Human ancestors used fire earlier than thought, study says

The glow of a campfire.
(Allen J. Schaben/Los Angeles Times)

Flame-bearing Prometheus may have visited humans earlier than we thought. An analysis of charred bones and plant ash in sediment from a South African cave suggests that Homo erectus was wielding fire a million years ago — and perhaps even cooking with it, according to a study released Monday by the Proceedings of the National Academy of Sciences.

The findings present the earliest clear evidence of such use of fire, experts said.

The ability to control fire marks an evolutionary turning point: It would have kept our ancient relatives warm in unforgiving climes and allowed them to cook their food, releasing trapped nutrients and getting more caloric bang per bite.

“Fire is more than simply a pleasant luxury — we have pretty good evidence that it was the basis for a tremendous number of changes in human evolution,” said Richard Wrangham, an evolutionary anthropologist at Harvard University who was not involved in the study.

The ability to cook food, Wrangham says, would have allowed early humans to spend less time looking for food and given them more expendable energy. It could help explain, among other body changes, why human teeth became smaller — less need to spend time chewing. It could have reduced the time between births, allowing for population growth, and perhaps allowed for the development of a larger brain.

But it’s unclear who lighted the first man-made flame. Convincing evidence for the habitual use of fire goes back nearly 400,000 years, coinciding with both archaic Homo sapiens and Neanderthals. Some scientists believed that fire must have been in use much further back in time, while others remained doubtful.

To look for earlier evidence of burning, an international team led by archaeological scientist Francesco Berna of Boston University studied the sediments in Wonderwerk Cave in the Northern Cape province of South Africa. Among the bits of rock, team members found plant ash, probably from burned twigs and grasses used to fuel the flames, as well as charred bone fragments.

But it’s difficult to tell — with the naked eye, at least — whether a grayish bone turned that ashy color because it was cooked or because it was mineralized. So the researchers put the bone fragments under a microscope and shone infrared light on them, to get more information about the bone’s mineral structure.

Bones are filled with a mineral called hydroxylapatite, which gives them their strength. It forms in tiny plate-like crystals that slowly fuse together as an old bone is fossilized. When a bone is heated to high temperatures, however, the crystals change shape, growing into large needles rather than small plates.

The researchers found that the bone fragments indeed contained the large-needled crystals rather than the more conventional plate-like patterns. Based on their analysis, the bones had to have been heated to more than 750 degrees Fahrenheit.

The results caught Berna by surprise. “I needed some time to convince myself — and then I needed some time to convince my colleagues,” he said.

The fact that the burned bones were discovered about 100 feet deep inside the cave was further indication that the charred matter was probably not the result of a wildfire, but had been intentionally burned by humans within the cave, perhaps for heat and for cooking.

Though the scientists can’t say who exactly lighted those fires, the most likely suspect would be Homo erectus, thought to be the longest-surviving of the early human relatives. There are even burned bits from the cave that indicate fire use goes back 1.7 million years, Berna said — although it’s far too early to say that for sure, he added.

There are a few caveats, however. A burned bone isn’t automatic evidence of cooked meat — those cave-dwellers could have eaten the flesh raw and then tossed the bones in the fire, Wrangham said.

And, Berna admits, the research team found no actual stone-encircled hearths in the cave, which would have been the archaeological equivalent to a smoking gun.

But the evidence is mounting that hominin species used fire well before the era of modern humans, researchers said. And this may fundamentally alter our perception of our ancestors’ intellectual capability, physiology and evolutionary success — and how that relates to our own.

“If you can say, ‘Sorry, Homo sapiens, you didn’t invent fire,’ it kind of changes how we view our place and what defines us,” said Chris Organ, an evolutionary biologist at the University of Utah who was not involved in the study.