Sat, 17 Nov 2012 14:07 UTC
It was among early man's greatest technological feats: a fully engineered weapon that combined a wooden shaft, mixed adhesives and a stone that had been chiseled to a lethal point.
To many anthropologists, the creation of the stone-tipped, or hafted, spear was a watershed moment in human evolution. Not only did it amplify the killing power of early hunters, it also demonstrated clearly that they had developed the capacity for complex and abstract reasoning.
Pinning down this moment in prehistory has been difficult, however. It was long held that Neanderthals and Homo sapiens first lashed stone tips to spears 200,000 to 300,000 years ago. But a study published in Friday's edition of the journal Science contends that a third species, Homo heidelbergensis, developed the technology about 500,000 years ago.
For the record:
Ancient spears: In the Nov. 16 Section A, an article about the discovery of 500,000-year-old stone-tipped spears that were made by ancestors of modern humans said that researchers studied 13 stone artifacts uncovered in South Africa. They examined 210 ancient spear points and point fragments. -
Researchers based their findings on 13 stone artifacts uncovered in a sinkhole in South Africa's Northern Cape province.
To confirm that the triangular stones were in fact spear tips and not created through natural processes, the anthropologists created replica spears and used crossbows to fire them at animal carcasses. The chips and marks created during these simulated hunting sessions exactly matched those on the prehistoric artifacts, indicating the ancient marks could not have been caused by weathering or geologic processes.
"This changes the way we think about early human adaptations and capacities before the origin of our own species," said lead author Jayne Wilkins, a graduate student in the University of Toronto's anthropology department. "Neanderthals and humans did not independently invent the technology, but they inherited it from their last common ancestor."
Part of the difficulty in determining the precise time in which hafting was invented has to do with the limitations of dating technology. Radiocarbon dating has a range of only 50,000 years, so other, less precise methods must be used to date older objects.
In the case of the spearheads uncovered near the South African town of Kathu, researchers used radiation exposure dating techniques to estimate the age of a zebra tooth and soil samples unearthed at the site. These dating techniques determine roughly when materials were last exposed to sunlight or heat, before they were buried.
Although anthropologists had until now lacked direct dating evidence, many had considered it possible that Homo heidelbergensis had developed their own hafting technology. Fossil records show that brain size in human ancestors increased dramatically about 500,000 years ago.
"It's not a revolutionary conclusion," said Thomas Wynn, a University of Colorado anthropologist who was not involved in the study.
Wynn, who studies cognitive evolution, said it would have been interesting to know what the spear makers used to fix the stone point to the shaft. In many cases, early humans used substances like acacia gums or beeswax mixed with ocher and then heated over flame to glue the stone point to the shaft. In other cases, the wood was soaked or notched to help fix the stone, and some methods involved the use of a sinew as a tied fastener.
No matter what method was used, Wynn said, it is clear that those elements were not combined accidentally, and that a great deal of thought, testing and refinement had gone into building such a device.
"I don't know whether I'd compare it to putting a man on the moon, but in some senses it may have been more significant evolutionarily because it really upped the arms race," Wynn said. "If you look at it from the point of view of humans and animals, the penetrating power was much greater, the killing power was much greater and the payoff was much greater."
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