Since linguists are in agreement that tonogenesis represents some sort of universal process through which all tonal languages are generated from non-tonal ones, the abundance of tone languages in Africa, plus the lack of evidence for tonogenesis anywhere on that continent, should represent something of an embarrassment -- but apparently not. From what I've read in the surprisingly extensive literature on tonogenesis (not to mention many other topics in linguistics), linguists seem much too preoccupied with the discovery of universally valid principles and far too little concerned with the messy contingencies of history, as reflected in the worldwide distribution of the traits they study (the WALS project being a notable, and very welcome, exception).
Given the preponderance of tone language in Africa, it seems likely that the original Out-of-Africa migrants must have also spoken a tone language. And since this is generally understood as the founding group, both genetically and culturally, for all peoples outside of Africa, it seems likely that non-tonal languages could only have arisen via a process that must be regarded as the reverse of tonogenesis, i.e.: tonoexodus.
When I "coined" this term in a tongue-in-cheek comment on the previous post, I wasn't aware that it was already in circulation. And, yes, some linguists have considered the possibility of what they too have named (with a straight face, apparently) "tonoexodus":
Tone systems are not static. A language can acquire tones and then increase the complexity of this tone system but it can also decrease the number of its tones and ultimately become non-tonal. These two processes, acquisition and recession of tones, have been termed tonogenesis [Matisoff 1970, 1973) and tonoexodus [Lea 1973). Cases of tonoexodus are rare and it is not clear what the intermediate historical stages between the tonal and non-tonal stages are. (CONSONANT TYPES, VOWEL HEIGHT AND TONE IN YORUBA, by Jean-Marie Rombert, 1977, p. 174.)I suspect that "cases of tonoexodus are rare" only because 1. linguists aren't looking for them; and 2. they tend to focus on very specific processes within specific languages, rather than taking the big picture into account. I've seen countless studies of "tonogenesis" as it appears to have developed in a single language, but have noticed not one study of the topic as applied to the worldwide distribution of tone.
But the (apparently revolutionary) notion that tone language came first, is only part of the story. Because if the first language was a tone language, then it seems only logical to go a step farther to consider whether it might have consisted exclusively of tones. Or, to be more accurate, specific tones presented in specific rhythms, which also happens to be a way of defining music. In a comment on the previous post, Marnie reminds us that a great deal of content in a great many African languages can be conveyed by the "talking drum," limited exclusively to differences of tone and rhythm. She asks the very sensible question, "is it possible that pitch and rhythm developed together in our earliest languages?"
In response to my previous post, I received an email from a very perceptive reader, Alex Petrov, who provided a link to this extremely interesting Wikipedia article on Whistled Language. I had always assumed that so-called whistled "languages" were merely elaborate signalling systems, but there is clearly more to it than that:
A whistled language is a system of whistled communication which allows fluent whistlers to transmit and comprehend a potentially unlimited number of messages over long distances. Whistled languages are different in this respect from the restricted codes sometimes used by herders or animal trainers to transmit simple messages or instructions. Generally, whistled languages emulate the tones or vowel formants of a natural spoken language, as well as aspects of its intonation and prosody, so that trained listeners who speak that language can understand the encoded message.Especially interesting is the observation that "In continental Africa, speech may be conveyed by a whistle or other musical instrument, most famously the "talking drums . . . As two people approach each other, one may even switch from whistled to spoken speech in mid-sentence." If so much in so many African tone languages can be communicated by tone and rhythm alone, then it is only logical to wonder whether any of the other features of such languages are necessary -- and whether their existence could be undersood as the initial stages of a progression from a language of pure tones to a tonal language, and from there to a non-tonal language -- i.e.: tonoexodus.
Whistled language is rare compared to spoken language, but it is found in cultures around the world. It is especially common in tone languages where the whistled tones transmit the tones of the syllables (tone melodies of the words). This might be because in tone languages the tone melody carries more of the "functional load" of communication while non-tonal phonology carries proportionally less. The genesis of a whistled language has never been recorded in either case and has not yet received much productive study.