Energy and Society: Chapter 2: Organic Energy and the Low-Energy Society

October 7, 2012, 10:38 pm

If it is true that man is, everywhere and always, limited by the kind and amount of energy he can control, then we can find evidence for this by comparing all kinds of men during all periods of time that what we call man has existed, including those now living. There is substantial evidence that a common ancestor (Zinjanthropus) existed two million years ago. What has been called” wise man” (homo sapiens in Latin) has certainly existed forty thousand.

The differences between the various forms of man’s ancestors are attributable to a very wide variety of genetic, ecological, social, and cultural factors. Included among all of them, and all other organic forms, is the fact that the energy available to them came, with very small exceptions, from the sun.

There is little energy from the ocean tides, and the earth is continually bombarded with cosmic rays from astral bodies other than the sun. But this is tiny compared with the solar energy.

The elements available on the Earth evolved as the gases from which it derived were cooling. The great sources currently used by man include the sun’s radiant energy, nuclear energy, and the so-called fossil fuels such as coal, petroleum and natural gas. The latter come from plants and animals long buried beneath the Earth’s surface. They originally received their energy from the sun. It took millions of years to convert and store that energy. So for man’s purposes fossil fuel is a source that, once used is gone forever. This is also true of energy from uranium, thorium and other sources of fuel for nuclear fission.

Almost all the rest of the energy available to man is solar energy. The amount of radiant energy coming from the sun continuously is almost inconceivable. It varies from time to time, and place to place on Earth but the average is something around twenty million Calories a day per acre. Except as it may be used directly for light and heat, it must be converted into the form in which men use it.

So the limits placed on man by solar energy are not in the form of the total available amount, but are found in the difficulty, often the impossibility, of converting it to man’s use.

Plants as converters

Plant life, on the average, converts to organic matter only about .18 percent of the radiant energy falling on the earth. A very large part of that is in the forms of shrubs and trees that man is unable to use as a source of food. He relies on a few edible plants to provide him both with sustenance and the mechanical energy that his body can produce. This sun-plant-man system requires of him only a knowledge of what is edible. Plants reproduce themselves without the aid of men, so there is no necessity for special knowledge to supply the converters that he uses. This system is the prototype of all the systems man has created. However, since he began very early to eat animals, the sun-plant-animal-man food chain is almost if not equally as old.

Plants vary in their capacity to survive in various soils and climates. We can through the study of plant and animal ecology discovers the limits within which the survival of various plants is possible. Plants also vary in their capacity to convert the energy of the sun into plant structure. The limits of the use of radiant energy are fixed by the nature if photosynthesis itself. It is well established that only a small fraction of sunlight can ever be converted by plant life into other forms of energy. For example, it is estimated that only about 3? percent of the sunlight falling on the United States as a whole could be so converted. As a matter of fact, no crop grown in this country even approaches such a figure. Here corn is the crop that probably yields the largest heat-energy return, and a bumper corn crop returns only about one percent of the radiant energy falling upon the land on which it is grown. This return includes that heat which can be obtained by using the cobs, stalks, and leaves as well as the edible kernels. Such a return is exceptional. “Corn belt” corn is the product of extremely favorable geographic conditions, aided by scientific agriculture. In areas where the land is poorer and farming practices are less efficient, the returns are very much smaller.

The amount of energy each plant can convert is specific to that plant. The formula worked out by agrobiologic science is: divide 318 by the normal percentage nitrogen content of whatever agro-type is being considered; the quotient is the theoretical absolute maximum number of pounds of dry vegetable substance that the agro-type can yield on one acre of ground in one crop cycle. A plant also consistently yields a given quantity of energy per pound of dry weight. So it is possible to discover the limits that are self imposed on a people who choose a given crop as their basic diet. Rice is widely used. It apparently comes closest to yielding the various food elements in the proportion required by the human body; but maize, soya beans, millet, rye, and wheat have become the basic diet in some areas, as have potatoes, sweet potatoes, yams, and other crops in other areas. The particular crop which would provide the largest energy return in a given area is not necessarily the one used there. Factors other than energy efficiency also affect man’s choice of foods, and in a given instance the preference may be for a food that is less efficient than some other known and available food source. The total energy available to the people of a given area is thus determined by the efficiency of the particular plants that they have chosen to make their basic source of food.

Plants have in addition to their inherent efficiency another characteristic of great social significance. With few exceptions they are rooted in one place; thus the field in which a plant can act as a converter of solar energy is the area which the plant itself occupies. Concentrating the energy which they produce involves the energy costs of harvesting them. Moreover, any mechanical energy which is derived from using them must involve still another converter. This reduces further the energy man can utilize.

Where the only converters available consist of pants, animals used solely for food, and man, not only is man the controller and director of available energy, but his muscles provide all the mechanical energy he can use. And all operations which require the use of mechanical energy are limited to such as can be carried out by human beings.

Although man is a chemical-energy machine, his efficiency can be measured in the terms of the heat value of the food he consumes as contrasted with the heat value of mechanical energy he can deliver. Part of what a person consumes is utilized in such functions as digestion, reproduction, respiration and the circulation of the blood. Part is given off as heat; part leaves the body as indigestible waste product. Some energy is lost during sleep, and some is converted in the activity of the nervous system. So, as in the case of other engines, the total heat value of the fuel consumed can never be recovered in the form of mechanical energy. The average efficiency of the human being is about 20 percent. This means that for each 100 Calories consumed as food the average man can deliver energy equivalent to 20 Calories of heat.

Physiologists generally agree that taken on the average the daily consumption of food should supply not less than 2600 Calories per person per day. Recent research by the Food and Agricultural Organization has pinpointed energy needs for various specific sets of people. Their reference “male” requires 3200 Calories, but the reference “female” requires less, as do children and populations composed of smaller people such as the Bushmen. So it appears that no known population, consisting of men, women and children of various ages could consume more than 3,200 Calories per day per person without producing a lot of human fat that actually reduces rather than enhances the body’s ability to do mechanical work. If then we compare this with the energy available to a population that can meet only minimal requirements, say an average intake of 2,000 Calories, the difference between it and the maximum 3,200 is only 1,200 Calories per person per day. In terms of mechanical energy, the maximum difference between the society using the most and that using the least energy is equivalent of 240 calories, or little more than a third of a horsepower hour per person per day. And the total work done in a society using human muscle as the source of mechanical energy cannot be more than about a horsepower hour per person per day. Nor is this fact significantly affected by the use of animals in addition to plants as food.

Animals as converters

Man usually adds meat to his diet if he can, and under some circumstances his chances for survival may be tremendously affected by his ability and willingness to provide himself with animal food. The differences between those who consume plants only and those who make use of animals as well as plants for food are probably significant rather for the pattern than for the limits of the field generated.

The chief significance of the use of animals lies in the fact that some edible animals can assimilate plants – and parts of plants, such as grass and bark – which man cannot directly digest. Many of the grasses which are not directly consumable by humans grow in areas where it is not possible for man unaided by other sources of energy to replace them with edible plants. Animals graze over distances much greater than it is possible for a man to carry or drag the meat of their carcasses. But man is able, by following animals, to consume the plant products of an area enormously more extensive then he could otherwise make use of. But he must be mobile if he follows and hunts animals for food. The energy he expands this way limits what else he can do. It also affects the way he is housed, the number of his possessions, and the size of effective groups.

Similarly, man is able to live in climates where plants are not available the year around, partly by using the energy of plants stored in the form of animal products during the months when no plant food is available. Occasionally even carnivores are used to promote man’s survival. For example, the Plains Indians and some Eskimos sometimes lived through a hard winter by eating the dogs which had shared their kill during the summer months.

The use of animals for food is subject to the additional limitation that the animals so used are in competition with men for plants.

As I have shown, the number and kind of plants in an area sets the limit on the food available both for men and for other animals. If man permits animals to eat plants which he otherwise might himself eat, or permits land to be used to produce plants for feed which could produce plants for human food, he limits the number of men who can be fed from that land. Wheat, which is very widely used as a foodstuff, will serve as an illustration for this relationship. The amounts of energy made available to man through the use of wheat in the form of bread as compared with that existing from the use of animal products, are shown in the following table.

100 Lb. of Wheat



Consumed as


In Calories



















Since other feed crops can usually be grown more advantageously, wheat is only rarely raised to feed animals. However, other plants edible by human beings exhibit much the same pattern of loss as does wheat. Man gains through eating animals only a fraction of the energy contained in the plants eaten by those animals.

Nevertheless, in many areas people permit animals to survive even though this results in reducing the number of human beings who can live there. The case of the sacred cattle, rats and other animals that are permitted in India to eat food if consumed by humans would lengthen the life span of a large part of population, is an example. Sometimes, too, an inefficient use of animals is required by religious belief, as in the case of the Jews and the Mohammedans, who are prohibited from eating the flesh of swine, which happen to be more efficient converters of some plants than are cattle.

The hunters

Before he domesticated animals man could secure most animal protein only by hunting. Recently anthropologists and archeologists have been impressed with the differences between those food-gatherers who were confined to the use of plants and such animal life as shellfish and other low forms that they could gather, and those who had developed techniques for taking larger animals.

Although hunter-gatherers differ among themselves they have some characteristics that result from hunting that separates them from plant gatherers among whom there is similarly a wide range of characteristics. But all gatherers also differ in some ways from the food raisers about whom I will be talking later.

Gathering characterized man during 99 percent of the 2 million years he has been evolving. Two kinds of evidence show how he lived. One is found in the fossils, stone tools and ornaments, and some paintings that survive. Another uses studies of the few remaining societies that still rely almost exclusively on gathering to provide them with energy.

“Stone Age" man

The evidence from fossils and other stones shows how men changed as they learned how to adjust to the conditions imposed on them by plant and animal ecology. Energy in the form of fire permitted them to live in areas where it would otherwise have been impossible. Clothing from the skins of animals conserved body heat and had the same effect. They also learned who to make use of some of the vast variety of plants that existed in the different ecological systems into which they migrated. Eventually hunter gatherers occupied some areas in all the continent scattered over the whole habitable Earth.

They created a great many different social forms and practices that were carried forward from one generation to another. Some of these changes can be shown to have resulted from alterations in the amount of energy they controlled. Others apparently resulted from changes in the source and/or the pattern of the field of the converter they used, but not the amount of energy. Still other changes occurred when there was no apparent change in either the converters used or amount of energy available.

Some changes were forced on man by alterations in the climate or other geographical conditions. For example, the melting of the ice caps raised the level of the seas and created new shallow waters in which shell fish and other animals increased. This in turn provided a recurring source of animal protein that did not require men to move very far in harvesting it. Advancing and receding deserts also forced or encouraged man to move.

The spread of tools and weapons permitted some cultures to diffuse and reduced or destroyed others. There is convincing evidence that social organization, accompanied by changing value systems were also significant in modifying the way hunter gatherers lived. Our growing accumulation of evidence in the form of stone age artifacts permit us to make more and more reliable statements about these early men.

Modern "primitive" people

The other evidence about hunter gatherers has been produced by ethnologists who have been studying some of the few existing societies that still rely for energy almost exclusively on gathering plants and hunting animals. We do not know how nearly the existing hunters resemble any of those that previously existed. But we can compare the degree to which the evidence we do have stone age man resembles that which will survive after existing hunter gatherers have passed on. That gives us some basis for judging. And we know what they could have done by studying fossil energy. I will turn then to a discussion of what we know about existing hunter gatherers. It was once thought that all of them tended to live at the marginal levels resulting from the pressure of human population upon other elements of ecology. The size of the populations of hunters such as some Eskimo, Athabascan Indians and those of the upper Orinoco do seem still to vary directly with the increase or decrease of other forms of life. But recent studies show that there were also hunter gatherers who were relatively affluent in so far as food supply was concerned. Some such as the Kung Bushmen have populations that have remained stable though they were using less that half the food available for human consumption. Some hunter gatherers in California retained that pattern even when food raising cultures existed nearby. They were able with relatively little effort to supply the population that existed there with food adequate to meet their demands. Some writers have described some of the hunters as having been affluent because food was relatively abundant, and they had few material desires beyond the satisfaction of their drive to eat. Their other values required little expenditure of energy. However they may have been or are now to be seen by others those who still practice hunting as a major source of energy, have been supplanted by others that made use of food raising.

Why was this? In most cases it was difficult to keep the population in balance with the rest of the ecology even though some did. For example, let us see how the King Bushmen were able to do so. In that culture men do the hunting, women take care of children, gather food plants, and prepare the food. The plants they primarily depend upon grow in scattered groves. So they must carry those children that are unable to walk as they gather food and bring it back to camp. When the food in a given area becomes scarce they have to move their camp to another site, carrying with them all their possessions as well as those children unable to walk. The energy costs to transport are very high in terms of the ability of the female to assimilate food. So a pregnancy that occurs when the woman is already overburdened with carrying her children plus necessary food is disastrous. The culture provides means to prevent too frequent pregnancy. There are controls over sexual intercourse that while not consciously directed to this end have the required effect. Conception is limited. Limited infanticide is practiced. And of course children die young when the mother is incapable of doing all that must be done if they are to survive. So the population is kept below the limits that would be imposed by the food available from plants.

There are apparently other cultures where disease, accident or the harsh conditions of life directly limit human populations so that food is not the limiting factor.

In a good many places there is recurring drought or disease among the plants or animals on which people depend. Population is thus limited to what can survive under these conditions.

Some parts of the year, as during the salmon run in the American Northwest, may produce a glut of food, but unless it can be preserved it does not alter the permanent number of people that can live there.

The very limits on the growth of the population which preserved food gathering cultures made them vulnerable to pressure from food raisers who, living on the same territory, could greatly outnumber them.

In point of fact, once domestication of plants and animals has developed, the food gatherer has tended to be driven away from the areas in which food raising was possible. As a result, he currently exists chiefly where food gathering actually yields a higher return from existing resources than would an available alternative land use. The precarious existence of most contemporary food gatherers suggests why food gatherers often fail to survive in the face of more effective systems of energy exploitation.

Since wild plants rarely grow in such abundance that a group living on them can long remain in one place, everything that food gatherers use must be transported. Their means of transportation are, characteristically, limited to human portage or dogs. Consequently, tools must be simple and light in weight. Housing must either be improvised at many different sites or be very easily transportable. Clothing must be light and simple. No great energy can be devoted to the erection of shrines or otherwise expended in placating or worshipping the gods. The size of the social unit is necessarily small, for if any great number of people gather together, they soon exhaust the local supply of most of their energy sources and have to range far afield in the search for new sources. The resulting expenditure of time and energy in gathering and dispersing endangers rather than contributes to survival. At best the division of labor is limited, for almost everyone must spend a great deal of time and energy in the pursuit of food. Priests and other social functionaries who gather no food cannot contribute enough to food-gathering groups to offset the energy lost in supporting them. The kinship groups among food gatherers may carry an economic, political and religious functions, but such small units are incapable of creating or transmitting any very large culture base; consequently tradition, law, and religion remain relatively simple.[1] They provided only a limited number of controls for the guidance of the head of the household.

The Paiute of the American West provides an example of the social simplicity of the life of the food gatherer. He lived principally upon a few types of seeds, such as the pine nut and acorn, upon lizards and snakes, grasshoppers and grubs, and the rabbits and the rare deer which he could kill. To get the latter, the hunter usually went out alone with his dog. Finding his quarry, he then had to run it down relentlessly, perhaps for several days, until he could get close enough to shoot with a bow and arrow; he would then have to carry it painfully home on his back. And unless he was unusually lucky a good deal of the meat would spoil before it could be eaten. The Paiute clothed himself after a fashion in rabbit skins, piled up brush in a wickiup to shield himself from the storm, and usually died before he was twenty-five years old. Although he lived in an extremely adverse environment, much of which today does not support one person per square mile, he probably is more typical of the food gatherer than is the affluent hunter. Bilby’s account of the Eskimo in Nanook of the North describes another food-gathering people living under adverse conditions. The fact that Nanook, his chief informant and the central character of the book and the film, later died of starvation puts a fitting conclusion to that account.

As we learn more about the hunter gatherers we will probably be struck more with the great variety of cultures that existed within the narrow energy range within which he operated than with the characteristic things he shared with others who also had access only to the common energy source. Already we have to revise our estimates of his significance to us. He was the one who produced the biological types that now exist. As we learn more about how his behavior affected the natural selection of gene pools we may have to alter our ideas about the way such factors as genetically limited intelligence was selected among this great range of cultures, functioning in a multitude of ecological systems.

Again, as we learn more about his continuing effect on the food gathering cultures that still exist we can better understand how difficult it may be to force men into effective adjustment to rapidly changing societies. In any event we have to change our estimate of what he accomplished.

Hunter-gatherers were sufficiently adaptable that they had occupied most of the globe before food raising became the dominant source of energy. Their method of adaption was pollution free, and in most of the areas they occupied they were not able permanently to destroy the nature of climax ecology found there. Generally they were egalitarian, there could be a little accumulation to establish one set of people permanently able to rule another. There was apparently a stable family life, even if life itself was short. No elaborate formal organization could be sustained from the limited energy available, so social change was in some respects easier than in more affluent systems.

Food raisers

When we try to deal with the great range of societies that exist and have existed it becomes necessary to make some classifications that include a great variety of cultures. I have talked about food gatherers and food raisers as if they were distinct and separable sets of people. As a matter of fact, of course, there are no hard and fast lines that we can draw. Men gathered food in some places where it would be hard to know just when one could say they had become food raisers. In some parts of the Middle East some grasses, such as crested wheat, grew wild in such abundance that enough food could be harvested by a family in a few weeks to last them for a year. It was only when this plant was moved into other environments that planting become necessary to harvest. Similarly nomad-hunters who followed some herds throughout the year may have captured and used some animals in order to be able to move with the herd on whose meat they largely lived as the Laplanders and the Irkutz still do. The shift to a situation where some animals were corralled and kept for slaughter while the remainder of the herd moved on to greener pastures could have followed. At just what point the combination of domesticated plants and animals became characteristic of a particular people is seldom if ever known.

The use of draft animals

As we shall see, the domestication of plants and animals used for food had far reaching effects on the energy supply. But both of these developments left unaltered the fact that all mechanical energy had to come from man’s muscles.

The use of draft animals provided a supplementary source that had very far reaching effects which were often combined with those of food raising. There are many kinds of animals that are used for draft. To be exact it would be necessary to calculate the costs and output of each kind. However, since the horse is so widely used it will serve to illustrate the energy gains to be made through the use of draft animals.

As we have already indicated, Watt found that the horses in use in England in his day produced the energy equivalent to about ? horsepower, or about 6 horsepower-hours per 9-hour day. A modern horse weighing 1,500 to 1,600 pounds can convert about 1 horsepower steadily for 10 hours a day. The average horse is about 20 to 25 percent efficient. However, since horses in the United States today work only 800 to 1,000 hours a year, they deliver only 6 to 7 percent of the heat value of their average annual food consumption. A man who works 50 hours a week for 50 weeks a year delivers, then, only ¼ as much energy as a horse. But, the heat energy consumed by the horse is 10 times as great as that consumed by the man. Compared strictly on the basis of energy, under these conditions man is 2½ times as efficient as the horse.

The great value of the horse lies in the rate at which it is able to deliver energy. During a limited plowing season, for example, a man and a team can prepare a very much larger area for planning than can a man alone. Outside the tropics only a limited number of days can be spent in preparing the seedbed planting. Crops require a minimum growing season. The total planting time is equal to the difference between the necessary length of the growing season for a particular crop and the interval between the time when the ground can be worked to the time when frost or drought sets in. The limit on the size of the crop that can be raised is found in the length of the period during which land can be prepared. The horse, by permitting a great increase in the amount of land that can be plowed, may more than compensate for the days when it is idle.

It must not be forgotten, however, that the efficient use of draft animals takes place within distinct limits. In the first place, arable land is not always available in such quantities that plowing or harvesting is the limiting factor on the crop raised. Frequently the number of persons who have a right to share in the product of the land is great enough to make it possible for them to plant and harvest all the available land in time permitted by the growing season. In such cases the net cost of using the horse would be greater than the increase in the energy returned. Furthermore, in many cases land that cannot be cultivated by the use of the horse exists interspersed with land fit for horse cultivation and land fit only for pasture. Where this is so, an economy that made use of the hoe could support a larger population than could an economy that used only such land as could be cultivated by using horses.

Because man’s skill, intelligence, and dexterity enable him to do many things not possible to a horse, man can be employed many more hours of the year than the horse can. His efficiency rises proportionately. Thus those who control the method of cultivation may choose to rid themselves of horses in order to employ men. This might take place in an area dominated by the family as an economic unit because it would obligate family members to work for the food they had a right to share anyway.

In a feudal or slave system the value of men as a source of military power and prestige or as contributors to the bodily comfort of the landlord or slave-owner often resulted in the displacement of horses by men.

It appears that where other values and social structures prevail, the relative efficiency of men as compared with draft animals in securing the desired results has determined the choice as to which would be permitted to survive.

One of the early evidences of population pressure is the reduction in the number of food animals, followed by the reduction of draft-and-food animals, such as cows and horses, in favor of those draft animals, such as the water buffalo, which can survive on the plant product of land which will not yield nearly as much energy in the form of humanly edible food. Thus many areas which once supported draft animals and food animals now make use of almost none.

This tendency to regress has frequently been checked. The failure of a society to utilize its land in such a way that the land provides sufficient energy in the requisite form to maintain the population has often resulted in the society’s being overrun by outsiders. If a society uses its land in such a way that it passes the point of diminishing energy returns, it may be conquered by a neighbor with greater surplus, who then may ruthlessly restore land-to-population ratio which will yield maximum surplus. Feudal landlords who permitted the population to grow to the point where they had no horses were often defeated in battle by their horse-riding neighbors. The exploits in India and China of such horse-riding herders as Genghis Khan give evidence of some of the dangers of overpopulation.

The horse and the Plains Indians

The Plains Indians lived in a more favorable environment than did some other food gatherers. But because they had no draft animals they were unable to cultivate the land extensively and to raise crops that could compete successfully with the buffalo grass. In those few areas where trees killed off the grass the Indian could in turn kill the trees and for a few years get a crop from the land so cleared. In most of the prairie such cultivation methods supported only small groups of food raisers. The chief source of energy was the buffalo which was hunted afoot with the aid of the long bow and arrow. During the summer the Plains Indians gathered into large groups for the purpose of staging a drive in which the buffalo were driven to their deaths over a bluff or into a trap. Only thus could these Indians survive in groups larger than a few households. Continuous hunting would have disturbed the grazing herds. This would have meant continuous movement of the tribe, which in turn would have led to further disturbance of the buffalo. Hence the social, economic, and political units had to be small. The physical accouterments of life were few, though more numerous than in the case of the Paiute. The “man of distinction” was the hunter. The ritual connected with coming of age was designed both to teach the arts, skills, and attitudes necessary for effective hunting and to glorify or even sanctify them.

This pattern was changed whenever these Indians captured and redomesticated the horses which had escaped from the early Spanish expeditions. The introduction of the horse into these cultures serves as an excellent illustration of the effects which the adoption of a new converter may have. It also shows how the existing culture limits the use to which a new converter will be put. Forde 1946 says that “The introduction of the horse did not basically change the culture of the western Plains, but it widened the range of activities, greatly increased success in hunting and provided a wealth of food and leisure… It was also a “form of personal property which gave impetus to a wide range of modifications. As he points out, “the horse gave the ascendancy to the western nomadic hunting peoples, and the cultivators were either driven out of abandoned their more settled life and more advanced culture for the rich rewards of buffalo hunting.”

The introduction of the horse changed what was regarded as the ideal man from one having those qualities of stoicism, patience and skill which had characterized the hunter afoot with the long bow to one with the qualities of the daredevil rider wielding a lance to hamstring his kill or using the short bow from horseback. In time the skilled horse thief and warrior was elevated to a position equal if not superior to that of the hunter. The size of the effective social unit changed as the advantage of the large group for protection in warfare more than offset any residual value which the small group originally had in hunting. Social organization became necessary to control these larger groups. Picked hunters frequently brought in game for the whole community. Unskilled, slow, or crippled heads of households were denied the right to hunt lest they endanger the source of food for the whole group. The relationship between responsibility for the family and ability to meet that responsibility was altered by social fiat.

One squaw could not preserve all the meat or dress the hides of all the game killed by one horse-borne hunter. Since there was no change in the division of labor between the sexes, polygamy became the rule, and the accumulation of women, particularly by stealing, became a source of power and prestige.

Many of the pre-Columbian food-gathering tribes were confined to areas in which food raisers were unable to operate. As the Plains Indians acquired the horse, the energy available to them increased sufficiently to permit them to drive back the cultivators and thus extend their hunting grounds. The gain was, however, temporary. As the European settlers moved westward, bringing the harness and the plow, which enabled them to turn under the buffalo grass of the plains and replace it with crops that yielded a larger surplus, they relentlessly drove the food-gathering Indians from their ancestral homeland into less and less satisfactory areas. Here their culture was destroyed by their inability to get at the buffalo, whose energy had sustained it, and they survive today only as a colorful anachronism.

Most other food gatherers have met a like fate. Some have been able to maintain their existence by attaching themselves to agricultural regions, by gathering a product of desert, mountain, or forest to exchange for the products of a culture yielding more surplus energy. Some exist on sufferance, in areas unfitted for incorporation into dominant civilizations, as do the Seminoles of Florida, the Eskimo and isolated tribes in Alaska, Canada, and Greenland, and various native peoples in Africa, Asia, and South America.

The classifications I am using apply not only to primitive or prehistoric peoples but also to modern farmers. For present purposes the category “food raiser” has most analytical significance when it is restricted to those people who are or have been almost completely dependent upon cultivated plants and/or domesticated animals for energy plus those who, primarily dependent upon such sources, have secured supplementary energy through hunting wild animals and occasionally using wind or water power. Even when so restricted, “food raiser” is sometimes less useful than terms based upon other distinctions. For example, it is probable that there are more significant differences between people who are dependent primarily upon cereals grown on irrigated soil and nomadic herdsmen (who are also food raisers) than there are between those herdsmen and some of the hunters who occupy country where game in plentiful. Nevertheless, the significance of the domestication of plants and animals as contrasted with the use of these converters in the wild state is very great. Food raising represents an advance in the means regularly used to provide and secure energy surpluses far greater than those of any gatherer-hunter.

Some years ago it was thought that civilization started in the Eastern Mediterranean and the Middle East. It was assumed the great surpluses of energy came from the plants that in the wild state produced so much. These were thought to have been carried from there to other civilizations. Now it is pretty well established that civilization began independently in several areas. In each of these areas food raising was responsible for great increases in energy but different crops were used to get it. For comparison, the yield of barley in Norman England was only three times the seed with a total production of 15 bushels per year per person. On the other hand, in ancient Sumeria the yield was 80 to 100 times the seed. The total was 2,800 liters per hectare or nearly 32 bushels per acre, which is not a bad yield by today’s standards.

It is apparent that such great variability in yield at least established great differences in the energy limits under which men lived, however they may have used that energy.

The variations in environment to which cultivated plants are subjected are easily observable even in old and well-established agrarian societies. The yield from the same seed on different parts of the same field frequently varies greatly. Among farmers, or more particularly between regions, there is even greater variation.

Adverse factors take their toll in differing degrees. There may be a shortage of some of the nutrients required for optimum growth. During the growing season there may be either too little or too much total precipitation, or precipitation may come at the wrong time. There may be other organisms to contend with, both plant and animal. The very processes of cultivation may be such as to reduce rather than to increase yield.

Recently it has been discovered that the presence or absence of tiny traces of such minerals as cobalt and copper result in huge differences in plant yield. Where low yields are a consequence of a deficiency in minerals, that fact can now be determined and corrected; but a people dependent solely upon the energy of plants and animals could never develop the scientific knowledge necessary for the correction of such soil deficiency.

It is evident, then, that the limits imposed by the nature of the plants rarely constitute the only effective limits confronting those who depend upon those plants for daily living. In the first place, the land available sets limits to the amount of plant life that can be developed, whatever the character of the plants used. That plant life, in turn, sets limits upon the size of the possible population.

It is comparatively easy to show, for example, that when population increases much beyond 3 persons per acre the energy derivable from most plants will not provide the means to carry out the intensive cultivation and restorative fertilization which are the only methods by which so little land can be made to provide sufficient energy to ensure the survival of its cultivators. For example, to get enough energy from one person living on one third acre would require a daily average of around 9,000 calories yield per acre. This is equivalent to about 2,200 pounds of rice per acre year. For comparison, the world average production of rice in 1971 was 2,033.76 pounds per acre. This includes rice produced with the aid of insecticides, fertilizers and irrigation. At 2,200 lbs. per acre, ? acre would yield an average of 3,000 Calories per day, about what an active 150-pound man requires year round for an adequate diet. During the period of intense cultivation he will, of course, demand more than this, but he can conserve his strength at other times. If his family includes more than 4 people he can’t produce enough on an acre to feed them. And in most places he cannot cultivate more than 1½ acres even if there is more available land than that. A reduction of the amount of land per person below ? acre reduces the energy available to a point below that necessary for survival. Soya beans or sugar beets produce more than this per acre under specified conditions, but sugar beets require protein supplementation by other crops and do not yield more than rice does when all necessary factors are taken into account.

For a long time economists have been pointing to the law of diminishing returns, which sets an outer limit on the amount of food that can be produced in a given area. Sometimes they have confused the physical product of plant life with the “economic” value thereof. Sometimes they have extended the meaning of the law to cover all the economic effects of limited land, no matter what its use. In essence the argument stems from the facts to which we have just alluded. It is true that after a given point is reached a specific plant on a given piece of land will yield only so much plant product, no matter what increases in expenditure of labor or what additions to it in the form of nutrient are made, or how it is protected against disease or insects. Moreover, as that limit is approached it is highly probable that a great deal of what is done is not that which is required to permit the plant to reach its maximum output. Therefore, most of what is done will not yield a commensurate return or even any return whatsoever in increased energy to compensate for the energy expended. This is true even where soil is fertile and good management and plant science are used extensively. Where magic and religion and other practices interfere, the loss of energy is no doubt excessive.

In dealing with food raisers it is, therefore, necessary to distinguish between the total energy surplus which might be achieved under optimum food-raising conditions and what is actually secured under the existing conditions of man-land ratio, cultivation techniques, etc. These existing conditions can usually be improved only by the adoption of some new energy converter. The probability that a food-raising people will adopt a new converter seems to depend in considerable part upon their current ability to produce an energy surplus. In other words, the presence of an energy surplus is favorable to the adoption of a converter that will enlarge that surplus.

As will be shown, it is generally true that as the energy available to man increases, the variety of his activities increases. Where the energy available is only slightly in excess of that required for survival, any very great variation in behavior among those situated in any one place is impossible. Thus, whereas the variability of food raisers is very great as compared with that of food gatherers, it is small as compared with the variability of those who have larger energy surpluses. Food raising permits variability, but it also imposes limits which are reflected in some generally predictable results. Food raising decreases the time and energy spent securing food and thus permits men to do other things, but the mechanical energy available each day is still no greater than that of the human beings and the domesticated draft animals present. Food raising permits an increase in the number of persons who can be supported from a given piece of land and thus permits an increase in the surplus locally available. The increased surplus may be used in a variety of ways. It may be widely dispersed and result only in a general increase in leisure. However, such dispersal may, and often does, lead to an increase in population. The land available per person may decrease to the point where each unit of land is supporting all the population that it can. When this point has been reached, there is no surplus. The increased surplus may be used merely to increase the amount of waste. Or it can be concentrated, and the concentrated product, too, may be used in a variety of ways. It may be sacrificed to the gods. It may be buried in a tomb or destroyed at the death of a landlord or other ruler. It may be expended in the military conquest of areas which themselves yield lower surpluses. It may create a leisure class that is devoted to the cultivation of knowledge and the arts or that simply demands the continuous use of surplus in the creation of goods and services that are not productive of new arts, or knowledge, or new fixed structures. But there must be a surplus before it can be devoted to any such use.

A great variety of food raising cultures have appeared. Slowly we are learning how they developed. Recent studies of surviving “primitive” cultures, those relying exclusively on manpower for mechanical energy, show how those particular cultures and social practices were and are influenced by increased surpluses. In some cases gardens are limited to an area that produces no more annually than is required to maintain a stable population. In others, in most years more is produced than is harvested. This is a kind of insurance against the occasional year where a considerable part of the harvest is lost. In some cases this yearly surplus is fed to animals that can be eaten during a time of plant scarcity. In a great many self contained ecosystems, a steady state is reached, and if bad years become too numerous emigration is resorted to. But the accumulation of energy in the form of food over a very long period does not take place.

As we saw, some of the Hunters, like the !Kung bushmen stopped “work” when sufficient food had been gathered. The bulk of the food raisers probably developed the same kind of system. But some of them developed cultures requiring that they produce almost the maximum amount of plant life that their system could produce.

In a book called Pigs for the Ancestors, Roy Rappaport describes a New Guinea people whose belief system induces them to maximize their energy output. They hold that the ancestors must be placated or honored by the sacrifice of pigs. The frequency with which they can meet these demands depends upon their ability to raise pigs. The pigs are fed in part from uncultivated plants but primarily from the same gardens as are the people. They raise all the plants they can, eat what they desire and raise as many pigs as the surplus of food with permit. So it is not a case of raising food enough for the people and letting the animals have the leftovers. It is a case of maximizing food production with pigs getting all that men don’t eat.

Rappaport made a very careful study of the energy inputs that were made, and measured equally carefully the energy output in the form of food. The results may be surprising to those who think modern agriculture yields far more per acre than does hoe culture. These people produced from one acre, during a harvesting period of from 18 to 24 months, 5,300,000 calories. Sugar- sweet potatoes produce about 4,600,000 calories per acre during their harvesting lives. About 310,000 calories per acre were spent in cutting, fencing, planting, maintaining, harvesting and walking to and from the taro yam gardens. About 290,000 calories were required for the sugar- sweet potatoes. So their yield was about seventeen times the expenditure. On taro yams the ratio of output to input was 16:1.

These people are relatively small in stature. The daily intake of males was about 2,600 calories and the females ate 2,200 calories. Most of the protein they eat is vegetable but the pigs supply a very valuable source of animal protein.

The women who must spend 950 calories on basal metabolism has only about 1,500 calories left to bear and care for the children, plant, maintain, and harvest the garden, prepare food and take care of the pigs. It is obvious that the number of pigs she can tend is limited. When there are too many pigs a celebration is held in which the pigs are slaughtered and eaten. The land capable of being used to feed pigs was always in excess of that actually used. So other factors than biological ecology govern population size. But the ability to produce energy through intensive cultivation, together with a number of other factors, including religious belief, set limits on their system.

A number of similar studies have been made showing how the size of energy surpluses was involved in the systems that used food raising as the primary means of getting energy.

It was the existence of recurring energy surplus that made it possible for some people to establish fixed residence. There is evidence that some food gatherers lived on fixed sites before they practiced agriculture. Village life has some advantages for survival, particularly if there is mutual antagonism between sets of people, which is likely to be true if one set makes permanent exclusive claim to food resources also needed by neighboring food gatherers. But permanent settlement becomes possible to more and more peoples as they adopt agriculture for its ability to produce surplus energy.

As the number of fixed residences grew to become predominant, it became possible to do a great many things that had hitherto been impossible. This was the beginning of what we call civilization. As indicated above this process took place in different parts of the earth at different times. In the Near East the surplus energy from crested wheat played a major part. In Mexico it seems to have been the progenitor of maize or “Indian Corn”. Elsewhere it may have been rice, and so on. What is important for us is to realize that when considerable energy became available men began to practice increased subdivision of labor, form different kinds of social organization, develop new value hierarchies, and adopt new technologies.

They did not all have advanced technologies. For example, the Maya had no wheel, no draft animals, no metal tools. But they had a highly developed system of government and a calendar more accurate than that of the Spaniards who conquered them.

All the early civilizations practiced agriculture. All developed a ruling class and in centralized government. Their population density was much greater than that of the gatherers. Most of them developed some kind of writing.

While there is considerable variation among food- raising peoples, there are also numerous likenesses among them as a consequence of the limits inherent in food raising. Among all food raisers they family is the basic consumption unit, and to a large extent it is also the production unit for much of the goods and services produced. Division of labor is limited and is primarily based on differences in skill and learning, sex, and size and muscular power. Since so large a part of what must be done requires merely brute strength, there are also likely to appear status differences which assign whole sections of the population to physical tasks without regard for the potential skill, intelligence, strength, or sex of individuals. If the emergence of complex institutions depends upon the development of a surplus, so too the development of a surplus depends upon the existence of such institutions. Once a balance is attained, however, it is difficult to upset.

The Egyptians: an example

The Egypt of the age of the Pharaohs provides a good demonstration of the working of a balanced system in which a comparatively small energy surplus is utilized in such a way that there is no disturbance to the energy- producing procedures. The Egyptians left a durable record of their accomplishments, and these records have been subjected to a great deal of study. The Egyptian system operated, moreover, under physical circumstances which precluded a disturbance of the balance through soil exhaustion. The Nile regularly replaced the soil, and continuous cropping caused no depletion. The deserts, sea, and river cataracts formed barriers which could be crossed by an invader bent on conquest and plunder only with great expenditure or energy surpluses. The Egyptians were, under these favorable conditions, able to push food raising to a climatic[2] stage.

During long periods of its history the surpluses of Egypt were absorbed by the burial mounds or pyramids. These contain both direct and symbolic evidence of Egyptian accomplishments. During the reign of some of the Pharaohs almost the total surplus of the people was concentrated in the erecting and furnishing of the pyramid which was to honor the ruler upon his death. The ruling class was small and consumed no great amount of wealth, for the chief objective of its way of life was to accumulate surpluses to be taken into death. The population was held constant or diminished, since men were worked to death about as fast as they could be brought to maturity. Even so, the surpluses were never great. The Cheops pyramid, together with its furnishings, absorbed all the surplus energy produced during the lifetime of about 3 million people. During a 10-year period 100,000 slaves are said to have worked to produce the tomb. This was about 1/25 of the total population. We can calculate, then, that those who supplied the food to keep the pyramid builders alive each contributed only about 100 to 150 calories a day. Thus, although the Egyptians enjoyed most favorable geographic circumstances, the total energy available to them was by modern standards extremely low, however high it may have been in comparison with the energy production of other societies of the time.

At other periods in its history the surpluses enables Egypt to engage in conquest of all its neighbors. At still other times the surplus was exhausted in conspicuous expenditure and display among the living. At those times when controls over population broke down, the surplus was completely exhausted in civil war or by the increase in the number of mouths to be fed from the land.

It is possible to calculate the distance from their base on the Nile that the Egyptians could have advanced had they been willing to devote all their surpluses to conquest of neighboring peoples. The size of the surplus was one limiting factor: the surplus had to be carried or pulled from Egypt by men or asses. At some distance from the Nile the energy costs of transportation would have reduced the surplus derived from Egypt to a point below that available to the people being invaded. Egyptian expansion would at this point have been checked. The topography and the resources of the region invaded, the will to resist and the military technology, strategy, and leadership of its inhabitants also would have been involved in fixing the ultimate limit to which the Egyptians could have advanced. Similarly, the possible spread of Egyptian culture was limited by its capacity to yield surplus under the very different conditions that prevailed outside Egypt. Egyptian culture was adopted elsewhere only with great difficulty. When Egypt did conquer a people, it was seldom able to assimilate them. And when conditions in Egypt led to disorganization, the conquered people usually broke away and resumed their previous was of life. Such a resumption is reported in the Biblical story of the exodus of the Jews from Egypt.

The peoples of the Fertile Crescent contributed much to what we now regard as civilization. But the extent of their political holdings, the range over which they were able to secure and maintain cultural homogeneity, and the diversity of their skills and knowledge were slight by present standards. Their history shows cyclical variations within constant limits. The abuses of one system gave rise to another system, which in turn was defeated by its own weaknesses. None of these systems could, however, exceed the limits imposed by the basic converters, that is, plants and animals. And these same basic converters are depended upon by the greater portion of the people of the world today. Moreover, the cultures of the rest of the people of the modern world were developed in considerable part under the limitation imposed by the plant-animal-man-system.

Current low-energy societies

Societies such as those that now exist in India, Africa, and China have been greatly modified by the introduction of new converters but are still closely restricted by the limited energy which they have available. The population is in many of these areas so great that local resources will not supply an adequate diet. In Yunnan, before World War II, for example, about 100 families (500 to 600 people) share 150 acres. This is about all the people that plant life will support if the plants are eaten directly. Buck 1937 found that in the 1930’s nearly 90 percent of the potential farm area of China was in crops, while only 1.1 percent was in pasture. By comparison, in the United States 38 percent of agricultural land is in crops and 62 percent is being used to pasture animals. Moreover, in the United States much of the crop land is used for feed rather than for food. It is impossible at this time to get unbiased information about Chinese agriculture, but it is probable that the energy available from the animal power in China was and probably still is close to zero. The limits on the mechanical energy available in many Chinese villages might be ascertained simply by multiplying the number of persons by 20 percent of the heat value of the per capita food intake.

Under these circumstances the energy costs of transportation between village and field would, if the distances were great, cut deeply into the available surplus. Consequently villages are very small and located at frequent intervals. When the small surpluses available have been used to support centralization of control, the effect of that control on energy production has rarely been equivalent to its cost. Even the introduction of new sources of supply has tended to affect the old system adversely. For example, many Chinese villages had long paid their taxes and bought necessary imports by converting the leaves of the mulberry trees along the canal banks into silk. When Central Government was forced by foreign powers to protect trade in Japanese silk, American cotton, and British Commonwealth wool, many villages lost this source of income and were confronted by a great change in their way of life. Often the land was sold to pay taxes, and city people gained control over it. The consequence here was a great increase in tension between town and country, absentee owner and tenant, and an intense effort to restore the earlier balance. Under communist control there has been a great effort to return control over most production to the local people. The population was estimated to number 590 million and 1953 was numbered at more than 800 million in 1972. So great a number could only have been supported by very intense cultivation plus increased irrigation and more effective management. What will happen as greater numbers of females reach child bearing age is hard to estimate.

India shows many of the same characteristics. The average net cultivated area per capita of agricultural population in Bengal in 1939 was less than 1 acre, and 46 percent of farming families had less than 2 acres each18. The tillable land of India is today probably supporting the maximum number of people which it can maintain with the energy that is obtainable from it with existing practices. If higher demands are made on the soil, it will pass the point of diminishing returns. Here also the village community serves as the predominant spatial and functional unit. It supplies almost no surplus beyond that required for the local institutions themselves. The energy costs of national government or more extensive social organization must be provided by other energy sources. The Green Revolution increased crop production but only at the cost of increased energy inputs from outside the agricultural areas. It also resulted in some aggregation of small parcels of land into bigger units, with resultant social change. Recent studies show that over half the plots average about 1½ acres and only 5 percent was in plots of more than 2 acres.

In some areas that have used only organic sources for energy the population has been limited at a point short of that which characterizes the “overpopulated” parts of China and India. However, as land becomes scarce in relation to the population, the tendency has been for more and more intensive cultivation to be undertaken. This has frequently resulted in an effort on the part of each farmer to increase the only productive factor over which he himself has control, namely children. As a consequence, even greater pressure has been put upon the soil and even less energy has been available to devote to the development of new agricultural techniques or the enlargement of the area under cultivation.

Among the Bantu in Africa19 it is the labor of clearing the land that sets limits on cultivation. Every child thus becomes an economic asset, and there is continuous emphasis on increasing the size of the family. However, life there is so precariously balanced that a crop failure is likely to result in starvation and a reduction in the working population in the next crop cycle. This is also the case in at least some parts of China. In a village in Yunnan, Fei and Chiang found that the size of the farm can be worked by a man and his wife alone is too small to support a family. As a result children must work; in the absence of children the older adults will starve. Though the communists have modified this by forcing urban and white collar workers to labor on farms during periods requiring maximum labor, most peasants still rely on family labor.

Economic reciprocity between parents and children tends to become a necessity in societies that are dependent on organic converters. Children supply in these areas what is secured in industrial societies through unemployment, health, and disability insurance, and old-age allowances. Parents develop in the child values that will ensure their own survival, and the commandment “Honor thy father and thy mother: That thy days may be long upon the land…” is a statement of a functional relationship.

Their conservatism

Since the limits within which low-energy societies operate are so narrow, extensive conflict and its concomitant wastes cannot long be tolerated. Hence institutions develop which tend to reinforce rather than to weaken each other. The introduction of any new element is likely to be disastrous to one or more of the parts making up the web of the culture. When this happens, the traditional allocation of scarce resources is threatened, since men then no longer learn from all the sources of authority the same design for the “good life.” As a consequence, resistance to change frequently mounts as the ramifications of change appear. Moreover, change is often introduced into low-energy societies by “outsiders” who have their own reasons for inducing it. Frequently such change provides a more satisfactory was of life for only a few of the “natives,” while others are forced to bear costs which they consider totally disproportionate to any foreseeable gains. Those members of the society who value very highly certain of the gains to be made through the introduction of new converters, welcome change and encourage it. For others, whose pastoral and agricultural values are thereby destroyed, the “material benefits” which accompany the use of the new converters are not adequate compensation for the values lost, and they struggle to preserve the system that is jeopardized by the introduction of the new converters. Even in highly industrialized United States of today there is great respect for the virtues of the husbandman and for the rural institutions which support and are supported by many American Ideals. For example, the “family-sized farm” is widely held to be necessary to democracy, Christianity, and individualism even though it is rapidly disappearing.

Thus low-energy societies offer more barriers to change than just those imposed by the costs of securing the new converters needed to effect change. Added to these are the costs of social disorganization and of purposeful resistance.

If these barriers are to be overcome, there must be considerable energy in the hands of those who seek to bring about change. Since, we have indicated, most of the energy available in low-energy societies rests in the hands of those with traditional social claims to it- - for example, peasant, landlords, and others who will not want such change- - a great increase in energy is necessary in order to provide a surplus adequate to secure the introduction and use of new converters. In a low-energy society change must come slowly, for the range between the most and the least effective use is not, by modern standards, great. Therefore the conquest of users low-energy converters has frequently meant that the surplus produced merely passed from the hands of one group to another, its size remaining relatively constant and the culture remaining basically unchanged. Such drastic changes as the engulfment of the Plains Indians in the United States have been possible only with the extensive use of converters that were far more effective in delivering surplus energy than those that existed prior to the conquest.

In the main, then, the low-energy system of a people dependent wholly on food raising is inherently self-perpetuating. It develops a balance between population numbers, social institutions, energy usages, and energy production which is exceedingly difficult to disturb and which, if disturbed, tends to reassert itself. As a consequence, the impact of modern industrial technology on peasant societies is far weaker than is generally assumed, and those who have endeavored to introduce new converters to such peoples have had limited success.

caption Image by Brian Snelson (Wikimedia Commons)


  1. ^ Simple, that is, if the culture as a whole is compared with that of the large social units of urban society. Some single aspects, such as the kinship system itself, may be relatively complex, as in the case of the Aborigines of Australia.
  2. ^ This word is applied here in the same way it is used by ecologists. It indicates the culminating stage of the possible development in a region, given a limited set of plants and animals to begin with and assuming no major alternation in geographic conditions. We imply that given sufficient time the use of low-energy converters results in a type of persistent equilibrium between men and their environment.

This is a chapter from Energy and Society: The Relationship Between Energy, Social Change, and Economic Development (e-book).
Previous: Chapter 1: Energy & Society  |  Table of Contents  |  Next: Chapter 3: Inorganic Energy Sources: Wind and Water




Cottrell, F. (2012). Energy and Society: Chapter 2: Organic Energy and the Low-Energy Society. Retrieved from


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