Abstract
Languages evolve over space and time. Illuminating the evolutionary history of language is important because it provides a unique opportunity to shed light on the population history of the speakers. Spatial and temporal aspects of language evolution are particularly crucial for understanding demographic history, as they allow us to identify when and where the languages originated, as well as how they spread across the globe. Here we apply Bayesian phylogeographic methods to reconstruct spatiotemporal evolution of the Ainu language: an endangered language spoken by an indigenous group that once thrived in northern Japan. The conventional dual-structure model has long argued that modern Ainu are direct descendants of a single, Pleistocene human lineage from Southeast Asia, namely the Jomon people. In contrast, recent evidence from archaeological, anthropological and genetic evidence suggest that the Ainu are an outcome of significant genetic and cultural contributions from Siberian hunter-gatherers, the Okhotsk, who migrated into northern Hokkaido around 900–1600 years ago. Estimating from 19 Ainu language varieties preserved five decades ago, our analysis shows that they are descendants of a common ancestor who spread from northern Hokkaido around 1300 years ago. In addition to several lines of emerging evidence, our phylogeographic analysis strongly supports the hypothesis that recent expansion of the Okhotsk to northern Hokkaido had a profound impact on the origins of the Ainu people and their culture, and hence calls for a refinement to the dual-structure model.
Highlights
Patterns of linguistic variation among individuals often carry the signature of a speech community’s demographic past
Assuming that the patterns of linguistic diversity is shaped by the demographic dynamics of speakers, we predicted that if the recent evidence supporting the Okhotsk expansion scenario were correct, the estimated root age should overlap with 900–1600 before present (BP)
The estimated root age of the Ainu language across post-burn-in trees has a median of 1288 BP [mean: 1323 BP; 95% Highest Posterior Density (HPD): 820– 1862 BP], in strong agreement with the prediction
Summary
Patterns of linguistic variation among individuals often carry the signature of a speech community’s demographic past. Recent empirical evidence supporting this phenomenon includes a range of language phylogenies reconstructed with computational methods [5,6,7,8]. While the computational phylogenetic methods have been fruitful in shedding new light on language evolution and the speakers’ prehistory, their application has been focused mainly on inferring temporal and sequential aspects. Inferences about the homeland or geographic diffusion pattern often relied on heuristic approaches such as locating a monophyletic outgroup and formulating post-hoc diffusion scenarios from the branching order. Recent progress in phylogenetic methods is, producing innovative ways to embed phylogenetic inference in a geographical context, and allow us to explicitly estimate both temporal and spatial aspects of evolution while accounting for phylogenetic uncertainty [9,10,11]. We adopt these methodological innovations and directly reconstruct spatiotemporal evolution of the Ainu language: a nearly extinct language spoken by indigenous people of Japan whose origins remain obscure
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