Disease in history: The case of the austronesian expansion in the Pacific

Abstract

The expansion of speakers of Austronesian languages during the last 6000 years, from a homeland in Taiwan or the adjacent parts of mainland China, thousands of miles across the Pacific Ocean to Hawaii, New Zealand and Easter Island, and across the Indian Ocean to Madagascar, is the most extraordinary migration in history (Fig. 22.1). This chapter differs from others in this volume in focusing on a predominantly maritime landscape, peppered with thousands of islands. The Austronesian expansion has generated a great deal of controversy over the last 30 years or so. An interdisciplinary debate is taking place in which it is necessary to evaluate and accommodate the contributions of several different subjects, especially archaeology, linguistics, and genetics. The focus of the debate has been on attempts to relate the historical expansion of the Austronesian language family, which displays its greatest diversity in Taiwan (Blust 1995), to the prehistoric people who spread the so-called Lapita cultural complex (Spriggs 1984; Bedford 2003)-named after the type site in New Caledonia-and to the population history of the region as suggested by modern genetic and molecular analyses (Cox 2003). A number of different models have been proposed to relate the various categories of evidence. The "express train" and the "slow boat" models of human population movement have been widely discussed, as well as various intermediate models which incorporate elements of both of the two extremes (Gibbons 2001). Of these models Green's "Intrusion/Innovation/Integration (Triple I) model" is probably the most popular way of explaining the origins of the Lapita cultural complex among archaeologists today (Green 1991). It is not feasible to discuss all the various theories in detail here. Nevertheless the position adopted in this chapter is that the totality of the evidence of archaeology, of human genetics, of historical linguistics, and of the phylogenies of microorganisms that attack humans in Pacific populations, all agree in supporting an expansion out of Taiwan (or possibly the neighboring Fujian province of China) within the last 6000 years, punctuated by pauses in which Austronesian populations interbred to some extent with non- Austronesian populations, especially in the coastal areas of New Guinea and neighboring islands, before moving on again towards Polynesia (Gray et al. 2009; Moodley et al. 2009). The alternative "slow boat" theory (Oppenheimer and Richards 2001), which posits the origins of the Austronesian peoples in island south east Asia over a much longer timescale dating back to approximately 17,000 years ago, depends on a method of dating human genetic data which has recently been shown to frequently give unreliable results (Cox 2008) and is otherwise unsupported by evidence. Many environmental factors have been introduced into the debate. For example it has been suggested that changes in sea-level in the mid-Holocene, affecting the resources available in coastal habitats, compelled people to search for new homes, leading to the spread of the Lapita cultural complex (Gibbons and Clunie 1986; Dickinson 2003; Cabioch et al. 2008; Pope and Terrell 2008). The role of the spread of farming and the subsequent transformation of landscapes by farmers has also played a major role in the debate (Bellwood 1975). In general the various environmental factors are not necessarily mutually exclusive; the overwhelming balance of probability is that a comprehensive explanation of the Austronesian expansion would have to incorporate several different factors. This chapter concentrates on one factor, the role of some of the smallest inhabitants of the landscape, namely pathogenic microorganisms. Several different studies have demonstrated the utility of pathogens as a proxy tool for investigating human population history in the Pacific. For example the phylogeny of Pacific populations of the JC polyomavirus suggests that the spread of this rapidly evolving DNA virus follows and parallels the spread of its human hosts, albeit on timescales that are the subject of debate (Yanagihara et al. 2002; Takasaka et al. 2006; Kitchen et al. 2008). Similarly the phylogeny of strains of Helicobacter pylori, implicated in stomach ulcers and gastric cancer, has proved to be a very useful tool for following the spread of human populations across the Pacific. The strain HpSahul, found in Australian aborigines and New Guinea, diverged from the Asian populations of Helicobacter pylori 17,000-37,000 years ago (the statistical methods used in phylogenetic analysis can only yield a range of variation, not absolute dates). However, HspMaori (a subpopulation of the HpEast- Asia strain) has its greatest diversity among Taiwan aborigines and was spread to Melanesia and Polynesia later, accompanying the Lapita migrations (Moodley et al. 2009). Such studies are potentially possible in relation to other diseases as well. For example, the balance of strains of tuberculosis that occurs among the Taiwan aborigines is different from that among Han Chinese settlers in Taiwan (Dou et al. 2008). Filariasis is another very important disease in the Pacific which has been studied in relation to prehistoric human migrations (Pichon et al. 1982). These examples show that pathogens have followed the differentiation of human populations in the Pacific into different environments and habitats. Malaria is one disease that has greatly affected Indonesia and other islands in the western Pacific area. © Springer Science+Business Media B.V. 2010.