According to Sandgathe and his colleagues, hominids didn’t really master fire until around 12,000 years ago—well after Neanderthals had disappeared from the face of the planet (or merged into the human gene pool via interbreeding, depending on your view). Sandgathe and his colleagues excavated two Neanderthal cave sites in France and found, surprisingly, that the sites’ inhabitants used hearths more during warm periods and less during cold periods. Why on earth would Neanderthals not build fires when it was freezing outside? In “On the Role of Fire in Neandertal Adaptations in Western Europe: Evidence from Pech de l’Azé IV and Roc de Marsal, France,” Sandgathe advances the hypothesis that European Neanderthals simply didn’t know how to make fire. All they could do was harvest natural fires—those caused by lightning, for instance—to occasionally warm their bodies and cook their food. (This explains why Sandgathe found more evidence of fire from warm periods: Lightning is far less common during cold spells.)
Roebroeks and Villa think Sandgathe’s reasoning is flawed: After all, there isn’t evidence of fire at every modern human campsite, either, when you look at sites from the Upper Paleolithic period, which concluded about 10,000 years ago. “However, nobody would argue that Upper Paleolithic hunter-gatherers were not habitual users of fire,” they wrote in a response to Sandgathe et al.’s criticism of their work. Wrangham, meanwhile, thinks both Sandgathe et al. and Roebroeks et al. ignore some critical nonarchaeological evidence: his point that contemporary humans can’t survive on a diet of uncooked food. Accepting Sandgathe’s hypothesis, Wrangham wrote in an email, “means that the contemporary evidence is wrong, or that humans have adapted to need cooked food only in the last 12,000 years. Both suggestions are very challenging!”
Why on earth can’t scientists agree on whether people mastered fire 1.8 million years ago or 12,000 years ago? That’s a 150-fold difference. Well, figuring out who burned what, when, is not an easy business. For one thing, archaeologists can’t always tell what caused a fire: a volcano, for instance, a lightning strike, or hominid ingenuity. And even if there is clear evidence of hominid fire use—a hearth at a formerly inhabited cave, for instance—it’s almost impossible to tell whether it was created by people from scratch or merely stolen from a natural fire and then transported to a hearth, where it was kept alive as long as possible. Scientists call this kind of fire use opportunistic.
What’s more, even when people were creating fires, the evidence of said fires doesn’t always stay put. Ashes have a tendency to blow away instead of embedding themselves neatly in the archaeological record, while water can take evidence of fire from its original location and carry it someplace completely different. Then there’s human error: As Sandgathe et al. write in their discussion of the available evidence, “There are … examples where residues originally interpreted as the remains of fires are later identified as something else.” (I hate it when that happens.) At one site in China, for instance, layers of earth originally believed to be ashes were later revealed to be silt and unburned bits of organic matter.
Archaeological methods are improving, and they may well end up bearing out Wrangham’s hypothesis. In a paper published earlier this year, archaeologists used advanced techniques (known as micromorphological and Fourier-transform infrared microspectroscopy) to examine sediment and reveal evidence of fire at a million-year-old South African cave site.
Wrangham is also hopeful that other disciplines will provide evidence for his theory. “I suspect genetics will help,” he says. “If we can pin down the genes underlying the adaptation to cooked food, we may be able to date the control of fire close enough to settle the big question.”
“Sure, that would be pretty compelling evidence,” admits Sandgathe. But he’s hopeful that genetics will bolster his hypothesis: that Neanderthals survived frigid glacial periods not because they regularly used fire, but because they had thick body hair. “At some point someone may announce the discovery of the gene or genes that code for thickness of body hair, and so could answer that question,” he says.
Judging from the way things are going, this debate may rage on for a good while longer. And there is room for more than one right answer: It’s possible that different groups mastered fire independently of one another at different points in time. But laypeople can take comfort in knowing that, even if we don’t know yet who first mastered fire—our simple ancestors almost 2 million years ago, our more advanced cousins 400,000 years ago, or our direct antecedents about 10,000 years ago—there’s no doubt who holds the intellectual property rights to it today. We even put it in an oven and made it our own.