Traditional linguistic methods compare languages by noting the similarities in vocabulary between them. However, vocabulary changes at a relatively high rate, so beyond a few thousand years in the past, the shared vocabulary of two related languages will be about the same as that between two randomly chosen languages.
Language, however, is not limited to vocabulary, but extends to grammatical rules, syntax, phonology, etc. So, two related languages will be similar to each other in these respects as well. Perhaps by using the knowledge which they provide we might be able to reconstruct the relationships between languages beyond the time barrier posed by vocabulary, and into a Paleolithic time frame.
Michael Dunn and colleagues have applied phylogenetic methods inspired by biology to this problem. Biological populations are quite similar to languages, because they also change over time, becoming dissimilar when they are separated, while retaining some of the structure of their common ancestors. So, by applying biological thinking we might be able to reconstruct a linguistic phylogeny.
Dunn et al. first applied this approach to Oceanic Austronesian languages, confirming that their method is able to reproduce the branching pattern of a well-understood language family. Next, they applied their method to Papuan languages of Melanesia, which are considered isolates without any clear relationships to each other. The resulting phylogeny shows a remarkable correspondence with geography. Thus, phylogenetic methods applied to non-vocabulary elements of language were able to trace the differentiation of Melanesian languages during the Paleolithic settlement of that region of the world.
Science, Vol 309, Issue 5743, 2072-2075
Structural Phylogenetics and the Reconstruction of Ancient Language History
Michael Dunn et al.
The contribution of language history to the study of the early dispersals of modern humans throughout the Old World has been limited by the shallow time depth (about 8000 ± 2000 years) of current linguistic methods. Here it is shown that the application of biological cladistic methods, not to vocabulary (as has been previously tried) but to language structure (sound systems and grammar), may extend the time depths at which language data can be used. The method was tested against well-understood families of Oceanic Austronesian languages, then applied to the Papuan languages of Island Melanesia, a group of hitherto unrelatable isolates. Papuan languages show an archipelago-based phylogenetic signal that is consistent with the current geographical distribution of languages. The most plausible hypothesis to explain this result is the divergence of the Papuan languages from a common ancestral stock, as part of late Pleistocene dispersals.