Thursday, October 22, 2009

228. The Baseline Scenarios -- part 4

I've defined the Hypothetical Baseline Population (HBP) as "that population from which the ancestors of either the Pygmies or the Bushmen, or both, diverged, at some point during the Paleolithic era." I will now proceed to clarify this definition, being as specific as I can.

Let's begin by reviewing some of the phylogenetic trees we've already seen, gleaned from recently published papers by some of our leading population geneticists. First, a tree based on mitochondrial DNA (mtDNA), representing the female lineages of selected African groups, as produced by Sarah Tishkoff et al, in their 2007 paper, History of Click-Speaking Populations of Africa Inferred from mtDNA and Y Chromosome Genetic Variation:

(For this and all other diagrams, I suggest right-clicking and selecting "Open link in new window," to get a larger, clearer view.)


The oldest, deepest clades (i.e., branches) are on the left, with the more derivative, thus later, clades toward the right, as suggested by the treelike structure of the diagram itself. Each letter-number combination at the tip of each branch (e.g., L0d, L0k, L0f, etc.) stands for what is called a "haplogroup," a term representing related sets of "haplotypes," i.e., genetic markers that have proven to be especially diagnostic for this type of research. The numbers stand for the percentages of each haplogroup found in the sample for each of the population groups listed (by language name) in the leftmost column.

Under L0d, the leftmost (thus deepest) clade, we see that the highest percentages by far are found among the !Xun/Khwe, !Xun and !Kung, three Bushmen groups. It is probably significant that the most isolated and thus least acculturated group, the !Kung, has the highest percentage of L0d: 96%. Moving to the right, we see that the next haplogroup with high percentages is L1c, under which we find Mbenzele (97%), Biaka (or Aka) (77%) and BaKola (100%), three Pygmy groups, all representing the Western Pygmy population. Moving farther to the right, we see another high percentage (55%) under haplogroup L2, representing the Mbuti, or Eastern Pygmies. We see that significant percentages for the Mbuti are also found to the left, under two deeper clades: L0a (30%) and L5 (15%).

Note further that no other high percentages are to be found until we reach L4g, where we find the Hadza and Sandawe, two other hunter-gatherer groups. Note that all the other African groups included in this survey are split among several different haplogroups, suggesting that their populations are the result of genetic admixture, reflecting thousands of years of interconnection with other groups. The two rightmost symbols, labeled simply M and N, represent the deepest clades of, believe it or not, literally all the remaining branches of the mitochondrial tree found thus far in the rest of the world. No non-African population is represented by any of the clades labeled "L," the very deepest clades worldwide, though the M and N clades are clearly branchings from L, as indicated in the diagram.

Moving from the female to the male line, as represented by the Y chromosome (found only in men), we see a phylogenetic tree produced by a group calling itself "The Y Chromosome Consortium," as published in a 2002 paper, A Nomenclature System for the Tree of Human Y-Chromosomal Binary Haplogroups:

While group names are not included in this diagram, the accompanying text informs us that the deepest clades (at the top) are occupied almost exclusively by either Bushmen or Pygmies, with Bushmen classified under either A or B and almost all Pygmies (Aka and Mbuti) under B. With the exception of one Zulu individual, none of the other groups included in the study belongs to either of the two deepest clades, A or B.

Finally, let's have a look at a phylogenetic tree based on nuclear markers, combining both male and female components, also produced by Sarah Tishkoff, with a somewhat different team, as part of a comprehensive study recently published in Science: The Genetic Structure and History of Africans and African Americans (2009):

(For simplicity sake, I've reproduced only the bottommost segment of a larger diagram.) This tree, based on a study of "1327 nuclear microsatellite and insertion/deletion markers," is especially easy to interpret as it's organized according to populations rather than haplogroups, with the population names printed on the right. Once again we find Bushmen (!XunXhoe and "San" -- actually !Kung) occupying the very deepest clades, with Pygmies following closely on their heels -- though this time the Eastern Pygmies (Mbuti) rather than the Western Pygmies (Bedzan, Bakola, Biaka and Baka) occupy the next deepest clade.

Reviewing all three diagrams, it's not difficult to see why I've attached so much importance to Bushmen and Pygmies in defining HBP. As should also be clear from the same diagrams, the ancestors of the Bushmen and Pygmies can also be regarded as the ancestors of every human now alive, which means that HBP represents the ancestry of not only Pygmies and Bushmen, but every single one of us as well. However, it's very important to understand what I mean in this case by "ancestry," because we have ancestors going back very far, not only to the earliest "modern" humans (Homo sapiens sapiens) but to the earliest archaic humans as well, the ancestors of Homo Erectus, Homo Neanderthalus and a host of other human and proto human groups, and beyond, to the ancestors (or more accurately ancestor) of every living thing that ever dwelt on Earth.

I have therefore defined HBP very specifically, as that population "from which the ancestors of either the Pygmies or the Bushmen, or both, diverged." We can see that founding, ancestral, population represented, however vaguely, in all three of the above phylogenetic trees, by looking in each case for the most fundamental clade, or "root," from which all the others stem. But in all cases this "root" is ambiguous, because it could represent the very earliest "modern" humans, or even some prior human group, closer to Homo Erectus; neither of which can really teach us very much, because, aside from some archaeological relics, we have no way, at present, of inferring very much at all about either them or their culture.

More useful in this respect is the following table, from Chen et al., mtDNA Variation in the South African Kung and Khwe—and Their Genetic Relationships to Other African Populations, 2000. (Again I'll remind you to expand this image by right clicking and selecting "Open link in new window".)

Though this study is somewhat outdated, the information in this table, based on estimates that still seem reasonable, is nevertheless useful. However, what I want to focus on is the basic idea, not particularly evident in the phylogenetic trees, that the various nodes on all the trees indicate points of divergence, i.e., "moments" in history (representing time spans from just a day or so to periods of many years) when the ancestors of one group separated from the group to which they had previously belonged, with which they had previously shared a common culture.

Thus, according to both the genetic evidence and common sense, there must have been a time when the first Pygmy group or the first Bushmen group separated off from a group that can now be considered, in retrospect, as the common ancestor of both. According to the genetics-based estimates offered by Chen et al, the earliest time of divergence may have, very roughly, been between 77,600 and 102,000 years ago, when, according to their best estimates, the Biaka (Aka) Pygmies diverged from the common ancestor. According to the same methods (admittedly very hypothetical), the !Kung Bushmen (aka the Ju'/hoansi) diverged from the same ancestral group 41,000 to 54,100 years ago, with the Mbuti and Senegalese diverging at a considerably later date, roughly 18 to 23 thousand years ago.

Since genetic evidence gleaned from so many different sources is not yet fully consistent in this respect, I hesitate to base HBP exclusively on such evidence, though the results are consistent enough to tell us a great deal. Nevertheless, the Chen table is useful as a point of departure because it encourages us to think not so much in terms of a common ancestor, but a very particular common ancestor, i.e., the very specific ancestral group from which the first of the Pygmy or Bushmen groups diverged, at some point during the Paleolithic, possibly 77,600 to 102,000 years ago, as estimated by Chen, possibly at some other date either earlier or later. The divergence would certainly show up in the genetic evidence -- though the methodologies are not yet at the point that they are producing fully consistent results. This doesn't really matter so much, however, because we also have considerable cultural evidence pointing in exactly the same direction, back in time to a moment of divergence from a common ancestral group. It is the cultural traditions practiced by the common ancestors at the moment of divergence that concern me here. This very specific ancestral group, as they were living at this particular time in history, at some particular place in Africa, is what I am referring to as the Hypothetical Baseline Population. And the culture of this group, at this particular time and place, is what I am referring to as the Hypothetical Baseline Culture.

(to be continued . . . )

8 comments:

onix said...

uhm,i saw your comment on anthropology, you are becoming quite a specialist in !kung genetics.. it's somewhat etereal tho, i am much more interested in the interpretation of music. i used to compare old myths, typically they contain elements that have not been analysed(it would be an awfull pile of work) statistically, that could have paleographic value, wich may or may not correlate with musical baselines.

there is also linguistic research, that has not yet been interpreted as paleoarcheological schisma's because it more obviously focusses on historic and protohistoric developments. for example of the !kung i understand there is one group linguistically more related then any others, even it is far.

through statistical analyses, of grammar oral facets and words i wonder what could be interpreted.

the bottomline is many oral traditions deal with even events that possibly precede hominids, or speech, and i am quite confident a lot of archeological trace (i assume concerning distribution, but also into correlations between people/cultures) exists there.

Maju said...

With the exception of one Zulu individual, none of the other groups included in the study belongs to either of the two deepest clades, A or B.

However, nowadays we know that A3b2 makes up almost 50% of the Y-DNA of southern Sudan and more than a quarter of that of Ethiopia. However most other A is Khoisan almost exclusively.

B2 also makes up some 22% of southern Sudanese ancestry (most of which is B2a). B2b (the Pygmy-specific lineage) is similarly common among Tanzanian click-speakers. Some other A and B are found at smaller amounts through all Africa. B2a is also found among Mozambiquenhos at quite signficant levels (15%). All these lineages (A3b2, B2a, B2b) also make a sizable fraction of East African Y-DNA, addding up to 14%.

Maju said...

And also in Darfur, Chadic speakers and the West Sahel area (Mali, Niger), A+B appear significatively (20% in Darfur, 14% in Cameroun Chadics and 10% for West Sahelian peoples).

I'd say that Sudan/Ethiopia look like another node for some of these lineages (specially A3b2 and B2a), which may have spread maybe associated to "Nilotic" peoples (in the broad sense of originating at the Nile area, not the strictly linguistic one) in both westward and southward directions.

"the Dude" said...

Victor, you may be interested in John Hawks post on the 'tospeak' gene in primates and the unique gene controller found only in humans.

DocG said...

Hi onix -- no I am not a specialist in any aspect of genetics and still don't understand many things. But thanks to the way the geneticists present their results, particularly in their phylogenetic trees, it's possible for laymen like myself to get at least a rough sense of what they're up to.

As far as myths are concerned, and also the linguistic data, you are right. Many problems would be a lot easier to investigate if more databases, such as the Cantometrics database, were available. Unfortunately compiling a meaningful database of the world's myths and also the world's languages would be a formidable task. Musical style is much easier to handle in this respect, I would think.

I have a feeling, however, that some such databases do exist and I know of one article where someone is investigating comparative mythology very systematically, presumably using a database. I forget his name though.

Once we have a better handle on HBC, which is what I'll be working on soon, we'll be in a position to use that information as a kind of observatory to investigate myths and many other cultural manifestations worldwide. What has been lacking in all previous studies of that sort, in addition to worldwide databases, is a baseline -- which I am hoping to provide, at least provisionally.

DocG said...

Maju, it's not surprising that groups other than EP, WP and Bu are represented on some of the deepest clades, since the evidence points to many of these people as closely related descendants of HBP. It's possible too that some of them may in fact be genetically just as close to the root as EP, WP and Bu. And if that's the case, it would be very useful to learn more about the culture of these groups, to see whether at least some of their traditions might also derive from HBC.

The reason I'm focusing on these three particular populations is that there is so much information available about them and so much of it seems to point so decisively to a common ancestor, both genetically and culturally. Once the baselines are established, however, then we can look around for other groups that might be a part of the same pattern.

Ethiopia is especially interesting in this respect, especially certain groups living in highland areas of SW Ethiopia, where we find many examples of P/B style vocalizing and also very interesting hocketed pipe ensembles. To my knowledge, however, the genetic makeup of these groups has not yet been investigated.

DocG said...

Hi Dude. Thanks for the heads up. I've taken a look at Hawk's post and yes it looks interesting. But I haven't had time to investigate any farther, as yet.

German said...

Onix,

The databases of myths have been compiled and analyzed by the Russian scholar Yuri Berezkin. You can google him up. He published some stuff in English. Comparative and typological linguistics also operate with large databases (see, e.g, Nichols, Linguistic Diversity in Space and Time, 1992). Finally my analysis of kinship systems (see Dziebel, The Genius of Kinship: The Phenomenon of Human Kinship and the Global Diversity of Kinship Terminologies, 2007) draws on a database of some 2500 languages (www.kinshipstudies.org). Comparative ethnology and linguistics give little support for out of Africa, and as you correctly pointed out genetic phylogenies are too ethereal to be real.