A central issue in Austronesian higher-order subgrouping concerns the position of the Philippine languages. Despite considerable debate, it remains unsettled whether these languages represent multiple intersecting MalayoPolynesian primary branches forming a linkage, or whether they descend from a single shared ancestor distinct from Proto-Malayo-Polynesian. We present three new lines of evidence supporting the former view. First, the absence of a genuine *d/*z merger in Central Luzon and Minahasan languages undermines the sole phonological argument for a Proto-Philippine branch. Second, the geographical distribution of the purported Proto-Philippine-defining lexicon favors a diffusion-based explanation. Third, the distribution of an underexplored morphological innovation across Philippine languages suggests frequent contact among major island groups, excluding interior and peripheral areas. These findings not only highlight the absence of defining innovations for a cohesive Proto-Philippine but also point to extensive horizontal transmission across the archipelago, extending beyond lexical exchange. We further propose that the *d/*z merger is better understood as an areal drift rather than a diagnostic innovation. We conclude that Philippine languages are best analyzed as intersecting Malayo-Polynesian primary branches, in line with recent perspectives. Moreover, the high number of proposed lexical innovations attributed to Proto-Philippine likely reflects contact-driven processes—diffusion, borrowing, and linkage histories—rather than retention from a unified ancestor.
Chen et al. (Sun,) studied this question.