What is quite surprising . . . is that there are no documented cases of tonogenesis in Africa, despite the wide variety of languages . . . and the widespread presence of tone on the continent. (George Tucker Childs, An Introduction to African Languages, 2003, p. 86.)Since almost every single language in sub-Saharan Africa is tonal, "widespread presence" is something of an understatement. To illustrate, let's take a look at the world map of tone languages produced by WALS, the World Atlas of Language Structures:
The red and pink dots represent tone languages, the white dots non-tone languages. As is clearly evident, Sub-Saharan Africa is simply saturated with tone languages, with only two or three exceptions represented in the enormous WALS sample. It's interesting to note that a similar degree of tonal saturation is depicted for Southeast Asia and Melanesia. I've discussed the possible meaning of this very odd distribution in an earlier post, but it need not concern us here.
What does concern us at this point is the overwhelming genetic and archaeological evidence that's developed over the last 20 or 30 years pointing to Sub-Saharan Africa as the locus for the development of "modern" humans (homo sapiens sapiens), who are thought to have migrated from there to the rest of the world roughly 60,000 to 80,000 years ago. Since most historical linguists now agree that all human languages must have had a common ancestor, then, if the Out of Africa model is correct, that ancestor could only have originated in Africa. And since just about every language in Africa (including Khoisan, considered by many to be the oldest surviving language) is a tone language, then there is clearly something very wrong with the widespread assumption that the earliest languages must have been non-tonal, and linguistic tone could only have been produced via "tonogenesis."
Which returns us to the experiments by Diana Deutsch (see previous posts), and the surprisingly strong correlations she found between tone language and absolute pitch. Unlike some of the other common features of language and music, such as interactivity, cooperation, phrasing, etc., the use of discrete pitches is the only one generally regarded as uniquely musical. And the puzzle we've been considering, of how such tones could have developed, and, more important in the context of the present discussion, what sort of adaptational advantage they might have posed, can now be seen in an entirely new light.
Based on the evidence presented above, the following sequence may now be considered:
1. Interactive "hooted" vocalizations of early primates and pre-humans, along the lines of the "duetting" and "chorusing" of certain contemporary ape and gibbon populations. The adaptational advantage of such behavior would most likely be the facilitation of both long distance communication and cooperation.
2. The development from the above, among early humans, of precisely pitched vocalizations. Among the various means by which this may have come about, one stands out as particularly suggestive as far as adaptation is concerned. Since many birds sing using discrete pitches, there would have been an advantage for humans in learning how to imitate bird songs as a lure. This could have been accomplished through the morphing of pre-human "hooting" into precisely pitched yodeling. Since yodeling involves a process akin to the "overblowing" of wind instruments (such as pipes, flutes, etc.) to produce discrete overtones, it might have been the simplest means by which humans would have become aware of certain basic pitch relationships. Another possibility might have been the discovery that simple reed pipes or hollow bones could be blown into in such a way as to produce discrete pitches that in many cases could be used as bird-call imitations. Since each reed or bone could only play a single note, it would require close cooperation on the part of a group to imitate multi-pitched bird songs. Reed ensembles of this type are still widely found in Africa and elsewhere among indigenous peoples, and such performances are in many cases associated with birds and their calls. Vocal ensembles organized along similar lines may have developed either independently or in imitation of the wind ensembles.
3. Since bird songs are precisely pitched, hunters with absolute pitch would have been more effective than those without it, giving a selective advantage to those with absolute pitch.
4. On the basis of the above, admittedly speculative, sequence, it's not difficult to see how both vocalizing and playing with discrete pitches could have led to the development of a language of sorts, based exclusively on tonal relations. For one thing, each such musical sequence would have symbolized a specific species of bird. For another, it's possible to see how, for those with perfect pitch, each pitch could have been perceived as an easily identified semiotic "module," very close, in fact, to a linguistic phoneme, which it could have anticipated.
5. If the earliest "language" consisted essentially of discrete pitches, then we can see how, for early humans, the development of musical awareness would have had a powerful adaptational advantage (now lost, of course). This would also explain the widespread presence of tone languages in the continent where early humans developed, since the use of tonal phonemes would have persisted even after non-tonal elements were added.
The above is highly speculative of course. A great deal depends on whether or not Deutsch's results, based on research among East Asians, can be replicated with African subjects.