Another probable example is provided by two pygmy tribes—Yaka (Aka) and Baka—that live in the rainforests of Central Africa. Yaka and Baka are neighbors, although there is minimal interaction between the two peoples. The languages in question belong to very different linguistic groups: Yaka is Bantu C10, Baka is Ubangian. Despite this, Yaka and Baka are close not only physiologically, but also culturally and economically: both tribes are hunter-gatherers, as opposed to the neighboring non-pygmy farmer tribes. As described by S. Bahuchet (1992; 1993; 2012: 28-31), Yaka and Baka share more than 20% of their vocabulary, concerning especially food-gathering and other specific rain-forest activity (some shared terms are also related to society, music and religion). An important fact is that these words are apparently unetymologizable within Bantu or Ubangian languages. The rest of the lexicon of Yaka and Baka (including the majority of basic terms), however, differs according to its genetic affiliation (Bantu C10 and Ubangian). There are also some grammatical elements and features of neither Bantu nor Ubangian origin shared by Yaka and Baka, e.g., specific demonstrative pronouns (Duke 2001: 74-78). In such a situation, the most tempting solution is to treat these specific cultural terms as the remains of the pygmy protolanguage (the so-called proto-Baakaa) that were retained due to socio-economic factors after the Yaka and Baka tribes had shifted to the languages of the neighboring farmers (thus Bahuchet). An alternative solution, which seems less likely, is to assume that Yaka and Baka originally spoke Bantu and Ubangian languages, respectively, whereas the discussed common words represent parallel borrowings from a language of extinct rain-forest dwellers into Yaka and Baka. The third, more complex, solution is discussed by Blench (1999; 2006: 173-175).

Bahuchet, Serge
1992 Dans la forêt d’Afrique Centrale: les pygmées Aka et Baka. Paris: Peeters-Selaf.
1993 “History of the inhabitants of the central African rain forest: perspectives from comparative linguistics.” In C. Hladik, et al., eds., Tropical forests, people, and food: Biocultural interactions and applications to development. Paris: Unesco/Parthenon, pp. 37-54.
2012 “Changing language, remaining pygmy.” Human Biology, 84/1, 11-43.

Blench, Roger M.
1999 “Are the African pygmies an ethnographic fiction?” In K. Biesbrouck, S. Elders & G. Rossel, eds., Central African hunter-gatherers in a multi-disciplinary perspective: challenging elusiveness. Leiden: Centre for Non-Western Studies, pp. 41-60.
2006 Archaeology, Language and the African Past. Lanham, Maryland: AltaMira Press.

Duke, Daniel J.
2001 Aka as a contact language: sociolinguistic and grammatical evidence. University of Texas, Arlington, MA Thesis. Available at: wwwsil.org/Africa/Cameroun/bydomain/linguistics/theses/Complete%20Thesis-DDuke.pdf"