The law of population fluctuations

The law of population fluctuations is the proposed principle that no species maintains a constant population indefinitely: numbers build, reach a climax, and decline, sometimes with striking speed. In the novel, this idea links the Great Disaster’s threat to humanity with the recurring surges of animals and insects that reshape the survivors’ surroundings. It is presented as a biological hypothesis, not a guarantee of predictable cycles, and its force comes from the contrast between gradual growth and sudden collapse.

Definition and Examples

The discussion begins by rejecting the assumption that an event’s never having happened makes it impossible. A species may seem secure through a long period of increase, yet its population can still turn sharply downward. Insects such as locusts and Grasshoppers provide an immediate example: their numbers can rise far beyond their usual level, then sink to a small fraction of their recent abundance. The same pattern is proposed for larger animals, whose slower breeding rates may mean that their cycles unfold over longer periods.

Lemmings and snowshoe rabbits illustrate fluctuations among mammals. Snowshoe-rabbit numbers can build over several years until the animals seem ubiquitous, then fall dramatically. The account notes that some zoologists have suggested a general biological law of such increase and decline, with the duration of a cycle related to the animal’s breeding rate. The qualification matters: the book presents the law as a scientific proposal, rather than as a precisely established timetable capable of predicting the fate of any particular population.

The African buffalo supplies a longer historical example. During much of the nineteenth century, it was common on the veldt, powerful and subject to few natural enemies. Its numbers appeared to increase steadily; near the century’s end, they reached a high point before rinderpest sharply reduced them. In some parts of its range the animal became extinct, while over the following fifty years its numbers slowly increased again. The sequence makes the law more than a pattern of sudden disappearance: population decline can be followed by recovery, though that recovery may be slow and uneven.

Humanity and the Great Disaster

The principle is extended to humanity without suggesting that people stand outside nature. Human numbers had increased for ten thousand years despite wars, pestilences, and famines, and that increase had become increasingly rapid. The narration likens this sustained upward trend to an uninterrupted run of good fortune. If human populations are subject to the same general flux as other species, such a long ascent offers no assurance of permanence; it makes humanity’s position perilous when a global disease emerges.

The disease described in the pre-disaster news reports had spread into major centers of civilization, apparently outpacing quarantine, while news services in some cities had failed. A bacteriologist offered several possible origins, including an animal reservoir, a newly mutated microorganism, or a laboratory release; none was established as the answer. These possibilities locate human vulnerability within a wider biological world, but they do not prove that the pandemic itself is an instance of the proposed population law. Rather, the pandemic makes the human population’s long expansion suddenly precarious, showing how little an apparent history of uninterrupted growth can promise about what comes next.

The Pattern in the Survivors’ World

After the disaster, fluctuations become visible in the survivors’ daily landscape. Ants and Rats had already become familiar plagues, and cattle continued to multiply until they became a nuisance. In the year the survivors called the Year of the Bulls, crossing the countryside could mean encountering a charging bull. Killing one near the houses created further work: its carcass had to be buried or removed. The population surge was both a source of plentiful, if tough, meat and a disruption to ordinary movement and settlement.

The next year exposed how abundance can turn into vulnerability when conditions change. Drought left little grass, and the numerous cattle grew thin and ranged widely for food. One night a hungry herd broke through the fence around the vegetable plot. The men fired at the milling animals, but the garden was ruined by trampling before the cattle could be driven away. Grasshoppers then descended and consumed what the cattle had not reached, stripping leaves from trees and eating the flesh from ripening peaches. Their own numbers, too, collapsed: they died, leaving the survivors to confront the aftermath of the infestation.

Rain offered a counterpoint to these losses. Two weeks after the first rainfall, sprouting grass made the hills faintly green, and the community’s despair eased. The return of growth did not erase the garden’s destruction or establish that every species would recover on the same schedule. It did, however, remind the survivors that the earth could renew itself when conditions changed. In this sequence, population pressure, drought, damaged food supplies, insect abundance, and renewed vegetation form a connected but not mechanically predictable ecological story.

Human Communities and Adaptation

The law also illuminates the survivors’ concern with the future of their own small community. The Tribe’s early increase was marked by births: by the end of one year, seven adults and four children lived on San Lupo Drive, with Evie besides. In the following year all four women bore children, and the number of children reached ten, exceeding the number of adults. The account connects this growth to the adults’ memory of isolation and their hope that each new child strengthened the community’s hold on life. Human population change is therefore not only a count; it shapes the group’s sense of continuity and its response to the surrounding uncertainty.

Later, the community’s decisions about admitting outsiders show another consequence of demographic limits. When a smaller group sent a messenger proposing union, The Tribe debated disease, distrust of strangers, and the need to strengthen its numbers. Fewer girls had been born in recent years, leaving some young men without prospective wives, while universal blood relationship made marriage among cousins a concern. Em argued that life could not be preserved by refusing every risk. The Tribe voted unanimously to admit the newcomers; the Others contracted measles but soon recovered. This episode does not turn population fluctuation into a simple rule for social policy. It shows instead how people respond to vulnerability through judgment, debate, and cooperation, while recognizing that growth and survival remain uncertain.

The law’s narrative significance lies in the repeated contrast between apparent security and reversal. Insects can swarm and vanish; cattle can become abundant and then face scarcity; humanity can expand for millennia and still be exposed to catastrophe. Yet decline is not always final: the African buffalo gradually rebuilt its numbers, and rain brought grass back to the survivors’ hills. The pattern is not a promise that every loss will be repaired, but a warning against mistaking past abundance for permanence—and against assuming that a history of no disaster means disaster cannot come.