Stone Age innovation out of Africa

Two phases of cultural development in southern Africa heralded Stone Age human migrations, a new study suggests.

Technological revolutions rocked our world long before the information age. Between 80,000 and 60,000 years ago, it was spurts of innovative toolmaking, rather than extreme climate changes, in southern Africa’s Stone Age cultures that heralded a human exodus out of Africa, a new investigation suggests.

Environmental changes in southern Africa, including those brought on by a massive volcanic eruption in Sumatra around 74,000 years ago, played a secondary role at best in instigating ancient cultural advances and intercontinental migrations, say geologist Zenobia Jacobs of the University of Wollongong, Australia, and her colleagues. Other researchers regard ancient climate fluctuations as key motivators of human movement out of Africa.

Jacobs’ team dated sediment at nine sites that have yielded remains of either of two key toolmaking traditions in southern Africa, known as the Still Bay and Howieson’s Poort industries. Still Bay tools were made by striking flakes off prepared pieces of stone for use as lance heads or skinning knives. Howieson’s Poort implements included small blades, scrapers and chisels. Symbolic artifacts and personal ornaments have been found with both tool types.

“Still Bay and Howieson’s Poort industries may be the southern African manifestations of a pan-African technological revolution that catalyzed human migration out of Africa,” Jacobs says.

Both industries flourished for brief periods, the scientists report in the Oct. 31 Science. The Still Bay industry only lasted from about 72,000 to 71,000 years ago. The Howieson’s Poort industry emerged around 65,000 years ago and ended shortly after 60,000 years ago. No known climate changes accompanied the rise of these ancient cultures, suggesting that such bursts of innovation were not responses to environmental change, the investigators propose.

Age estimates relied on measures of doses of ionizing radiation trapped in single grains of quartz from artifact-bearing soil. The method can determine how much time has passed since soil was exposed to light. The researchers calibrated those dates with earlier age estimates for the sites based on oxygen isotope data from Antarctic ice cores — providing more precise dates.

“This is the single most important geochronology paper on the origins of modern humans in the last 20 years,” remarks anthropologist Curtis Marean of Arizona State University in Tempe. Jacobs’ group provides the best estimates to date for the timing of the Still Bay and Howieson’s Poort industries, he says.

Other researchers have suggested that a time gap existed between these Stone Age cultures, notes anthropologist Teresa Steele of the University of California, Davis. But more surprising is the new study’s further suggestion that about 10,000 years passed between the end of the Howieson’s Poort industry and the start of ensuing toolmaking traditions in southern Africa, Steele says.

Jacobs’ new age estimates for the two ancient cultures may vary by as much as several thousand years in either direction, making it difficult to confirm that environmental changes did not inspire toolmaking innovations, she adds.

Evidence of a roughly 7,000-year gap between the Still Bay and Howieson’s Poort industries suggests that people left southern Africa during cold, dry episodes that regularly occurred as the last Ice Age approached, comments anthropologist Stanley Ambrose of the University of Illinois in Urbana. Genetic and linguistic studies indicate that those groups moved to eastern Africa.

Ambrose suspects the new dates for the two tool industries are slightly off, though. Ice cores such as those used by Jacobs’ team offer limited insight into the timing of ancient climate changes, he says. Sections of cores can only be dated by correlating geochemical markers in the ice with evidence from datable events elsewhere, he says.

A better set of comparison dates for Jacobs’ study comes from another Stone Age site in southern Africa, Blombos Cave, Ambrose asserts. Still Bay artifacts found there have been dated to between 77,000 and 74,000 years ago. If that’s true, then the Still Bay industry may have been cut short by a widespread ice age that followed a massive volcanic eruption on Sumatra 74,000 years ago, he hypothesizes.

When the Howieson’s Poort industry eventually got off the ground, it represented the first time that local bands in southern Africa expanded into a network of interacting groups, Ambrose holds. That not only sparked a huge increase in the long-distance transport of stone for tool making but enabled risky journeys out of Africa, in his view.

Jacobs doubts that the Sumatran volcanic eruption or any other climatic event directly affected ancient southern Africans’ cultures. Innovations in stone toolmaking may either have caused or resulted from population expansions and migrations within Africa, she says.

Scientists now need to gather data on local environmental changes in southern Africa to see if they correspond to the Still Bay and Howieson’s Poort industries, Marean suggests. “That is soon to come,” he says.

Bruce Bower

Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.

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