The God Species_ How the Planet Can Survive the Age of Humans - Mark Lynas [14]
One human innovation is often neglected in accounts of our evolution—and it may be one of the most important of all, because it allowed us to fuel our process of encephalization (increased braininess). The brain is a very energy-hungry organ, consuming a quarter of all our energy use, as compared with 10 percent in other primates and 5 percent in most mammals.9 So how were the extra food requirements satisfied? Part of the answer is almost certainly the increasing amounts of animal protein in the human diet—hominid species quickly supplanted leopards as the dominant hunters on the African plains. But just as important was the advent of cooking, which enables food to be transformed into much softer and more calorific forms before being eaten. For over a million years humans have been eating cooked food, giving us a dietary advantage no animal has ever enjoyed before.
Cooking, of course, needs fire. Indeed there is a strong biological case for seeing humans as a coevolved fire species. Fire made us physically what we are, by allowing us to grow vastly bigger brains through eating cooked food. The human gut is much smaller, and uses far less energy, than the digestive system of comparable animals. We also have weak jaws, small mouths, and underdeveloped teeth compared with other primates. That first acquisition of fire acted as a powerful evolutionary driver, enabling humans to become the first truly sentient beings in history.
Fire, however, is a very special tool. Not for nothing is it identified in many human cultures as the preserve of the gods. Bonfires lit at the Celtic festival of Beltane symbolize the return of the sun to warm the Earth after the freezing nights of winter. In Navajo tradition, Coyote—who was a friend of humans—tricked two monsters on “fire mountain” into letting him light a bundle of sticks tied to his tail, which he then took back to people. Perhaps the best known fire tale of all is that of Prometheus, the Titan of the ancient Greeks (and son of Gaia, goddess of the Earth), who stole fire from the supreme god Zeus and brought it back to people. For this transgression he was punished by being chained to a rock and having his liver eaten out each day by an eagle.
And rightly so, for fire dramatically changed our relationship with the natural world. Acquiring the power of gods separated humans permanently and irretrievably from all other species. As well as cooked food, it afforded protection against predators and warmth on cold nights, allowing early humans to spread north out of Africa during the depths of the last ice age. Fire may have facilitated the spread of genes for hairlessness, as the need for body insulation diminished. However, once our hair was lost and our guts had shrunk, we were tied to the hearth—we could no longer exist without it.
No human can hope to survive in the wild today without fire, and this dependence marks a major qualitative shift in human relations with the biosphere. Other animals need only food. We are the only animal that has learned to harness an external energy source in a systematic way, through our reliance on fuel. It is this food-fuel relationship that most defines the fire-ape, Homo pyrophilus. Moreover, this innovation was perhaps the most important one in unbalancing our relationship with nature, for being armed with fire put the rest of the world at our mercy.
However, our dependence on fuel could also be a weakness. Once the forests were chopped down and the landscape denuded, humans might no longer be able to flourish. The story of the modern era, however, is the story of our transcendence over even this limitation. For modern humans were to discover a new source of fuel that would allow us to expand both our numbers and our dominance dramatically. This new fuel, in the form of underground