It is well-known today that natural fires from lightning strikes occur much more frequently in warm conditions—whether in more temperate places or during warmer parts of the year. Similarly, lightning would have been much more prevalent during the warmer phases of the Pleistocene Epoch (which lasted from roughly 2.6 million years ago to around 10,000 years ago) than during the colder periods. If the Neanderthals lacked the ability to start fire themselves and could thus only obtain it from natural fires, then we would expect to find much more evidence of hearths during warmer periods and less during colder ones. Which is why it is likely that Neanderthals had not yet entered the third stage of interacting with fire. That technological development occurred either elsewhere or at a later time.

The evidence from Pech IV and Roc de Marsal clearly shows that the Neanderthals at these sites lived without fire not only for long periods but also during the coldest periods. This alone raises even more questions about how they were able to survive. There is no clear evidence that they could make clothing (although some researchers today seem to think Neanderthals were likely making some articles of clothing, even if they were very crude), so perhaps an old theory about Neanderthals—that they were really hairy—is correct. (This notion, from the early 1900s, was discarded in later decades because it was seen as dehumanizing Neanderthals.) It might also mean that they relied more on food—especially meat—that did not need to be cooked.

So while we are obligate fire users today—we could not survive without fire in some form—Neanderthals, according to our research, had no such dependence. Perhaps fire dependency arose later, in the Upper Paleolithic (40,000 to 10,000 years ago), and it is almost certain to have existed by the time agriculture developed at the beginning of the Neolithic period (roughly 10,000 years ago in the Middle East). But there is still much we do not know.

If chimpanzees can effectively interact with wildfires, can we assume that the same was true for some of the earliest hominins, such as Australopithecus afarensis? When did our hominin ancestors first start to collect burning material and carry it back to their campsites, as portrayed in Quest for Fire and as probably practiced by Neanderthals? And, of course, when did humans first learn how to make fire? These are just a few of the mysteries that remain unsolved.

The ability to take advantage of the properties of fire is one of the most important technological advances in our evolutionary past. What we are realizing now, however, is that it was not the result of a single accident or stroke of genius. It was, instead, a process that likely unfolded over hundreds of thousands of years. And for the Neanderthals, the process was punctuated by periods of intense cold in which, when the benefits of fire would have been greatest, they simply had to make do without it.