Can Bayesian phylogeography reconstruct migrations and expansions in linguistic evolution?

Abstract

Bayesian phylogeography has been used in historical linguistics to reconstruct homelands and expansions of language families, but the reliability of these reconstructions has remained unclear. We contribute to this discussion with a simulation study where we distinguish two types of spatial processes: migration , where populations or languages leave one place for another, and expansion , where populations or languages gradually expand their territory. We simulate migration and expansion in two scenarios with varying degrees of spatial directional trends and evaluate the performance of state-of-the-art phylogeographic methods. Our results show that these methods fail to reconstruct migrations, but work surprisingly well on expansions, even under severe directional trends. We demonstrate that migrations and expansions have typical phylogenetic and spatial patterns, which in the one case inhibit and in the other facilitate phylogeographic reconstruction. Furthermore, we propose descriptive statistics to identify whether a real sample of languages, their relationship and spatial distribution, better fits a migration or an expansion scenario. Bringing together the results of the simulation study and theoretical arguments, we make recommendations for assessing the adequacy of phylogeographic models to reconstruct the spatial evolution of languages.

Triangulation supports agricultural spread of the Transeurasian languages

“…The results of our analysis are represented on a map (Supplementary Data 3). As Bayesian phylogeography must contend with a number of limitations 55,56 , we complemented it with other homeland detection methods such as linguistic palaeontology and the diversity hotspot principle to reach a balanced location for the homelands of the root and nodes of the Transeurasian family (Supplementary Data 4). Linguistic palaeontology.…”

Testing methods of linguistic homeland detection using synthetic data

“…The only other simulation-based study looking at the performance of Bayesian phylogeography (but excluding other approaches from its purview) [24] similarly finds directed, migratory steps to be problematical. In this study, simulations were specifically designed to assess the performance of the relaxed random walk and constant directional random walk models as implemented in BEAST 1.10.4 in a situation where languages have spread in a directional fashion versus a situation more akin to a random walk.…”

“…The lack of performance tests of linguistic homeland detection methods motivates this paper. We are only aware of a single other work of a similar nature [24]. Even the biological literature is found wanting in comparative performance tests of phylogeographic methods, as has been repeatedly pointed out [24–26].…”

“…We are only aware of a single other work of a similar nature [24]. Even the biological literature is found wanting in comparative performance tests of phylogeographic methods, as has been repeatedly pointed out [24–26]. Tests have focused on technical aspects of individual methods, mainly as applied to epidemiology [27,28].…”

Clocks with bursts: Phylogenetic inference of schismogenesis in language evolution

“…To further test whether schismogenesis is a plausible driver of punctuated evolution we could investigate the phylogeography of the languages [53]. Since schismogenesis is an active process that involves contact between the speaker communities, its effects should be stronger where the distance between related languages is smaller.…”