Partly because of my training in biological anthropology, partly because of my years as a migrant worker, and partly because of my model of low-input agriculture, I am quite convinced of the efficiency of the human engine.
Many years ago, my girlfriend and I set out from Tungsten Mine in the Pasayten Wilderness in Washington state, walking to the trailhead at Irongate Camp. Just after us a party of horse packers left the old abandoned mine to go the same distance. We arrived at the trailhead well before the other party. This was a distance of 18 miles and we had already done the 3 miles down from Cathedral Pass in the morning before we set out from the mine, so our total was 21 miles for the day and we carried all our gear. The horse packers may have done a little sightseeing and the horses probably got a little time for grazing, but it was quite easy for us to cover the same distance as the horses while carrying full packs. Our input (female 2000 plus male 2500 for the whole day) was 4500 calories or less. Each horse's input was 12,000 - 15,000 calories, depending on their load, plus there were riders using up around 1500 extra calories or more per person. Clearly, us humans could do the work of carrying gear and covering the distance required at a much lower energy input than the horses.
The human engine is very efficient. As you step out, neurons fire and muscles contract. Then the pendulum action of your step moves the mass of your body forward. As you step down again the muscles contract again, but also use some of the energy stored by the pendulum action. As you continue in motion, alternating right and left legs, you use the kinetic energy in a rhythmic motion that moves you forward in a very efficient manner. The pendulum is the key to the efficiency of bipedal motion. Efficient quadrupeds, like wolves, can travel greater distances in a day's time - up to a 100 miles per day in winter - but they need large quantities of high energy foods, like moose meat, to do so. Horses are pikers compared to wolves and humans.
The human hand is a very efficient tool, especially with the opposable thumb. Because of the length of our thumb and its position on the hand, we can do all kinds of things our nearest relatives, the chimpanzees and bonobos cannot. With our grotesquely-enlarged brain we can invent all kinds of tools to help us manage our daily lives, but the arrangement of our digits means we start out with 10 tools at our disposal - 5 on each hand.
Let me provide an example of how efficient the human engine really is. As many of you know, I farm using tillers and human labor, because the quantities of gasoline and diesel needed for tractor agriculture makes it unsustainable. In other words, my inputs from human labor and the 15-20 gallons of gas I use in my tillers per year to grow food on 1.5-2.0 acres is much lower than my outputs in food calories. Tractors use even more fuel than tillers, so the general rule is if you are riding on it while you are working, it is unsustainable because the fossil fuel calorie inputs will exceed the food calorie outputs. Sitting while working becomes the tipping point in sustainability.
Three days ago, I tilled up about 15,000 square feet, or a little over a third of an acre, in 3 hours. I used a gallon of gas, which has a thermodynamic value of 31,000 calories per gallon. My human calorie value was 375 calories guiding the self-propelled tiller as my overall work is calculated at 125 calories per hour. Total inputs for 15,000 square feet were 31,375 calories or 2.09 calories per square foot. Rounding to 2 calories per square foot for convenience, the question is: "How much soil could I till up in one hour with a shovel, hoe and/or cultivator at 2 calories per square foot?" Since I work at a rate of 125 calories per hour all day long and I am not even breathing hard and barely sweating, I calculate I should be able to dig up 62.5 square feet of garden and rake it to the same consistency of a first pass with a tiller in one hour. It should be noted that this is not sod, but half bare ground that wasn’t covered over the winter and half with a cover crop on it. The cover crops were favas and wheat, which provided a range of tilling difficulty.
62.5 square feet of ground is less than an 8 x 8 foot square, so the question is, “Can I dig up an 8 foot square in an hour?” That’s easy! Of course I can! Two days ago I and one other person dug up the soil in two hoop houses in less than an hour. Each hoop house was 30 x 10 feet, so the total area came to 600 square feet. One of us used a hoe and the other a bent-tine cultivator, what I call a potato fork. The ground in the hoop houses had been planted with a vetch/rye cover crop last fall and we had whacked it down to ground level a week before to make it easier to dig. Some rye had grown up again, but it wasn't jungley at all. The digging was fairly straightforward - just whack at it and turn it over. A shovel would have taken longer, but using the right tools, the calorie load for two people for one hour - 250 calories - and a conservative estimate of one hour for 600 square feet, the input calculation comes out to .42 calories per square foot to work up ground with a mowed cover crop on it. We should add in a little time to mow the crop down with a scythe or for chopping the cover crop in (the reason some people use oats, by the way, as it chops in easily), so rounding up to 1/2 calorie per square foot using hand tools seems reasonable.
So . . . 2 calories per square foot using a self-propelled walk-behind tiller and a human to guide it versus 1/2 calorie per square foot using human labor and hand tools. Quite a difference in the overall picture isn't it? The human with a shovel or hoe is 4 times as efficient as a tiller and probably many times more efficient than a tractor. [I will have to get some data on tractor fuel use for a more rigorous comparison.] In the future, as we run out of fossil fuels and are gasping for breath in a carbon-laden atmosphere, we will still be able to till up ground, prepare seed beds, plant, weed and harvest using the most efficient engine on the planet - the human organism. Right now, we could put the unemployed to work digging up land and growing food by hand to feed the starving masses, but we would have to have a massive redistribution of wealth to pay their wages. Even though it makes sense and is doable right now, it is unlikely because of the inequities built into our modern life. In the future, after the American empire has collapsed, maybe we can get it done. The model is right in front of you. You just have to pay a fair wage to people to do the work.