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Chapter 2: Why Civilization?

So, having analyzed some of the base requirements for civilization, some questions naturally arise.  What’s the point?  What makes cities (or, at least, the societies that are capable of supporting them) so great?  Why have I chosen to begin my investigation with this seemingly arbitrary definition?

The answer to all of these questions is best seen by analyzing human societies through the lens of thermodynamics.  If we treat an entire society as a black box and just examine its interfaces with the natural world, we see some interesting patterns in the flows of energy thus revealed.

It is necessary for a population to consume at least 2,000 kCal/person/day in food energy over the medium run in order to sustain itself.  In economics parlance, this is the minimum average productivity permitted by nature.  If a society falls beneath that level for any length of time for any reason, the result is invariably famine, often attended by collapse.

Forager societies operate at this threshold.  Occasionally, additional energy inputs were used.  For instance, in addition to the food value of a successful hunt, the skins and bones would be harvested for practical use.  Rocks were collected and improved for use as tools.  Wood was also collected and burned to release stored energy as heat.  But a kilocalorie is a lot of energy!

According to this chart (, there are 16.2 MJ/kg of recoverable energy in dry wood.  This is an estimate, of course, since the actual numbers are dependent on the species of wood and such, but for our purposes it should serve.  That comes out to about 3,874 kCal/kg.  And wood that is acquired through foraging isn’t going to be dry, which adds an effective penalty of perhaps 50%, since when burning the wood much of the energy needs to be spent evaporating away the waste water before the wood can reach the proper temperature for burning.

The upshot here is that gathering wood isn’t going to change the energy consumption numbers of a society significantly above the 2,000 kCal/person/day when building a few campfires a night.  To take a concrete example of the numbers here, a tribe of 150 people would need to harvest and burn 50 kg of wood a day to bump their energy consumption numbers up to about 2,650 kCal/person/day.  That’s perhaps a cord of wood a month, or roughly the amount of firewood you could get by cutting down and processing a hundred year old maple tree.[1]

Civilized societies are interesting largely because they have proven to be able to regularly and substantially exceed this threshold.  The surplus energy they produce can be spent in at least three broad categories that are worth discussing here.

First, and perhaps most obviously, the surplus can be spent on extensive growth.  In other words, energy can be used to scale society out.  More land can be brought under cultivation, through either conquest or colonization.  Notably, both methods require an initial investment, which should then presumably pay back after the new lands are integrated into the society.  Analogously, an increase in the population growth rate also requires an energy surplus.  This is because children are net energy sinks for many years.  So, in order to support a baby boom, you need some surplus to kick things off before the children are able to pay themselves back.

Second, the surplus can be spent on intensive growth.  Instead of using the surplus to get more input resources, it can instead be consumed to scale up (or add complexity to) the existing society.  This is where division of labor comes into play.  When the food producers are efficient enough to be able to spare some productive people from the necessity of generating their own 2,000 kCal/day, those people can then specialize in other useful pursuits.  From the black box perspective, the society becomes more efficient in its utilization of input energy, but the overall input energy won’t necessarily increase.

Third, the surplus can be directly consumed.  Professional art, philosophy, science, great monuments, large-scale religious rituals … basically, every expenditure that is typically thought of as “culture”, whether “high” or “low”, can be seen in this light as a consumption of energy for some purpose other than the growth and maintenance of the system itself.  When we remember our forebears, it’s typically because of how they consumed their civilizational surplus.  One or more of these pursuits are generally considered the best justification for civilized life.

Given that civilization has the potential for exponential growth at a measurable rate and other forms of human organization do not, you’d expect that the long-run trend would be for civilization to dominate the planet.  And, from a sufficiently broad view of history, that is in fact what we see.  Both Ian Morris[2] and Robin Hanson[3] report exponential world GDP growth, to a first approximation, since at least the Neolithic until now.

The historical record offers support for this trend as well.  The best lands for farming – in the Middle East, Europe, India, and the Far East – have been occupied continuously by civilized farmers for thousands of years.  Over the past five hundred years, civilized states have extended their dominion over almost the entirety of the globe, generally allowing forager-style social arrangements to persist only at the pleasure of the local dominant state.  Some excellent examples of this pattern are the conquest and colonization of the Americas and the subjugation of the Russian steppe.

Real nomadic hunter-gathering, of the type practiced in the Neolithic or earlier, only persists well into the historical era in the most marginal of places on Earth.  But more complicated and energy-intensive forms of nomadic and semi-nomadic forms of social organization were made possible through animal husbandry.  Unlike farming, which must by necessity focus on the control of territory, the economic logic of pastoral society centers on the needs of the inherently mobile herd.

Obviously, it’s profitable for civilized societies to domesticate animal species.  It’s also possible for largely nomadic peoples to make good use of agriculture by migrating between camp sites at different times of the year.  But there is a fundamental conflict here between people who think of themselves as ranchers (migratory herdsmen) and those who think of themselves as farmers (stationary agriculturalists).  I remember being first introduced to the importance of this conflict in the classic musical “Oklahoma!”[4] in junior high school, oddly enough, but the pattern recurs all throughout history.

In the parlance I’ve been using here (largely adapted from Robin Hanson[5]), pastoralist society is the heir to forager society.  In other words, when you scale up forager society with technology, you get roving herdsmen.  But farmer-style organization is qualitatively different, in both the demands it makes on its members and the results it gets.

So, basically, the case for civilization can be summarized in three points.  First, civilization yields exponential growth in energy capture at a substantially higher rate than any non-civilized alternatives.  Second, the process has proceeded so far by this point that there really isn’t any room for any conceivable alternative.  The technological and military disparities mean that any alternative exists by the leave of the massively more powerful party.  Third, most of the things that people currently consider valuable in their lives are the result of surplus energy expenditure, made possible by civilized social organization.

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