Social Anthropology and the Bantu Expansion

Razib is now officially a fantasy science blogger. When he recently called his readers “stupid, ignorant or lazy” and put up a stringent comments policy (I bet inspired by my own) rallying them to show their “A-game,” I knew it was a game changer. The new comments policy is a ploy to deflect attention from the fact that Razib’s own writings are increasingly a “C-game.” When he decided to address the “Bantu expansion a couple of days ago, he presented the colonization of South, Central and East Africa by the Bantu using the following metaphors:

“Imagine, if you will, the Bantu expansion being driven by men racing forward in Zulu-like military units, clearing territory of hunter-gatherers, killing and starving them out (and taking the occasional girl as a concubine). A Mfecane writ large! What stopped them in the end in Southwest Africa was ecology: the agricultural toolkit of the Bantu was not suitable for the arid or Mediterranean climates of this region. Until then the Bantu knife cut through the hunter-gatherers like butter, wiping them from the surface of the earth.”

The problem with some science bloggers is that they expose themselves to large amounts of different information, ranging from the Holocaust to dog shows, but they don’t have the training to manage it. This information turns into a cocktail with mangled parts of reality sticking out as reminders of what kind of ingredients went into the cocktail.

Razib obviously heard about the Holocaust of Jews in Europe, about the genocide of Tutsi by Hutu in Rwanda and about Shaka Zulu. Then he looked at some genetic data and took away that the Bantu are wide-spread but very homogeneous. He concluded that Bantu agriculturalists used their state apparatuses to very quickly exterminate African hunter-gatherers across most of South Africa. He thus imputed to science the discovery of a Holocaust of foragers by Bantu agriculturalists, to the cheering of some of his “stupid, ignorant and lazy” readers (e.g., Gcochran, who recently got caught spamming his own website with pharma promotions, loudly celebrated this prehistoric “ass-kicking”).

Having painted a pseudo-scientific picture of African prehistory, Razib suddenly attacked “anthropologists” for being African Holocaust deniers:

“A few years ago I ran into someone who told me that an anthropologist friend explained that the Bantu expansion had been debunked. This sort of thing is why I think cultural anthropology is quite often such a joke discipline. They should stick to their picketing the econ department, and leave the description of the human conditon as it is to those with a genuine interest.”

This is just the weirdest kind of journalist pulp summoning hearsay to celebrate ignorance and laziness. A nameless anthropologist friend of Razib’s unknown acquaintance told him that the theory built by people with genuine interest, which Razib is now converting into a gory Tarantino-like fantasy, was debunked. I wish Razib would develop a “genuine interest” in something else than blogging or science (software development or playing computer games seem to be good options for him).

Let’s peel the onion on the issue so awkwardly addressed by a poor blogger. Having worked side-by-side with Africanist anthropologists in both Russia and the U.S., I have never heard of anyone who would consider the Bantu expansion debunked. An older generation of anthropologists always accepted Joseph Greenberg’s classification of Niger-Congo languages and his theory of the origin of Bantu from the Cameroon Highlands in West Africa, which he first advanced in 1964 in an obscure collection of papers (Greenberg, Joseph. 1964. “Historical Inferences from Linguistic Research in Sub-Saharan Africa,” Boston University Papers, African History 1: l-15). A perusal of my comprehensive bibliography of kinship studies and social anthropology suggests that the most recent overview of independent contributions by anthropologists to the “Bantu expansion” problem dates back to Adam Kuper’s “Social Anthropology and the Bantu Expansion” (1978). In it, Kuper revisited the famous American anthropologist of the mid-20th century, George Peter Murdock, who argued that “the Bantu began their widespread dispersal with an avunculocal and matrilineal social system.” No denial of the “Bantu expansion” at all.

The reality is the opposite from the way Razib presents it: anthropologists haven’t contributed much to the problem of the Bantu expansion since Murdock. So, they pretty much have left it to people with “genuine interest.” The debunking that Razib referred to must refer to the reevaluation of the Bantu expansion orthodoxy initiated in the early 1990s by a new comprehensive phylogeny and lexicostatistics of the Bantu languages conducted in Tervuren on the basis of 542 languages and dialects (see Bastin, Y., A. Coupez, and M. Mann. 1999. Continuity and Divergence in the Bantu Languages: Perspectives from a Lexicostatistic Study,” Annales, Sciences Humaines 162: 1-226). This research received support from an eminent linguist, Johanna Nichols (“Modeling Ancient Population Structures and Population Movement in Linguistics and Archeology,” Annual Review of Anthropology 26: 359-384, 1997) and by a foremost Bantu historian Jan Vansina (“New Linguistic Evidence and the ‘Bantu Expansion’, Journal of African History 36: 173-195) who concurred, without simplifying the issue, that Bantu languages and cultures spread mostly by diffusion, without a massive demographic expansion.

Geneticists were somewhat late to the game the rules of which were set by linguists, archaeologists and historians. Some studies argued for the massive Bantu expansion on the basis of genetic homogeneity across Bantu speakers, the high frequency (68.5% AVG) of one single Y-DNA lineage E1b1a, with widely-shared subclades E1b1a7a (23% AVG) and E1b1a8 (35% AVG), in both Western and Eastern Bantu (Cesare de Filippo et al. (2011). “Y-Chromosomal Variation in Sub-Saharan Africa: Insights Into the History of Niger-Congo Groups,” Molecular Biology and Evolution 28 (3): 1255-1269) and the close correspondence between the E1b1a genetic phylogeny and the Niger-Congo linguistic phylogeny. Others (Montano et al. 2011. The Bantu Expansion Revisited: A New Analysis of Y Chromosome Variation in Central Western Africa,” Molecular Ecology 20: 2693-2708) painted a more complex picture:

“In this way, we were able to detect some noteworthy differences within and among Bantu-speaking populations, mostly due to haplogroups E1b1a7a (U174), E1b1a8a (U209) and E1b1a8a1 (U290), which contribute to their high level of interpopulation differentiation and to the presence of distinct regional patterns of genetic variation. All these findings contradict the current view of Bantu speakers as a homogeneous group of populations whose gene pools are mostly if not exclusively the result of a relatively recent population expansion. In fact, the strongest signal of diversity is given by Cameroonian populations. The presence of non-Bantu ethnic groups in this country raises the possibility that the diversity of Cameroonian populations from other Bantus could be the result of differential admixture. However, such a scenario is in contrast with previous studies on Y-chromosome and nuclear loci which do not support occurrence of gene flow between the Bantu speakers of South Cameroon and the Afro-Asiatic and Adamawa populations from the northern part of the country” (p. 2704).

The “Bantu expansion” is still a wide open question. There seem to be enough reasons to believe that the spread of Bantu languages involved a demographic component. It was likely stronger, more rapid and happened earlier in the territories occupied by Western Bantu than in the territories occupied by Eastern Bantu. It’s more likely that West Africa has been “pumping” populations into East, Central and South Africa since long before the onset of agriculture around 5,000 YBP (Nichols 1997; Blench, Roger. 2006. Archaeology, Language and the African Past. Lanham: AltaMira Press.), so every new wave of migrants, driven first by early Holocene climate change, then by agriculture, then by iron technologies, mixed with the old ones. Outside of Hadza, Sandawe and South Khoisan populations, there is no secure evidence for a strong foraging substratum locked in Central, East or South Africa for tens of thousands of years prior to the onset of these multiple migrations from West Africa. Eastern and Western Pygmies share with farmers lineages from the same clades. Filippo et al. (2011) write,

“The presence of both E1b1a7a and E1b1a8 in all Pygmy groups — directly genotyped in the C.A.R. and D.R.C. Pygmies and inferred from STR data for the Cameroon and Gabon Pygmies—may be the result of sex-biased migrations between agriculturalist and hunter-gatherer societies, where paternal lineages move from the former into the latter (Destro-Bisol et al. 2004; Tishkoff et al. 2007; Quintana-Murci et al. 2008). However, judging from the networks for both haplogroups, recent admixture with Bantu-speaking neighbors may not account for the origin of all of these haplotypes. Although some haplotypes are shared with, or differ by only a few mutational steps from, Bantu speakers and hence may indeed reflect recent admixture, other haplotypes found at the periphery of the network are unique to Pygmies. The Pygmy groups tend to exhibit high levels of STR variance along with low levels of haplotype diversity, indicating the presence of a few very divergent (and therefore probably old) lineages. The older age of E1b1a8 in Pygmies than in Bantu, in contrast to the similar age of E1b1a7a in both Pygmies and Bantu (table 3), suggests the possibility that a few individuals belonging to haplogroup E1b1a8 were present in Pygmies prior to their contact with Bantu-speaking groups; individuals belonging to E1b1a7a were introduced at an early stage of the expansion (for instance, when the Bantu agriculturalist started to explore the rain forest), with later introgression of new haplotypes of both haplogroups after contact.”

Linguists and geneticists are exploring various scenarios. Geneticists are keen on bringing anthropologists into their research because “the asymmetric gene flow, polygyny, and patrilocality, and, hence, the sociocultural factors underlying them, have an important role in determining and differentiating the genetic structure of sub-Saharan populations” (Destro-Bisol et al. (2004). “Variation of Female and Male Lineages in Sub-Saharan Populations: the Importance of Sociocultural Factors,” Molecular Biology and Evolution 21 (9): 1680). But one hypothesis that they are definitely not exploring is Razib’s idea of a genocide of foragers by farmers. Without ancient DNA data, we obviously can’t say whether some of the foragers were exterminated without a trace. But be that as it may, the question of massive forager extinction is irrelevant to our understanding of the prehistory South, Central and West Africa.

Anthropological linguist Jeff Marck recently partnered with the Bantu linguist Koen Bostoen, who often co-authors mainstream papers on the population genetics of the ‘Bantu expansion’ (such as Cesare de Filippo et al. (2011)), which Razib and his readers probably read. Marck & Bostoen (“Proto-Oceanic (Austronesian) and Proto-East Bantu Kin Terms ca. 1000 BC,” Kinship, Language and Prehistory. Salt Lake City: University of Utah Press, 2010) harness anthropologist William Divale’s theory of matrilocality as caused by external warfare to suggest, using ethnographic and linguistic evidence, that the expanding Bantu farmer populations were originally matrilocal because men were heavily involved in warfare with indigenous hunter-gatherers and in long-distance exploration. Once they established themselves in the newly colonized territories, they began switching from matrilocality to patrilocality. This model predicts that mostly patrilineal West Bantu, which are also most divergent linguistically (see below, Fig. 2.2 from Clare Holden and Russell Gray. (2006). “Rapid Radiation, Borrowing and Dialect Continua in the Bantu Languages,” in Phylogenetic Methods and the Prehistory of Languages, edited by Peter Forster and Colin Renfrew. Cambridge, p. 21) used to be matrilineal and matrilocal but had more time to develop patrilineal and patrilocal institutions.

Previous research on Austronesian expansion demonstrated the power of post-marital residence to predict haploid variation, and Marck & Bostoen are now applying the learnings to the Bantu expansion. The genetics of Austronesian-speaking populations is characterized by low mtDNA diversity and the prevalence of “Asian” mtDNA lineages in Oceania and high Y-DNA diversity and the prevalence of “Papuan” lineages in Austronesian speakers. In this case, matrilocality explains the pattern nicely: the incoming matrilocal Austronesians absorbed patrilineally-transmitted genetic contributions from the vastly divergent “Papuans.” In the Bantu case the situation is different. The evidence of Y-DNA homogeneity among Bantu indicates that the Bantu colonization did not involve intensive Y-DNA admixture with vastly divergent foragers. Farmers admixed with foragers who either came from the same area of West Africa during an earlier wave of migration or who constituted a hunting caste (pace Roger Blench, see here) within an economically and socially diverse early Bantu society. Destro-Bisol et al. (2004, 1679) discovered that

“because of the combined effect of asymmetric gene flow and different levels of polygyny and patrilocality … genetic drift had been more effective on maternal than on paternal lineages of HGPs [hunter-gatherer populations.-G.D.], whereas gene flow is expected to be the prevailing microevolutionary force on their paternal lineages. The opposite situation is expected for FPPs [food-producing populations.G.D.]. Consequently, HGPs should show a higher intrapopulational diversity for paternal than for maternal lineages, whereas the opposite should be valid for FPPs. To test these expectations, we compared HVR-1 mtDNA and Y-chromosome microsatellite haplotype diversity in the same populations for both genetic systems. From this comparison, we found that HGPs show the lowest level of haplotype diversity for mtDNA but nearly the highest for the Y chromosome (fig. 3).”

This pattern of lower Y-DNA diversity and higher mtDNA diversity sets the “Bantu expansion” apart from the “Austronesian” expansion. African foragers are a better match to Austronesian farmers in terms of the patterns of asymmetric gene flow. This raises questions about the Marck & Bostoen’s (with roots in Murdock), reconstruction of matrilocality for early Bantu. It’s possible that there was a “matrilocal” stage in the evolution of Bantu social organization, which is better captured by Pygmy genetics, later superseded by the “patrilocal” stage reflected in the genetics of Bantu farmers.