THE CONTINUING CONUNDRUM OF THE SIZE OF THE HUMAN POPULATION

The specter of “too many people” emerges at various scales, from observing the poor single mother with 10 children living in abject poverty in some out-of-the-way place in the Global South, to quantitative estimates of how much energy is fixed by the sun and how many people ultimately could be supported on the earth with that much energy.  It is an old argument.   It has attracted political attention, either accolades or attacks, from its popularization in the 18^th century by Malthus to more recently by some environmental activists. And it worms its way into debates for which it is only questionably relevant, such as the rights of women and the sustainable use of natural resources. 

            At one level this NeoMalthusian position is almost tautologically correct, what might be referred to as the stoichiometric level.  Individual people require energy and the earth has the capacity to produce only so much energy, so there is obviously a limit.  Individual children require a minimum amount of food, a single mom can only provide a limited amount of food.  It is all a question of balancing energy inputs with energy availability.  So, as a colleague of mine once remarked, in looking over a landscape of small farms (clearly a very sparse population), “if only there weren’t so many people here.”  And it is a comment that can always be made, for any situation at all, when taking this point of view.  No children are far easier to care for than ten and no people in the landscape clearly use less energy than millions (or one).

            So it always appears to be the case that whatever environmental problem is of concern, if only there weren’t so many people, that problem would be less severe.  It seems like incontrovertible logic.  But is it?  Consider the following thought experiment.  Suppose you are responsible to plan long term population policy for a country of approximately half a million square kilometers.  Would the country be better off with a population of 127 million people or 2 million people?  Many people would quickly conclude that 2 million is the obvious answer.  However the example stems from a comparison of Japan (378,000 km²) to Botswana (582,000 km²).  Clearly no rational person would suggest that Japan would be wise to reduce its population by 98%.  The difference, of course, is that Japan’s population is engaged in maintaining a modern industrial society, a task that would be impossible with a population of two million.  Yet it would obviously be folly to argue the inverse – that Botswana would prosper like Japan if only it had 125 million more people.  In both cases how those people create the conditions that provide what is necessary for the society to function makes all the difference in the world.

            Japan, like any industrialized country, needs a certain minimum population density to keep its society functioning.  It needs some people to consume the goods that are produced by other people and some people to collect the garbage produced by so many people and people to be police, firefighters, stockbrokers, construction workers, gamblers, architects, scientists, teachers, carpenters, painters, artists, filmmakers, and many many more niches that need to be filled if the society is to be called “developed” or “industrial.”  This is simply to say that there is some minimal number of people that are needed to produce a given level of technological and social development – the “necessary” population.  On the other had, it is certainly clear that a given level of technological development is able to produce only so much of what the society requires.  That is, the given technology can provide for and sustain only a certain number of people – the “sustainable” population.  There is no logical reason that the necessary population and sustainable population need be in balance, at least in the short term.

            Viewing the human population from this perspective is quite different from viewing any other species in the world within the same framework.  It may not seem this way at first, but humans are a completely different kind of species.  Beavers, for example, also have a given level of technology.  They need a certain number of beavers to support a beaver dam of a given height, which is what makes the beaver pond bigger.  A bigger beaver pond makes for more resources for the beavers, meaning that the sustainable population of beavers is larger with a larger beaver pond.  If there are more beavers than the sustainable number, some beavers die.  But as long as there are enough beavers to keep building the dam higher, the pond will continue to expand and more beavers will be born and the actual population will continue expanding.  It will continue expanding, that is, as long as it is below the sustainable population level.  But what happens when the necessary number, the number needed to keep the dam at its current level, is greater than the sustainable number?  If the natural situation requires say 10 beavers to keep the dam at its current level, but the pond that results from that level can sustain only 9 beavers, the population of beavers will decline by one, to a density of 9.  But with only 9, the dam cannot be maintained. When the dam gets lower so that 9 beavers can maintain it, the resulting pond will have resources for only 8 (say) beavers, leading to further decline.  The necessary population can construct a niche for itself to provide sustenance for only a certain number of individuals, the sustainable population.  In general, when the sustainable population is equal to the necessary population, we can expect an equilibrium – no further changes.   

            A moment’s reflection reveals how the human animal is profoundly different.  Because we are capable of complicated language and social constructions, we interact with one another in ways no other social species could possibly imagine.  A beaver population below its sustainable level will inevitably increase its numbers.  But a human population below its sustainable level may or may not increase, depending on decisions made by the individuals, decisions that are a complex consequence of negotiated perceptions of the environment.  To take an obvious example, consider a small farming community producing agricultural products for its own consumption.  Whatever the agricultural technology (irrigation canals, or terraces, for example), its maintenance will require a certain number of people – the necessary population.  And with that technology enough food can be produced to sustain a particular population density – the sustainable population.  Consider what happens when the existing population is less than the necessary population.  By definition, the technological infrastructure cannot be maintained.  Suppose at the same time the existing population is less than the sustainable population.  That means that more food than necessary will have been produced, again, by definition.  The experience of the population will be “we have used a very intensive technology to produce more food than we need!”  Why produce more than necessary?  Indeed, under such a circumstance the tendency will be to reduce the intensity of the agricultural technology to bring production in line with the population’s requirements. 

            Consider an alternative situation in which the available technology has produced less than the existing population needs, which is to say the existing population is greater than the sustainable population (for the given level of agricultural technology).  The experience of the population will be one of food shortage.  Viewing food shortage, the population will almost inevitably try and increase the level of agricultural technology so as to produce more food next year.  But what if the population size necessary to increase that technology is greater than the extant population?  The experience of a food shortage is almost certainly going to trump the evident fact that there are not enough people to maintain, let alone increase, the agricultural technology.  Thus, there will be a tendency to increase agricultural technology, and perhaps even a tendency to look for more people to incorporate into the population (calling on relatives from nearby villages to move in to help with the work, or even, if it is a longer term perception, seeking to have more babies). 

            These two scenarios point to the fact that humans create a population dynamics that is the reverse of all other animals.  When the existing population is below the sustainable but above the necessary density, the tendency is to decrease technological intensity.  When the existing population is above the sustainable, but below the necessary the tendency is to increase technological intensity, and perhaps to increase the population.  The exact reverse of what beavers (and all other animals) do. 

            In general terms, human social decisions create the technologies that provide for the needs of the population.  A certain minimal population is necessary to provide for those needs.  But also, a given technological level can sustain only a certain number of people.  If that sustenance is below what the actual population requires, the local experience is not one of “overpopulation” but rather of scarcity and the response is always to produce more.  Producing more, however, generally requires more people.  The irony is that the increase in production that may result is not guaranteed to be sufficient to accommodate the increase in population required by that increase in technological intensity.  A subtle snowball effect may thus emerge with a population striving to produce more and more and, in order to do so, bringing more and more people into the environment, requiring yet more to be produced.  While such a dynamic process is not inevitable, it is certainly is plausible, and probably characterizes many historical examples.

            In summary, within this general framework it is not the case that population is irrelevant, but the simple idea of  “overpopulation” looses any sensible meaning.  Certainly the crude stoichiometric calculations of Malthus and his followers fail to provide interesting insight.  There are times when it is rational to want more people to come into a population, and other times when the reverse is true.  It depends on socioeconomic and political considerations, not discourses about numbers.

Reference:

Perfecto, I., and J. Vandermeer. 2010.  The agroecological matrix as alternative to the land-sparing/agriculture intensification model.  PNAS 107:5786-5791.