Analysis of language diversity on islands requires adequate statistical modelling - a comment on Bromham, Yaxley and Cardillo (2024)

In a recent study, Bromham, Yaxley and Cardillo (BYC) assembled an impressive database of 1,197 languages spoken across 13,100 islands to examine how predictions from island biogeography theory (IBT) apply to linguistic diversity and whether islands act as drivers of language change. I commend the authors for the significant effort in compiling such a truly global dataset of island languages, and for quantitatively demonstrating that islands hold a disproportionately greater share of the world’s languages than expected based on their land area. However, I here contend that the core model used to test the predictions of IBT and the hypothesis that islands shape language evolution is empirically implausible and plagued by several critical issues.