Research throws new light on ancient artifacts

Professor Geoffrey Bingham and a team of former students and archeologists have thrown new light on a longstanding paleolithic puzzle: the purpose of the large number of spherical stone artifacts at a major archaeological site in South Africa, dating from 1.8 million to 70,000 years ago.

Published this August in Scientific Reports, the research drew on the framework and methods developed in Bingham’s Perception/Action Lab. Its lead author Andrew Wilson, now at Beckett Leeds University in England, was a former Ph.D. student in the lab, as was co-author Qin Zhu, now at the University of Wyoming. In tandem with Lawrence Barham and Ian Stanistreet, archaeologists at the University of Liverpool in England, the researchers concluded that the stones likely served as projectile weapons for hunting and defense before the advent of spears.

“Our research,” explains Bingham, “suggests that the throwing of stones played a key role in the evolution of hunting.”

Bingham has been studying the mechanics and function of this complex human action – throwing – and its potential role in human evolution. Over the years he and his collaborators have continued to develop their theories on this capability and to develop virtual simulations to measure the mechanics of the task.

Last year Wilson was delivering a talk on their most recent work, when Barham and Stanistreet approached him to discuss the ancient stones. Together they embarked on the project, analyzing a sample of 55 of the ballshaped stone objects from the South African site. 

Using Bingham, Wilson and Zhu’s research on “affordances,” optimal qualities of an object for throwing in terms of size, weight and shape at maximum distance, speed and damage, the researchers simulated the projectile motions the spheroids would undergo if thrown by an expert. These simulations were then used to estimate the probability of these projectiles causing damage to a medium-sized prey such as an impala.

Previous research has suggested that spherical stones were used as percussive tools for shaping or grinding other materials; however, most of the objects analyzed by the team had weights that produce optimal levels of damage from throwing, rather than simply being as heavy as possible.

“Imagine a human, searching for an object to throw so as to cause the most damage possible to potential prey or a competitor,” suggests Wilson. “This is a perceptual task: the person needs to perceive throwing-relevant properties of objects and be able to discriminate between objects that vary in those properties. Other research has shown modern humans to be exceptionally good at this task.”

“Humans are the only animals -- the only primates even -- with that talent,” Bingham adds. “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.”

“The ability to throw great distances,” he observes, “was not a small thing: it was how we got lunch.”