In the Journals - Human expansion across the Pacific mapped by language and bacteria

Just as I finish reading (or rather, re-reading) chapters concerning the fate of Easter Island (Rapanui) and of Henderson and Pitcairn Islands in Collapse: How Societies Choose to Fail or Survive by Jared Diamond, the 23rd January issue of Science arrives, bearing two articles on the spread of humans (Austronesians) from Taiwan and onwards across Micronesia to Polynesia.  One of these papers, by Gray and colleagues, presents a linguistic analysis of langauages across this region.  The second, by Moodley et al looks at the variation of the human pathogen Helicobacter pylori in these same peoples.  Both strands of evidence documenting this population spread are in striking agreement.

I have no experience in the kind of linguistic analysis carried out by Gray and colleagues, so my understanding is informed by Colin Renfrew's Perspectives article in this issue of Science.There are over 1000 polynesian languages, making it one of the largest language families.  Ultimately, the populations that eventually colonised even the most remote islands such as Easter were ultimately derived from a migration that can (at least in one theory) be traced back to origins in Taiwan (upper panel in the figure below).  Other possibilities include origins in island Southeast Asia.  Genetic evidence (such as that provided by mitochondrial DNA sequences) has been ahrd to interpret, and may not support the Taiwan origin of the Austronesian speaking people.  On the other hand, such evidence may be complicated by post-colonial gene flow.

Gray et al have applied computer analysis to languages across the Pacific diaspora. They have analysed a large database of 210 basic vocabulary (basic in the sense that they are words representing basic activities, and which are the words/concepts that tend to be conserved as languages evolve), and plotted the time course of the Austronesian languages.  It seems that their analysis indicates a pause-pulse mode, in which there were two pauses in expansion.  The first coincides with the crossing of350km Bashi channel between Taiwan and the Phillipines, and the second between the colonisation of  Western Polynesia and that of the remoter Eastern Polynesian islands.  Both the pauses are thought to have ended with technological advances the the sea canoe technology (for example the development of outriggers, improved navigational  techniques, and double hulled canoes.  In the lower panel of the figure below, the related-ness of the languages is tied to the map above by colour coding, and the pauses are indicated.

In the second paper, Moodley et al have analysed 212 H. pylori samples taken from Taiwanese aboriginals, New Guinean highlanders, Melanesians and Polynesians.  Seven genomic fragments were sequenced, revealing 196 haplotypes, which were compared with haplotypes from Europeans in Australia and other haplotypes derived from populations across Asia and the Pacific.

From my position of ignorance about linguistics, it would seem that sequence-based phylogeny reconstruction must be the easier of the two analyses (though I'm happy to be corrected on this).  The figure below shows the phylogenetic relationships between the H. pylori haplotypes (in B) and the geographic spread of samples (in A).

In addition, the global spread of H. pylori is assessed, clearly showing that the New Guinea and Australian colonisation was distinct from the much later colonisation of the Pacific.  What's quite striking is the correspondence between the two trees, as presented in the accompanying Perspectives article, which concludes with the hope that a sysnthesis of linguistic and genetic approaches may be possible on a global scale.

R. D. Gray, A. J. Drummond, S. J. Greenhill (2009). Language Phylogenies Reveal Expansion Pulses and Pauses in Pacific Settlement Science, 323 (5913), 479-483 DOI: 10.1126/science.1166858 Y. Moodley, B. Linz, Y. Yamaoka, H. M. Windsor, S. Breurec, J.-Y. Wu, A. Maady, S. Bernhoft, J.-M. Thiberge, S. Phuanukoonnon, G. Jobb, P. Siba, D. Y. Graham, B. J. Marshall, M. Achtman (2009). The Peopling of the Pacific from a Bacterial Perspective Science, 323 (5913), 527-530 DOI: 10.1126/science.1166083 C. Renfrew (2009). ANTHROPOLOGY: Where Bacteria and Languages Concur Science, 323 (5913), 467-468 DOI: 10.1126/science.1168953