The Technology of Fire
Episode #3 of the course Technologies that transformed humanity by Richard L. Currier, PhD
Once the transition to walking and running on two legs was complete, the hominids’ forearms and grasping hands became free to serve other purposes, including the unique ability to handle fire. Prehistoric hominids learned to carry burning branches back to camp from naturally-occurring wildfires, to gather firewood, and to keep a campfire burning continuously.
The Control of Fire Revolutionized Hominid Life-Ways
Since all other animals fear and avoid fire, the hominids’ unique ability to control fire made possible new ways of living. Hominids became the only primates (except for the massive gorilla) capable of sleeping safely on the ground. Using fire to drive bears, leopards, snakes, and other predators out of caves, hominids took over these natural shelters for themselves.
When they began to make fires, sleep with fires, and cook food, the lifestyle of the hominids changed dramatically. No longer having to sleep in the trees for safety, they lost the long, semi-grasping toes and long arms of the tree-dweller. And because long body hair catches fire easily, they lost the thick fur that covers all other primates and became the “naked ape.”
The Hominid Invention of Cooking Food
There was another revolutionary change in human anatomy that evolved from the cooking of food: the massive expansion of the human brain.
Chimpanzees, gorillas, orangutans—our closest relatives—all have large, swollen abdomens; these species need very large digestive tracts to process the raw vegetation that constitutes the bulk of their diets. They also spend tremendous amounts of time—up to 50% of their waking hours—simply chewing their food. People, on the other hand, spend only 5% of their waking hours chewing the mostly cooked food that is a staple of every human diet.
Cooking vegetables converts the indigestible cellulose in plant foods to easily digested starches and sugars, and cooking meat converts the hard-to-digest collagen in lean meat into easily digested, protein-rich gelatin.
Studies and research have shown that when anatomically modern humans eat even highly nutritious and pre-mashed or ground-up raw foods for a long periods, they lose significant amounts of weight, men lose sexual desire, 50% of women entirely cease to menstruate, and all experience moderate to severe loss of energy. This is because the energy required for humans to digest raw food is so great that they end up with an “energy deficit” that leaves them progressively weaker over time.
The Human Brain Is the Body’s Most “Expensive Tissue”
Five organs of the human body are “expensive tissues” in terms of the energy they consume: the brain, heart, liver, kidneys, and digestive tract. (The muscles use lots of energy, but only when actively working.) The human brain is the most “expensive” of these organs: It consists of only 2% of the body’s weight, yet it consumes as much as 20% of the body’s energy.
As humans evolved, the brain expanded massively in both size and energy requirements, requiring one of the other “expensive tissues” to grow smaller. Yet, the vital functions of neither heart, liver, nor kidneys could be reduced. But cooking allowed the digestive tract to become significantly smaller, freeing up energy to power the expanding hominid brain.
The invention of cooking allowed the hominid brain to nearly triple in size over the past million years. Before cooking, the volume of the hominid brain was about 550 cubic centimeters (cc), only slightly larger than the 450cc chimpanzee brain. After cooking began, the human brain grew rapidly until it was between 1,300 and 1,500cc in size. Without our immense brains, modern humans would never have been able to create the incredibly complex languages, cultures, and technologies that distinguish us from all other animals.
If it had not been for the control of fire, our species would have remained little more than an intelligent two-legged African ape that used long spears and digging sticks to find its food and that climbed into the trees every night to avoid its natural enemies while it slept.
In tomorrow’s lesson, you will learn how the invention of clothing and shelter enabled prehistoric humans to migrate out of their ancestral homelands in the tropics and successfully colonize virtually every environment on Earth.
The Expensive-Tissue Hypothesis: The Brain and the Digestive System in Human and Primate Evolution
Food for Thought: Dietary Change Was a Driving Force in Human Evolution
Man Entered the Kitchen 1.9 Million Years Ago
Catching Fire: How Cooking Made Us Human by Richard Wrangham
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