Has Australia Backdated the Human Revolution?

Article excerpt

Recently, two views have predominated about the peopling of Australia. For some workers, there were two original colonizations of the continent (Thorne & Wolpoff 1992; Frayer et al. 1993). An early one, originating from the archaic Homo erectus people of Java, introduced a robust population at perhaps 50,000 BP. This colonization event was represented by the Willandra Lakes human fossil known as WLH-50, and by subsequent populations sampled at sites such as Kow Swamp, Cohuna and Coobol Creek. A second colonization, supposedly derived from China, arrived via an eastern route and brought the more gracile people known from the Mungo fossils at about 30,000 BP and sampled at later sites such as Keilor and King Island. Under the dual-origin hypothesis, present-day Australian Aborigines were the result of Holocene hybridization between the robust and gracile peoples. A second, and contrasting, view saw the robust and gracile peoples as parts of a single morphologically variable population. Their differences probably developed within Australia following a single colonization event, with modern Aborigines representing the end product of this process (Pardoe 1991; Brown 1992).

Exactly when people first arrived in Australia has remained unclear. The site of Jinmium was recently claimed to have red-ochre use dating from about 75,000 BP, and artefactual evidence at perhaps twice that age (Fullagar et al. 1996). Such an early colonization could have been accomplished, it was argued, by pre-modern humans emanating from Java. However, the ancient luminescence dates obtained on the Jinmium sands have not been confirmed by subsequent analyses using luminescence and radiocarbon, which instead suggest that the site was only occupied within the last 20,000 years (Roberts et al. 1998). Nevertheless, two other sites do appear to contain artefacts dating from about 50-60,000 BP, based on luminescence dates (Roberts et al. 1990; Roberts et al. 1994; but compare O'Connell & Allen 1998). These are the rock-shelters of Malakunanja II and Nauwalabila I. However, in none of these sites were associated human remains preserved, thus leaving the nature of the first Australians uncertain.

Now, one of the Mungo fossils, the Mungo 3 burial (FIGURE 1), has been re-dated, using a combination of the techniques of gamma-ray uranium series dating on skull fragments, electron spin resonance on a piece of tooth enamel, uranium series on attached sediment, and optically stimulated luminescence applied to the sands containing the burial (Thorne et al. 1999). The dates obtained are about 62,000 [+ or -] 6000 BP, approximately double the ages originally estimated from radiocarbon (Bowler & Thorne 1976). It is as yet unclear how these new estimates impact on the age of the Mungo 1 cremated individual found nearby, and there will undoubtedly be critical debate about the accuracy of the new determinations, and how they relate to wider regional questions (O'Connell & Allen 1998).

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However, if these dates are indeed accurate, they imply that gracile people were the first inhabitants of Australia. This is because a related study dated skull fragments of the supposedly more archaic fossil WLH-50 by the gamma-ray method, obtaining a preliminary age estimate of only about 14,000 BP (Simpson & Grun 1998). Thus this specimen, and the other robust crania so far dated, all apparently succeeded the last glacial maximum which occurred at about 20,000 BP (Brown 1992). The sequence of morphologies supports the model of diversification within Australia, not derivation from separate ancestors. Otherwise, one would have to postulate the movement of gracile people through Indonesia into Australia by 60,000 BP, followed by the arrival of robust people from the same source region. Additionally, the description of the robust crania as archaic and Homo erectus-like (Thorne & Wolpoff 1992; Frayer et al. …