The homo sapiens mental revolution took place between 100,000 and 40,000 years ago, following the development of grammatical speech. But Homo erectus was pretty smart already judging by evidence that fire had been discovered over 1.6 million years ago. Could fire really have been such an early discovery?
Ever watched a bunch of grown men try to light a campfire? Dancing around a tottering pile of wood with spluttering matches and singed fingers. Huffing and puffing to turn a faint glow into a proper flame. Filling the air with pagan curses and eventually, perhaps, choking clouds of smoke. Humans seem adapted for many things. Our brains and bodies are designed for talking, spear throwing, handling tools and communal living. But lighting fires just ain’t on that list.
New evidence, however, suggests that human exploitation of fire may be quite incredibly ancient, going back some 1.6 million years. Recently developed forensic techniques are strengthening the case that some long-disputed fire remains found in Kenya, East Africa, were indeed kindled by our ancestors. And dramatic new findings show evidence for the presence of fire at other sites including the famous Olduvai Gorge in Tanzania--the missing link in the eyes of many fire researchers. Scientists are now planning to go back to Africa to reopen old excavations in the hope of ending once and for all the controversy about the origins of fire.
Within palaeoanthropological circles, there will be many fingers crossed hoping the latest findings just aren’t true. This is because hominid control of fire at 1.6 million years poses huge problems for current thinking about human evolution. The story goes that technologically sophisticated humans arrived with a "big bang" only about 40 000 years ago, with the development of grammatical speech. If the very early date for the control of fire holds up, then either we have to believe that kindling a roaring blaze is essentially--indeed literally--a pretty dumb skill. Or else we must be willing to upgrade the mental abilities of our forebears rather considerably.
The dating of the origins of fire got off to a false start in the 1940s when the pioneer fossil hunter, Raymond Dart, reported finding blackened animal bones near some 3 million year old hominid remains in a South African cave. Ironically, a lingering Victorian distaste at being descended from the apes meant scientists were happy to push the development of both fire and language as far back into the mists of time as possible. So this ancestor was quickly dubbed Australopithecus prometheus--the giver of fire.
The burning eventually turned out to be just mineral staining. But in the 1970s and 1980s, further tantalising evidence of campfires was uncovered at Koobi Fora and Chesowanja in Kenya. At both sites, archaeologists found the bones and stone tools of Homo erectus--the first hominid species to have a markedly larger brain and fully human-proportioned body. At Koobi Fora, the excavations also uncovered a scattering of ten small, half-metre diameter, "lenses" of baked orange earth dating to around 1.6 million years ago. At Chesowanja, there was just a single lump of baked earth, about 1.4 million years old, that had broken up and washed down a stream bank. Given the close association between bones, tools and burnt patches of ground, the researchers proclaimed here was the true Homo prometheus.
Jack Harris of Rutgers University, New Jersey, who was at Koobi Fora, remembers they only twigged the significance of the discoloured earth when they saw that local tribespeople left exactly the same lens-shaped burnt patches from their overnight campfires. For Harris, the find explained a lot about Homo erectus. Unlike earlier hominid species who appeared to be hugging the cover of Africa’s Great Rift Valley, erectus was using fire to move out into the more open highlands in search of big game.
"At night, a fire would have helped keep the other large carnivores at bay," says Harris. "But it also gets down to zero on the side of the Rift. You’d need a fire so as not to freeze to death at that elevation." He believes that even discounting the many other possible benefits of fire, such as cooking, preserving meat, smoking out game, hardening wooden tools, or driving away biting insects, its control would have been critical to the way erectus managed to break out and start to move around the world. Homo erectus eventually spread through Europe and Asia--good going for a hairless, rather defenceless, warm-adapted, great ape.
While a few of Harris’s fellow researchers were convinced, others said not so fast. The "burnt" patches of soil could be the result of bushfires, lightning strikes, puddled iron deposits or even a weird fungus. There was no corroboration in the form of ash, hearth stones, fire-lighting tools or food remnants. But more than this, controlling fire simply seemed too intellectually sophisticated a feat for this creature. After all, Homo erectus had only just emerged 1.6 million years ago, it was a primitive toolmaker and showed no signs of symbolic thinking over the million years or more of its existence.
Harris’s assertions just didn’t fit with the "big bang" theory of human mental evolution, which paints us as nothing more than smart, bipedal apes for the first 4 million years. While we grew steadily bigger in body and brain, we made meagre advances in lifestyle and tool use. The theory goes that the human race only took off around 40 000 years ago, when one branch of our hominid ancestors developed the capacity for a highly structured form of vocal communication. Overnight we were transformed into modern Homo sapiens--a species driven by language and culture. There was an explosion in our potential for symbolic thought and self-awareness which brought with it a matching explosion in art, tool-making and social complexity.
Throughout the 1980s and 1990s, such thinking led palaeoanthropologists to downgrade Homo erectus at every turn. Rather than big game hunters, it was felt more likely they were mere carcass scavengers, coming somewhere between hyenas and vultures in the savannah pecking order--that is if they even ate meat rather than just scrounging for nuts and locusts.
Even their characteristic hand axes--the tear-drop shaped flints that were the hallmark of erectus--became a badge of inferiority. Originally, the hand axe had suggested these hominids were thinkers and planners. Rather than picking up the nearest shard of smashed rock, they must have travelled long distances to find the right grade of stone and then patiently crafted it according to some mind’s eye model. But by the 1990s, anthropologists were arguing that the axe shapes might be purely accidental--they were the core, the bit that got chucked away, after a succession of simpler flakes or scrappers had been knocked off round the perimeter. And even if Homo erectus was deliberately manufacturing the hand axes, the same old style was then churned out for the next million years with little further refinement. These hominids were not innovators.
This doubting attitude was also applied to the question of fire. If erectus had managed to master the simple campfire so early, then why was this never taken to the next level? Why not the rapid appearance of hearths, firestrikers and positive signs of cooking. And why such a suspiciously patchy record of fire use? At least hand axes were found at nearly every dig. But burnt earth was found at just a few isolated sites. No, more likely that these erectus guys really were mute dunces and the baked earth the remnant of some long ago bushfire.
There the matter lay until quite recently when a more detailed picture began to emerge and the pendulum of opinion started to swing again.
First off, research showed that the baked earth lenses were indeed the result of fire. Ralph Rowlett of the University of Missouri-Columbia in Missouri, working with colleagues, made a detailed analysis of a cluster of four possible campfires found at a single large excavation at Koobi Fora. Thermoluminescent dating--which relies on the radiation clock of an earth sample being reset by exposure to heat--proved that the discoloured ground was "newer" than surrounding ground, and so not likely to have been produced by mineral staining, fungus or some other non-thermal cause. Rowlett also ruled out lightning strikes by examining the site of genuine strikes and showing that lightning creates not much more than coin-sized pits together with characteristic lumps of fused earth known as fulgerites.
So, campfire or bushfire? Rowlett and others, including Randy Bellomo of the University of South Florida, measured the likely temperature of the fires by looking for signs of crystaline melting in the earth and found they had burned at around 400 ˚C. This compares to bushfires which normally burn at just 100 ˚C or so. Bellomo also used another technique known as archaeomagnetism, which relies on the fact that heating causes iron in the soil to realign with the Earth’s constantly wandering magnetic pole. This showed that the Koobi Fora sediments had a mix of three or four slightly different magnetic orientations, implying the campfires had been relit as erectus revisited a regular haunt over the space of a few years.
Doubters countered that the concentrated heat and repeated burning were probably just the result of bushfires setting light to old tree stumps. So Rowlett went out to a friend’s farm in the Missouri prairie and set light to a few stumps. When he dug out the remains, the earth was burnt in a cone spreading into the ground with the roots rather than in the shallow lens-shape found under a campfire.
Rowlett then carried out a phytolith analysis of the soil at Koobi Fora. Phytoliths are microscopic silica deposits found in the stems and tissues of plants. Being almost indestructible, they survive long after the ash and other remains of a fire have leached away. Furthermore, over the past decade archaeologists have learnt to recognise exactly what kind of plant material was burnt from the shape of individual phytoliths.
Rowlett reported that the phytoliths from three of the Koobi Fora campfires turned out to be from a mix of grasses and woods, with palm tree dominating. Even today palm wood is preferred in Africa for being quick to kindle and bright of flame. These looked like fires of collected wood. Still more tellingly, when Rowlett checked a fourth, rather irregular patch of burnt earth that lay away from the other three fires, it turned up just a single species of phytolith as if this was indeed an old tree stump caught in a bushfire. Patient analysis was strengthening the case for fire at Koobi Fora. Even so, Rowlett says he surprised a few people when he summarised his findings at a conference held in China last October.
Then in April a bombshell was dropped. At the Paleoanthropology Society annual meeting in Philadelphia, Brian Ludwig, from Rutgers University revealed evidence that fire use by erectus was widespread. Ludwig, a student of Harris, had carried out an exhaustive analysis of flint artifacts and the debris of tool-making, personally inspecting some 40 000 pieces collected from over 50 sites in Africa and covering the period from 2.5 million to less than 1 million years ago. His aim was to see whether flint knapping skills really did remain static over this period. "I wasn’t even looking for signs of fire," says Ludwig. But he found them anyway.
"When stones like basalt or quartz are exposed to intense heat, like being left around near a campfire, they change colour and also get these potlid fractures--little dimples--on the surface," says Ludwig. He found these signs of thermal alteration all over the place, and there was a clear pattern. No potlid fractures on any of the stone tools until around 1.6 million years ago. Then after that, they occur consistently across many sites, including the post-1.6 million year old strata at Olduvai on the shores of Lake Turkana where, despite remarkable preservation of other artifacts, fire had never been reported before. While not as direct evidence as burnt earth, the burnt tools considerably broaden the claim for early fire.
It’s hardly surprising that these findings have met with some opposition. Henry Bunn of the University of Wisconsin-Madison says the control of fire is such a crucial development that it is going to require much stronger evidence to convince everyone in the field. And Ofer Bar-Yosef of Harvard’s Peabody Museum, is also sceptical. He only recently helped score a goal for the anti-fire camp by showing that the famous layers of ash in the caves of "Peking Man"--the 1920s finding of 500 000 year old Homo erectus skeletons in Zhoukoudian near Beijing--are probably not ash at all but sediment. The rock hollow "hearths" look more like water carved features and charred animal bones may have been washed into the caves.
But even the cautious minded Bunn and Bar-Yosef believe there is good evidence that Homo erectus did use fire later on. From about 400 000 years ago proper hearths--rings of stones--burnt bones, and other clear evidence of fire become common throughout Europe. New finds are made nearly every year with recent discoveries, soon to be described in more detail, including Beeches Pit in Suffolk, Britain, and SchØ ningen in Germany.
Bar-Yosef says the 400 000 year old SchØ ningen site is particularly significant because beautifully carved wooden spears and butchered horse remains were also found there. The wooden spears have been a huge shock to researchers, forcing them to accept that late Homo erectus was a skilled hunter and skilled tool maker. "People had been trying to split erectus and even the Neanderthals off from every kind of cultural activity, saying they couldn’t really have done this or that until 40 000 years ago. But that’s rubbish," says Bar-Yosef. "Erectus would have needed fire just to be in Europe during the ice ages. And even the latest dates that people accept--around 250 000 years ago--would be a problem for the idea that everything important starts to happen with Homo sapiens."
But Clive Gamble of the University of Southampton, argues that what count is not what our ancestors did, but how they did it. And language made an explosive difference. Gamble says erectus had a "15-minute culture". Essentially, they made tools for immediate use and then discarded them. It was a case of mechanically producing something very practical, rather than living within a culture with language in which every activity becomes invested with elaborate rituals and beliefs. No elaboration means no pressure to experiment and no new tool traditions to pass from one generation to the next. The result was technological stasis.
Gamble says that if erectus had used fire, it would have followed the same pattern. Campfires would have been lit as necessary for warmth or protection, eventually even for cooking. But they would not have had the symbolic significance they have in Homo sapiens culture where the first act of any gathering of hunter-gatherers is to light a campfire, then sit around it eating, talking, singing, remembering. Language was needed to transform the daily activities of early hominids from the dully practical into something where every slightest act became socially expressive and personally meaningful.
As to whether this pragmatic version of erectus could have managed the trick of fire, Gamble says it might be less of a stretch than people think. Erectus was already an energetic banger of rocks so could easily have discovered how to make sparks fly. And the SchØ ningen wooden spears now hint that erectus may have managed the more efficient method of a wood drill.
So the "big bang" theory of human mental evolution could be stretched to accommodate a somewhat more capable version of Homo erectus while also retaining the idea that language had a transforming effect on first the culture and then the technology of Homo sapiens. Even a very early control of fire could be conceded without giving the whole game away.
There are still plenty of holes in the story, though. If Homo erectus was a fire lighter, then why are there no obvious fire striking stones in the archaeological record until about 100 000 years ago? And if humans have been using fire for 1.6 million years, then surely we ought to have hands as tough as oven gloves or a fire-nurturing instinct wired into our brains? There has been plenty of time for more obvious signs of genetic adaptation. And when exactly did cooking start? From the first, Homo erectus had significantly smaller teeth and jaws--thought to be a result of their switch from a diet of tough plant material to more meat. But it was not until modern Homo sapiens that there was a second dramatic drop in tooth size, as if these people had started eating more chewable food.
So the controversies will continue. But Harris says at least the recent spate of fresh evidence has shocked a few people into realising how much the mental implications of fire were being ignored. "This has got people thinking again," he says.