Human evolution wouldn’t be the same if our ancestors hadn’t learned to control fire. By harnessing fire, prehistoric hominins were able to cook food, unlocking extra nutritional value that allowed their brains to grow. This evolutionary turning point is still obscured by the question of when these hominins first used fire, but fossilized clues within a South African cave may provide answers.
A study published in PLOS One has found evidence that Homo erectus populations living at Wonderwerk Cave in South Africa likely used fire between 1.07 million and 1.79 million years ago. The cave dwellers maintained fires with an unexpected ingredient: regurgitated owl pellets carrying the bones of tiny mammals. Researchers found from their analysis of these now-fossilized bones that many were burnt, indicating that H. erectus may have repeatedly brought fire into the cave and placed it on owl pellets to keep the flames burning strong.
Read More: How Ice Age Humans Mastered Fire During the Coldest Era in History
Digging Up the Oldest Evidence of Fire Use
Wonderwerk Cave, occupied intermittently for 2 million years, has been a key site for understanding when human ancestors began using fire. Previous research at a layer of the cave referred to as Stratum 10, dated to about 1 million years ago, uncovered burnt bones, sediment, and ash together; this led archaeologists to propose that hominins had been controlling fire as early as 1 million years ago.
A return to Wonderwerk Cave in the new study, however, has yielded evidence that humans were likely using fire even earlier, between 1.07 million and 1.79 million years ago.
This time, researchers focused on the even older Stratum 11. To understand when H. erectus was using fire, they examined small mammal fossils that were once contained in owl pellets (dense balls of undigested fur, teeth, and bones from prey that owls have eaten). The researchers sorted the bones based on those that were non-burnt and those that were burnt.
Shining Light on Burnt Bones
Identifying whether a bone is burnt presents a significant challenge: the texture and color changes of a bone affected by fossilization processes can mimic a burnt bone.
To get the most precise results possible, the researchers used two complementary methods. The first is Fourier Transform Infrared spectroscopy (FTIR), a technique used to measure how materials absorb infrared light.
But since FTIR can’t document burning below the temperature threshold of around 998 degrees Fahrenheit, and char does not maintain its molecular structure past this threshold in an oxidizing environment, the researchers needed to use a second method that involved illuminating bones in high-intensity blue light; with the help of an optical filter that blocks shorter wavelengths and allows longer wavelengths of light to be observed, the researchers were able to observe the burnt bones glowing red, while the non-burnt bones didn’t emit any light.
“The methodology we have developed allows us to distinguish burned fossils from those that have undergone chemical alterations during fossilization, such as fluoridation or manganese deposits, which can visually mimic the effects of fire. We have improved the resolution with which we can identify burned fossils in very old contexts,” said study author Yolanda Fernández-Jalvo, a researcher at the National Museum of Natural Sciences in Madrid, Spain, in a statement.
Burning Owl Pellets
Based on the analysis of burnt mammal bones, the researchers concluded that H. erectus would take seasonal wildfires from outside and introduce them into Wonderwerk Cave.
They theorize that the cave’s floor was covered in owl pellets, since birds of prey have occupied the cave for almost 2 million years. H. erectus, they say, may have burned these pellets, with bones being left behind after the rest of the pellet was incinerated.
This burning of the owl pellets may have happened sporadically, although H. erectus didn’t necessarily know how to produce fire from scratch in these cases.
“The fire was not an isolated event because it appears in different stratigraphic levels, separated by tens of thousands of years, which reinforces the idea that they already knew how to transport and maintain fire in protected spaces,” said Fernández-Jalvo.
Read More: The Dawn of Fire: When Did Early Humans First Discover Fire?
Article Sources
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- This article references information from a study published in PLOS One: New evidence for Early Pleistocene use of fire at Wonderwerk Cave (South Africa)
