An analysis of 150 round, baseball-sized stones found at a site where early humans lived 1.4 million years ago shows that they were intentionally knapped into spheres. This rules out the idea that they became round after being used as hammers, but doesn’t tell us why they were shaped.
“Unfortunately, we still can’t be confident about what they were used for,” says Antoine Muller at the Hebrew University of Jerusalem.
Signs of ancient occupation at ‘Ubeidiya, in what is now northern Israel, were discovered in 1959. A few human bones and thousands of stone tools have been uncovered there. The site is thought to have been used by some of the first members of our ancestor species Homo erectus to move out of Africa.
The finds include nearly 600 stone balls made of flint, basalt and limestone. Similar discoveries have been made at many other early human sites dating as far back as 1.8 million years ago. The objects, known as spheroids, were made by knapping, but why this was done remains a mystery.
It has been suggested that they are a byproduct of the creation of other stone tools, or that they are stones deployed as hammers that became round as they were used rather than being deliberately shaped.
To test this idea, Muller and his colleagues scanned 150 limestone spheroids from ‘Ubeidiya, which are of varying degrees of roundness and around 8 centimetres in diameter, roughly the size of a baseball. They worked out the sequence of strikes responsible for each ball’s shape.
The researchers conclude that these spheroids required similar levels of skill and planning to make as hand axes, rather than being accidental creations. But the team can’t say if the same is true of any other spheroids, says Muller.
“Clearly, whoever made these objects was working hard to make them spheres,” says Andrew Wilson at Leeds Beckett University, UK, who in 2016 showed that the shape and weight of typical spheroids are suitable for throwing.
“To my mind, this certainly looks more like they were crafting projectiles than, say, hammers,” says Wilson. “I know from my work that these rocks would make good hunting weapons for a group of humans.”