Control of Fire: When Humans Learned to Use Fire

Fire before fire-makers

Long before anyone could make fire, fire made itself. Lightning strikes a dry tree, the grass catches, and a wildfire races across the plain. Animals run, but some fall behind. Imagine early humans walking through the black, smoking ground afterwards. They would find roasted seeds, nuts, roots and the meat of animals that did not get away. Cooked food is often softer and sweeter than raw, and these first meals may have been a lucky gift from the sky. Scientists think this scavenging is a likely first step, though nobody can prove it, because ash of that age rarely survives.

Homo erectus meets the flame

The best candidate for the first fire-user is Homo erectus, who lived in Africa and Asia from about 1.9 million years ago. The strongest early evidence comes from Wonderwerk Cave in South Africa. In 2012 a team studied thin slices of the cave floor under the microscope and found burned bones and plant ash in a layer about one million years old. The ash lay far inside the cave, away from the entrance, so scientists think people carried the fire in. Older claims from Kenya, about 1.5 million years old, are still debated.

From visitor to habit

Burning a fire once is not the same as using it every day. The clearer sign of daily use comes later. At Qesem Cave in Israel, people lived between about 420,000 and 200,000 years ago, and they left layers of ash, burned bones and burned flint, again and again, in the same part of the cave. Around one spot, it seems, the group cooked and worked together. Researchers read this as habitual use of fire by about 400,000 years ago. Fire slowly turned from a rare tool into part of ordinary life.

Three things a flame needs

Why does a fire burn at all? It needs three things at once, called the fire triangle: fuel, heat and oxygen. Fuel is wood, dry grass or dung, anything that can burn. Oxygen comes from the air, which is about 21 percent oxygen. Heat brings the first bit of fuel to its ignition point, roughly 300 °C for wood, and then the flame makes more heat to keep itself going. A wood fire burns at about 600 to 1000 °C. Take away any one side of the triangle and the fire goes out: no fuel, no air, or too much cooling. Move the three sliders in the sandbox and watch the flame shrink, then die.

Spinning wood, striking stone

Keeping a fire alive is hard work, so at some point people learned to make it. With a hand drill, you set a straight stick in a notch in a wooden board and roll it quickly between your palms. Friction heats the wood dust until it glows as an ember, which you tip into dry grass and blow into flame. The other way uses a spark: flint struck on pyrite, a golden mineral of iron and sulphur. Flint hand axes about 50,000 years old from Neanderthal sites in France carry wear marks that, scientists suggest, came from pyrite. When people first made fire is not known.

A cooked meal

What did fire change? One famous idea is the cooking hypothesis of the primatologist Richard Wrangham, set out in a book in 2009. It is a theory, not a settled fact. Cooking softens food and makes more of its energy available. A body that spends less time chewing and less energy digesting can use the saving elsewhere. Wrangham suggests that cooked meals helped Homo erectus grow a smaller gut and a bigger brain. The brain uses about a fifth of our resting energy, so it is costly. Many scientists find the idea attractive but unproven, since clear evidence of daily cooking arrives later.

Warm nights, together

Fire did more than feed people. It warmed them on cold nights and in Ice Age winters, which helped them live in colder lands. It gave light after dark, so the day grew longer. Smoke and flames kept many animals away, and a burning branch could scare a predator. Above all, fire drew people together. A study of the Ju/'hoansi people of southern Africa found that evening talk around the fire was mostly stories, while daytime talk was mostly about work. Fire gave people a place to sit, listen and share what they knew.

The Gift of Fire