Point well taken. If the genetic evidence points to the Pygmies and Bushmen occupying the deepest clades in the homo sapiens family tree, and their common ancestors, who would therefore have been our ancestors as well, were making music in P/B style anywhere from 70,000 to 150,000 years ago, then why do we find this style today only among Pygmies and Bushmen, why don't we find it practiced among a great many people throughout the world? In other words, why did music evolve in such a way that there are so many different styles of music making in different parts of the world? And why did the original style survive only among African Pygmies and Bushmen?
As I see it, the answer may be much simpler than anyone might suspect. If the presence of this very distinctive style is so strongly correlated with the genetic evidence, as certainly appears to be the case, then it would make sense to assume that its survival among certain populations, but not others, could have essentially the same cause as the survival of the ancient genetic markers among the same populations, but not others. And, by the same token, whatever changes took place in the musical stylistic markers over the millennia, among so many different populations, could stem either directly or indirectly from the same causes responsible for the changes in the genetic markers among the same populations. This makes more sense than it might seem when we realize that in both cases we are dealing with neutral markers, i.e., distinctive features (of music or genetics) that appear unrelated to evolution in the Darwinian sense, i.e., natural selection based on adaptation to the environment.
The above statement might be too abstract or technical for anyone to easily accept or even fully grasp at this point, but I'll toss it out here anyhow, as it might come in handy for future reference.
Another clue comes from the realm of linguistics, a basic principle of which I was unaware, until reading the following, from the Supporting Online Materials published with the Tishkoff group's latest paper:
Our observation that the Pygmies appear to share common ancestry with several Khoesan-speaking populations raises the possibility that the indigenous Pygmy language may have contained click consonants. A recent examination of the skeletal evidence for the development of the human vocal tract indicates that full human language capacity evolved before 50 kya but after 100 kya (S119). Considering that the normative directions of phonological evolution are from greater to lesser markedness, and that clicks are among the most marked of all sounds, the fact that click consonants exist at all in present day languages favors their existence back to the earliest human languages of 100-50 kya (p. 20).What interests me here is the notion that the characteristic clicks of Khoesan, of which there are several distinct types, may well have been present in the earliest languages and subsequently lost -- because "the normative directions of phonological evolution are from greater to lesser markedness, and . . . clicks are among the most marked of all sounds." I was not aware of that phonological principle, but it interests me, because I see an analogy between Khoesan markedness and P/B musical style, which can also be understood as heavily "marked," in the sense that it would appear to contain far more distinctive features than any other type of music to be found in any other indigenous or "folk" repertoire. Could there be an "evolutionary" tendency, based on the same principle, for both languages and musical styles to lose "markedness," i.e., complexity and/or nuance, over time? This would correspond to what appears to have happened to P/B over time -- contradicting earlier notions of musical evolution based on the opposite view, that music begins with the simplest utterances and gradually evolves in the direction of increasing complexity.
Again, I think maybe I'm being too technical in the above, and also getting ahead of myself, so please allow me to start over once again:
The place to start is, obviously, Africa. And what I'd like to do next, rather than speculate further about basic principles, is to, more concretely, consider the distribution of P/B style, or musical styles similar to P/B in certain respects, on that continent. And yes, there are many groups in Africa that sing and/or play instruments in a manner resembling P/B -- though rarely in all respects. Here again we might want to pay close attention to "loss of markedness" since I think it might help us understand what can happen to a musical tradition over time.
(to be continued . . . )