Today Is Yesterday’s Tomorrow - The 1977 presidential address to the Societas Internationalis Limnologiae Theoreticae et Applicatae

By John R. Vallentyne
Volume 23, Number 3 (Spring 2013)
Issue theme: "The manic quest to grow Canada's population"


Editor’s note: This is an abridged version of an address given by Vallentyne as president of the Societas Internationalis Limnologiae Theoreticae et Applicatae (SlL) at its XXth Congress in Copenhagen, Denmark, August 8, 1977, and published in 1978 in Verhandlungen der Internationale Vereinigung für Limnologie, vol. 20, pp. 1-12. It is notable as the first use of per capita energy consumption as a general index of per capita environmental impacts and a way of comparing the demophoric (demotechnic) growth and consumption-adjusted populations of different nations. Material omitted here includes most tables and text relating to the resolution referred to in his long title and the formation of a committee to draft such.

It is not within my nature to let such an opportunity as this pass without disturbing the tranquility of our minds. I intend to depart from the tradition of SIL presidential addresses in three respects.

Rather than focus on inland waters, the common interest we share as members of this international association, I intend to talk principally of events on land. Rather than promote the development of knowledge, one part of the aim (theoreticae) that binds us together in this association, my attentions will focus on the other part of our aim (applicatae). And, rather than direct my words solely to you as an audience, I desire to talk with you and through you to humane persons throughout the world.

The question I put to you in my title is simultaneously an abstract, conclusion, and recommendation. My object is your approval of a SIL resolution in support of its intent. There is nothing in the title or resolution that should cause you serious concern, except the consequences of our failure to act. My argument should be accepted as reasonable by anyone familiar with the notions of environmental carrying capacity, ecosystems, and man. I present four propositions and three questions.

Proposition Number 1 . For given times and conditions, there are limits to the carrying capacity of the Earth for man.

I have neither the knowledge nor the conceit to state what these limits have been, are, or will be. But, I do have the intelligence to state that there are limits and, whatever they may be, they must be thought of in terms of metabolism rather than numbers of heads….

Proposition Number 2 . The carrying capacity of the Earth for man cannot meaningfully be evaluated in terms of human heads or physiological metabolism alone.

Our species is unusual in the living world in the extent to which we have external (technological) in addition to internal (biological) components of mass and metabolism. While this must always have been obvious to members of the human race, it was not explicitly recognized in ecological terms until the 1970’s. Three papers appeared then that will forever make it difficult to view the human ecological scene as simply as we did before. One of these stated the nature of environmental concerns in a way that combined the physiological metabolism of humans and “energy slaves,” adding a technological factor modifying the environmental impact of both (Bryson & Ross 1972). Another contribution discussed the internal and external metabolism of Homo sapiens in a broad ecological and evolutionary perspective, including the significance of transportation and mobility as factors in human ecology (Margalef 1973). The third invented a word, “demophoric” (from demos, population; phora, production), describing and epitomizing the dual and interactive nature of the internal and external metabolism of man in a way that suggested a basis for achieving global human control (Vallentyne 1972; Vallentyne & Tracy 1972).

Adopting the viewpoints expressed in these papers, I have converted data on energy consumption in the Statistical Yearbooks of the United Nations into human equivalents— in the terminology of Bryson & Ross (1972), as “energy slaves,” I have used a daily intake of 2,300 kilocalories per individual as an average generally applicable to the internal metabolism of human populations. The fact that average calorific intake values vary among different nations (Borgstrom 1968) does not substantially affect the general argument presented here.

A consumption of one metric ton of coal equivalent per year in external metabolism is equivalent on this basis to maintaining a population of 8.1 non-technological humans, i.e., energy slaves, for a year. You may shudder to find me referring to numbers of “heads,” rather than energy flow, but because nonscientists are likely to find it easier to think in these terms I have chosen to express my data that way. Children, perhaps even better than adults, know that life depends on a continued supply of bread and water and that machines do not run when their energy supply is cut off.

Tables 1 to 9 list data for 1973, the year of the energy crisis. P is the population in human heads, T the population of “energy slaves,” and D the sum of the two expressed in D-units (P+T). The D (demophoric) index is the ratio of external (technological) to internal (biological) metabolism (T/P). One D-unit is equivalent to 829,000 kilocalories per year (2,300 kilocalories per day for 365 days). [Editor’s note: the per year value should be 839,500 kcal, but effect on calculated D values is minor. Tables 2-7 and 9 are omitted here. D-index values based on 1990 energy consumption data are given for all nations in Mata, Onisto, and Vallentyne (2012) and further discussed in Hurlbert (2012). In those papers, (P+T) is termed “consumption adjusted population”].

On this demophoric basis, the human “population” of the Earth in 1973 amounted to 66,700 million D-units, with an average global D-index of 16. The human population equivalent of livestock (Borgstrom 1968) was approximately 16,000 million human equivalents in 1973. Considering demophoric growth since 1973, and including Borgstrom’s concept of the human population equivalent of livestock, it is probable that the total “human population equivalent” for the Earth may be close to 100,000 million, now, in 1977.

I draw your attention to Table 1, which lists, in order of D-units, the twenty most energy-consumptive nations of the Earth. As centers of political control, they are the most obvious places to look for beneficial reductions in the rates of consumption of the natural resources of the Earth. National, continental, and global inequalities in D-indices are exposed in Tables 2 to 9.

Proposition Number 3 . The carrying capacity of the Earth for man has been changed by man.

Forests have been cleared, plants and animals domesticated, fire controlled, geochemical cycles altered, and external anatomical systems developed to the point that I can realistically claim to eat oil, have wheels as legs, think through a computer, talk over millions of kilometers, and have a body composed of metal, plastic, and stone.

The increase in the carrying capacity of the Earth for man has resulted from interacting influences too complicated to summarize other than by saying that they have created improved conditions as measured in terms of human life expectancy at birth and prevention of human impairment through injury and disease. No one can deny that this has been the case up to now. Whether or not this persists depends upon our ability to determine where we stand in relation to future limits of the carrying capacity of the Earth for man, and actions we take in that regard.

Proposition Number 4 . Runaway rates of demophoric growth are no longer in the interest of Homo sapiens.

The most significant feature of the Statistical Yearbooks of the United Nations is the absence of zero values and minus signs in national tabulations of the annual rates of growth of human population and per capita consumption of resources. Population growth rates vary from 0 percent per annum to 8.5 percent per annum with a global average of about 2 percent per annum. The latter value corresponds to an average global population doubling time of 35 to 40 years. The annual rates of growth of per capita consumption for energy and other natural resources are typically twice these values, with doubling times of 15 to 20 years, in many instances even less.

None of these values, singly or jointly, nationally or globally, can be maintained indefinitely. Whether by human intervention, or pestilence, famine, war, and disease, we must eventually come to fluctuate, with a certain error, about a carrying capacity roughly consistent with zero demophoric growth.

Whenever somebody talks about zero growth, it makes other people feel uneasy. Perhaps this is because of an exaggerated importance of growth carried over from childhood memories of domination by older and larger persons. Perhaps it is also because we tend, erroneously, to think of zero growth as a static thing.

But under conditions of zero demophoric growth people will continue to be born, grow older and wiser, make love on park benches, wander into new and exciting locations, go shopping or fishing, raise children, and in fact do all these and other things that humans have done or are likely to do, world without end. There is in fact a higher probability that humans will do these things, and do them humanely, under conditions of zero demophoric growth than under the present regime of localized greed and global indifference.

I can make this claim because I am speaking in terms of human demophoric metabolism in relation to the biospheric resources needed to sustain it. Metabolism moves in time. It is not static. It is dependent on the flow of resources, where and when they are needed. When this flow is imperiled, life is imperiled.

There is another reason why I can make this statement. That is because as humans take over the management of more and more segments of the biosphere, there will come a time when the cost of additional demophoric growth, either through an increase in human population or an increase in per capita consumption, will rise exponentially like flood waters out of control.

Three questions

As that time nears, and more and more people and leaders perceive that their countries, individually and collectively, are growing demophorically at rates threatening the demophoric carrying capacity of the Earth for man, three questions will arise.

The first question is: On the basis of human population, what is the lead time to achieve an orderly political progression to an eventual state of zero demophoric growth? The answer is about 70 years. If someone proposed that this minimum lead time could be shortened to 50 years, I would not vehemently object in view of the way we throw some human values about.…

The second question is one on which we, as limnologists, have something to say: What are the probable recovery times from errors in tuning ourselves to the future demophoric carrying capacities of the Earth for man? The answers depend, of course, on the nature of the errors and ease of their reversibility….

The third question is: When is it generally perceived that the demophoric carrying capacity of the earth for man is rapidly being approached, or has been exceeded, and that control measures must be taken in the general interest, how will the cost of these controls be partitioned, nationally and internationally, and between the biological and technological metabolism of man? At what point will there be a trade-off in the setting of a thermostat, the number of cars per family, the equipment in scientific laboratories, or the level of an air-conditioner on a hot humid day, and something going on around the corner of our community, nation, or planet in respect to resources needed for the sustenance of human life? ….

In conclusion

The long title of this paper poses my question in terms of resources of use to man. That is as it should be for the fulfillment of material demophoric needs. On the other hand, my analysis of the interaction between human population and technology is based on an energy equivalence. That likewise is as it should be in terms of achieving equitable, humane measures of control. Global incentives for the reduction of demophoric consumption in energetic terms will leave more to local ingenuity and initiatives than more complex and unwieldy economic measures based on material controls. …

The onus for action lies with the most highly consumptive individuals, regions, and nations of the Earth. The most consumptive nations on a demophoric energy basis are identified in Tables 1 to 9, If controls are to be accepted and initiatives taken, they must be implemented first and foremost by these nations because they are at one and the same time the gluttons of the Earth and the focal points of control.

There is complexity in the question I have posed and even greater complexity in the answers it intends to provoke. I do not claim to understand this complexity, but I do claim to have phrased the question in a practicable form which may be resolved by others more knowledgeable and influential on the global scene.

We cannot resolve this question, but we can contribute global knowledge and experience from our area of expertise. I doubt that governments can, or will, initiate action on this question because of their preoccupation with intra-national issues and obsession with sovereignty. What is needed is a group of internationally respected humane and knowledgeable persons acting as individuals in the interest of humanity rather than as representatives of organizations or particular nations. It would fall to them to suggest a set of principles that nations might adopt concerning exploitation and use of the natural resources of the Earth.….

I hope that you will not let the question posed in the title of this paper die here or when you return to your homes on August 14. Put it in places where it may be developed and used. Collectively in SIL, we have the knowledge and accompanying professional obligation to warn when there is not an adequate margin of safety in human design with the biosphere.… ■


Borgstrom, G., 1968: Principles of Food Science, II, 473 pp. The Macmillan Co., New York.

Bryson, R.A. & Ross, J. E., 1972: On the nature of environmental concern. Univ. Wisconsin lnst. far Environm. Studies Working Paper 8:1-24.

Margalef, R., 1974: Ecological theory and prediction in the study of the interaction between man and the rest of the biosphere. In Okologie und Lebenschutz in internationaler Sicht, 307-363, ed. by Harald Sioli. Verlag Rombach, Freiburg.

Statistical Yearbook of the United Nations, 1974: E/F. 75. XVII. 1. United Nations Publications, New York.

Vallentyne, J.R., 1972: Freshwater Supplies and Pollution: Effects of the demophoric explosion on water and man. In: The Environmental Future, 181-211, ed. by Nicholas Polunin. The Macmillan Press, London.

Vallentyne, J.R., and Tracy, H.L.,1972: A new term introduced at First Conference on Environmental Future. Biol. Conservation 4 (5):371-872. Reprinted in 1973 in Bull. Atomic Scientists 29 (5): 24.

References added:

Hurlbert, S.H., 2012. Tribute to an ‘obnoxious’ ecocatalytical demotechnician: Jack Vallentyne on population. Ethics in Science and Environmental Politics 12:21-34.

Mata, F.J., Onisto, L.J., and Vallentyne, J.R., 2012. Consumption: the other side of population for development. Ethics in Science and Environmental Politics 12:15-20.

About the author

John R. Vallentyne was a biologist with the Fisheries and  Marine Service,  Ontario  Region, Canada; Centre for Inland Waters, Burlington, Ontario, Canad.