Using a newly developed technique that can detect signs of burning in fossilized bones, researchers identified repeated evidence of fire deep inside the cave. Because these traces were found far beyond the reach of natural wildfires, the findings suggest that early humans were deliberately bringing naturally occurring fire into the cave and keeping it burning.

The research was carried out through an ongoing collaboration led by Dr. Liora Kolska Horwitz of the Hebrew University of Jerusalem's National Natural History Collections (co-director of the Wonderwerk Cave project with Prof Michael Chazan, University of Toronto) together with an international team of scientists from Spain, Argentina, Canada, USA, South Africa, Portugal and Israel. The project combines archaeology, paleontology, geology, and other scientific approaches to investigate one of the most important developments in human evolution: the use of fire.

Earlier Evidence of Fire Use

The new study builds on earlier work at Wonderwerk Cave, located in South Africa's Kalahari Desert. In 2012, members of the research team reported evidence of fire dating to about ~1 million years ago (published by members of the team in 2012 in PNAS), which was considered the oldest known evidence of intentional fire use anywhere in the world.

Continued excavations and analysis have now extended that timeline. Researchers identified traces of fire use in archaeological deposits dating from 1.07 to 1.79 million years ago, making Wonderwerk Cave one of the oldest known sites associated with hominin fire use. The findings, published in PLOS One, provide new insight into how ancient human ancestors may have interacted with fire long before they learned how to produce it themselves.

Fire offered many advantages, including warmth, protection from predators, light after dark, and eventually the ability to cook food. Even so, determining when humans first began using fire has remained one of archaeology's most difficult questions.

"Evidence of fire from such ancient sites is often subtle and difficult to detect," said the Dr. Kolska Horwitz. "Our study provides new tools for identifying traces of ancient burning and reveals that fire was repeatedly present deep inside Wonderwerk Cave."

New Technique Detects Burned Fossil Bones

The study also introduces a new approach based on the light-emitting properties of burned bone.

When exposed to specific wavelengths of light, bones that have experienced intense heating produce a distinctive glow. Researchers combined this non-destructive luminescence method with established chemical analyses, allowing them to identify burned animal bones with a high level of confidence.

The technique is portable, non-invasive, and can be used on large fossil collections without causing damage.

To test the method, the team examined hundreds of tiny fossil bones left behind by owls that once roosted inside the cave. Because these remains accumulated naturally over time, they provide an independent, non-anthropogenic record of past events preserved on the cave floor.

Fire Deep Inside Wonderwerk Cave

The researchers discovered clear evidence of burning within an archaeological layer associated with early Acheulean artifacts, likely linked to Homo erectus. The burned remains were found approximately 30 meters inside the cave, far beyond the area that could have been affected by natural wildfires. They were also located in a layer that lacked guano deposits, ruling out spontaneous combustion as an explanation.

The evidence does not suggest that these early humans were capable of creating fire whenever they wanted. Instead, the findings indicate that they likely collected fire from natural sources, such as lightning strikes or wildfires on the African savanna.

According to the researchers, these ancient humans brought fire into the cave on multiple occasions and maintained it for a period before it eventually went out. The team also suggested that owl pellets may have served as fuel, which could explain why the tiny rodent bones contained within them show signs of burning.

Even so, the ability to transport fire and keep it burning inside a cave represents a major behavioral milestone.

"These discoveries show that early humans were not simply passive observers of natural fires," Dr. Kolska Horwitz explained. "They were actively engaging with fire and incorporating it into their lives."

A New Window Into the Origins of Fire

In addition to extending the timeline of fire use, the study provides archaeologists with a valuable new tool for exploring when and how humans first began using fire.

As scientists apply this technique to archaeological sites around the world, it could help answer long-standing questions about the origins and evolution of one of the most transformative technologies in human history.