Language Log

Computational phylogeny of Indo-European

June 27, 2025 @ 6:24 am · Filed by Victor Mair under Classification, Computational linguistics, Evolution of language

Alexei S. Kassian and George Starostin, "Do 'language trees with sampled ancestors' really support a 'hybrid model' for the origin of Indo-European? Thoughts on the most recent attempt at yet another IE phylogeny". Humanities and Social Sciences Communications, 12, no. 682 (May 16, 2025).

Abstract

In this paper, we present a brief critical analysis of the data, methodology, and results of the most recent publication on the computational phylogeny of the Indo-European family (Heggarty et al. 2023), comparing them to previous efforts in this area carried out by (roughly) the same team of scholars (informally designated as the “New Zealand school”), as well as concurrent research by scholars belonging to the “Moscow school” of historical linguistics. We show that the general quality of the lexical data used as the basis for classification has significantly improved from earlier studies, reflecting a more careful curation process on the part of qualified historical linguists involved in the project; however, there remain serious issues when it comes to marking cognation between different characters, such as failure (in many cases) to distinguish between true cognacy and areal diffusion and the inability to take into account the influence of the so-called derivational drift (independent morphological formations from the same root in languages belonging to different branches). Considering that both the topological features of the resulting consensus tree and the established datings contradict historical evidence in several major aspects, these shortcomings may partially be responsible for the results. Our principal conclusion is that the correlation between the number of included languages and the size of the list may simply be insufficient for a guaranteed robust topology; either the list should be drastically expanded (not a realistic option for various practical reasons) or the number of compared taxa be reduced, possibly by means of using intermediate reconstructions for ancestral stages instead of multiple languages (the principle advocated by the Moscow school).

Discussion and conclusions

In the previous sections, we have to tried to identify several factors that might have been responsible for the dubious topological and chronological results of Heggarty et al. 2023 experiment, not likely to be accepted by the majority of “mainstream” Indo-European linguists. Unfortunately, it is hard to give a definite answer without extensive tests, since, in many respects, the machine-processed Bayesian analysis remains a “black box”. We did, however, conclude at least that this time around, errors in input data are not a key shortcoming of the study (as was highly likely for such previous IE classifications as published by Gray and Atkinson, 2003; Bouckaert et al. 2012), although failure to identify a certain number of non-transparent areal borrowings and/or to distinguish between innovations shared through common ancestry and those arising independently of one another across different lineages (linguistic homoplasy) may have contributed to the skewed topography.

One additional hypothesis is that the number of characters (170 Swadesh concepts) is simply too low for the given number of taxa (161 lects). From the combinatorial and statistical point of view, it is a trivial consideration that more taxa require more characters for robust classification (see Rama and Wichmann, 2018 for attempts at estimation of optimal dataset size for reliable classification of language taxa). Previous IE classifications by Gray, Atkinson et al. involved fewer taxa and more characters (see Table 1 for the comparison).

Despite all the energetic discussions of our previous attempts, it appears that the question of IE phylogeny has not yet been put to bed.

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