In 1968 a Stanford biologist named Paul Ehrlich published a book called The Population Bomb, and its opening line has aged badly:

“The battle to feed all of humanity is over.”

He meant that mass starvation was already unavoidable because the planet could not carry the people who were coming. The book sold millions of copies and helped fix a generation’s assumption that the central problem of the future would be too many humans.

That forecast failed. The global population continued to grow, but food production rose faster than Ehrlich expected and fertility began a steep decline.

Why smart people were sure the planet would be overrun

Ehrlich deserves a fair hearing, because the fear was not irrational.

In 1963 the global fertility rate was about 5.3 children per woman, and the population was growing at its fastest recorded pace. His underlying logic sounded airtight: “We have a finite planet with finite resources and in such a system, you can’t have infinite population growth.”

As abstract logic, that is hard to argue with. Where it fell apart was the leap from “growth cannot continue forever” to “catastrophe is imminent and unavoidable.” The famines Ehrlich forecast for the 1970s and 1980s did not occur on anything like the scale he described. Instead, agricultural productivity increased and fertility fell across most of the world, driven mainly by social and economic change rather than coercive population controls.

From 5.3 children to about 2.2 in six decades

The UN puts the global fertility rate at 2.25 births per woman in 2024, down from 3.31 in 1990. Over the longer arc, it has fallen from about 5.3 in 1963, meaning it has more than halved in roughly six decades.

The decline is not confined to very rich countries. More than half of all countries and areas are already below the replacement level of roughly 2.1 births per woman, the rate needed for a population to maintain its size over the long term without migration. 

Why the decline happened, and why it was mostly not coercion

The intuitive story is that governments frightened by Ehrlich-style warnings clamped down. China’s one-child policy, launched in 1979 and ended in 2015, is the case everyone reaches for. But a recent study using China’s 1982 and 1990 census data, comparing Han women subject to the policy with minority women who were largely exempt, estimated that it accounted for about 38% of the decline in second births during the 1980s. The remaining 62% was likely associated with broader forces such as rising education, urbanization and the increasing cost of raising children.

It seems what did much of the work elsewhere was quieter. A 2020 analysis by Daphne Liu and Adrian Raftery at the University of Washington found that modern contraceptive use and, to a lesser extent, girls completing lower-secondary education accelerated fertility decline in high-fertility countries. Family planning had the larger measured effect, though the two reinforced each other. Kenya offers a striking example: as the share of girls reaching lower-secondary education rose from 12% to 59% and contraceptive use increased from 5% to 51%, fertility fell from 7.64 to 4.06 births per woman.

What strikes me about that mechanism is how unlike a “bomb” it is. Women gained more choices and better means to act on them, and family sizes fell country by country, decade by decade.

The new worry: below replacement around 2050

The forecast that has replaced the old one points in the opposite direction. The UN projects the global fertility rate falling to 2.07 by 2054 and crossing below 2.1 around 2050. World population is still expected to rise from 8.2 billion in 2024 to about 10.3 billion in the mid-2080s before edging down.

Some countries are already far beyond that threshold; the UN estimates China’s 2024 rate at about 1.01 births per woman.

It helps to be careful about what “below replacement” means. It does not mean the human population starts shrinking next year. Populations have momentum, and the UN still expects roughly two billion more people before the peak. What it flags is a long-run turn toward older populations and fewer working-age adults relative to retirees.

Those are real challenges, but they are not the same kind of emergency as the mass famine Ehrlich predicted.

How I’d read all this

Perhaps the cleanest lesson is about forecasting. Ehrlich correctly saw that infinite growth on a finite planet was impossible, but he was disastrously overconfident about timing, technology and human behaviour. Population rose, yet agricultural output rose faster, while fertility fell for reasons his catastrophe scenario did not adequately anticipate.

That does not make today’s UN projections equivalent to Ehrlich’s claims. Modern demographic projections are built from country-level data, updated regularly and presented with explicit uncertainty. They may still be wrong, especially over many decades, but the logical response is probably neither panic nor dismissal. Aging societies are real and worth planning for. So is the possibility that the woman of 2080 will make choices today’s models cannot fully foresee.