Our Technological History

Burn Notes

The Technology Tsunami

 Over time, we manipulated the metabolisms of our domesticated plants to divert their energy into the starches and sugars that fuel our bodies. Today, the fruits and vegetables we find in the market look like grotesque energy-packed carnival freaks compared to their wild ancestors.

We played the same trick with our domestic animals. By protecting them from natural predators and picking the winners and losers in reproduction, we favored those that allocated more energy into growth and milk production. Under our management, these species evolved into soft, dumb, reliable sources of fat and protein. They provided a metabolic engine for converting grasses and other forage that was inedible to us into milk, blood, and meat for our consumption.

Horses and other large species provided a new kind of engine as well—a source of mechanical work to augment or replace our own physical abilities. As James Watt, inventor of the steam engine, deduced through experiments at the dawn of the Industrial Revolution, a horse can comfortably produce around 640 kcal of work per hour (the definition of horsepower) and sustain that output for ten hours, day after day. That number is even more impressive than it might seem. Muscles are, at best, only about 25 percent efficient at converting metabolic fuel into mechanical work. To produce 6,400 kcal of work in a ten-hour day, a horse burns over 25,000 kcal of energy—and that’s in addition to the energy spent on BMR, digestion, and its other physiological needs.

In early farming cultures around the world, fertility rates accelerated as mothers and babies benefited from the extra calories that domestication provided. In the centuries that followed the adoption of agriculture, family sizes grew by an additional two children per mother. We can see these effects in hunter-gatherer and mixed foraging-farming populations today. A typical Hadza woman will have six children over the course of her lifetime, while a Tsimane woman, with the caloric benefits of some traditional farming, will have nine.

As populations grew, early farmers encountered strange new problems that their hunter-gatherer forebears never had to deal with, like overcrowding and the difficulties of public sanitation. Communicable diseases that would have fizzled out quickly in sparse hunter-gatherer encampments became full-blown plagues, tearing through early farming towns and cities.

Larger populations meant more people living, working, and thinking together. Putting more heads together has a synergistic effect on the development of new ideas, a phenomenon that Joe Henrich, a human evolutionary biologist at Harvard, calls the collective brain. Greater capacity to produce food also meant that people could diversify. Some were free to spend their adult lives on tasks other than food production, a luxury that no hunter-gatherer would recognize. Over three thousand years ago, cultures in the Mediterranean, South Pacific, and elsewhere had figured out how to harness the power of the wind to sail. Watermills appeared over two thousand years ago, as people learned to harness the energy of a flowing river to grind grain, lift water into irrigation systems, and perform a wide range of other work. Windmills joined them a few centuries later. Each invention and refinement expanded our external engines and the energy we could command.

Fossil fuels represent the collective metabolisms of uncountable plants and animals in the distant past, toiling away over millions of years. When we burn them, we’re releasing the energy stored in those ancient organisms.

Oil and natural gas production followed, moving from marginal sources of fuel to mainstays of global energy use following the development of commercial drilling in the mid-1800s. Today, these fossil fuels combine to provide over 35,000 kcal of energy every day for every person on Earth, 80 percent of our species’ external energy expenditure.

Our modern food system requires an immense amount of energy. Food production in the United States consumes roughly 500 trillion kilocalories each year. A third is burned as gasoline or diesel in farm machinery and transportation. Another third is the fossil fuel used to make fertilizers and pesticides. Electricity to run farms, storehouses, and supermarkets takes up most of the rest. Those trillions of kilocalories channeled into food production have profound effects on both the energy cost and energy content of our diet.

Hadza adults acquire roughly 1,000 to 1,500 kcal per hour of foraging.

The Tsimane and other foraging-farming societies, the rate of energy production is around 1,500 to 2,000 kcal per hour.

In the United States in 1900, with industrialization already in stride, an hour of physical labor in a manufacturing job could buy you more than 3,000 kcal of flour, eggs, bacon, and other staples. As the flow of fossil fuel energy increased, so did our purchasing power. Today, an hour’s wage could buy an American laborer roughly 20,000 kcal of those same staples.

• Processing has flipped the usual relationship between cost and energy content on its head. The result is a highly processed, supercharged diet. The energy density of an industrialized diet is 20 percent higher than the Hadza diet, and it requires little or no physical effort to acquire. Our hunter-gatherer ancestors would be stunned.
• Another result of increased energy density is the ability to recover quicker from pregnancy, and yet, birth rates have gone down. Some attribute this to increased life expectancy and others to access to education and family planning services.

Unintended Consequences

It is a basic rule of life that no species can persist if it spends more energy foraging than it acquires in food. Mammals in the wild typically get around 40 calories of food for every calorie they spend foraging. Humans in hunter-gatherer societies like the Hadza or mixed foraging-farming societies like the Tsimane fare a bit worse, with each calorie of work spent on food production yielding around 10 calories of food. Our modern food production system violates the fundamental laws of ecology. When we include the fossil fuel energy consumed in food production, we burn 8 calories for every calorie of food we produce.

The energy consumed in food production is just one part of our energy economy. Each year in the United States, we consume a staggering 25 quadrillion kilocalories. With a population of approximately 330 million, annual U.S. energy expenditure works out to 77 million kilocalories per person. That’s 210,000 kcal per day, equivalent to the daily energy expenditure of a nine-ton mammal. Each American consumes more energy than do seventy hunter-gatherers.

Globally, our species consumes 141 quadrillion kilocalories each year, an average of 47,000 kcal per person per day, nearly sixteen times the energy expenditure of our internal metabolic engine. There are 7.7 billion people on the planet, but we’re burning energy like there’s 120 billion of us.

Human-caused climate change is well under way, with the Earth 0.8°C (1.4°F) warmer than it was in the late 1800s, when fossil fuel use began to take off. The current generation of climate models, which have done an incredibly accurate job predicting our increasingly warm and wild weather, predict an additional 8°C warming globally in the next century or two if we burn the remainder of known fossil fuel reserves.

So far, our species has figured out four ways to generate power at meaningful scale that don’t emit greenhouse gases: hydropower, wind turbines, solar power, and nuclear fission. Hydropower is essentially maxed out. We’ve run out of big rivers to dam, and it causes massive ecological damage in any case. That leaves solar and wind, which currently combine to provide 2 percent of global energy, and nuclear, which generates 5 percent.

Building a Better Zoo

We have to make the cost of food more reflective of its impact on our health. One approach is to increase the cost of unhealthy foods. Taxes on soda and other sugar-sweetened beverages are often unpopular, but they seem to work. Extending those taxes to other highly processed foods might lower their intake as well, and in any case would provide a source of revenue for governments grappling with the ever-expanding health costs of our ever-expanding waistlines. We also need to make healthy unprocessed foods cheaper and easier to find.

We need walkable cities and towns, and real investment in human-powered movement. Cities like Copenhagen are leading the way on this, designing bicycle friendly urban areas that favor people over cars. Bike share systems have enormous potential to help, too, increasing daily physical activity and reducing disease.

With farming, and then again with industrialization, came major revisions to the social contract. Class differences and hierarchies emerged as wealth was consolidated in land and then in capital. This worked well for the upper class, of course, but was a disaster for those stuck at the bottom, who were used as slaves or otherwise exploited for their labor. The rest were caught somewhere in the middle, eager to climb the socioeconomic ladder but also desperate not to be caught in the gears below.

The stresses that result from this socioeconomic arrangement, from fears about money to the aching feeling that we’re being left behind to the daily assaults on our dignity, are new for our species. We don’t seem to handle them well. Living at the unhappy end of the socioeconomic spectrum makes us sick and shortens our lives. People living in poverty suffer from higher rates of obesity, diabetes, heart disease, and other cardiometabolic illness than the wealthy, and the effect is larger than anything we’d expect from diet and exercise differences alone. Likewise, people of color and other marginalized communities have worse health and shorter lives. If we’re serious about changing our environments to improve our metabolic health, then we need to address socioeconomic disparities, not just diet and exercise.

Daily physical activity is lower, for one thing. We are also less socially connected. Families are smaller and more dispersed. Loneliness has become so prevalent that it’s now a recognized medical condition. Modernization also brought us indoors. Time outside can relieve stress and promote physical activity, and it seems to improve cardiometabolic health more than physical activity alone.