Free Lone Survivors by Chris Stringer Page A

that contained either both industries or one or the other. The results were striking: rather than spanning periods of 50,000 years or more, as some other methods had suggested, both the Still Bay and the Howiesons Poort industries were rather brief cultural episodes that seemingly appeared and vanished quite suddenly over large areas of southern Africa. Remarkably, the Still Bay lasted only a few millennia, around 72,000 years ago, while the Howiesons Poort appeared around 65,000 years ago, ending abruptly at about 60,000 years. Moreover, the people who succeeded the Howiesons Poort only returned after a gap of a few thousand years and were making more conservative Middle Stone Age tools (comparable to the Middle Paleolithic of western Eurasia), apparently without the innovations of their predecessors.
    It is, of course, possible that the manufacturers of the previous industries did not disappear but simply moved to locations that have not so far provided any archaeological records. (For example, they might have relocated farther out on the coastal shelves, which are now submerged.) But they do not seem to have reappeared even at a later date, suggesting that these really were brief episodes, like a light turning on and then being extinguished, perhaps forever. Environmental deterioration in the face of rapid climate change has been invoked to explain these episodic patterns, and I will return to their significance in chapter 8. Meanwhile, I would like to examine a global event that has controversially been claimed to lie behind even wider changes in human populations and behaviors, including the innovations of the Still Bay industry: the eruption of the Toba volcano in Sumatra.
    About 73,000 years ago, the large island of Sumatra in Indonesia was the source of the most powerful volcanic eruption of the last 100,000 (some calculations suggest 2 million) years. The eruption was about a thousand times larger than the famous Mount St. Helens in Washington State in 1980, and it expelled the equivalent of about 1,000 cubic kilometers of rock in the form of ejecta of many different sizes, as well as huge volumes of water vapor and gases. Thick ash deposits from the eruption were found in cores stretching from the Arabian to the South China seas, and some archaeological sequences in India are interrupted by ash falls several meters thick. The undoubted scale of the eruption led to some sensational claims about its effects on the Earth through a resultant “volcanic winter,” where the whole planet would have lacked summers for many years, as a result of clouds of dust and droplets of sulphuric acid residing in the upper atmosphere. The resultant drop in temperature and the lack of summer sun would have devastated plant growth and everything that relied on it, including the early human populations of the time. Some suggested it destabilized the Earth’s climate for a thousand years, or that it even triggered a global ice age, shrinking human numbers to only a few thousand people. On the other hand, studies of faunas in southeast Asia, closest to the eruption, suggested that any effect was minor and short-lived, since they were not devastated. Moreover in India, archaeological sequences studied by Mike Petraglia and his colleagues similarly indicate that the impact on human populations was not severe. I have been very cautious about Toba’s effects on humans globally. (After all, the Neanderthals living in temperate Europe and the Hobbit living in Flores in Indonesia, as well as our ancestors in Africa, certainly survived the effects of Toba somehow.)
    However, two recent studies by Alan Robock and his colleagues and Claudia Timmreck and her colleagues, using different models of its effects around the globe, do point to a severe, if shorter-lived, impact. Their work did not back up the idea that it could have triggered a glacial advance, but did conclude that it could have produced up to a decade of cold, dry, and dark