Saturday, July 11, 2009

165. The Pygmy/Bushmen Nexus -- Part 5

(. . . continued from previous post.)
Destro-Bisol's research was based on Mitochondrial DNA (mtDNA), inherited strictly along the female line. A more recent study, published this year, by Etienne Patin et al, was based on a wider range of markers, found in the cell nucleus and X chromosome, representing descent from both parents combined. Though the focus of the study was a comparison of African Pygmies and farmers, the data representing the various Pygmy groups tends to bear out Destro-Bisol's mtDNA findings.

Before considering any more genetic evidence, however, let's take a closer look at the various Pygmy populations. While the African Pygmies can be divided into two large groups, Eastern and Western, there are subdivisions of each, especially among the Western group, each subdivision constituting a separate population, with its own history, traditions, language, etc. Among the best known, in the Central African Republic can be found the Aka (also known as Biaka), BaBinga and Ba-Benzélé; in Cameroon, Gabon and the Republic of Congo, the Baka (sometimes confused with the Aka), Bedzan and BaKola; in the Ituri Forest, far to the east, we have the Mbuti, Efé, Asua and BaKongo; also to the East, in Ruanda and Uganda, the Ba-Twa. It must be noted that there is a certain amount of confusion regarding the naming and classification of the various Pygmy groups, so that we can find different names and even different groupings when consulting various sources.

We are now in a better position to interpret the Patin group's results, as encapsulated in Figure 2 from their paper. (If you right-click and select "Open link in new window," you'll get a more readable version of this image.)
As you can see, seven Pygmy groups are represented in the uppermost diagram, BaKola, G. Baka (Baka from Gabon), C. Baka (Baka from Cameroon), Biaka (or Aka), Mbuti, Northern Twa and Southern Twa. Each of the four graphs in the upper diagram represent different degrees of detail in the evaluation of the genetic markers. The most detail can be found in the lowermost graph, labeled K = 5, which is therefore the most useful for our purposes.

The very strong genetic difference between Western and Eastern Pygmies, as noted by Destro-Bisol, is clearly seen here in the contrast of color between the first four groups, colored mostly in green, and the Mbuti, colored mostly red. The next two, both representing the Twa, present a more complex picture, with streaks of both red and orange. The remaining groups, colored mostly in orange, are non-Pygmies, mostly Bantu speaking farmers.

(The lowermost diagram, labeled B, presents a simplified model in which most individuals of mixed ancestry were excluded -- as you can see, the Twa groups, now almost compeletely red, fit more clearly with the Mbuti.)

The Patin group's conclusions are succinctly summarized in the "Author's Summary" on page 2:
By means of simulation-based inferences, we show that the ancestors of Pygmy hunter–gatherers and farming populations started to diverge 60,000 years ago. This indicates that the transition to agriculture—occurring in Africa 5,000 years ago—was not responsible for the separation of the ancestors of modern-day Pygmies and farmers. We also show that Western and Eastern Pygmy groups separated roughly 20,000 years ago from a common ancestral population. This finding suggests that the shared physical and cultural features of Pygmies were inherited from a common ancestor, rather than reflecting convergent adaptation to the rainforest.. ("Inferring the Demographic History of African Farmers and Pygmy Hunter–Gatherers Using a Multilocus Resequencing Data Set," by Etienne Patin et al., in PLoS Genetics, April 2009, Volume 5, Issue 4, p. 2).
This is a result closely consistent with the findings of the Destro-Bisol group, who estimated the divergence of Western from Eastern Pygmies at roughly 18,000 years ago. Note also, that both Pygmy groups appear to share a common ancestor, estimated to have diverged from the ancestor of the farming populations at a much earlier date, roughly 60,000 years ago.

As far as the music is concerned, the Biaka (Aka), BaBinga, BaBenzélé, Baka, and Mbuti, representing both the Western and Eastern Pygmies, all share essentially the same style, characterized most distinctively by the use of elaborately interlocking vocal parts and yodel, though detailed study would be needed to determine whether or not there are significant differences among them with respect to certain other aspects of either musical structure or cultural context. The Bedzan would appear to share a very similar style, though for some reason, unlike any of the others, they apparently do not yodel. Since all these groups seem to have had a common ancestor roughly 18,000 to 20,000 years ago, it's not difficult to conclude that their shared musical style must, in all likelihood, be at least that old. (We're not done, of course, since we still have the Bushmen to consider.)

The only Pygmy group known to me that vocalizes in a clearly different manner are the BaTwa, who sing in the call and response style so common for most Bantu groups and indeed, as is evident from the above diagram, appear to have heavily intermixed with neighboring Bantu peoples over many years. As Patin et al. have written,
With respect to the two populations of Twa Pygmies, they clearly
clustered with South-East African farmers for K=4, consistent with these Pygmy groups being admixed (some anthropologists describe them as ‘‘Pygmoids’’), and with the complete shifting of their cultural practices towards those of neighboring agricultural populations . . . (ibid., p. 3).
I am not familiar with the music of the other Pygmy groups. But since the BaKola too appear to be heavily intermixed genetically with neighboring Bantu peoples, it's possible that they too may no longer sing in the more distinctive and complex Pygmy manner.

(to be continued . . . )

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