There is a specific tool that is worth examining in more depth, because it is paradoxically destructive. The world has burned for billions of years. Fire is a relentless force of nature, a chemical reaction that destroys all in its wake, from the bonds of molecules that fuel combustion, to the life that expires in the face of temperatures living cells will not tolerate. The vital molecules of biology contort and break apart, the water in our cells boils. Fire and life are incompatible.
However, fire is part of our environment and our ecology, and the ability to adapt to, control and use such raw power is a force that has shaped evolution. We live on a mantle atop a raging molten core that has been pushing brimstone and igneous rock into the world since before life began. Indeed, we now think that the action of lava forcing its way out of the seabed four billion years ago was not just instrumental but crucial in the formation of the rocky nurseries in which chemistry transitioned into biology, and life began.1 We didn’t merely adopt fire; life was born from it, and is moulded by it.
Darwin described humans’ discovery of the art of making fire as ‘probably the greatest, excepting language’. He might not be wrong, though maybe today we are not quite as dependent on fire as we were during the white heat of Victorian ingenuity when he wrote those words, and perhaps we don’t see open fires or furnaces nowadays as often as he did.
Nevertheless, we are pyrophiles – fire lovers. We burn the energy of the Sun that has been trapped into the carbon of wood both living and so long dead it has become compressed into coal, and in the carcasses of animals that perished so long ago that they have been literally pressured into becoming oil. It is in the destruction of the chemical bonds of those once vital carbon molecules that fire releases its energy. This has shaped the modern world and, perversely, now threatens it, as the carbon dioxide that we continue to pump out into the atmosphere itself holds more energy than other components of air, and the greenhouse effect warms our world.
Fire is a tool that has utterly transformed our existence, not just in the industrial age, but from well before our particular type of human being had settled into the form we currently enjoy. We have good evidence that Homo erectus, that highly successful human who walked all over the Earth from 1.9 million years ago until around 140,000 years ago, was a fire user in some capacity. The dates when they first utilised fire remain disputed. Sifting through the dirt of ancient human sites is a fiddly business, and while there is molecular evidence of burnt bones and flora as long ago as 1.5 or 1.7 million years ago (depending on where you look), these are open-air sites, and it’s not clear that these are not the result of wildfires triggered by lightning strikes or local volcanoes, rather than deliberate use by early humans. Some have suggested that based on the shapes of their teeth and other morphological dimensions, Homo erectus was cooking food as long ago as 1.9 million years. The earliest secure date for fire in an archaeological context is probably around one million years ago in the Wonderwerk Cave in South Africa.
However and whenever the transition took place, humans moved from an opportunistic use of fire to habitual use, and eventually to obligate pyrophiles. This transition, as with all the stories in human evolution, almost certainly occurred slowly and incrementally over time – there was not one single spark, but many. Archaeologists argue over the earliest evidence of controlled use of fire. Then again, archaeologists argue about a lot of things.
By 100,000 years ago, we had it largely under control. As a source of heat and light, man’s red fire is of obvious benefit, as is the ability not just to control it, but to generate fire from a spark. The Jungle Book’s orangutan-in-chief King Louie expresses his desire to be just like you, specifically by owning this uniquely human ability, and he is wise to sing so. The impact of fire on the development of humankind is incomparable. We expanded north with fire as a source of heat beyond the temperate and tropical zones whence we evolved. This gave us access to a whole new range of beasts both large and small to hunt, cook and feast upon and make tools and clothes and art from their bodies. As is the case today, the social significance of congregating around a hearth or a fire should not be underestimated. Social bonds are forged and consolidated around a fire, stories told, skills passed on and food prepared and shared.
We are the only animal that cooks. Energy and nutrients are sometimes held deep inside the vegetation and flesh that we consume, and digestion is the process whereby they are released. This can be chemical, and mechanical. Teeth can be for grinding, tearing and chewing, but all are for some form of maceration, the process by which food is broken down to make it more accessible to the enzymes that will chew with molecular precision. Plenty of animals use artificial mechanical means to aid digestion. Birds don’t have teeth to macerate, but they do have gizzards – muscular pouches in their digestive tracts that some fill with grit which grinds up food, making it easier to chemically digest. We call these ‘gastroliths’ – stomach stones – and this is an ancient practice. The fossilised remains of many dinosaurs from the Cretaceous and Jurassic periods have been found with smoothed stones inside their body cavities, where once the soft tissue of gizzards would have been.
We outsourced some of our digestive abilities by externalising them. By cooking foods, we break the bonds of complex molecules, and make them easier to digest in our stomachs. Meat is tenderised by heating. Softer foods are quicker to eat too, in that we spend less time chewing a boiled cabbage than a raw one, which means we get access to the essential nutrients more efficiently. Dining is a period of vulnerability: when your face is occupied with ingesting a meal, it is less alert to danger from predation. Spending less time eating means less time being potentially eaten.
All of these things make cooking a desirable and essential part of our evolution. Some researchers have suggested that we became a pyrophilic primate by living among iterant burning ecology and adapting to the benefits it brings. Some have suggested that the origins of cooking, or at least an understanding of how heat changes food, might have begun by apes foraging in burnt landscapes. It’s difficult enough to roast a turkey to perfection in a twenty-first-century oven, so it’s not unreasonable to suppose that animals roasted in wildfires are most likely to be burnt or undercooked. But it may be that these first hot meals were the spark of the idea of using heat to change food for the better.
The other obvious benefit of safely standing to the side of a raging furnace is that you can be presented with an exodus of other animals fleeing from the danger. If these animals are of interest to you as food, then fire provides a free all-you-can-eat buffet. We think that South African vervet monkeys do this, and enjoy an unprecedented access to invertebrates scuttling out of the fire, and into their mouths. We also think that the monkeys know this well, and so increase their normal foraging range into wildfire regions, especially after a recent blaze. There’s another set of benefits from this behaviour too. Vervet monkeys stand up on their hind legs to look out for predators, and thus can see over the grasses and plants. When they are cleared by being burned to stubble, the monkeys can see further. Vervet monkeys in scorched plains spend more time feeding, and feeding their young, and less time standing erect on the lookout for something that will eat them.
Even closer relatives to us, savannah chimpanzees in Fongoli, Senegal, live among fire as part of their natural ecology too. It is hot in the grasslands anyway, but since 2010, the onset of the rainy season has become increasingly erratic. From October, fires start which encroach upon three-quarters of the chimps’ thirty-five square-mile range. These most often ignite at the beginning of the rainy season, when rolling thunder and lightning meets arid bush.
Scientists have been watching these chimps for decades, and in 2017 reported on their relationship with fire. There are several things worth noting. The first is that they are untroubled by wildfires. Mostly they ignore the burning brush, but sometimes wander into and explore areas that were on fire just minutes before. They appear to navigate in burnt areas frequently, which may be the same trick the vervet monkeys are using to increase their lookout range to avoid predators. We know that in the Mara-Serengeti in Kenya, other large herbivores congregate in scorched areas at higher densities than in healthy grasslands, including zebra, warthogs, gazelles and topi. It may also be easier and quicker to traverse land flattened by plants being burned to ash.
The fact that these chimps behave in a specific predictable fashion when their world burns suggests that while they cannot control fire, they certainly can conceptualise it, and crucially predict its behaviour. This is a cognitive benchmark, in which the animal is capable of rationalising and approaching something dangerous, rather than simply taking the safest course of action, which is to flee. It’s a sophisticated reaction too: the way a fire burns is a complex and capricious process, which depends on what is burning, the wind, and a host of other factors, and can change in a flash. Within seconds, fires reach temperatures incompatible with life, and can release smoke and noxious gases that are also threatening to apes.
The vervets and the savannah chimps are potential clues for us when we think about the genesis of our own relationship with fire. We look to nature today to draw comparisons and speculate that what we see now might have been similar to what happened way back when. This may be egocentric. All data is useful in some way, but there is a whiff of presumption in the notion that behaviours in our fellow apes reflect our own journey to the present.
Is this what we did? Do the chimps today mimic our own evolution 100,000 years ago, or even a million? These are hard questions to answer. Behaviour is not well preserved in bones nor in the ground. We can see how bodies change in relation to changing environments, such as the subtle shifts away from an arboreal life, and infer what behaviour was facilitated by those bodies. We do have better clues and tools to answer the question of how fire changed us, though the evidence is almost as fleeting as wisps of smoke. We look for charred remains buried in the dirt, or for evidence of hearths and kitchens. We also look at the morphology of ancient humans, to see if cooked food was a necessity for shaping their bodies, or at least the hard parts that remain for us to scrutinise today. We can look at body mass and feeding times to construct models of the energy required to make those bodies, and calculate that they demanded particular dietary requirements. We construct tests in our living primate cousins and see how they tally with the behaviour that we are just beginning to observe in the small pockets of monkeys and chimps who encounter fire on a regular basis.
These are data points that may build up a theory, but we should be cautious. Most great apes do not live on the savannah. Most chimpanzees, bonobos, gorillas and orangutans live in dense forest environments, where blazes are only devastating, and mercifully rare. There are few formal reports on the effect of forest fires on great ape lives, but peat burning in Indonesian national parks (which is associated with expansion of palm oil farming) has only had a detrimental effect on orangutans. In 2006, hundreds were estimated to have died as a direct result of forest fires.
Savannahs did expand during our evolution in Africa, forests shrank, and our morphology inched away from being adapted to an arboreal life. Single causes are rarely persuasive arguments for how we evolved to be what we are today. Though our transition into the species Homo sapiens occurred in Africa, I think we are moving towards our being a kind of hybrid derived from multiple early African humans. Certainly, though the strongest evidence comes from the east of Africa, we haven’t really looked that hard over the rest of that vast landmass, and the earliest known Homo sapiens are actually found in Moroccan hills to the east of Marrakesh. What this means is that fire is undoubtedly one of the great driving forces of human evolution, but it is not the only one. Our existence in the perpetual presence of savannah fires will have profoundly changed us. But not all of our ancestors lived on the plains of Africa.
Darwin said that of all the animals, Homo sapiens ‘alone makes use of tools or fire’. There, he is quite wrong. None bar us can ignite a fire or create a spark. However, we are not alone in using fire as a tool. We have already seen that the corvids are adept tool users. Until 2017, raptors – that is, birds of prey – were not known for their tool-using abilities. Raptors is an informal and broad classification, one which includes kites, eagles, osprey, buzzards, owls and so on, and therefore doesn’t necessarily relay evolutionary relatedness. Owls are closer to woodpeckers, and falcons closer to parrots than either raptor is to hawks or eagles. They are all hunters though, with curved talons and beaks, and tend to have keen eyes, some with impressive varifocal vision, honed to zoom in on a tiny mammal when soaring above.
A few raptors are pyrophiles too. Fire-foraging birds of prey work on similar principles to the vervet monkeys. Tasty critters will be flushed out of a burning bush and are easy pickings. Plenty of raptors eat carrion too, and there will be lots of roasted small mammals in among the ashes. This behaviour has been noted in the scientific literature as early as 1941, all over the world, including east and west Africa, Texas, Florida, Papua New Guinea and Brazil.
But some of these raptors are even smarter. Black kites, whistling kites and brown falcons all have international ranges, and are indigenous to Australia, where they hunt and scavenge carrion, particularly in the baked northern tropical savannah. These Australian lands are hot and tinder dry, and they burn regularly. Aboriginal Australians know this well and have managed the fires with great sophistication for thousands of years. They use fire to raze particular flora and encourage the growth of edible plants and grasses that attract kangaroos and emu, both of which make good meat.
The indigenous people also know the local fauna. Over a number of years, culminating in a study published in 2017, Aboriginal rangers and subsequently Australian scientists reported that black kites, whistling kites and brown falcons have all been seen doing something very thoughtful. They pick up burning or smouldering sticks from bush fires and carry these torches away. Sometimes they drop them because they are too hot – but the intention is to place them in dry grassy areas and set a new blaze. Once the grass is alight, the birds perch on a nearby branch and await the frenzied evacuation of small animals from the inferno, and then they feast.
Aboriginal Australians have known of these firestarters for a while.2 They refer to the birds as ‘firehawks’, which feature in several religious ceremonies, and there is a sighting in one account from I, the Aboriginal, the 1962 autobiography of an indigenous man called Waipuldanya:
I have seen a hawk pick up a smouldering stick in its claws and drop it in a fresh patch of dry grass half a mile away, then wait with its mates for the mad exodus of scorched and frightened rodents and reptiles. When that area was burnt out the process was repeated elsewhere. We call these fires Jarulan . . . It is possible that our forefathers learnt this trick from the birds.
In the diaphanous academic literature on this incredible phenomenon, there has been some historical dispute over whether this fire-starting is deliberate or not. This most recent study, which is the first formal scientific account, concludes from multiple eyewitness testimonies over many years that this fire-starting is fully intentional.
It is, as far as I am aware, the only documented account of deliberate fire-starting by an animal other than a human. These birds are using fire as a tool. By any of the definitions mentioned earlier of what constitutes a tool, this behaviour satisfies all of them. It also goes some way to explain how fire can apparently jump over human-crafted and natural fire barriers, such as barren paths or creeks. It is possible that Aboriginal Australians learnt to start jarulan from the birds, and later adopted it into their management of the fires that have burned throughout Australia’s history. If true, this is a beautiful example of cross-species cultural transmission. It is also possible that our ancient ancestors did the same more than a million years ago, when we began a relationship with fire that will never be extinguished. Or maybe it is just a good trick, and only us and the raptors have worked it out. Either way, the ability to start a new blaze is one of the first steps in being able to control fire.
This does not mean the next steps will follow. It does not mean that these hawks are en route to forging metal or cooking food. This knowledge is one step beyond what the vervet monkeys and the Fongoli chimps do. It requires a cognitive understanding of the behaviour of fire, not least how dangerous it is. But it also demonstrates an ability to plan ahead, to calculate a considerable risk. At what age would you let a child handle a burning stick? The falcons and kites are using a lethal force of nature to manipulate the environment for a meal that otherwise would have remained safely hidden in the bushes.
Fire is part of nature. The world has burned since before there was life, and nature, with its tenacious ability to adapt to the environment in front of it, has repeatedly embraced the inferno. We have gone a few steps further and created a total dependence on this raw power. There are serious health risks associated with eating only raw food. We do have other sources of energy nowadays, but we remain utterly dependent on burning the remains of long-dead animals and plants, at least for the foreseeable future. Using fire is part of our nature, and you can’t start a fire without a spark. We are the only ones who can do that, but now we know we are not the only ones who see fire as a means for getting what we want.
1 Our current best-fit theory for the origin of life is in so-called white smokers, hydrothermal vents driven up from the sea floor during the Hadean period some 3.9 billion years ago. These towers were (and are to this day) formed of the mineral olivine and percolated with labyrinthine pores and channels driven by the tumult of the living rock below. We call it ‘serpentinised’, and the presence of hydrogen sulphide and other charged chemicals swirling in and out of these microscopic chambers gave rise to the first cells.
2 This research is led by Bob Gosford, an Australian ethno-ornithologist who lives, appropriately enough, near Darwin in the Northern Territories. Gosford and his team refer to IEK – indigenous ecological knowledge – and go to great and necessary lengths to acknowledge, engage with and build on the long-standing traditions and skills of the first peoples of Australia. This is a somewhat new practice but shows clearly how much is to be gained in the sphere of understanding our world by respecting indigenous people with humility and grace.