A Bayesian Investigation of the Origin Hypotheses of the Dravidian Family

A Bayesian investigation of the origin hypotheses of the Dravidian family

Dravidian language family has about 81 languages according to Glottolog1. The Dravid- ian languages are well-studied [Krishnamurti, 2003] from a historical linguistics viewpoint. Re- cently, phylogenetic methods originating from bioinformatics have been applied to infer absolute chronologies of language trees for range of language families such as Indo-European [Rama, 2018, Chang et al., 2015], Pama-Nyungan [Bowern and Atkinson, 2012], and Dravidian [Kolipakam et al., 2018] based on lexical cognate data. The recent study by Kolipakam et al. [2018] infers a time depth of 4500 years for the root age of the Dravidian family (for 20 languages) based on calibration points such as the antiquity of Old Tamil (2100 Before Present [B.P]) and the first attestation of Telugu inscriptions dating to 1300 years B.P. The inferred tree does not group South-Dravidian I and II groups together under a single node. Although, the authors infer an age that matches with the age proposed by Krishnamurti [2003], the location of Proto-Dravidian has not been inferred through phylogeography techniques. Apart from assigning an age, Krishnamurti [2003] links Proto- Dravidian to Indus Valley Civilization. On the other hand, based on linguistic innovations and archaeological record Southworth [2004], associates Proto-Dravidian to be spoken in Lower Godavari Basin. We test the statistical support for both the origin hypotheses by applying phylogeography techniques to the lexical cognate dataset under different assumptions. The results of the first set of dating experiment where the phylogenetic tree is topologically constrained according to the findings of the comparative method is given in table 1. The inferred ages do agree with the ages posited based on linguistic and archaeological evidence.

Constraint Southworth [2004] Median Inferred age Root 4500–4000 4284 PSD 4000–3000 3205 PSDI 2600 (latest) 2515 PSDII – 2407 CD – 2141 ND – 3063

Table 1: Comparison of inferred ages of major subgroups with expansion dates from linguistic and archaeological evidence. Missing ages are shown by ‘–’.

As the next step, we infer the possible homelands for the internal nodes of the chronologically dated tree using a random walk model. The result shows that the Dravidian homeland would be located in peninsular India as postulated by Southworth and not . The migration of Brahui is a debated topic [Elfenbein, 1987] and is generally believed to have migrated from central India [Elfenbein, 1998] as opposed to be a remnant from original migration into India. The random walk model supports migration from central India hypothesis as shown in the ﬁgure 1. The

1https://glottolog.org/resource/languoid/id/drav1251. Accessed on 12-14-2019

1 next steps would consist of joint inference of phylogeny and geography and expansion of the lexical word lists to include more number of languages.

Figure 1: Geographical spread of Dravidian family. Blue lines/dots show the dispersal of synchronic languages and red lines/dots show reconstructed nodes.

References

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