land. Horses and oxen hauled timber, pigs and sheep devoured grass and roots. It required about an acre of cleared forest to support one human being. Any growing population needed to expand the land available for burning and sowing. Like all technological revolutions, fire liberated people and reduced their dependence on nature. But no sooner had he achieved symbiosis with fire than bipedal man fell into the resource trap. In his quest for freedom and happiness, he was constantly destroying the very resource that made him prosper.
Groups of people moved from place to place looking for firewood. These people had neither maps nor even word-of-mouth information about their environment. When they found a forest they could use, they settled there until they had burnt everything flammable. In need of timber, humankind migrated north, to the wooded tracts of Europe. But there were already similar creatures living there – the Neanderthals. Shorter but more heavily built than Homo sapiens, the Neanderthals were intelligent and aggressive. They lived in small communities, were capable of collective action and used fire and stone tools. They coped with the cold climate more easily than H. sapiens. Their brains were bigger than the brains of early modern humans, their sight was sharper, their muscles stronger. For five millennia, H. sapiens and Neanderthals lived side by side in Europe, mating and learning from each other. Then the Neanderthals died out. Archaeologists have found teeth marks from H. sapiens on their bones: early humans had eaten Neanderthals. The anthropologist Pat Shipman has proposed that the main difference between the Neanderthals and the ancestors of modern man was the symbiosis between man and wolf. Homo sapiens and wolves complemented one another. One species could track game; the other could kill it. One was swift-footed and had a superb sense of smell; the other had a big brain and tools. Hunting with dogs gave early humans their greatest advantage over Neanderthals.4
American archaeologists investigated adjacent settlements of humans and Neanderthals in the mountains of the Southern Caucasus. The main source of food there was the Caucasian goat. Both groups knew this animal’s seasonal migration routes and settled in the vicinity. They behaved more like breeders than hunters, eating only adult animals and leaving the juveniles to mature. The Neanderthals lived in smaller groups than the humans. Their tools were more primitive because they made them out of local stone. In the human camps the archaeologists found knives made of obsidian, the nearest source of which was 100 kilometres away. With these knives, humans could split strong bones into needles.5 These implements were highly prized and used over and over again for scraping skins and sewing them together, making clothes and shoes. These goods entailed a huge amount of labour, but they could be exchanged for other things such as obsidian. This is probably the first example of long-distance trade in human history, but the pattern was fully developed: a rare, distant natural resource was exchanged for products of human labour.
Having left their subtropical Eden, humans needed to dress in furs and skins. The Neanderthals had more subcutaneous fat and more body hair, and they did not need fur garments in the temperate climate. They could scrape animal skins but used them as bedding. In contrast to the human traders who exchanged sheep and skins for obsidian, the Neanderthals lived by subsistence farming. Along with dogs, trade gave humankind an advantage in its first battle for survival. Perhaps humans’ symbiosis with wolves was connected to their ability to carry out trade. Hunting with dogs relies on the ability to relate to another creature who has different needs from your own. This is also the basis of trade.
Roman fires
The level of harnessed energy reached a temporary peak in ancient Rome. The historian Ian Morris has used the number of kilocalories harnessed per head of population per day as ‘the measure of civilization’.6 Those religions that worshipped the sun as the ultimate source of life – the religions of the Egyptian pharaoh Akhenaton and the Persian prophet Zoroaster – understood this. Burning wood provides energy that can warm man and raise him up but can also destroy him. It is up to man which of these alternatives happens.
The building boom in ancient Rome required enormous quantities of timber. The exhaustion of forests caused the move from wooden walls and roofs to structures made of brick and ceramics; but the firing of clay in kilns also needed fuel. 150 cubic metres of dry firewood were needed to make 1 cubic metre of bricks; it took 10 tons of firewood to burn the limestone to produce 1 ton of cement. To heat ancient Rome, with its underfloor heating, huge baths and cooking stoves, required the cutting down of 30 square kilometres of forest per year.7 Those who worked on the felling, transporting and processing of timber were not slaves but hired hands, either peasants or barbarians. The smelting of bronze, iron and silver created the need for quality wood to make props for the mines and charcoal for heating the smelting cauldrons. Time after time, the authorities claimed the forests as state property, but this did not improve the supply. Rome’s drive towards the north, to the forests of Germany and even Britain, was connected with its thirst for timber and energy.
Emerging from the forests, the barbarians put out this fire. By the seventh century, the level of energy harnessed per person fell by a factor of two. Only many centuries later did the mass consumption of Dutch peat and British coal allow societies to exceed the energy consumption reached by the Romans. Like any other activity, extracting fuel requires energy. The production of a kilogram of firewood or coal takes about 5 megajoules. When wood is burnt, it produces three times the amount of energy used to produce it. For coal, the figure is up to a hundred times greater and, for oil, up to a thousand times. Different forms of stored energy have very different characteristics, and they shaped different societies. Cities heated by wood, such as Rome, are organised differently from cities heated by peat, such as Amsterdam, and from cities heated by coal, such as London. The Romans dreamt of gold, of miraculous machines and voyages to other worlds. None of them could have guessed that the peaty sludge and black stone they found in their chilly colony would turn out to be the greatest miracles of the new world.
Ships
Humans’ earliest sources of energy were renewable. The wind filled sails, sending adventurers off in search of raw materials or their substitute, gold. Commodities floated downstream, and animals hauled goods upstream. Always on the front line of technology, shipbuilding sent people back to the forests. Ships required timber of the highest quality and of various sorts: straight oak for the planking, crooked oak for the ribs, pine for the masts, beech and spruce for the decks. And ships needed other products from the northern lands – tar for caulking the hull planks, hemp for ropes and linen for sails. But, in Southern Europe, forests remained only in the most inaccessible areas, on islands or on mountainsides. Wars were fought over these vital supplies of timber, and they were turned into colonies – Cyprus and Sicily, Istria and Macedonia, and later the Tyrol and Galicia. Sawmills and quays had to be constructed at river estuaries. All this activity depended on the population living on the river banks and sea coasts. But the imperial exploitation of the forests came into conflict with the native ways of using them and led to the policing of increasingly distant and inhospitable lands.
The Roman trireme had a wooden hull and deck, about 200 oars and two masts. Building such ships required thousands of trees of rare species. The Vikings’ ships were simpler and lighter, but more seaworthy thanks to their use of tar. This sticky, impermeable substance, produced by the dry distilling of pine or birch wood, protected the craft from leaks and rotting. The Vikings dug a big clay pit, filled it with chunks of pine, covered them with turf, and set them alight. After several hours, tar trickled down out of an opening at the bottom of the pit. The sailors of antiquity also knew the recipe for making tar, but it required pine trees in quantities which they could hardly obtain. The Vikings produced tar on an industrial scale, 300 litres at one go; two such distillations would produce enough tar to caulk one craft. The sails, which the Vikings made out of wool, were also soaked in tar – they turned black. It is only thanks to the archaeologists who found these tar pits that we understand why the Vikings were better seafarers than the Romans or the Phoenicians.8
Republics and empires alike were preoccupied by the shortage of oak for hulls, beech for decks and pine for masts. It took up to 2,000 oak trunks, preferably from hundred-year-old trees, to build one large warship; but