If you’re here to find out why prehistoric butchers were believed to to be so tough that they’re imagined as having rock-hard testicles, you’ve come to the right place. If you’re looking for an explanation for the mysterious 2-million-year-old hand-sized stone balls that have been found around the world, you’re also in the right place. If you’re not a fan of prehistoric double-entendres, send your complaints to archeologist Ella Assaf of Tel-Aviv University for discovering who first had these stone balls, why they held them and what their relationship was to bones.

“The presence of shaped stone balls at early Paleolithic sites has attracted scholarly attention since the pioneering work of the Leakeys in Olduvai, Tanzania. Despite the persistent presence of these items in the archaeological record over a period of two million years, their function is still debated.”

As described in her study published in PLOS/One, Ella Assaf led a team of researchers studying a set of 29 stone balls discovered in Qesem Cave, a Lower Paleolithic archeological site 12 km (7.4 miles) east of Tel Aviv occupied by early humans between 400,000 and 200,000 years ago. These hand-sized stone balls were similar to those found around the world in similar sites – many far older than this one. All but one were dolomite or limestone, indicating they were brought to the cave from somewhere else. Out of the 29, 10 stood out because they showed evidence of unusual wear and residue in their visible ridges. An analysis using digital stereomicroscopy and metallographic microscopy revealed the surprising cause of both.

“Archaeological residues have morphological features, appearance, colour, and distribution compatible with compact and spongy bone, organic bone glossy film, collagen fibers, and animal fatty matters observed on experimental stone balls used in bone marrow extraction activities.”

So, the stone balls were used by prehistoric butchers to break open animal bones for easy access to the high fat marrow inside. To prove this, the researcher created similar balls and used them on cow and sheep bones. Smooth balls didn’t work well, which suggested that the ridges in the prehistoric balls might be there intentionally. Sure enough, grinding ridges it the modern ones not only opened the bones more easily but also made cleaner breaks. Finally, the balls had a shiny layer which indicated they had been used outdoors for some other purpose before the residents of Qesem Cave found them and brought them to the cave for butchering activities.

That explains the stone balls in Qesem Cave. Were all of the stone balls found around the world in the same period used for the same purpose? That’s likely, although more study is needed using Assam’s findings. Bone marrow’s high fat content fed more calories to the early human brains, allowing them to evolve quickly, walk upright, develop fire and more sophisticated tools, etc.

Some things never change. Just like our Paleolithic ancestors, success comes not from having the biggest balls but from knowing how to use what you have.