There is a well-known saying that something is “small potatoes”, meaning something is insignificant and lacking value. Anyone who has spent half an hour harvesting or preparing small potatoes versus a few minutes on great stonking ones has a visceral sense of the meaning of the idea. When given a choice people will always harvest the bigger potato and reel in the larger fish, just as society tends to cut down the biggest trees or drill the biggest oil fields first. The concentration of resources is a critical part of their value to us, since they represent a goal with a higher return on investment. A cup and a half of dry rice can provide about half the calories you need in a day. If that rice was hanging on a couple of stalks of grain it would represent a very valuable resource, while if it was scattered over a wide area you could potentially spend more than a day on your hands and knees picking it up one grain at a time. You would need to be desperate to invest such time, and if the rice was scattered too widely you would actually be better off sitting still and starving more slowly.
Another thought experiment might be illustrative. A medium sized apple contains about 400 kJ energy. A human needs about 10 000 kJ per day. Humans use an extra 1.2 kJ/hr when walking about 5 km/hr, a negligible amount compared to resting metabolism. Allowing for 16 hours to sleep and rest and 8 hours of walking, a human then could walk 40 km per day and could survive in an environment where apples were spaced every 1.6 km apart. If the apples were spaced further apart then the environment would be unable to support humans, much like deserts that are mostly home to energy efficient reptiles. The more closely spaced the apples the larger the tribe of humans walking together could be, and the more time they could spend doing other activities. If apples were dense enough in the environment they could even stop walking and settle in one location. Humans are also unusual in being able to carry food over long distances. In this case the 25 apples per day would weigh about 5 kg, meaning a walker could comfortably carry about two days’ worth of apple energy.
Apples are probably a poor example since most of their mass is water. For environments where water can be found along the way it makes sense to work with more concentrated food sources. Dry carbohydrate like pure starch contains about 15 000 kJ/kg, so a person could carry 18 days’ worth of food energy. Fat is even more concentrated and a person could carry over 40 days’ worth of food energy. For this reason fat was always a prized resource and may have been a key catalyst in the evolution of human physiology that is dependent on highly concentrated foodstuffs. Much like high performance race cars that are designed to function with highly refined fuel while a plodding steam engine can run on lower quality coal or wood, similar patterns are seen in living things. A panda or gorilla spends most of its day eating low quality plant matter and needs a large and slow digestive system, while a hummingbird can only survive on highly concentrated fast burning nectar that suits its highly reduced intestines. Humans are highly unusual in predigesting our food, and even more unusual in how flexible we can be at adapting to different food types. Instead of adapting our teeth and digestive system to specialise in a limited range of food sources like every other animal instead we are incomparable generalists. Instead of doing mechanical digestion with our teeth we use rocks to crack nuts and grinding stones to reduce seeds and tubers to a soft paste. The lack of selective pressure on our mouths for breaking down food freed them up to become suited to making complex speech. Instead of doing chemical digestion and detoxification we instead learned to break down food with heating and fermentation, freeing up our metabolism to support our large brains instead of our guts. We even use external technologies like clothing and housing to further reduce the need to produce body heat. Humans also supplement our impressive ability to store body fat with the ability to store food externally, either as a simple string bag full of nuts or a village sized granary with fired clay pots.
The peculiar way humans relate to their food environment has some serious consequences. Our total food energy needs are about the same as any other mammal our size but our dependence on heat to cook our food greatly increases our energy foot print. In pre-industrial villages where fossil fuel energy is not in use individuals consume about 1-5 kg of fire wood per day for cooking, representing another 16000 to 80 000 kJ per day, or up to 8 times more energy than is consumed as food. Shifting to heating fuels that are more energy dense than wood (16 000 kJ/kg) like coal (33 000 kJ/kg) and oil (43 000 kJ/kg) allowed humans to live in ever more dense societies. The near complete shift from wood to fossil fuels in the most heavily industrialised societies has allowed considerable forest regrowth around communities in places that had been denuded moonscapes just a few generations ago. With the eventual depletion of fossil fuel resources humans might be forced to go back to using wood as a major fuel, at the very least for food preparation that our physiology it highly dependent upon. Our population densities have increased substantially in the time since wood was phased out as a fuel, meaning a return is likely to have devastating consequences for our regrowing forests. Cold regions where wood is also used for heating will suffer additional pressure. An analysis of the relatively sparsely populated USA estimated even the most heavily forested regions would consume their forests within three decades without fossil fuels. Various forms of renewable energy suffer from harvesting very low concentration energy, be it sunlight or wind. A future society powered by renewables is likely to end up being like the person walking from apple to apple, with the fruit too widely spread to sustain the walker. Renewable technologies are likely to end up being like using a very large net to catch a few very small fish in a big ocean.
Today we live in a world awash with cheap energy, supplied directly and indirectly by fossil fuels that are currently produced in astonishing quantities. Those fossil fuels subsidise the production of food by industrialised agriculture, meaning that carbohydrates and fats are cheaper and more reliable than they have ever been in history, even in the poorest nations. As a result many populations are struggling with obesity. At the same time the great distances between where food is grown and consumed has meant that the most delicate and perishable food items have become relatively unaffordable. Growing your own vegetables in the context of an industrial calorie foundation makes sense but humans cannot live on leaves and fruit. In the industrialised world this has elevated the apparent importance of fruits and vegetables in the human diet at the same time as carbohydrates and fats have been demonised. A good example of this effect can be seen in how most people handle the humble pumpkin. I recently harvested a big hybrid with 3 kg of flesh (likely reduced to 1.5 kg once the skin is peeled). This pumpkin flesh contains about 1600 kJ, along with some vitamin A. By contrast the fruit also produced 150 g of seed, yielding an impressive 3400 kJ, including a large amount of protein, fat and key minerals like zinc. Despite its meagre size the pumpkin seed contains much more nutritional value than the flesh. Most people scoop the seeds into the bin (or maybe compost them if they are feeling extra green), not realising that they are discarding the most concentrated and valuable part. Washed, dried and lightly toasted the seeds can be eaten whole in some varieties or crushed to a rich meal in those with tougher seeds. Pumpkin was originally domesticated by humans as a seed crop, with mutants with sweet and abundant flesh only emerging thousands of years later. My personal aim now is to select varieties with the best seed production and quality. The watery flesh can go to the goats as a treat, to be turned back into more concentrated milk and meat and I will concentrate on the more concentrated forms for myself.
Zero Input Agriculture 