Genetic classification

 

Introduction

Genetic classification

Refers to the way languages are categorized according to their descent.  Languages that developed historically from the same ancestor language are grouped together and are said to be genetically related. Genetic relationships therefore have to do with the linguistic characteristics that are inherited by one generation of speakers from another (as opposed to those which are acquired from other sources). That is, “all languages of the world are classified into families. All languages belonging to a particular family are believed to have the same origin, that is, they originated from the same ancestor language”(Blench 2006)

The purpose of genetic classification is to group languages into families according to their degree of diachronic relatedness. So far, most of the languages of the world have been grouped only tentatively into families, and many of the classificatory schemes that have been proposed will no doubt be radically revised as further progress is made.

A typological classification groups languages into types according to their structural characteristics. For example, the Latin suffix -is represents the combination of categories “singular” and “genitive” in the word form hominis “of the man,” but one part of the suffix cannot be assigned to “singular” and another to “genitive,” and -is is only one of many suffixes that in different classes (or declensions) of words represent the combination of “singular” and “genitive.”s (Blench 2006)

Bantu represents the largest African language family in terms of number of languages occupied territory and number of speakers. Bantu languages are generally thought to have originated in the Cameroonian Grass fields area neighboring Nigeria, and started to spread, possibly together with agricultural technologies through Sub-Saharan Africa as far as Kenya in the east and the Cape in the south. The evolution of the Bantu languages has been suggested as fitting a branching-tree model, but this model does not entirely explain the variation observed in the linguistic data (Blench 2006)

In addition, the modality of spread of Bantu-speaking peoples across Sub-Saharan Africa has been under debate in various disciplines during the last few decades. Contrasting models for the migration of Bantu-speaking groups have been proposed, sometimes even from studies using the same lexicostatistical dataset. The major debate concerns the spatial and temporal dispersal of Bantu languages in Sub-Saharan Africa. One hypothesis states that Bantu languages split at an early stage north of the rainforest, from which the Western and Eastern Bantu languages are derived as two primary branches. A contrasting hypothesis argues that there was a major migration to the south of the rainforest, with a later split of the Eastern Bantu languages from the Western group only (Achille 1967)

The expansion of Bantu-speaking peoples is not only debated with regard to the underlying events and the route taken, but also whether the spread of the languages took place as the result of ‘demic diffusion’ via an actual movement of people or whether it was rather a cultural diffusion involving the movement of languages via language shift without concomitant gene flow. Genetic studies have highlighted the strong demographic impact of the Bantu migration on the gene pool of Sub-Saharan African populations ( Blench 2006)

The Bantu languages descend from a common Proto-Bantu language, which is believed to have been spoken in what is now Cameroon in Central Africa. An estimated 2,500–3,000 years ago (1000 BC to 500 BC), speakers of the Proto-Bantu language began a series of migrations eastward and southward, carrying agriculture with them. This Bantu expansion came to dominate Sub-Saharan Africa east of Cameroon, an area where Bantu peoples now constitute nearly the entire population. Some other sources estimate the Bantu Expansion started closer to 3000 BC (Derek & Philippson 2003)

The technical term Bantu, meaning human beings or simply people was first used by Wilhelm Bleek (1827–1875), as the concept is reflected in many of the languages of this group. A common characteristic of Bantu languages is that they use words such as muntu or mutu for human being or in simplistic terms person, and the plural prefix for human nouns starting with mu- (class 1) in most languages is ba- (class 2), thus giving bantu for "people". Bleek, and later Carl Meinhof, pursued extensive studies comparing the grammatical structures of Bantu languages.  Genetic markers and linguistic data are used together for the first time to shed light on the dispersal of Bantu languages and peoples in Sub-Saharan Africa. The study addresses two major questions.

(i)                 The examination whether the expansion of Bantu languages was a cultural dispersal (such as language shift) or a joint movement of languages and people (demic diffusion) by using data from mitochondrial DNA, Y-chromosomal and autosomal markers. The demic diffusion model predicts that the genetic distances among populations speaking Bantu languages should be lower than those between Bantu-speaking populations and populations speaking other languages, whereas the cultural dispersal model predicts no consistent differences in the genetic distances among Bantu-speaking populations versus between Bantu-speaking populations and those speaking other languages.

(ii)              The test of the two most commonly cited models for the Bantu expansion: the early-split versus the late-split model. For this purpose, we use an alternative method to previous linguistic studies that reconstructed models of expansion only from trees (or networks) of languages based on a quantitative comparison of Bantu lexical cognates.

The method uses the migration distances between populations predicted by the early-split and late-split models, and correlates these distances with both linguistic and genetic distances. A third model of expansion (isolation by distance, IBD) is included as an alternative explanation to test whether recent migration or language contact may have played a role in the expansion of the Bantu languages (Larry 2003)

Analytical approaches to describe the origin of Bantu languages

(a)   Genetic data and analyses

The compilation of genetic datasets from published data for African populations with a sample size of at least 10 chromosomes. The DNA dataset consisted of 5018 sequences of the first hyper variable segment and individuals with a high amount of missing data. For further details, see the electronic supplementary material. The Pygmy populations, who are known to have adopted the languages of their neighbors (e.g. Bantu), were considered as a separate group and excluded from the Bantu-speaking groups when testing the models of Bantu migration (Derek & Philippson 2003)

  (b) Linguistic data and analyses

The linguistic dataset consists of lists of 92 basic words for 412 Bantu languages electronic supplementary material, the linguistic distances among languages as patristic distances from the trees generated with Bayesian phylogenetic methods in order to take into account heterogeneity of replacement rates across words and rate changes of the same word over time  (Achille 1967)

(c) Model-based geographical distances

In order to calculate the model-based geographical distances between Bantu-speaking populations, we grouped the Bantu languages and populations according to the Bantu classification proposed by Vansina with some modifications. Languages were assigned to 13 different groups (electronic supplementary material. Based on this classification the geographical distances were calculated as predicted from both early-split and late-split models (see electronic supplementary material. Geographical distances based on the IBD model were calculated as great-circle distances between two populations/languages ( Larry 2003)

d) Analysis of Molecular Variance (AMOVA) and standard diversity indices for the Y-chromosome haplogroups and Y-STR haplotypes, plus Φst and RST matrices of distances for the complete mtDNA sequences and the Y-STR haplotypes, respectively, were computed in Arlequin ver. Multi-dimensional scaling analyses of matrices of genetic distances based on Y-chromosomal haplogroup frequencies and complete mtDNA sequences were plotted in Statistica ver.(Achille 1967)

e) Bantu language characterized by specific haplogroups both on the Y chromosome and the mtDNA, which are found in considerable frequencies only in these populations or in groups with a known history of contact with such populations. Among Bantu-speaking populations of southern Africa, the amount of detectable intermarriage with Khoisan peoples varies between regions and populations and is not always correlated with the presence of click sounds in the languages they speak (Larry 2003)

 

 

Conclusion

The dispersal of Bantu languages was coupled with the movement of people (such as demic diffusion), as demonstrated by the lower genetic distances among Bantu populations when compared with those between Bantu and all the other major ethno linguistic groups, as well as by the reduction of mtDNA and Y-chromosomal diversity proportional to the distance from the Bantu homeland. Furthermore, the strong correlations between genetic and linguistic (as well as geographical) distances as additional evidence of a demic diffusion. With regard to the geographical routes underlying the Bantu expansion, our analyses indicate that the early-split model, which postulates an initial split into Eastern and Western Bantu languages approximately 4000 ya, finds little support in the lexical and genetic data.

References

 Larry.M.H(2003). Basaá. In Derek Nurse & Gérard Philippson (eds.) The Bantu Languages. London: Routledge.

Blench .R (2006) Language, Archaeology and the African Past. Lanham MD: AltaMira Press.

Achille E. M(1967) Bantu Grammatical Reconstructions. Africana Linguistica

Derek. N & Philippson. G (eds.) (2003) The Bantu Languages. London: Routledge.