公地悲剧_哈丁

The Tragedy of the Commons Garrett Hardin At the end of a thoughtful article on the future of nuclear war, Wiesner and York (1) concluded that: “Both sides in the arms race are . . . confronted by the dilemma of steadily increasing military power and steadily de- creasing national security. It is our considered professional judgment that this dilemma has no technical solution. If the great powers continue to look for solutions in the area of science and technology only, the result will be to worsen the situation.” I would like to focus your attention not on the subject of the article (national secu- rity in a nuclear world) but on the kind of conclusion they reached, namely that there is no technical solution to the problem. An implicit and almost universal assumption of discussions published in professional and semipopular scientific journals is that the problem under discussion has a technical solution. A technical solution may be de- fined as one that requires a change only in the techniques of the natural sciences, de- manding little or nothing in the way of change in human values or ideas of morality. In our day (though not in earlier times) technical solutions are always welcome. Be- cause of previous failures in prophecy, it takes courage to assert that a desired tech- nical solution is not possible. Wiesner and York exhibited this courage; publishing in a science journal, they insisted that the solu- tion to the problem was not to be found in the natural sciences. They cautiously qual- ified their statement with the phrase, “It is our considered professional judgment. . . .” Whether they were right or not is not the concern of the present article. Rather, the concern here is with the important concept of a class of human problems which can be called “no technical solution problems,” and, more specifically, with the identifica- tion and discussion of one of these. It is easy to show that the class is not a null class. Recall the game of tick-tack- toe. Consider the problem, “How can I win the game of tick-tack-toe?” It is well known that I cannot, if I assume (in keep- ing with the conventions of game theory) that my opponent understands the game perfectly. Put another way, there is no “technical solution” to the problem. I can win only by giving a radical meaning to the word “win.” I can hit my opponent over the head; or I can drug him; or I can falsify the records. Every way in which I “win” involves, in some sense, an aban- donment of the game, as we intuitively understand it. (I can also, of course, open- ly abandon the game—refuse to play it. This is what most adults do.) The class of “No technical solution problems” has members. My thesis is that the “population problem,” as convention- ally conceived, is a member of this class. How it is conventionally conceived needs some comment. It is fair to say that most people who anguish over the population problem are trying to find a way to avoid the evils of overpopulation without relin- quishing any of the privileges they now enjoy. They think that farming the seas or developing new strains of wheat will solve the problem—technologically. I try to show here that the solution they seek cannot be found. The population problem cannot be solved in a technical way, any more than can the problem of winning the game of tick-tack-toe. What Shall We Maximize? Population, as Malthus said, naturally tends to grow “geometrically,” or, as we would now say, exponentially. In a finite world this means that the per capita share of the world’s goods must steadily decrease. Is ours a finite world? A fair defense can be put forward for the view that the world is infinite; or that we do not know that it is not. But, in terms of the practical problems that we must face in the next few generations with the foreseeable technology, it is clear that we will greatly increase human misery if we do not, during the immediate future, assume that the world available to the terrestrial human popula- tion is finite. “Space” is no escape (2). A finite world can support only a finite population; therefore, population growth must eventually equal zero. (The case of perpetual wide fluctuations above and below zero is a trivial variant that need not be discussed.) When this condition is met, what will be the situation of mankind? Specifical- ly, can Bentham’s goal of “the greatest good for the greatest number” be realized? No—for two reasons, each sufficient by itself. The first is a theoretical one. It is not mathematically possible to maximize for two (or more) variables at the same time. This was clearly stated by von Neumann and Morgenstern (3), but the principle is implicit in the theory of partial differential equations, dating back at least to D’Alembert (1717– 1783). The second reason springs directly from biological facts. To live, any organism must have a source of energy (for example, food). This energy is utilized for two pur- poses: mere maintenance and work. For man, maintenance of life requires about 1600 kilocalories a day (“maintenance cal- ories”). Anything that he does over and above merely staying alive will be defined as work, and is supported by “work calo- ries” which he takes in. Work calories are used not only for what we call work in common speech; they are also required for all forms of enjoyment, from swimming and automobile racing to playing music and writing poetry. If our goal is to max- imize population it is obvious what we must do: We must make the work calories per person approach as close to zero as possible. No gourmet meals, no vacations, no sports, no music, no literature, no art. . . . I think that everyone will grant, with- out argument or proof, that maximizing population does not maximize goods. Bentham’s goal is impossible. In reaching this conclusion I have made the usual assumption that it is the acquisi- tion of energy that is the problem. The ap- pearance of atomic energy has led some to question this assumption. However, given an infinite source of energy, population growth still produces an inescapable problem. The problem of the acquisition of energy is re- placed by the problem of its dissipation, as J. H. Fremlin has so wittily shown (4). The arithmetic signs in the analysis are, as it were, reversed; but Bentham’s goal is still unobtainable. The optimum population is, then, less than the maximum. The difficulty of defin- ing the optimum is enormous; so far as I know, no one has seriously tackled this problem. Reaching an acceptable and stable solution will surely require more than one generation of hard analytical work—and much persuasion. We want the maximum good per person; but what is good? To one person it is wil- derness, to another it is ski lodges for thou- sands. To one it is estuaries to nourish ducks for hunters to shoot; to another it is factory land. Comparing one good with another is, we usually say, impossible because goods are incommensurable. Incommensurables can- not be compared. The author is professor of biology, University of California, Santa Barbara. This article is based on a presidential address presented before the meeting of the Pacific Di- vision of the American Association for the Advancement of Science at Utah State University, Logan, 25 June 1968. ARTICLE www.sciencemag.org z SCIENCE z VOL. 162 z 13 DECEMBER 1968 1243–1248 Theoretically this may be true; but in real life incommensurables are commensurable. Only a criterion of judgment and a system of weighting are needed. In nature the criterion is survival. Is it better for a species to be small and hideable, or large and powerful? Natural selection commensurates the incommensu- rables. The compromise achieved depends on a natural weighting of the values of the variables. Man must imitate this process. There is no doubt that in fact he already does, but unconsciously. It is when the hidden deci- sions are made explicit that the arguments begin. The problem for the years ahead is to work out an acceptable theory of weighting. Synergistic effects, nonlinear variation, and difficulties in discounting the future make the intellectual problem difficult, but not (in principle) insoluble. Has any cultural group solved this prac- tical problem at the present time, even on an intuitive level? One simple fact proves that none has: there is no prosperous population in the world today that has, and has had for some time, a growth rate of zero. Any people that has intuitively identified its optimum point will soon reach it, after which its growth rate becomes and remains zero. Of course, a positive growth rate might be taken as evidence that a population is below its optimum. However, by any rea- sonable standards, the most rapidly growing populations on earth today are (in general) the most miserable. This association (which need not be invariable) casts doubt on the optimistic assumption that the positive growth rate of a population is evidence that it has yet to reach its optimum. We can make little progress in working toward optimum population size until we explicitly exorcize the spirit of Adam Smith in the field of practical demography. In economic affairs, The Wealth of Nations (1776) popularized the “invisible hand,” the idea that an individual who “intends only his own gain,” is, as it were, “led by an invisible hand to promote . . . the public interest” (5). Adam Smith did not assert that this was invariably true, and perhaps neither did any of his followers. But he contributed to a dominant tendency of thought that has ever since interfered with positive action based on rational analysis, namely, the tendency to assume that deci- sions reached individually will, in fact, be the best decisions for an entire society. If this assumption is correct it justifies the continuance of our present policy of laissez- faire in reproduction. If it is correct we can assume that men will control their individ- ual fecundity so as to produce the optimum population. If the assumption is not correct, we need to reexamine our individual free- doms to see which ones are defensible. Tragedy of Freedom in a Commons The rebuttal to the invisible hand in popu- lation control is to be found in a scenario first sketched in a little-known pamphlet (6) in 1833 by a mathematical amateur named William Forster Lloyd (1794–1852). We may well call it “the tragedy of the com- mons,” using the word “tragedy” as the phi- losopher Whitehead used it (7): “The es- sence of dramatic tragedy is not unhappiness. It resides in the solemnity of the remorseless working of things.” He then goes on to say, “This inevitableness of destiny can only be illustrated in terms of human life by inci- dents which in fact involve unhappiness. For it is only by them that the futility of escape can be made evident in the drama.” The tragedy of the commons develops in this way. Picture a pasture open to all. It is to be expected that each herdsman will try to keep as many cattle as possible on the commons. Such an arrangement may work reasonably satisfactorily for centuries be- cause tribal wars, poaching, and disease keep the numbers of both man and beast well below the carrying capacity of the land. Finally, however, comes the day of reckon- ing, that is, the day when the long-desired goal of social stability becomes a reality. At this point, the inherent logic of the com- mons remorselessly generates tragedy. As a rational being, each herdsman seeks to maximize his gain. Explicitly or implic- itly, more or less consciously, he asks, “What is the utility to me of adding one more animal to my herd?” This utility has one negative and one positive component. 1) The positive component is a function of the increment of one animal. Since the herdsman receives all the proceeds from the sale of the additional animal, the positive utility is nearly 11. 2) The negative component is a func- tion of the additional overgrazing created by one more animal. Since, however, the effects of overgrazing are shared by all the herdsmen, the negative utility for any par- ticular decision-making herdsman is only a fraction of 21. Adding together the component partial utilities, the rational herdsman concludes that the only sensible course for him to pursue is to add another animal to his herd. And another; and another. . . . But this is the conclusion reached by each and every ratio- nal herdsman sharing a commons. Therein is the tragedy. Each man is locked into a sys- tem that compels him to increase his herd without limit—in a world that is limited. Ruin is the destination toward which all men rush, each pursuing his own best inter- est in a society that believes in the freedom of the commons. Freedom in a commons brings ruin to all. Some would say that this is a platitude. Would that it were! In a sense, it was learned thousands of years ago, but natural selection favors the forces of psychological denial (8). The individual benefits as an individual from his ability to deny the truth even though society as a whole, of which he is a part, suffers. Education can counteract the natural tendency to do the wrong thing, but the inexorable succession of generations re- quires that the basis for this knowledge be constantly refreshed. A simple incident that occurred a few years ago in Leominster, Massachusetts, shows bow perishable the knowledge is. During the Christmas shopping season the parking meters downtown were covered with plastic bags that bore tags reading: “Do not open until after Christmas. Free parking courtesy of the mayor and city council.” In other words, facing the prospect of an in- creased demand for already scarce space. the city fathers reinstituted the system of the commons. (Cynically, we suspect that they gained more votes than they lost by this retrogressive act.) In an approximate way, the logic of the commons has been understood for a long time, perhaps since the discovery of agricul- ture or the invention of private property in real estate. But it is understood mostly only in special cases which are not sufficiently generalized. Even at this late date, cattlemen leasing national land on the western ranges demonstrate no more than an ambivalent understanding, in constantly pressuring fed- eral authorities to increase the head count to the point where overgrazing produces ero- sion and weed-dominance. Likewise, the oceans of the world continue to suffer from the survival of the philosophy of the com- mons. Maritime nations still respond auto- matically to the shibboleth of the “freedom of the seas.” Professing to believe in the “inexhaustible resources of the oceans,” they bring species after species of fish and whales closer to extinction (9). The National Parks present another in- stance of the working out of the tragedy of the commons. At present, they are open to all, without limit. The parks themselves are limited in extent—there is only one Yo- semite Valley—whereas population seems to grow without limit. The values that vis- itors seek in the parks are steadily eroded. Plainly, we must soon cease to treat the parks as commons or they will be of no value to anyone. What shall we do? We have several op- tions. We might sell them off as private property. We might keep them as public property, but allocate the right to enter them. The allocation might be on the basis SCIENCE z VOL. 162 z 13 DECEMBER 1968 z www.sciencemag.org1243–1248 of wealth, by the use of an auction system. It might be on the basis of merit, as defined by some agreed-upon standards. It might be by lottery. Or it might be on a first-come, first-served basis, administered to long queues. These, I think, are all the reason- able possibilities. They are all objection- able. But we must choose—or acquiesce in the destruction of the commons that we call our National Parks. Pollution In a reverse way, the tragedy of the commons reappears in problems of pollution. Here it is not a question of taking something out of the commons, but of putting something in— sewage, or chemical, radioactive, and heat wastes into water; noxious and dangerous fumes into the air, and distracting and un- pleasant advertising signs into the line of sight. The calculations of utility are much the same as before. The rational man finds that his share of the cost of the wastes he discharges into the commons is less than the cost of purifying his wastes before releasing them. Since this is true for everyone, we are locked into a system of “fouling our own nest,” so long as we behave only as indepen- dent, rational, free-enterprisers. The tragedy of the commons as a food basket is averted by private property, or something formally like it. But the air and waters surrounding us cannot readily be fenced, and so the tragedy of the commons as a cesspool must be prevented by different means, by coercive laws or taxing devices that make it cheaper for the polluter to treat his pollutants than to discharge them un- treated. We have not progressed as far with the solution of this problem as we have with the first. Indeed, our particular concept of private property, which deters us from ex- hausting the positive resources of the earth, favors pollution. The owner of a factory on the bank of a stream—whose property ex- tends to the middle of the stream, often has difficulty seeing why it is not his natural right to muddy the waters flowing past his door. The law, always behind the times, requires elaborate stitching and fitting to adapt it to this newly perceived aspect of the commons. The pollution problem is a consequence of population. It did not much matter how a lonely American frontiersman disposed of his waste. “Flowing water purifies itself every 10 miles,” my grandfather used to say, and the myth was near enough to the truth when he was a boy, for there were not too many people. But as population became denser, the natural chemical and biological recycling processes became overloaded, calling for a redefinition of property rights. How To Legislate Temperance? Analysis of the pollution problem as a func- tion of population density uncovers a not generally recognized principle of morality, namely: the morality of an act is a function of the state of the system at the time it is performed (10). Using the commons as a cesspool does not harm the general public under frontier conditions, because there is no public, the same behavior in a metropolis is unbearable. A hundred and fifty years ago a plainsman could kill an American bison, cut out only the tongue for his dinner, and discard the rest of the animal. He was not in any impor- tant sense being wasteful. Today, with only a few thousand bison left, we would be ap- palled at such behavior. In passing, it is worth noting that the morality of an act cannot be determined from a photograph. One does not know whether a man killing an elephant or set- ting fire to the grassland is harming others until one knows the total system in which his act appears. “One picture is worth a thousand words,” said an ancient Chinese; but it may take 10,000 words to validate it. It is as tempting to ecologists as it is to reformers in general to try to persuade others by way of the photographic short- cut. But the essense of an argument can- not be photographed: it must be presented rationally—in words. That morality is system-sensitive es- caped the attention of most codifiers of ethics in the past. “Thou shalt not . . .” is the form of traditional ethical directives which make no allowance for particular circumstances. The laws of our society fol- low the pattern of ancient ethics, and there- fore are poorly suited to governing a com- plex, crowded, changeable world. Our epi- cyclic solution is to augment statutory law with administrative law. Since it is practi- cally impossible to spell out all the condi- tions under which it is safe to burn trash in the back yard or to run an automobile with- out smog-