FYI:

Language trees with sampled ancestors support a hybrid model for the
origin of Indo-European languages

Paul Heggarty, Cormac Anderson, Matthew Scarborough, Benedict King, Remco
Bouckaert, Lechosław Jocz, Martin Joachim Kümmel, Thomas Jügel, Britta
Irslinger, [...], and Russell D. Gray +23 authors

Science
28 Jul 2023
Vol 381, Issue 6656
DOI: 10.1126/science.abg0818

Editor’s summary

Languages of the Indo-European family are spoken by almost half of the
world’s population, but their origins and patterns of spread are disputed.
Heggarty et al. present a database of 109 modern and 52 time-calibrated
historical Indo-European languages, which they analyzed with models of
Bayesian phylogenetic inference. Their results suggest an emergence of
Indo-European languages around 8000 years before present. This is a deeper
root date than previously thought, and it fits with an initial origin
south of the Caucasus followed by a branch northward into the Steppe
region. These findings lead to a “hybrid hypothesis” that reconciles
current linguistic and ancient DNA evidence from both the eastern Fertile
Crescent (as a primary source) and the steppe (as a secondary homeland). —
Sacha Vignieri

Structured Abstract

INTRODUCTION
Almost half the world’s population speaks a language of the Indo-European
language family. It remains unclear, however, where this family’s common
ancestral language (Proto-Indo-European) was initially spoken and when and
why it spread through Eurasia. The “Steppe” hypothesis posits an expansion
out of the Pontic-Caspian Steppe, no earlier than 6500 years before
present (yr B.P.), and mostly with horse-based pastoralism from ~5000 yr
B.P. An alternative “Anatolian” or “farming” hypothesis posits that Indo-
European dispersed with agriculture out of parts of the Fertile Crescent,
beginning as early as ~9500 to 8500 yr B.P. Ancient DNA (aDNA) is now
bringing valuable new perspectives, but these remain only indirect
interpretations of language prehistory. In this study, we tested between
the time-depth predictions of the Anatolian and Steppe hypotheses,
directly from language data. We report a new framework for the chronology
and divergence sequence of Indo-European, using Bayesian phylogenetic
methods applied to an extensive new dataset of core vocabulary across 161
Indo-European languages.

RATIONALE
Previous phylolinguistic analyses have produced conflicting results. We
diagnosed and resolved the causes of this discrepancy, two in particular.
First, the datasets used had limited language sampling and widespread
coding inconsistency. Second, some analyses enforced the assumption that
modern spoken languages derive directly from ancient written languages
rather than from parallel spoken varieties. Together, these methodological
problems distorted branch-length estimates and date inferences. We present
a new dataset of cognacy (shared word origins) across Indo-European. This
dataset eliminates past inconsistencies and provides a fuller and more
balanced language sample, including 52 nonmodern languages for a denser
set of time-calibration points. We applied ancestry-enabled Bayesian
phylogenetic analysis to test rather than enforce direct ancestry
assumptions.

RESULTS
Few ancient written languages are returned as direct ancestors of modern
clades. We find a median root age for Indo-European of ~8120 yr B.P. (95%
highest posterior density: 6740 to 9610 yr B.P.). Our chronology is robust
across a range of alternative phylogenetic models and sensitivity analyses
that vary data subsets and other parameters. Indo-European had already
diverged rapidly into multiple major branches by ~7000 yr B.P., without a
coherent non-Anatolian core. Indo-Iranic has no close relationship with
Balto-Slavic, weakening the case for it having spread via the steppe.

CONCLUSION
Our results are not entirely consistent with either the Steppe hypothesis
or the farming hypothesis. Recent aDNA evidence suggests that the
Anatolian branch cannot be sourced to the steppe but rather to south of
the Caucasus. For other branches, potential candidate expansion(s) out of
the Yamnaya culture are detectable in aDNA, but some had only limited
genetic impact. Our results reveal that these expansions from ~5000 yr
B.P. onward also came too late for the language chronology of Indo-
European divergence. They are consistent, however, with an ultimate
homeland south of the Caucasus and a subsequent branch northward onto the
steppe, as a secondary homeland for some branches of Indo-European
entering Europe with the later Corded Ware–associated expansions. Language
phylogenetics and aDNA thus combine to suggest that the resolution to the
200-year-old Indo-European enigma lies in a hybrid of the farming and
Steppe hypotheses.

https://www.science.org/doi/10.1126/science.abg0818

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