The domestication of fire

Fire and hominins before domestication

Fire is a process of combustion of organic matter. A momentary conjunction of three conditions is needed for it to occur: there has to be sufficient fuel, a sufficient supply of oxygen, and heat that is of a sufficiently high temperature so that it can ignite the fuel.

Ignition, the most ephemeral of the three conditions, is also the most ancient. Its most frequent cause, lightning, must have struck at land and water alike ever since the planet was formed. Volcanic eruptions and perhaps falling rocks may also have caused spells and moments of great heat. As long, however, as the other two conditions were lacking, no fire ensued.

Oxygen became a substantive part of the planetary atmosphere when, some 2.5 billion years ago, living organisms began producing it in processes of photosynthesis and emitting it into the air.1⁰ When, between 500 and 400 million years ago, large parts of the land surface had become covered with plants and trees, the proportion of oxygen in the air stabilized at a rate of about 21 per cent. At the same time, and by the same token, fuel became available in the form of abundant vegetation, and the world was ready for fire.¹¹

By the time our earliest hominin forebears appeared, some 8 to 10 million years ago, fire was a regularly occurring feature in their habitats. It is, therefore, misleading to say, as is often done, that humans ‘discovered', let alone ‘invented' fire. Every hominin that reached adulthood was likely to have come across a fire at least once in his or her lifetime.

In a recent monograph the primatologist Frances Burton addresses on the basis of a wide range of current scientific knowledge the problem of how the unique relationship between humans and fire emerged.^{[269] [270] [271]} She postulates a long and protracted phase of ‘association' with fire, during which hominin groups gradually familiarized themselves with fire, spending the nights around it together, adjusting themselves to its presence, enjoying both the heat and the light as well as the protection it might offer from predators, and eventually learning to ‘nourish' it with fuel and to transport it to cave entrances where it was sheltered against the rain.

This is a likely scenario, supported by evidence from many divergent sources. In the overall process preceding the actual domestication of fire, biogenetic evolution seamlessly coalesced with sociogenetic, or cultural, evolution (or development). Clearly, in the process of collectively learning to handle fire and fuel, the evolution of a larger and more complex brain played a part, and so did the evolution of walking on two legs, with the hands free for carrying objects - from branches that could serve as fuel, to burning sticks with which fire could be transported to another site or used as a weapon to ward off bears or lions. The very same physical features that were first preconditions for mastering fire may well have become mechanisms of selection in human evolution once the domestication of fire was underway.

Odd though it may sound, in order to form an image of what happened in the very early phase preceding domestication, it may be helpful to describe it in terms in which our early ancestors themselves may have experienced it: as a struggle to change the balance of power between themselves and fire - a struggle that was often lost, until in the long run the balance was tilted definitely towards increasing human control, in circumstances created according to their own ideas about the conditions for burning.

The domestication of fire meant a shift in the balance of control: the course taken by a fire was no longer solely determined by ‘natural' forces, but it was determined, at least in part, by human direction. Our early ancestors may not have been aware of all the implications of what they were doing, but they did have a sense of how the fire would behave and, most importantly, how they wished it to behave. They applied their own information in order to conduct the combustion of matter.

There was, of course, another side to it: in order to submit the fire to their intentions, they had to adjust their own behaviour to the requirements of the fire.

From mere association to incipient control

The history of the human bond with fire is about human control over a non­human or extra-human force - fire, including, as a necessary precondition for fire, some control over fuel.

Such a balance must also have existed from the start between the biogen- etic and the sociogenetic aspects of the human attitudes towards fire. Bio- genetic information warns us, as well as our early ancestors, to stay away from fire, to avoid contact with it. Sociogenetic information, acquired by collective learning, has added the insight that it is possible to manipulate fire (and thus exploit fuel) without touching it.

The capacity to acquire this information and to pass it on to future generations must have developed along with the evolution of a large and differentiated brain, ‘expensive tissue' as some archaeoneurologists call it, hinting at the disproportionately great amount of energy this organ con­sumes. Another precondition, equally evident, was the upright position, making it possible to walk and run on two feet, with the hands free for carrying objects, if necessary even burning matter as long as it was kept isolated from the carrier's skin. Both ‘preconditions' probably co-evolved with the changes in behaviour towards fire.

Just as the brain was ‘expensive tissue', a human-controlled fire (a ‘camp­fire') was an ‘expensive' social institution. It demanded foresight and care: foresight already with regard to its location: preferably at a cave entrance, where it would not be quenched by rain, and still receive sufficient oxygen- saturated air. In order to be sure of having a fire available in wet seasons too, was useful to keep it burning continuously, with a stock of dry fuel at hand. Care was also required in order not to hurt oneself or other group members; and social co-ordination was needed to make sure that the fire was tended and protected against possible invaders.

The immediate effect of fire was always, put in the most neutral words, a re­arrangement of matter - a rapid re-arrangement that not only totally destroyed the combusted fuel, but also did so in a way that was irreversible. This destructive effect was turned into what from a human point of view was its very opposite: production. That began with cooking, the activity that in Richard Wrangham's appealing phrase ‘made us human'. Cooking in the most elementary sense amounted to exposure of organic matter to great heat, thus making a whole range of nutritious ingredients digestible that would have remained very difficult or even impossible to digest without prior heating.

A very different use of fire was to employ it as a weapon, exploiting the pain it would cause when inflicted upon living skin. This made hominins and humans far more formidable and fearsome to any opponents in inter-species contests. By virtue of their familiarity with fire they could afford to spend the night sleeping on the ground, without fear of predators. The new behaviour towards fire led to a shift in the balance of power between hominins or humans and all other large animals. The ensuing differentiation of behaviour and power reinforced the commitment of hominins and humans to fire and fuel. From its very start, the species monopoly was a precious and costly privilege.

Phaseology and chronology

The previous section is written from the perspective of phaseology rather than chronology. Chronology has the great advantage of providing us with a fixed grid of years and centuries marked by regular intervals. As such it is an excellent instrument for locating events in time. But strictly speaking it only allows us to arrange those events in a scheme of what came earlier or later, in the ‘one damned thing after another' mode. Thinking in terms of phases has the advantage of being based on a certain logic, the logic of sequences. As pointed out above in the section ‘Phases', there is an irrefutable logic in the statement that a phase 3, when all human groups had fire was preceded by a phase 2, when some groups had fire, and that phase again was preceded by a phase 1, when there were no groups with fire.

According to her own estimate, Burton's scenario of phases covers a period from about 8 to 3 million years ago. Wrangham dates the origins of cooking on the basis of palaeo-anatomical finds at between 1.9 and 1.8 million years ago. Archaeologists, who generally prefer to use traces of human activity as the basis of their evidence, make more modest estimates. Until recently they were prepared to accept finds from 250,000 years ago as their oldest reliable evidence for active human fire use; all claims about more ancient evidence were rejected as unproven.

The tide is turning, however. There have been finds in Israel (at Gesher Benot Yaaqov) and in South Africa (at Wonderwerk Cave) pointing to active use of fire at least 800,000 years ago.^[273] If it is possible to stretch the chronology so far, there is much to be said for assuming a far longer, and fuzzier, phase of transition when groups of hominins sometimes lived with fire for a while, until that was extinguished, and they had to return to living without fire, for we can only guess how long. Meanwhile, they also acquired greater dexterity in ‘clearing land', by setting fire to the undergrowth of forests every so often, thus extending the territory they could safely use for hunting and gathering food. In these various ways, the incipient human-controlled fire regime gave a wider scope to the human domain, the ‘anthroposphere', in the overall biosphere.