Early humans may not have needed to continuously reinvent the proverbial wheel. A newly discovered cache of stone tools representing 11,000 years of human habitation suggests that perhaps human innovations didn't flicker in and out of early human history as once suspected, driven into obscurity by external pressures such as climate change. Instead, researchers suggest, at least some ancient humans apparently managed to pass an innovative type of stone tool down to their descendants. Other researchers welcome the additional evidence of ancient technological know-how, but say that other sites show that such technologies do indeed appear and disappear across human prehistory.
The new find amounts to a few dozen slivers of stone, slightly curved on one edge, that are only a few centimeters long on average. But they are tens of thousands of years old, and the product of the longest and most complex known manufacturing process devised by early Homo sapiens. The stone slivers, which were excavated from the Pinnacle Point caves on South Africa's southern coast, are actually sharp miniature blades that would've been incorporated into arrows or other projectile weapons. Crafting the blades, the researchers argue, was a long, painstaking process that included using a primitive kiln to heat the stone, making it easier to shape. Only humans who'd evolved sophisticated thought could've been up to the task, the researchers say.
"When we find these complex-recipe technologies, that's a signal that people have complex cognition," says paleoanthropologist Curtis Marean of Arizona State University, Tempe, and one of the paper's authors.
The 11,000-year timespan of the blades shows that this know-how was handed down from older to younger toolmakers. It "indicates populations were large enough … and people were smart enough to transmit technology between the generations consistently, over a long period of time," Marean says. That imparting of knowledge may have involved another innovation—language.
Over the course of 6 years of excavations at Pinnacle Point, Marean and his colleagues excavated a massive layer of sediment rich with objects made by ancient humans. Among the recovered items were tiny, sharp-edged chips of stone carefully blunted on one edge. The blunt edge was likely glued into a groove along an arrow shaft or into a projectile for an atlatl, a device for hurling a spear or dart. These blunted miniblades show signs of heat treatment, which was in use at Pinnacle Point as early as 162,000 years ago , according to previous research by some authors of the new paper.
The researchers determined the age of the blades by dating the sediments in which they were found. They used a technique known as optically stimulated luminescence , which measures how much time has passed since a mineral grain was last exposed to sunlight. The earliest blunted miniblades at the site are 71,000 years old; the most recent, 60,000 years old , the team reports online today in Nature.
The finding touches on a puzzling aspect of early human history in Africa, the place where anatomically modern H. sapiens—the species to which present-day humans belong—appeared roughly 200,000 years ago. Excavating at sites across Africa, scientists trying to pinpoint the beginnings of modern thought have found telltale artifacts such as shell beads and carefully engraved bones dating back at least 100,000 years. The makers of such objects must have been capable of symbolic thought, one of the signatures of modern human cognition.
But these relics have a "flickering" distribution: They appear at an ancient site, only to be absent from the archaeological record for thousands of years before reappearing again. Some researchers have taken this stuttering pattern to mean that humans repeatedly developed new technologies and rituals, only to lose them  under the pressure of factors such as climate change and shrinking populations.
Marean argues that his newest results help bury the idea that humans let their innovations slip away. More likely, he says, is that scientists have not explored Africa well enough to establish a continuous archaeological record.
The findings indicate "that this very advanced technology … doesn't have a flickering characteristic to it," he says. What's more: "Our results suggest that basically, what we have at 71,000 years ago is people like you and me."
Other scientists, however, have mixed views. Several said the paper's dating looks sound and that it's useful to know that this technology dates to 71,000 years ago, roughly 6000 years older than previously recognized. But it's not surprising to the experts to find evidence that the humans of 70,000 years ago were thinking and behaving like the humans of today. That's "a point of view that's fairly widely accepted," says Nicholas Conard of the University of Tübingen in Germany, who has done excavations at another South African cave.
Francesco d'Errico, director of research for CNRS, the French national research agency, attached to the University of Bordeaux, adds that other sites counter the paper's contention that blunted miniblades are an "enduring" technology. Excavations in South Africa's Border Cave, for example, found no evidence of such blades over a time span from 60,000 to 40,000 years ago, he says. Nor are there such blunted miniblades from 70,000 years ago at South Africa's Blombos Cave, which is close to Pinnacle Point.
"These people were submitted to selective pressure," d'Errico says. "They were creating innovations, they were losing innovations. … There were people who at some stage decided they did not want to produce these (blades) any more. They changed their technology."
Marean responds that it's worth pointing out that the people of 70,000 years ago had modern habits of thought, because many scientists think there must have been a major improvement in cognition aiding the human spread out of Africa 50,000 years ago. And he says that climate change, which made trees in southern Africa scarce around 60,000 years ago, helps explain why blunted miniblades are not seen at Border Cave : Wood is needed to heat-treat the stone. So the technology was temporarily put on the shelf.
Whether miniblade use was continuous or not, Marean says it gave its developers a huge advantage. A bow and arrow or an atlatl allows users to attack prey—and enemies—from a safer distance than does an ordinary spear. Such weapons, he says, would have helped modern humans dominate the world once they moved out of Africa.