Concern about humanity's future once focused on overcrowding and resource shortages. Now, some economists say the more serious risk may be birth rates that fall too low to keep populations stable.
If that happens, it would overturn the late-1960s "population bomb" concern and could carry major consequences for economies, workforces, and family life for generations to come.
Here's what to know
The key threshold is 2.1 children per woman, the standard replacement rate. A new study highlighted by Reason says the global fertility rate may already be below it, and its authors, economists Jesús Fernández-Villaverde of the University of Pennsylvania and Patrick Norrick of Northwestern University, see no sign of a rebound, raising the prospect of population decline later this century.
That outlook is a significant departure from Stanford biologist Paul Ehrlich's 1968 book "The Population Bomb." Reason noted that when Ehrlich made his case, the world had just over 3.5 billion people and a fertility rate of just under 5 births per woman. He famously wrote that "The battle to feed all of humanity is over," but the worldwide famine scenario he forecast did not happen on that scale.
What worries researchers now is the possibility that global deaths could someday exceed births if fertility keeps dropping. They called that scenario "Terra Incognita," saying this kind of sustained worldwide decline "has never happened before, not in wars or pandemics."
More background
One of the study's more surprising findings is where fertility is falling fastest: in lower-income countries and among women with less education. As Reason reported, that pattern challenges the older expectation that fertility mainly declines as incomes rise.
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Rather than pointing to one clear explanation, the economists say several forces may be involved, including housing costs, changing social norms, women's education, and technology. Still, they argue that "modernity itself" is behind the overall shift.
In their words, "We live in a society built around large organizations and formal credentials, which makes a third child expensive and childlessness cheap."
As populations age and fewer people enter the workforce, economic growth can slow while younger workers face more pressure to support older generations.
What can be done?
According to the study, as Reason summarized it, there is no simple fix. Policies like subsidies, parental leave, and free daycare generally raise birth rates only modestly, and no single household can reverse a worldwide demographic trend.
The researchers also argue that small shifts in cost or circumstance can affect family-size decisions. "Any explanation [for the fall in fertility rates] only has to account for the quarter of women who switch, not for the 75% who do not," they wrote. "A woman at two may easily switch to one, or from one to zero, in response to relatively small changes in relative prices or opportunity costs."
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