麻豆传媒

EVER watched a bunch of city slickers trying 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 curses and eventually, perhaps, choking clouds of smoke.

Humans are adept at many things. Our brains and bodies are adapted for talking, spear throwing, handling tools and communal living. But lighting fires just doesn鈥檛 seem to be on the list. Yet, astonishingly, there is growing evidence that humans 鈥� or at least our ancestors 鈥� have been using fires for an incredibly long time, as long as 1.6 million years.

Within palaeoanthropological circles, many people will be crossing their fingers, hoping the latest findings just aren鈥檛 true. This is because hominid control of fire over a million years ago poses huge problems for current thinking about human evolution. The most widely held theory is that technologically sophisticated humans arrived with a 鈥渂ig bang鈥� just 40 000 years ago, with the development of grammatical speech. If the very early date for the control of fire holds up, it must mean one of two things: either you don鈥檛 need to be very smart to kindle a roaring blaze, or our forebears were not as dumb as we think.

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 3-million-year-old hominid remains in a South African cave. At the time, a lingering Victorian distaste for the idea of being descended from the apes meant scientists were happy to push the development of fire and language as far back into the mists of time as possible. So this ancestor was quickly dubbed Australopithecus prometheus 鈥� giver of fire.

The 鈥渂urn marks鈥� eventually turned out to be mineral stains. But in the 1970s and 1980s, more 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 with a markedly larger brain and fully human proportions. At Koobi Fora, the excavations also revealed a scattering of ten 鈥渓enses鈥� of orange earth about half a metre wide and around 1.6 million years old. At Chesowanja, there was just a single lump of this discoloured earth, about 1.4 million years old, that had broken up and washed down a stream bank.

The researchers only realised their significance when they saw that the campfires of local people left exactly the same lens-shaped burned patches, recalls Jack Harris of Rutgers University in New Jersey. Given the close association between the bones, the tools and the burned patches of ground, the researchers proclaimed that here was the true human Prometheus.

For Harris, the find explained a lot about H. erectus. Unlike earlier hominid species, which appear to have hugged the cover of Africa鈥檚 Great Rift Valley, H. erectus moved out into the more open highlands in search of big game. Harris believes that fire made this possible. 鈥淎t night, a fire would have helped keep the other large carnivores at bay,鈥� he says. 鈥淏ut it also gets down to zero on the side of the Rift. You鈥檇 need a fire so as not to freeze to death at that elevation.鈥�

Harris 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 H. erectus managed to break out and start to move around the world. H. erectus eventually spread through Europe and Asia 鈥� good going for a hairless, rather defenceless great ape adapted to warmer climates.

Yet while a few of Harris鈥檚 fellow researchers were convinced, others were more cautious. The 鈥渂urned鈥� patches of soil could be the result of bush fires, 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, H. erectus had only evolved around this time. They were primitive toolmakers, and showed no signs of symbolic thinking over the next million years or more of their existence.

Harris鈥檚 assertions just didn鈥檛 fit with the 鈥渂ig bang鈥� theory of human mental evolution, which paints our early ancestors as nothing more than smart bipedal apes. While they grew steadily bigger in body and brain over the first 4 million years, they made meagre advances in lifestyle and tool use until around 40 000 years ago, when one branch of our hominid ancestors developed the capacity for a highly structured form of vocal communication. Overnight, the theory goes, we were transformed into modern Homo sapiens, a species driven by language and culture. The explosion in our potential for symbolic thought and self-awareness brought with it a matching explosion in art, tool-making and social complexity.

Throughout the 1980s and 1990s, such thinking led palaeoanthropologists to denigrate H. erectus at every turn. Rather than big game hunters, it was felt more likely that these hominids were mere scavengers, coming somewhere between hyenas and vultures in the savannah pecking order 鈥� if they even ate meat at all rather than just scrounging for nuts and locusts.

Even their characteristic hand axes 鈥� the tear-drop shaped flints that were the hallmark of H. erectus 鈥� 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 to find the right kind of stone and then patiently crafted it according to some model in their mind鈥檚 eye.

Mute dunces

But by the 1990s, anthropologists were arguing that the axe shapes might be purely accidental 鈥� they were merely the core, the bit that got chucked away, after a succession of simpler flakes or scrappers had been knocked off round the perimeter. And, they said, even if H. erectus was deliberately making the hand axes, they churned out the same old style for the next million years with little further refinement. These hominids were not great innovators.

This attitude was also applied to fire. If H. erectus had mastered the simple campfire so early on, then why was it never taken to the next level? Why didn鈥檛 hearths, fire strikers and signs of cooking rapidly follow? And why is there such a suspiciously patchy record of fire use? Hand axes have been found at nearly every dig. But burned earth has been found at just a few sites. No, more likely that these erectus guys were mute dunces and the baked earth the remnant of some long-ago bushfire.

There the matter lay until recently, when a more detailed picture began to emerge and the pendulum of opinion started to swing again. First, research showed that the earth lenses were indeed the result of fire. Last year Ralph Rowlett of the University of Missouri-Columbia and his colleagues published 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 a sample being reset by exposure to heat, proved that the discoloured ground was 鈥渘ewer鈥� than surrounding ground, and so was not likely to have been produced by mineral staining, fungi or some other non-thermal cause. Rowlett also ruled out lightning strikes by examining the sites of genuine strikes. He found that lightning creates not much more than coin-sized pits together with characteristic lumps of fused earth known as fulgerites.

So, campfire or bush fire? Rowlett and others, including Randy Bellomo of the University of South Florida, gauged the likely temperature of the fires by looking for signs of crystalline melting in the earth and found they had burned at around 400 掳C. Bushfires, in contrast, normally burn at just 100 掳C or so.

Bellomo also used another technique known as archaeomagnetism, which relies on the fact that heating causes iron in the soil to align with the Earth鈥檚 constantly wandering magnetic pole. This showed that the Koobi Fora sediments had a mix of slightly different magnetic orientations, implying the campfires had been relit as hominids revisited a regular haunt over the space of a few years.

Doubters countered, however, 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鈥檚 farm in the Missouri prairie and set light to a few stumps. When he dug out the remains, the earth was burned in a cone spreading into the ground with the roots, not 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. What鈥檚 more, over the past decade archaeologists have learned to recognise exactly what kind of plants different phytoliths come from.

Rowlett reported that the phytoliths from three of the Koobi Fora patches turned out to be from a mixture of grasses and woods, with palm tree dominating. Even today, palm wood is preferred for fires, being quick to kindle and bright of flame. These looked like fires of deliberately collected wood. More tellingly, when Rowlett checked a fourth, rather irregular patch of burned 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, this April a bombshell was dropped. At the annual meeting of the Paleoanthropology Society in Philadelphia, Brian Ludwig from Rutgers University reported the results of an exhaustive analysis of flint artefacts and the debris of tool-making. He personally inspected around 40 000 pieces collected from over 50 sites in Africa, covering the period from 2.5 million to less than 1 million years ago. His aim was to see whether flint knapping skills really had remained static over this period. 鈥淚 wasn鈥檛 even looking for signs of fire,鈥� says Ludwig, a student of Harris. But he found them anyway.

鈥淲hen 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 鈥� little dimples 鈥� on the surface,鈥� says Ludwig. He found these signs of thermal alteration on many of the tools, and there was a clear pattern. No potlid fractures on any of the stone tools until around 1.6 million years ago. After that, they occur consistently across many sites, including the Olduvai Gorge (see Map) where fire had never been reported before despite remarkable preservation of other artefacts dating from between 2 million and 1.3 million years ago. While not as direct evidence as burned earth, the burned tools considerably broaden the claim for early fire.

It鈥檚 hardly surprising that these findings have met with some opposition. Henry Bunn of the University of Wisconsin at 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鈥檚 Peabody Museum is also sceptical. He recently helped score a goal for the anti-fire camp by showing that the famous layers of ash in the caves of 鈥淧eking Man鈥� 鈥� the 500 000-year-old H. erectus skeletons found near Beijing in the 1920s 鈥� are probably not ash at all but sediment. The rock hollow 鈥渉earths鈥� 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 H. erectus did use fire later on. From about 400 000 years ago, proper hearths consisting of rings of stones, burned 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, being made in places such as Beeches Pit in Suffolk, Britain, and Sch枚ningen in Germany.

Bar-Yosef says the 400 000-year-old Sch枚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 H. erectus was skilled as a hunter and toolmaker. 鈥淧eople had been trying to split erectusand even the Neanderthals off from every kind of cultural activity, saying they couldn鈥檛 really have done this or that until 40 000 years ago. But that鈥檚 rubbish,鈥� says Bar-Yosef. 鈥淓rectus would have needed fire just to be in Europe during the ice ages. And even the latest dates that people accept 鈥� around 250 000 years ago 鈥� would be a problem for the idea that everything important starts to happen with Homo sapiens.鈥�

But Clive Gamble of the University of Southampton argues that what counts is not what our ancestors did, but how they did it. And language made an explosive difference. Gamble says H. erectus had a 鈥�15-minute culture鈥�. 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 H. 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 H. sapiens culture where the first act of just about 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 hominids from the dully practical into something where every slightest act became socially expressive and personally meaningful.

As to whether this pragmatic version of H. erectus could have managed the trick of fire, Gamble says it might be less of a stretch than people think. Erectuswas already an energetic banger of rocks, so individuals could easily have discovered how to make sparks fly. And the Sch枚ningen wooden spears hint that erectus may have managed the more efficient method of lighting fires using a wood drill.

So the 鈥渂ig bang鈥� theory of human mental evolution could be stretched to accommodate a somewhat more capable version of H. erectus while still retaining the idea that language transformed first the culture and then the technology of H. 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 H. erectus was a fire lighter, then why are there no obvious fire-striking stones in the archaeological record until about 100 000 years ago? If humans have been using fire for 1.6 million years, then why don鈥檛 we have hands as tough as oven gloves or a fire-nurturing instinct wired into our brains? And when exactly did cooking start? From the first, H. 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 H. sapiens appeared that there was a second dramatic drop in tooth size, as if our species had started eating more chewable food.

So the controversies will continue. But the recent spate of fresh evidence has shocked a few people into realising how much the mental implications of fire were being ignored, Harris says. 鈥淭his has got people thinking again.鈥�