Archaeologists working at South Africa’s famous Wonderwerk Cave have uncovered the strongest evidence yet that early humans were using fire deep inside caves nearly 1.8 million years ago, pushing back the timeline for controlled fire use by hundreds of thousands of years.
The findings, published in the journal PLOS One, centre on tiny burnt animal bones recovered from two Early Pleistocene layers at the site.
Researchers say the evidence suggests early Acheulean hominins — most likely Homo erectus — deliberately carried fire deep into the cave on multiple occasions, rather than the burning being caused by natural wildfires spreading into the site.
The study builds on earlier discoveries at Wonderwerk Cave, already considered one of the world’s most important prehistoric sites for early fire use. In previous work, evidence of burning in a layer dated to around one million years ago was found. The new research extends that chronology even further, with evidence from a deeper layer dating to perhaps 1.07 million years ago, or earlier.
Wonderwerk Cave has long fascinated archaeologists because of its remarkably preserved record of human occupation dating back almost two million years. Unlike many open-air African sites where natural bushfires may complicate interpretations, the evidence at Wonderwerk comes from deposits that are only 30 metres deep in the cave—far from the reach of wildfires.
The new study examined 161 fossilised micromammal bones recovered from the cave’s archaeological layers. Many of the bones were left behind by barn owls whose pellets were deposited on the cave floor over thousands of years. These pellets might indeed have been combustible when early humans brought fire into the cave, according to the research team.
To determine if the bones had indeed been burnt, the scientists used Fourier Transform Infrared Spectroscopy (FTIR) and a new luminescence technique developed in forensic science.
The method uses a specialised blue light and optical filters to detect thermal changes in bone that are invisible under normal lighting conditions. Burnt bones produce a reddish glow when viewed through the filters, while unburnt bones do not.
Researchers say the approach is fast and non-destructive in identifying early burning events and could change the way we think about the late fire use at archaeological sites worldwide.
The team tested the method on fossils from Wonderwerk Cave as well as experimentally burnt modern bones and archaeological objects from a Bronze Age site in Spain for comparison. The luminescence analysis results were in line with FTIR tests.
Importantly, the researchers found strong evidence for burning in both Stratum 10 and the older Stratum 11 deposits at Wonderwerk Cave. In Stratum 11, every white and grey fossil bone tested positive for burning using both methods.
In addition to this, the researchers found distinct clusters of burnt remains within the cave, suggesting that fires were not random events but repeated activities occurring in specific areas over long periods of time.
Although the findings suggest early humans were bringing fire into the cave, the researchers say there is still no evidence these hominins were capable of creating fire themselves. They were probably fed fire naturally from wildfires and maintained it for limited periods.
The ability to use fire is seen as one of the most crucial developments in human evolution. Fire provided warmth, protection from predators and extended daylight hours and eventually cooking enabled humans to develop better nutrition and brain development.
When did humans first learn to control fire, however, is still one of the most fiercely argued questions at present one of archaeology’s most eagerly debated ones.
Some of the oldest evidence of fire use was found in Kenya and South Africa dating back to around 1.5 million years ago, but many of those discoveries remain controversial because natural fires cannot be ruled out.
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Sources : PLOS ONE – https://doi.org/10.1371/journal.pone.0347480
