K, L, R) or the Eastern group (covering zones D, E, F, G, M, N, P, and S). Words reconstructed for these two groups are known as "Proto-Bantu A" ("PB-A") and "Proto-Bantu B" (PB-B") respectively, whereas those which extend over the whole Bantu area are known as "Proto-Bantu X" (or "PB-X").
Building on the work done by A. E. Meeussen in the 1960s, a publicly searchable database of all the Bantu vocabulary items which have been established or proposed so far is maintained by the Royal Museum for Central Africa at Tervuren in Belgium (see External links).