A new theory put forward by a team of researchers may indicate the use of stone weapons by ancient humans from nearly 2 million years ago. The round stones, first excavated in South Africa’s Cave of Hearths 30 years ago, have been analyzed by a team of archaeologists, kinesiologists and psychologists, bringing them to the conclusion that the stones may have been used as throwing weapons.

The 55 mysterious spheroids, each about the size of a tennis ball and dated to between 1.8 million to 70,000 years old, have been found to be just the right size, weight and shape, to hit a target about 25 meters (82 feet) away when thrown.

"Our study suggests that the throwing of stones played a key role in the evolution of hunting," explained Geoffrey Bingham, a professor in the IU Bloomington College of Arts and Sciences’ Department of Psychological and Brain Sciences. "We don’t think that throwing is the sole, or even primary, function of these spheroids, but these results show that this function is an option that warrants reconsidering as a potential use for this long-lived, multipurpose tool."

Bingham’s team, tasked with the study of human perceptual capabilities and coordinated actions, evaluated the stones’ throwing affordance, using a variety of parameters that determine an object’s suitability for use as a projectile. The team’s research has found that the combination of the human shoulder joint and our perceptual capabilities are ideally suited to throwing objects at a distance of 20 to 30 meters.

"Humans are the only animals—the only primates even—with that talent," Bingham elaborates. "We can throw something to hit something else—like a quarterback throwing to the running back all the way down the field. That’s how in large measure we survived the ice ages. The available food was largely on hoof, or it was ‘mega-fauna,’ such as a mammoth. You don’t want to get close to them."