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A Reasonable, but Incomplete, Account of How Humans Mastered Fire

Michael Denton

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In a recent article, “The discovery of fire by humans: a long and convoluted process,” J. A. J. Gowlett cites Darwin’s view that the discovery of fire was second in importance only to the discovery of language. He argues that the advances derived from man’s mastery of fire over the later Pleistocene played a critical role in our biological evolution and in the development of our first primitive technologies.

He speculates that the increased nutritive value of cooked food, which followed from our habitual use of fire, may have played some role in the increase in brain size and associated cognitive abilities that occurred during those critical two million years. He claims, moreover, that the light provided by fires would have increased the length of waking hours available to our ancestors for tool making and social interactions. Humans spend twice as long awake as most mammals. In conjunction with the necessity for social cooperation in foraging for fuel, this would have further promoted human sociality. These factors together with the cognitive stimulus of tool manufacture (including the frictional methods of “fire initiation”) may even have played some synergistic role in promoting the emergence of language.

As to the very beginnings of man’s discovery and utilization of fire, Gowlett speculates that this may have been aided by the frequency of lightning-induced fires on the African savannah during Pleistocene times. The benefits of fire foraging for food is a technique that, as Gowlett points out:

…is not restricted to humans [such as modern day Australian Aborigines] but is also practiced by animals and birds … For hominins, benefits could include retrieval of birds eggs, rodents, lizards and other small animals, as well as of invertebrates. Although fire does not create such resources, it renders them far more visible, and chance cooking might well improve their digestibility.

Millennia later, long after its first utilization on the Pleistocene savannah, new fire-assisted technologies were discovered. Gowlett writes:

Within the last 20,000 years, there came major new [fire-assisted technologies] … the first associated with pottery, which appears to have originated in China … From around 10,000 years ago, agriculture would potentially have widespread effects. Fixed Neolithic settlements, such as Çatalhöyök, would have required wide-ranging foraging for firewood, but there are indications in the Levant that woodland was sometimes managed … Soon afterwards, from roughly 5000 years ago come the beginnings of metalworking, first copper and bronze, and then iron. Such interventions involve the raising of temperatures far above those of open fires — the development of a true pyrotechnology.

I have no real problem with Gowlett’s scenario. It seems on the whole reasonable, and the evolutionary path from discovery to mastery of fire must surely be largely correct. Yet it is certainly incomplete in one profound and crucial aspect. It omits any mention of a very fundamental fact, that the conquest of fire and the subsequent development of technology were only possible because of an extraordinary fitness in nature to that end, involving multiple environmental conditions and very specific properties of particular types of matter. Without a set of truly remarkable facilitating coincidences in the nature of things, man would never have mastered fire or started on his long journey of technological discovery, which led from a “pre-fire” stone age to the “post-fire” advanced technological society of the 21st century.

To begin with, the reaction between carbon (C) and oxygen (O), which releases enormous quantities of heat and energy, is only “safe” because of the relative unreactivity of carbon and a unique and remarkable inertness of oxygen at ambient temperatures. This is why, despite the “thermodynamic energy” locked up in the reaction because of these kinetic barriers, we don’t spontaneously combust at body temperatures. It is why our carbon constituents don’t combine with oxygen in an explosive uncontrollable reaction. This inertness is experienced in the difficulty of starting a campfire. Of course, once the fire is initiated it becomes self-sustaining. That is because the heat of the fire converts the relatively inert form of the oxygen that exists at ambient temperatures into a very reactive form that readily combines with the carbon in the fuel (wood) of the campfire. But even after fire is initiated and oxygen activated, the rapidity of fire or flame spread is attenuated by another environmental factor: the quenching activity of nitrogen in the atmosphere, which, because of the relatively high specific heat of nitrogen, retards the speed of flame spread.

Without the inertness of oxygen at ambient temperatures, we would not be here and carbon based life would be restricted to anoxic environments. And without this inertness plus the quenching effect of nitrogen, mankind would never have been able to initiate or control combustion. Consequently, ceramics, metallurgy, and other fire-assisted technologies, which Gowlett mentions, and which followed man’s initial discovery and mastery of fire, would never have been developed. Thus mankind’s long journey to a technological society would have been forever forestalled.

Of course, to have carbon compounds to burn in an oxygen-containing atmosphere requires a biosphere that provides both the wood (the fuel) and oxygen. Only in a carbon-based world similar to our own, with large woody plants to provide the fuel, and plants to provide the oxygen via photosynthesis, is fire possible.

The unique utility or fitness of the carbon atom for the construction of complex replicating chemical systems, which might form the basis of living systems and make possible a biosphere like that on earth, has been noted since the mid 19th century. The subject was reviewed in Henderson’s classic The Fitness of the Environment (1913). No other atom comes close, and all subsequent advances in chemical knowledge support Henderson’s contention. Even Carl Sagan (no friend of teleology) conceded in his book Cosmos that he was a carbon chauvinist (p. 105).

And remarkably, only in the ambient temperature range for terrestrial life (approximately 0-50 C) can the great fitness of carbon for biochemical manipulation be exploited (above 200 C most carbon compounds decompose). This also happens to be the temperature range in which water, the one fluid supremely and uniquely fit for life’s matrix, is a liquid at the atmospheric pressure on earth. It is also the temperature range in which oxygen, the energizer of all advanced life on earth, exists in a relatively inert form.

But this is only to touch upon some of the chain of coincidences that make fire possible. The oxygen in the atmosphere is generated by the process of photosynthesis. This depends on another set of exacting conditions. These include the very remarkable fact that the gases of the earth’s atmosphere — oxygen (O2), carbon dioxide (CO2), nitrogen (N), water vapor — let through the vital visual light which provides the energy to oxidise water, leading to the release of oxygen into the atmosphere. At the same time, two of the gases (water vapor and CO2) retain the sun’s heat (the greenhouse effect). This is essential for maintaining the temperature of the earth in the ambient temperature range, needed in turn for the reactions of living (carbon) chemistry, including the synthesis of sugar in the reaction center of the chloroplast. Even more arresting is the fact, also crucial to life on earth, that the very gases that let through the “good” electromagnetic (EM) energy also absorb nearly all of the “bad” EM radiation in the far UV, X, Gamma ray, and microwave regions of the spectrum.

Without the right atmospheric conditions, that is, without the properties of the gaseous constituents being almost exactly as they are, there would be no photosynthesis, no oxygen, and no advanced forms of life. Such life, unlike more primitive and simpler forms, requires copious quantities of oxygen to support demanding metabolic needs. In short, without photosynthesis there would be no fire and there would be no beings like modern humans — beings capable of handling and utilizing fire!

This brings us to the question of the need, which is critical to support fire, for a percentage of oxygen in the atmosphere of about 20 percent. Coincidentally and very fortuitously, this percentage of oxygen is also sufficient to support metabolically active terrestrial organisms like ourselves, deriving our oxygen directly by absorbing it from the atmosphere. So fire and human respiration, although very different processes, can occur in an atmosphere containing about 20 percent oxygen. Many atmospheres exist containing oxygen and nitrogen at various pressures, which support combustion but not respiration or, vice versa, respiration but not combustion. Without the existence of an atmosphere that supports both these very different processes we may have thrived as biological beings on a planet like the earth but never wouldhave made a fire. That means no ceramics, metallurgy, and so forth. Mankind would have been locked in an eternal stone age culture.

What about wood? Again, conditions have to be just right if large woody plants are to thrive. It is only the unique remarkable cohesiveness of water that confers on it one of the highest surface tensions of any familiar fluid (apart from mercury) as well as a remarkable tensile strength (columns of water in small tubes “stick together”). These together allow water to be drawn to the top of tall woody trees. Without water’s unique cohesiveness, there would be no trees and perhaps no sustainable fire. Fire constructed out of grass and other less substantial fuels would burn out quickly and be hard if not impossible to maintain. Fires need wood, and wood needs trees, and trees need the properties of water to be exactly as they are.

In the story of fire, a further intriguing element of fitness is more relevant to the later development of metallurgy. It is the fact that the smelting of iron and copper from their ores necessitates temperatures of more than 1200 C. Such temperatures are very hard to reach in ordinary wood fire, and instead require the firing of kilns with charcoal, which is essentially wood cooked in a low oxygen environment. Burning charcoal in ventilated kilns generates not only sufficient heat to smelt ore but also the reducing atmosphere necessary to draw the oxygen from the metal in the ore. I think it can be asserted that without these properties of charcoal, the utilization of copper and iron might never have been achieved.

And again the temperature range in which metals possess the tensile strength for the manufacture of tools (e.g., iron), and can serve as conductors of electricity (copper), is that same ambient temperature range at which, as mentioned above, water is a liquid, in which carbon compounds can be manipulated for biochemistry, and in which oxygen is relatively inert. We see a series of temporal coincidences upon which, it is no exaggeration to claim, literally everything depends.

As Gowlett rightly observes, we are the only animals that have mastered fire. But this in itself is no mystery. Other intelligent animals that might have come to utilize fire — dolphins, parrots, ravens, elephants, even chimps — are simply anatomically ill-equipped to initiate fire. Only beings of our particular android design and size possess a superb manipulative tool — the hand — and can therefore make and master fire, developing what Gowlett terms a “true pyrotechnology.”

And a final point — about lightning. Gowlett may be right in inferring that it was the frequency of lightning strikes on the dry Pleistocene savannah that introduced man to the phenomenon of fire, and that in turn led to fire foraging and eventually knowledge of fire’s great utility. As he says, in the wet environment of the rain forests that covered much of Africa before the late Pleistocene, lightning strikes would be far less likely to cause fire.

Note again how lightning itself depends on conditions being just right — on the electrical conductivity or insulating properties of the atmosphere, on the friction caused by upwelling of moist air, and many additional factors which are not yet clear. What is not in doubt is that if many parameters were different, lightning strikes might be far less frequent. It is easy to envisage a counterfactual world in which the frequency of strikes was far less than the 44 per second that are estimated to strike the earth’s surface today. That would perhaps be too infrequent to promote early man’s interest in and knowledge of the phenomenon of fire. Even as things are, lighting is far less frequent at sea, in the Arctic and Antarctic, and in the central Sahara.

In short, the discovery of fire, our subsequent mastery of it, and the road it opened up to an advanced technology were only possible because of our inhabiting a world almost exactly like planet earth, complete with atmospheric conditions exactly as they are, along with the properties of carbon and oxygen atoms (and indeed many of the other atoms of the periodic table), and because we possessed a unique anatomical design (including the hand) uniquely fit for fire-making.

This is not to say that only on our planet are there fire-makers. But one thing is certain. If there are others on other worlds, they will be similar to our selves. Virtually simulacra, they will inhabit a planet in which the environmental conditions are very similar to those on earth.

So again, while much of what Gowlett says is correct, he leaves out any discussion of the crucial fitness of the cosmic environment for fire and for man, the fire-maker. The reason for ignoring this elephant in the room is not because there is no elephant in the room or because the facts are in dispute. The reason has to do with the truly remarkable nature of these facts. Any reference to or discussion of them would inevitably break one of the most persistent and vigorously guarded taboos in current intellectual and academic circles. That is, no mention or discussion should ever be made of factsthat may raise or be seen to support in any way the old anthropocentric worldview, a dreaded specter long since supposedly put to rest with the rise of modern science in the 16th and 17th centuries.

The truth is that no matter how unfashionable it may be in the context of our present culture, and whatever the causal explanation may eventually prove to be, we do occupy a special place in nature. The coincidences are so extraordinary that the inference to design is surely at least worthy of serious consideration.

Photo credit: Mark Wolfe/FEMA (FEMA Photo Library) [Public domain], via Wikimedia Commons.