An ancient spear-throwing tool enabled prehistoric hunters to boost the distance they could launch a feathered projectile 鈥� but the unexpected negative effects of gravity on the tool may explain why it was never adopted by Neanderthals and some Homo sapiens groups.
The spear-throwing tool 鈥� which is known as an atlatl 鈥� is a handheld stick with a groove at the end for holding a projectile. It acts as a lever to amplify the projectile-flinging momentum that can be achieved by the human arm.
Researchers assumed that an atlatl-launched projectile and a hand-thrown javelin would both gain a velocity boost from gravity when hurled downward from a greater height 鈥� like how prehistoric hunters potentially launched projectiles from cliffs or trees down at prey animals below 鈥� but, in fact, only the javelin benefited from the height advantage.
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鈥淲e were thinking they would both see an increase due to gravity,鈥� says 聽at Kent State University in Ohio. 鈥淎nd then once we started observing and looked at the data we were like, 鈥榳ow, this is really different.鈥欌��
Bebber and her colleagues arranged for two team members to launch lightweight atlatl projectiles or heavier javelins while standing on a scissor lift set at increasingly greater heights, including 3, 6 and 9 metres. They used a high-speed camera to measure each weapon鈥檚 velocity and kinetic energy.
The hand-thrown javelins steadily gained in kinetic impact energy when thrown from the greater heights, with up to a 100 per cent boost at the 9-metre height compared with performance on level ground. But the kinetic impact energy of the atlatl projectiles generally declined as the throwing platform height increased, with around a 20 per cent reduction at the 9-metre height.
Steeper downward launch angles may be deactivating the atlatl鈥檚 lever motion and making it harder to exert throwing power with the tool, says Bebber. The thin and lightweight atlatl projectile may also be more susceptible to wind gusts or air resistance on the way down.
Such results may explain why Neanderthals who hunted in rugged terrain relied on javelins, says research team member , also at Kent State University. 鈥淭he lack of invention of the atlatl by Neanderthals is not any sort of fault or deficiency 鈥� they were actually using the optimal weapon for the hunting grounds that they pursued,鈥� he says.
The supposedly simpler javelin鈥檚 experimental performance 鈥渦nderpins why the javelin 鈥� or hand-thrown spear 鈥� was retained by Homo sapiens alongside subsequent innovations, and remains in use by small-scale forager societies today鈥�, says at the University of Reading in the UK.
Journal of Archaeological Science: Reports
