Why does language borrowing make Papuan languages difficult to classify?

Language borrowing significantly complicates the classification of Papuan languages because it obscures the distinction between genetically inherited linguistic features and those acquired through contact.

In the fragmented and multilingual environment of New Guinea and its surrounding regions, speech communities frequently adopt features from neighboring groups, including basic vocabulary, pronouns, grammatical patterns, and discourse styles. This widespread cross-influence makes it difficult for linguists to isolate the original, inherited traits necessary to establish clear genetic relationships between language families. The challenge is further intensified when borrowings occur between languages that are already genetically related or when the source language is now extinct.

Because of this, comparative linguistic analysis requires extreme rigor. Researchers often rely on bound morphological forms—such as specific verbal prefixes—as the most reliable evidence for genetic links, as these elements are generally more resistant to borrowing than other linguistic features. However, due to the complexity of these interactions and a lack of historical documentation, much of the work to classify these languages remains in its infancy.1