Chapter energy and technology the enhancement of skin

5.4. The dawn of civilization and the beginning of agriculture

The upright hairless hominids divided into several branches during the last million years. The proto humans also learned to devise traps and simple weapons, made from bones or stones, such as flint. This period is known as the paleolithic age. The word “lithic” refers to stone) Soon after that they also learned how to make spears for defense against larger predators and also for purposes of hunting.

Human hunter-gatherers needed a lot of land, from 20 to 100 hectares per capita, depending on location. Our ancestors used dogs for hunting at least 32,000 years ago. Hunting was evidently responsible for the extinction of some species, such as the giant mammoth (whose remains are still being uncovered, from time to time, in northern Siberia). And, as they became more efficient at hunting, they also took advantage of the warmer inter-glacial periods to migrate north into Europe and Asia, and eventually across the Bering Straits “land bridge” from Siberia into North America. As far as we can estimate, the exergy budget of those early human hunter-gatherers was about two kilowatt-hours (2 kWh) per day, per capita.

The species of hominids competed with each other for living space. Finally, one species (Homo Sapiens) eventually conquered (and probably massacred) its chief rival, Homo Neanderthal. The details of that war are unknown, but it seems to have happened around 40,000 years ago. (It seems that the Neanderthals did not use dogs, whereas Sapiens did. I wonder if that was a factor in the outcome?) By the time of the Homo Sapiens final victory, the average energy consumption per person had risen to around six kilowatt-hours (6 kWh) per day.

The oldest artifacts that we can date with some confidence are the cave paintings of large animals, in the Vézères Valley of south central France. A large number of inhabited caves have been found in the area, some of them decorated. The famous paintings at Lascaux have been dated at 17,300 years ago. That period is known as “Upper Paleolithic”.

Human “civilization”, consisting of centralized governments over large regions, wars of conquest and large towns, probably began either in the so-called “fertile crescent” between the Euphrates and Tigris rivers in what is now Iraq, or along the Nile River. Between twelve thousand and ten thousand years ago the last glaciers were receding and the average temperature of the Earth was in the process of rising by about 5° C. to the level we have enjoyed for the past several millennia.

In this new, warmer, environment – which must have seemed like paradise compared to the preceding ice age – Homo Sapiens took another great leap forward: the “neolithic revolution”. Of course “Neolithic” is another word for “stone age” and it is interesting that a factory for manufacturing, storing and exporting flint tools existed in central France (the Claise Valley) in the third millennium BCE. Farming (of grain) and cattle breeding were literally invented. Instead of just hunting and gathering food from wild plants and animals that live in grasslands, forests, and surface waters, our ancestors learned how to harvest solar energy more systematically, by cultivation of plants for food.

We can imagine a Neolithic woman – call her “Eve” – who collected edible seeds from nearby clusters of wild grasses. (Not the kind of grass we see in lawns or on golf courses). They were precursors of the grains we now call wheat and corn (maize). She naturally collected the biggest and ripest seeds. Her family ate most of the grain she collected. But some seeds got scattered around the hut or cave. Those seeds grew and produced more of the big seeds. She realized, perhaps for the first time, that plants grow from seeds. It was one of the great Eureka moments in human history.

Fire also helped, for land clearing. In fact early agriculture was mostly of the kind what we now call “slash and burn”. A tribe would clear a small area by burning it (which also released nutrients in the ash), and then would move on when the fertility “spike” from the fire was used up. This type of agriculture is still practiced in a few remote areas. However, that type of agriculture was still inefficient in land use: it needed 2-10 hectares per capita. The floodplains of major river valleys in Mesopotamia or along the Nile took care of the need for annual renewal of fertility, and the land requirement dropped to 0.5-1.5 hectares per capita.

Meanwhile the hunters – like her man, call him “Adam” – made a comparable great discovery. It was that, when a baby animal orphan of some (not all) species was raised by humans in a human environment, it became tame and biddable. This probably worked first for dogs. The dogs (prehistoric wolves?) probably started by following human hunting parties to scavenge. But in the course of time the dog-packs occasionally left behind orphan babies that were adopted by human families and tribes. (Who can resist cuddling a puppy?)

Over the centuries dogs that had been raised by humans became “different” from the wild dogs. They became guardians and helped with tracking and hunting of other animals. The cynical saying about human relationships, that “if you want a friend, get a dog”, is also saying something about dogs. There are numerous documented cases of pet dogs dying of grief after the death of a master, or giving up their lives to protect, or save, a master.

Eventually the domesticated dogs drove off the wild dogs (and wolves). The ancient relationship between humans and dogs (and wolves) is the basis of the legend of Romulus and Remus. They were unwanted by their father, King Amulius (who was afraid they would grow up and depose him). So, the twins were set adrift in the Tiber river– a form of infanticide. But the babies were found and suckled by a she-wolf. They later grew up and founded Rome.

Humans learned how to control the animal breeding process. Later, cattle, sheep, goats, camels, horses, donkeys, oxen, pigs, geese, ducks, chickens and some other large animals (e.g. elephants) were gradually domesticated during those thousands of years. Some humans become sheep or cattle herders. Domestic animals provided skins, fur and hair (wool), meat, milk, eggs, manure for fertilizing the land and muscle for tilling the soil. Horses, donkeys and camels also provided mobility and carrying capacity.

Not every wild animal can be tamed. In fact, most of the animals now seen in zoos, from zebras, antelopes, giraffes, rhinos, hippos, and large members of the cat family are difficult or impossible to domesticate. Small cats seem to have made themselves useful – probably by catching rodents – without ever becoming teachable or “biddable” in the way that dogs and horses are.

It seems that most of the animals suitable for domestication were originally found in Eurasia, not in Africa or the Americas. Furthermore, agricultural innovations diffused much more easily along Eurasia’s east-west axis than along Africa’s and the America’s north-south axis, broken up by geographic and climatic obstacles. Around those two axes, it has been noted, turned the fortunes of history {Diamond, 1998 #1520} {Diamond, 1998 #1520}.

Since hunting for large animals, such as deer, is an easy way to feed a group of people for several days, the invention of farming seems likely to have been triggered by game (and firewood) scarcity. We now know from skeleton sizes, teeth, and other evidence that the agricultural population of Neolithic times was considerably less well-nourished (and had to work much harder) than their earlier hunting-and gathering ancestors {Diamond, 1991 #6618 Chapter 10}. Probably agriculture, as a primary occupation, was a desperate response to over-hunting, land clearing and over-crowding.

It began where population had grown too great to live on the proceeds of hunting. Land clearing, for purposes of cultivation, drove the wild animals further away. Early agriculture was not very productive, as can be seen today by comparing the skeletons of prehistoric farmers with the skeletons of the hunters who had previously lived off the same land. The hunters were as much as six inches taller and they lived longer. For the people struggling for a bare survival it must have seemed as though they had been kicked out of a paradise of plenty. This racial experience has been described in stories handed down through the generations, such as the expulsion of Adam and Eve from the Garden of Eden.

I mentioned the limits of fire as a source of light. But during the Paleolithic era, from 15 thousand to 40 thousand years ago some tribes learned how to make stone dishes, with shallow depressions, capable of retaining melted animal fat. These were the first lamps, of which several hundred have been found by archeologists. It is estimated that such a lamp, burning animal fat, produced about the same amount of light as a candle {Nordhaus, 1998 #7666}. Terracotta lamps burning oil (probably sesame oil) existed in Babylon 5000 years ago, and were used (at least) in the temples.

As an indication of the price, it seems a common laborer at the time earned about one shekel per month, which was the price of ten liters of sesame oil. Nordhaus says that a quarter cup of oil (with a wick) burned for 17 hours in a Roman copy of such a lamp, producing 28.6 lumen-hours, or 17.5 lumen-hours per thousand Btus. From then until 1992, Nordhaus estimates that the labor-cost of illumination declined by a factor of 350,000 (ibid). It is still declining, thanks to light emitting diodes (LEDs) that have been commercialized in recent years.

Other consequences of primitive agriculture include the need for means of storage, and the need for protection of the immobile farmers and their crops from mobile predators, both animal and human. The need for protection was probably the cause of walled cities and armies, not to mention class differences, epidemics, starvation and gender discrimination {Diamond, 1991 #6618 Chapter 10}.

Despite their impressive cultural achievements, agrarian civilizations have always been handicapped in their development by the limitations of the physical work that can be derived from human or animal muscles. Wheels, levers, inclined planes, pulley blocks, water mills, windmills and sails have provided limited help to surmount human biological limitations. The earliest farmers had to do the cultivation of land themselves – with the assistance of children – and this is why agriculture began in river valleys where there was a reliable annual deposition of fresh silt that was easy to plow and not already occupied by trees or deep-rooted grasses and shrubs. Of course plowing, back then, was probably nothing more elaborate than dragging a sharp stick through the damp silt to make a groove in which to drop the seeds.

The taming of animals to do the plowing, probably oxen at first, eventually enabled farmers to leave the river valleys and cultivate higher grass-lands. This task was very challenging, and required much more brute strength than humans could provide. Several inventions were required to make this possible. One was a more elaborate plow, initially of wood, but later of crude metal. Another was some form of harness to enable the animals to pull the plow. Horses were more difficult to tame and harness than oxen, but they were naturally more at home in grasslands. They were also quicker than oxen and could also be tamed (and ridden). Later, horses were also used to pull wheeled vehicles. Horses gradually replaced oxen for plowing in most of the upper-story world outside the river valleys.

It is tempting, but quite wrong, to think of horses or oxen as workers capable of feeding themselves, i.e. as “free lunches” so to speak. It is true that these animals can feed themselves by munching on grass; they do it in their natural habitat. But if a horse is working, harnessed to a plow (or a cart) all day, it must be fed some more concentrated form of nutrition. Moreover, hay (dried grass) is not sufficient as feed for working animals. It will not provide enough either of energy (Calories) or of protein. A working horse needs grain, usually oats.

To put it terms of modern units, a working horse generates roughly one “horsepower” which is equivalent to about 700 watts or 0.7 kilowatts of power. By comparison, a working human can generate only 50 to 100 watts of power {Smil, 2008 #6578}. In terms of work output, a horse can produce around ten times the output of a human worker. Not only that, a colt can start working after a year or so, whereas a human child cannot do hard physical work beyond sorting seeds or tubers or feeding chickens, until he (or she) is at least twelve or thirteen years old.

The energy (Calorie) content of the feed (for a horse) or the food (for a human) must be at least seven times as great as the energy equivalent of the food produced. This is because the energy conversion efficiency of the animal metabolism is not more than about 14-15 percent at most (ibid). This is a biological limit that has not changed in the last 5000 years since animals were first domesticated. Among other things, the need to provide high-energy feed (not just hay) for working animals means that about 15 to 20 percent of all cultivated land has always been needed for that purpose.

The quantity and plant composition of crops depend on two properties of the biosphere: One is weather and climate, i.e. the short term and longer term fluctuations of sunshine and rain. Another factor is the natural fertility of the land. This means its content of humus, nitrogen, phosphorus (and other useful trace elements), on the one hand, and the absence of noxious salts (and pests), on the other. Technical progress in tilling the soil, like the transition from the wooden pickaxe to the animal-drawn iron plough, cut the labor (and energy) inputs needed for tillage. Also, crop rotation and the use of animal manure for retaining soil nutrients have increased crop yields enormously – if it were not so, China and India could not feed themselves today.

Domesticated grazing animals, especially cattle, sheep and goats, convert cellulosic biomass into food available to humans. However, the thermodynamic efficiency of producing animal biomass from grass is fairly low. For instance about 8 tons of dry vegetable matter is converted into a ton of dry milk by cows. Chickens make eggs somewhat more efficiently, which accounts for their wide exploitation. Fish are even more efficient convertors because, being cold-blooded, they do not need energy to maintain body heat. Thus, in times of population growth and food scarcity shifting from pasture to cultivation can increase the output of edible food energy by something like a factor of five. Estimates for different agricultural technologies arrive at the following annual yields of food energy per hectare (= 10000 square meters), including the fallow periods:

• 
  Rice with fire clearing (Iban, Borneo): 236 kWh
  
• 
  Horticulture (Papua, New Guinea): 386 kWh
  
• 
  Wheat (India): 3111 kWh
  
• 
  Maize (Mexico): 8167 kWh
  
• 
  intensive farming (China) 78056 kWh
  

Hunters and gatherers only obtain between 0.2 to 1.7 kWh per hectare per year. Thus, as compared to Chinese intensive farming, as many as 50,000 times more people can live on the produce of a given area than under pre-agricultural conditions.

There are people today (mostly living in cities) who imagine that it would be a great idea to return to an economy of small self-sufficient farms, such as envisioned by Thomas Jefferson, the author of the Declaration of Independence of the 13 American colonies. This was possible, even in his native Virginia, when he was alive. But it is possible no longer. To feed the current global population of the Earth (7.5 billion or so by now), intensive (and somewhat industrialized) agriculture is unavoidable.