Muscles, wood, water and wind: energy before fossil fuels: Foraging and farming: food as the first energy system

2.1 Foragers lived on net energy returns, at densities below one person per square kilometre

Foraging is a balance of energy spent and energy gained. Walking, digging roots, climbing for fruit, tracking and hunting typically cost four to five times basal metabolism, about 900 kJ an hour. A band could survive only if what it gathered exceeded those costs by enough to feed children, the old and the sick.

Returns varied enormously with the resource. Collecting high-yield plants such as nuts or starchy roots, or killing a large mammal, often returned 10 to 20 times the energy spent. Small game, scattered seeds and small fish returned much less. Foragers therefore moved through the seasons to follow the best returns, carried few possessions and lived in small bands.

Because wild plants and animals are thinly spread, population densities were very low. In deserts and dense forests they were well under one person per square kilometre, and across all foraging societies they spanned about three orders of magnitude. The densest lived on rich coasts and rivers. Peoples of the Pacific Northwest of North America, harvesting salmon runs and sea mammals, built permanent villages, carved monumental wooden art and developed social hierarchies without any farming.

Meat played an outsized role. In Should We Eat Meat? Smil argues that hunting and scavenging supplied energy-dense, protein-rich food that helped support larger brains and smaller guts. Fire and cooking were the other great foraging innovation: cooked food yields more digestible energy and needs less chewing and digesting.

Smil avoids both romantic and grim stereotypes. Foragers were neither an original affluent society with endless leisure nor permanently starving. Outcomes depended on habitat, season and luck.

• Smil, Energy and Civilization: A History (2017) · via Smil Mastery Course, M3 'Foraging: gathering, hunting, fishing'
• Smil, Energy in Nature and Society: General Energetics of Complex Systems (2008) · via Smil Mastery Course, M3 'Foraging: gathering, hunting, fishing'
• Smil, Should We Eat Meat? Evolution and Consequences of Modern Carnivory (2013) · via Smil Mastery Course, M3 'Foraging: gathering, hunting, fishing'

2.2 Agriculture won by feeding more people per hectare, not by saving work

Plants and animals were domesticated independently in several places: wheat, barley and lentils in the Fertile Crescent about 11,000 to 10,000 years ago; millet and rice in China; maize, beans and squash in Mesoamerica; potatoes in the Andes; and other crops in Africa, New Guinea and South Asia. Sheep, goats, cattle and pigs came early; horses and camels later.

The energy logic is often misunderstood. Early farmers frequently worked longer hours than foragers and ate a less varied diet, and skeletons from early farming villages often show shorter stature and more signs of disease. The gain was in land productivity. A hectare of cultivated grain could feed many times more people than a hectare of wild land, so farming communities grew and eventually displaced or absorbed foragers.

In many regions the first farming was shifting cultivation. A plot of forest is cleared and burned, cropped for a few years using the nutrients in the ash, and then abandoned for a decade or more while the forest regrows. This supported tens of people per square kilometre of total territory, more than foraging but far less than permanent fields. It still survives in parts of northeast India, Southeast Asia and Africa.

Why farming began is still debated. Population pressure, the warmer and more stable climate after the last Ice Age, competition for status and feasting have all been proposed. Smil warns against single-cause explanations; several factors probably reinforced one another.

Settled life brought new possibilities: stored food, property, specialised crafts, cities, states and writing. It also brought new costs: diseases passed from animals and spread by crowding, dependence on a few crops, and the risk of famine when harvests failed.

• Smil, Energy and Civilization: A History (2017) · via Smil Mastery Course, M3 'Why agriculture began'
• Smil, Grand Transitions: How the Modern World Was Made (2021) · via Smil Mastery Course, M3 'Why agriculture began'
• Smil, Harvesting the Biosphere: What We Have Taken from Nature (2013) · via Smil Mastery Course, M3 'Why agriculture began'

2.3 Traditional farming intensified with animals, water, manure and rotations

For about ten millennia farming ran entirely on current solar flows: sunlight for the crops and food or feed for the people and animals working the fields. Within that limit, farmers found many ways to raise output.

Grains became staples everywhere because they are storable and energy-dense, about 15 MJ per kilogram, and give good yields: wheat and barley in West Asia and Europe, rice and millet in East and South Asia, maize in the Americas. Storage carried people through lean seasons and fed the soldiers, priests and craftsmen who did not farm.

Draught animals multiplied the power available for ploughing, threshing and carting. An ox delivers about 250 to 400 W, a good horse 500 to 800 W, several times a human. Irrigation raised and stabilised yields, from basin flooding along the Nile to Chinese canals, Persian qanats and the tanks of South India.

Nitrogen was the nutrient most often in short supply, and traditional farmers supplied it by recycling. They spread animal manure, human waste, crop residues and ashes, and grew legumes such as beans, peas, lentils and clover, whose root bacteria fix nitrogen from the air. Rotations combined these: the Norfolk four-course rotation of 18th-century England cycled wheat, turnips, barley and clover, feeding livestock and restoring the soil at the same time.

These methods allowed remarkable densities. Ancient Egypt supported roughly one person per hectare of farmland. The most intensive traditional systems, in parts of 19th-century China, supported more than five people per hectare by double-cropping, recycling almost every organic waste and investing huge amounts of labour.

• Smil, Energy and Civilization: A History (2017) · via Smil Mastery Course, M3 'Traditional farming and its intensification'
• Smil, Energy in Nature and Society: General Energetics of Complex Systems (2008) · via Smil Mastery Course, M3 'Traditional farming and its intensification'
• Smil, Enriching the Earth: Fritz Haber, Carl Bosch, and the Transformation of World Food Production (2001) · via Smil Mastery Course, M3 'Traditional farming and its intensification'

2.4 The organic ceiling: low yields, scarce nitrogen and recurrent famine

Even the best traditional farming hit hard limits. Wheat yields in medieval Europe were often below 1 tonne per hectare, with only three to five grains harvested for each grain sown, so a fifth to a third of the harvest had to be saved as seed. Today's best European wheat yields are around 8 to 9 tonnes.

Nitrogen was the binding constraint. Manure, night soil and legumes could recycle and add only so much. To push yields higher, crops needed far more nitrogen than organic sources could provide on the same land. That ceiling was broken only in the 20th century by synthetic fertiliser made by the Haber-Bosch process, using fossil energy to make ammonia from the nitrogen in the air.

Animals competed with people for land. A working horse could need the feed from one to two hectares, so in countries that relied on horses a large share of farmland grew oats and hay rather than food. Diets were monotonous: most people got 70 to 90% of their energy from cereals or tubers, ate little meat, and suffered seasonal hunger and stunting.

Harvest failures caused famines whenever drought, floods, cold or pests struck. The worst famine in history, however, was made by policy on top of a fragile system: Smil's work on China documents roughly 30 million excess deaths in 1959-1961 during the Great Leap Forward.

The organic ceiling also explains the slow growth of population before 1800. Over millennia, the world's population grew on average by well under 0.1% a year. The rapid growth of the last two centuries required breaking that ceiling with fossil fuels, both directly for machinery and indirectly through fertilisers.

• Smil, Energy and Civilization: A History (2017) · via Smil Mastery Course, M3 'The limits of traditional farming'
• Smil, Grand Transitions: How the Modern World Was Made (2021) · via Smil Mastery Course, M3 'The limits of traditional farming'
• Smil, Enriching the Earth: Fritz Haber, Carl Bosch, and the Transformation of World Food Production (2001) · via Smil Mastery Course, M3 'The limits of traditional farming'
• Smil, China's Past, China's Future: Energy, Food, Environment (2004) · via Smil Mastery Course, M3 'The limits of traditional farming'

See it in the table

Check your understanding

What was the main energetic advantage of early farming over foraging?

What role did legumes play in traditional farming?

Why did keeping horses reduce the food available to people?