A new analysis of microscopic fractures on spear points provides the first empirical evidence that America's first hunters really did use spear-throwers, sometimes called 'atlatls', from an Aztec word for the device.
     Stick-like tools that contained a hook or spur at one end to hold a dart, atlatls can be used to propel flexible, pointed shafts at high speeds across long distances with greater force. Archaeological evidence indicates that hunter-gathers in the Old World used spear-throwers beginning at least 18,000 years ago.
     Archeological evidence for spear-throwers in North America has been lacking because these tools were often made of wood, which doesn't preserve well. In comparison, ancient spear-throwers from Europe were often made of ivory or bone.
     However, study author Karl Hutchings, an archaeologist at Thompson Rivers University in Canada, says that if a spear point hits a target hard enough, the energy of the impact will cause the tip to break, and that, "When it breaks, it sends a shock wave through the stone that produces fractures, which are related to the amount and kind of force involved." Analysing the fractures present in hundreds of spear points looking for clues that the tips endured high-velocity impacts, Hutchings calculates how quickly the fractures spread through the material.
     Hutchings determined the fracture velocities for 55 out of 668 Palaeo-Indian artefacts that he examined. Of these, about half exhibited fracture velocities that can only be achieved using an atlatl and dart, or a bow and arrow. Because Palaeo-Indians aren't thought to have had bows and arrows, the findings suggest that they most likely used atlatls.
     The method may allow scientists to trace the origin of technologies across societies and continents. "We can get a better resolution of when these technologies occurred, how they spread and why they spread," Hutchings concludes.

Edited from LiveScience (28 January 2015)