Since the explorations of Alfred Russel Wallace and Eugene Dubois in the nineteenth century, Southeast Asia has been one of the world's focal points for studies of biogeography and biodiversity, human evolution and dispersal, environmental change, and the spread of culture, farming, and language. Yet despite its prominence, reliable chronologies are not available for many of the critical archaeological, evolutionary, and environmental turning points that have taken place in the region during the last 1.5 million years. In this paper, we discuss some of these chronological problems and describe how luminescence dating may help overcome them. "Luminescence dating" is a term that embraces the techniques of thermoluminescence (TL) and optical dating, which can be used to estimate the time elapsed since ubiquitous mineral grains, such as quartz and potassium feldspar, were last heated to a high temperature or were last exposed to sunlight. Luminescence methods have been successfully deployed at late Quaternary archaeological, paleoanthropological, and geological sites around the world, but not to any great extent in Southeast Asia. Here we describe the principles of TL and optical dating and some of the difficulties that are likely to arise in dating the volcanic minerals found throughout the region. We also outline several long-standing archaeological and paleoanthropological questions that are the subject of a current program of luminescence dating in Southeast Asia, and present recent dating results from Liang Bua in Indonesia and Bukit Bunuh in Malaysia. Keywords: luminescence dating, archaeology, paleoanthropology, Quaternary, Southeast Asia, Liang Bua, Bukit Bunuh.
Robust chronologies for the extinction of Homo erectus, the arrival of modern humans (Homo sapiens), and the dispersal of Neolithic peoples throughout Southeast Asia and Oceania are needed to assess general models of human evolution and dispersal worldwide. At present, the lack of adequate age control has created a deadlock between proponents of the "multiregional" hypothesis of modern human evolution, who argue that modern humans arose by evolutionary changes in earlier hominid populations in many parts of the Old World, and advocates of the "out of Africa" hypothesis, who hold the view that modern humans first appeared in Africa less than 200,000 years ago and then dispersed across the world, eclipsing all earlier hominid populations (Brauer and Smith 1992; Storm 2001; Stringer 2002, 2003; Templeton 2002). Reliable ages for the critical Homo erectus and early modern human sites in Southeast Asia (Figure 1) are needed to discriminate between these two models and their variants. The recent discovery of a new species of hominin (Homo floresiensis) from late Pleistocene deposits on the island of Flores in eastern Indonesia (Brown et al. 2004; Morwood et al. 2004) further highlights the key role of Southeast Asia in the story of human evolution --a tradition begun more than a century ago by Eugene Dubois (Shipman 2001).
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From a regional perspective, the present lack of a robust chronology for the major turning points in the Southeast Asian cultural and evolutionary sequences makes it futile to speculate on whether Homo erectus, Homo sapiens, and Homo floresiensis ever came into contact; what form any contact may have taken; what impact archaic and modern humans may have had on the landscape, fauna, and flora; and what effect major environmental changes (e.g., volcanic eruptions, such as the Toba explosion about 74,000 years ago) may have exerted on the resident human populations through modifications to the climate and habitat (Ambrose 1998; Oppenheimer 2002).
The reasons for these chronological conundrums are multifarious and often complex. For example, Swisher et al. (1994) reported [sup.40]Ar/[sup.39]Ar ages of 1.6-1.8 million years for hornblende crystals collected from volcanic units thought to be directly associated with early hominid remains at Sangiran and Mojokerto in central and eastern Java. …