The essay’s main theme is that unchecked growth in the worldwide human population can lead to overuse of natural resources and environmental disaster.

Author Hardin’s argument begins with a prediction made in 1798 by theoretician Thomas Malthus, who asserted that gradual improvements in food production cause populations to rise geometrically until starvation sets in. For Hardin, improvements in supplies lead to a “tragedy” whereby unchecked growth in population leads to overuse of freely available natural resources—the “commons”—until those resources, and their originating environments, collapse catastrophically.

As humanity approaches those limits, severe restrictions may be imposed: “No gourmet meals, no vacations, no sports, no music, no literature, no art” (Section 2, Paragraph 4). Hardin maintains that increasing populations will finally use up the advantages of civilization, causing everyone’s lifestyles to regress by Western standards.

Hardin begins with an example well known to economists: If a commonly used pasture is filled to capacity with sheep, a shepherd may be tempted to add one more sheep, which benefits the shepherd but causes the pasture to deteriorate slightly. That loss is spread over all the shepherds, who don’t notice it right away. As the shepherds add to their flocks, the stress builds up until the pasture no longer can produce grass fast enough to satisfy all those hungry sheep, and suddenly entire flocks are starving.