The evolutionary dynamics of ergative alignment of case marking

Languages have been claimed to globally disfavor ergatively-aligned case marking, possibly reflecting processing preferences. Phylogenetic research on Pama-Nyungan has cast doubt on this, showing a preference for retaining ergativity in the family. In this study, we re-examine the evolution of ergative alignment of case marking in a sample of over 200 languages from eleven language families (Pama-Nyungan among them) in a continuous-time Markov Chain model. Since one language can adopt multiple alignment patterns of case marking in its grammar (‘split’ alignment), we incorporate a third, split state into the models. In addition, we compare the goodness of fit across various models where clades can show different rates of change, defining evolutionary regimes that can cut across families. The results show that, across all families, the best-fitting model requires two connected regimes: one favoring non-ergative (S=A) and the other favoring split-ergative alignment (S=A and S≠A). These differences notwithstanding, the stationary probabilities of the model suggest that in the long run, non-ergative alignments are expected to be much more frequent than ergative alignment in case marking.