New fossil evidence suggests that modern humans arrived in Sumatra, Indonesia, between 73,000 and 63,000 years ago, before the catastrophic eruption of Mount Toba, reports a paper published online in Nature this week. Although previous genetic studies indicated that there was a modern human presence in southeast Asia more than 60,000 years ago, actual fossil evidence has been scant and circumstantial.
Lida Ajer is a Pleistocene cave in the Padang Highlands of Sumatra with a rich rainforest fauna, which was originally excavated in the late 19th century, yielding two human teeth. Kira Westaway and colleagues reinvestigated Lida Ajer, providing a secure identification that the teeth are characteristic of modern human and establishing a robust chronology using three different dating methods to determine the age of the fossils. They determined burial ages by dating the sediments using red thermoluminescence and post-infrared infrared-stimulated luminescence techniques, and bracketing ages using U-series dating of the associated cave formation.
Lida Ajer represents the earliest evidence of modern humans occupying a rainforest environment. The longstanding preferred route of modern humans migrating out of Africa had been along the coast, as marine environments would have offered favourable conditions for human sustenance. By contrast, rainforests - with their highly spaced, seasonal resources and nutritionally insufficient food - would have presented serious difficulties for human colonization. The successful exploitation of the rainforest environment would have required complex planning and technological innovations, which the authors’ data indicate existed in Asia well before 70,000 years ago.