When did humans discover how to use fire?

Fires blazed the way for humans to evolve into the species we are today. Scientists suspect that without a control over fire, humans probably would never have developed large brains and the benefits that come along with it. But when did humans first discover how to use fire?

"That's a tricky question," said Ian Tattersall, a paleoanthropologist and curator emeritus of human origins at the American Museum of Natural History in New York City. "Maybe the evidence for fire doesn't preserve very well, and what we're seeing is just the remnants of what was previously a much more rich record. But again, that's guesswork. We don't know."

What experts do know is that around 400,000 years ago, fire started popping up much more frequently in the archaeological record across Europe, the Middle East, Africa and Asia, according to a 2016 review article in the journal Philosophical Transactions of the Royal Society B. Experts consider these fires to be widespread, though sites with evidence are still relatively scarce.

Related: How smart were the Neanderthals?

At least two isolated sites show earlier humans using fire before 400,000 years ago, Tattersall said. For instance, at a site in Israel, dating back about 800,000 years, archaeologists have found hearths, flint and burned wood fragments, according to a 2012 study in the journal Science. At another site, this one called Wonderwerk Cave in South Africa, scientists found evidence that humans used fire about 1 million years ago, according to a 2012 study in the journal Proceedings of the National Academy of Sciences. In that cave, they found remnants of burned bone and plants and what appear to be hearths. 

"Where the evidence is coming from in the site is really far back into the cave," said Sarah Hlubik, a paleoanthropologist and postdoctoral researcher at George Washington University in Washington, D.C. "Even a landscape fire that's sweeping around isn't going to reach that far back." In other words, there's little chance that the data's a fluke, even though it is isolated in space and time.

Though Wonderwerk is the earliest site where most experts agree humans used fire, in theory they should have been using it much earlier. Around 2 million years ago, the gut of the human ancestor Homo erectus began shrinking, suggesting that something such as cooking was making digestion a lot easier. Meanwhile, its brain was growing, which requires a lot of energy. "Where else would you get the energy from without using fire to cook food?" Tattersall told Live Science, referring to cooking meat and vegetables.

To back up that argument, Hlubik is looking for signs of ancient controlled fires at sites in Koobi Fora, a region in northern Kenya that's rich in paleoanthropological remains dating back about 1.6 million years. So far, she has found burned bones clustered with other artifacts there. Burned sediment was clustered separately, suggesting that there was one area for maintaining fire and another area where ancient humans spent most of their time. 

"At this point, I'm confident to say, 'Yes, there was fire that was being used by people on this particular site,'" Hlubik said. "The next phase of the research is to then say, 'How many other sites in the region also have fire evidence?'" 

But not all experts agree with Hlubik. The fires at the site she excavated may not have been started by humans. It's possible the evidence could stem from bushes that were torched by natural wildfire.

Whenever fire use did arise, humans' ability to capture and control wildfires — or create fires of their own — had massive impacts on the species' evolution. It probably lengthened life spans, made humans more social by giving them a place to gather around and, along with the invention of clothing, helped them move into colder climates, Tattersall said. Using fires also likely increased human cognition, Hlubik added. "The benefits from using it reinforce the cognitive gains that you've already gotten and then create more. Because fire is a complex thing," she said. "You can get very hurt if you're using it incorrectly."

Originally published on Live Science.