Abstract
The origins of linguistic diversity remain controversial. Studies disagree on whether group features such as population size or social structure accelerate or decelerate linguistic differentiation. While some analyses of between-group factors highlight the role of geographical isolation and reduced linguistic exchange in differentiation, others suggest that linguistic divergence is driven primarily by warfare among neighbouring groups and the use of language as marker of group identity. Here we provide the first integrated test of the effects of five historical sociodemographic and geographic variables on three measures of linguistic diversification among 50 Austronesian languages: rates of word gain, loss and overall lexical turnover. We control for their shared evolutionary histories through a time-calibrated phylogenetic sister-pairs approach. Results show that languages spoken in larger communities create new words at a faster pace. Within-group conflict promotes linguistic differentiation by increasing word loss, while warfare hinders linguistic differentiation by decreasing both rates of word gain and loss. Finally, we show that geographical isolation is a strong driver of lexical evolution mainly due to a considerable drift-driven acceleration in rates of word loss. We conclude that the motor of extreme linguistic diversity in Austronesia may have been the dispersal of populations across relatively isolated islands, favouring strong cultural ties amongst societies instead of warfare and cultural group marking.
Highlights
Languages are the product of long-term cumulative cultural evolution [1]
The full models explained the majority of the proportion of the variance in rates of word gains, losses and overall lexical turnover (Bayesian R2 values of 0.59, 0.70 and 0.66 respectively), indicating that the five predictors had a stronger effect on rates of word losses
This is because it moderately increased the ability at which languages acquired new lexical items it severely increased the rate of word loss
Summary
Languages are the product of long-term cumulative cultural evolution [1]. Evolutionary changes have resulted in a vast array of over 7000 languages spoken in the world today [4], the questions of “why so many languages” and “why so unevenly distributed” are far from being answered. A vast corpus of research has emerged on the evolutionary, ecological and social correlates of the global distribution of linguistic diversity [5,6,7,8,9,10,11,12,13,14,15]. Various studies have focused on demography as a key determinant of rates of cultural and linguistic evolution [16,17,18,19,20,21,22].
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