A4 Demographic anomalies

Topic

Demographic collapse is a population anomaly that occurs when fertility remains well below replacement level; it constitutes the "Population" component—an element that the "Resource Regime" track carries over only partially when shifting stages, unlike "Economy" and "Cliodynamics," which it carries over fully. Demographic collapse is triggered when this sub-replacement fertility is not merely a temporary dip but persists over time: an isolated drop in fertility is insufficient; rather, fertility must remain well below replacement level for generations for a demographic collapse to take hold.

Unlike demographic collapse, which stems from sustained low fertility, the "youth bulge" is a population anomaly that occurs when the proportion of young people neither employed nor in education exceeds a critical threshold. The youth bulge is triggered precisely when this proportion crosses that threshold: as long as it remains below it, the youth population is absorbed into the education or labor systems; once the threshold is crossed, a mass of young people neither employed nor in education remains—large enough to activate the youth bulge.

Aging—the third population anomaly in this group, alongside demographic collapse and the youth bulge—is triggered when the old-age dependency ratio crosses a threshold: that is, when the proportion of elderly people relying on the working-age population becomes too large for that working-age population to support. As long as the old-age dependency ratio remains below that threshold, the working-age population is still able to support the elderly; once the threshold is crossed, aging shifts from being a gradual trend to an active anomaly. Demographic collapse, the youth bulge, and aging are thus three distinct population anomalies, each triggered by its own specific variable: fertility sustained below replacement level for demographic collapse, the proportion of young people neither employed nor in education for the youth bulge, and the old-age dependency ratio for aging. "Overshoot" belongs to this same family of population anomalies but, unlike the other three, does not yet have a specific triggering variable defined within this model.

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