Published in 1968, the essay “The Tragedy of the Commons,” by ecologist Garrett James Hardin, argues that human overpopulation will stress ecosystems beyond their limits and cause a resource catastrophe. The essay has greatly influenced environmentalists.

Hardin was a politically controversial, award-winning science writer who taught ecology at the University of California at Santa Barbara for over 30 years. Critics on both sides of the political spectrum have resented not only some of his proposed solutions to overpopulation but also parts of his rationale; Hardin was a utilitarian who believed the most moral course of action is that which maximizes the wellbeing of the greatest number of people—and this principle took precedence over the idea of natural or universal rights. Hardin therefore tended to favor anything that might reduce the possibility of overpopulation, from abortion to limits on immigration. Hardin has fallen into disfavor in many academic circles due to his eugenicist sympathies, beliefs in racial intelligence disparities, and stigmatizing remarks on poverty—but despite the pall this record casts, Hardin’s fusion of utilitarian pragmatism and scientific stringency left a formidable ecological legacy.

The opening paragraphs of “The Tragedy of the Commons” serve as an introduction that warns that technical solutions to big problems sometimes make those problems worse. He cites the Cold War development of nuclear weapons, each advance of which brought more danger than safety to the world. Solutions to such dilemmas require advances in human ethics rather than improvements in technology. This principle applies also to the problem of human overpopulation: As technology advances, societies increase in size and begin to overtax their environments.

Section 2, “What Shall We Maximize?” asks whether human population can grow indefinitely. The author answers that Earth’s resources are finite, and that population growth must therefore hover around zero or a disaster becomes inevitable. Economist and clergyman Thomas Malthus warned that continuous growth becomes “geometric,” or exponential, rising faster and faster until it outstrips all resources. Continuously growing populations will eventually require continuously increasing sacrifices, until utilitarian philosopher Jeremy Bentham’s hope for “the greatest good for the greatest number” becomes impossible (Section 2, Paragraph 2). Even an endless source of energy would likely be insufficient for an indefinitely increasing population.

People will have to decide what they’ll sacrifice for protection against catastrophic overgrowth. So far, though, no civilization has solved the problem of population growth, and already the fastest-growing countries often are the most resource-stressed.

Economist Adam Smith in 1776 popularized the idea of the “invisible hand” that permits individual workers, laboring strictly for private gain, to unintentionally create value for all. This idea, however, when allowed to run free in the realm of reproduction, leads to ever-increasing populations and worsening strains on the natural world and its resources. The freedom to reproduce, argues Hardin, may have to be restricted.

Section 3, “Tragedy of Freedom in a Commons,” describes how resources get overused as a population increases. Herders who use a common field, or “commons,” to graze their animals will, under stable conditions, add to their herds until the field is at capacity. At that point, adding an additional animal will still benefit the herder, and the resulting overgrazing will be shared by everyone and not solely by that herder. This leads to herders adding to their own herds until the common area, exhausted by overuse, can no longer feed the herds.

Tragedy is the inevitable unfolding of fate, and the logic of the herders leads inevitably to a catastrophe in the commonly used field. This logic also causes, for example, overgrazing on federal land in the western US, overfishing in the oceans, and overcrowding in America’s national parks.

Section 4, “Pollution,” describes another exploitation of the commons. It’s very cheap to dump pollutants into the environment instead of purifying them, and the polluting effects are small for the dumper. Over time, though, as everyone dumps pollutants, the effects accumulate and return to poison all within the environment. Even then, it’s still economically efficient to pollute: Each time, the cost of additional pollution is outweighed by the savings from dumping the effluents.

In Section 5, “How To Legislate Temperance?” the author asserts that the ethics of pollution depend on the situation: “[T]he morality of an act is a function of the state of the system at the time it is performed” (Section 5, Paragraph 1). Thus, a single American frontiersman in 1818 who kills a bison merely for its tongue had no discernible effect on the millions of buffalo around him, whereas such an act in 1968, when the number of bison had dwindled to a few thousand, would be considered appalling.

Attempts to judge the morality of a particular environmental action can backfire. Photos of a killed elephant or blazing grassland, without context, may mislead viewers; prohibitions can become unreasonable; bureaucrats who enforce the laws may become corrupted. Laws must be carefully thought out and bureaucrats given the correct incentives.

Section 6, “Freedom to Breed Is Intolerable,” argues that, in a state of nature, overbreeding by animals usually leads to fewer offspring in total, but the modern human welfare state rewards excessively large human families. The United Nations Universal Declaration of Human Rights of 1967 maintains that the total number of children in a family is the decision of that family. Given problems of overpopulation already present in the world, this covenant becomes a “tragic ideal.”

Section 7 is titled “Conscience Is Self-Eliminating.” The author presents evidence that conscience is an insufficient motivation for change. Citing Darwinian logic, Hardin maintains that appeals to parents to limit their family size for the good of humanity results in larger families: Those who limit their size get outbred by those who don’t, until most or all of the descendants tend to have larger, more selfish families. “To make such an appeal is to set up a selective system that works toward the elimination of conscience from the race” (Section 7, Paragraph 4).

In Section 8, “Pathogenic Effects of Conscience,” Hardin theorizes that people who are told to limit their own reproduction face a “double bind” that damns them if they agree and ostracizes them if they refuse. Such appeals to conscience, popular among political leaders, generally don’t lead to improvements but do cause a wasteful epidemic of anxiety.

Section 9, “Mutual Coercion Mutually Agreed Upon,” suggests a better approach whereby groups come to a consensus on which behaviors deserve punishment. Punishment is a form of coercion that no one likes, but it can be tolerated for its beneficial effects overall. As for the commons, the classic alternative is private property and inheritance. This system, Hardin admits, can be problematic—”An idiot can inherit millions” (Section 9, Paragraph 5)—but it’s better than the destructive misuse of a commons.

The author observes that reform sometimes gets stymied by those who believe any changes must be perfect, as if the current system already is perfect. In fact, all systems have flaws, including the old ways, and a rational comparison of old and new methods can help to determine the best choice.

The tenth and final Section, “Recognition of Necessity,” notes that the commons, once spaciously vast in a world of few people, becomes overwhelmed on a planet with billions of humans. Most resources and environments commonly held today are stressed by pollution and overuse; restrictions on such misuse will curtail individual freedoms but also resolve environmental and resource problems that, in themselves, constrain human action. The main liberty to curtail, then, is the freedom to reproduce at will. That is the only way to prevent an overpopulation disaster.