Population bomb was a dud. What follows 'peak humanity'?

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The world's massive human population is leveling off. Most projections show we'll hit peak humanity in the 21st century, as people choose to have smaller families and women gain power over their own reproduction. This is great news for the future of our species.

And yet alarms are sounding. While environmentalists have long warned of a planet with too many people, now some economists are warning of a future with too few. For example, economist Dean Spears from the University of Texas has written that an "unprecedented decline" in population will lead to a bleak future of slower economic growth and less innovation.

But demographers I spoke with say this concern is based more on speculation than science. A dramatic collapse in population is unlikely to happen within the next 100 years barring some new plague or nuclear war or other apocalypse. And if we need more creative minds in the world, we could stop doing such a terrible job of nourishing and educating the people we're already producing.

Predictions about future population levels that don't come with wide margins of error should always be taken with a grain of salt. Joel Cohen, a mathematician, biologist and demographer at Rockefeller University wants to see population projections treated like a real science with a proper accounting for uncertainty. We don't even know the exact number of people alive now, he points out. When the U.N. declared we'd surpassed 8 billion on Nov. 15, 2022, it was a "publicity stunt," he says.

The uncertainty in counting world populations is at least 2% — which adds up to about 160 million people or more. Since the world population grows at most by 80 million a year, we could have hit 8 billion two years earlier, or it might not happen until 2024.

This line of pessimistic thinking may sound familiar to those who remember the 1968 book by Stanford University scientists Paul and Anne Ehrlich, "The Population Bomb." The Ehrlichs famously — and incorrectly — envisioned a 20th-century starvation catastrophe. They failed to recognize that technological advances might meet increased need, and that women worldwide would change from having six to slightly under two children each, on average, in the coming half-century.

Today's forecasts account for multiple variables and recognize that population increases are leveling off, not spiking and then plummeting. Some of the most reliable projections, Cohen said, come from demographers with the U.N. Their latest estimate shows the global population will plateau at around 11 billion people by 2100.

A different model, created by the Institute for Health Metrics and Evaluation (IHME) and published in the Lancet in 2020, showed an earlier, lower peak around 2064 at 9.7 billion, followed by a steady decline, bringing us down to around 6 billion by 2100. Cohen doesn't find that alarming — that's about the number of people alive in 2000.

That inevitable rise in the near term worries Daniel Blumstein, an ecologist at UCLA who is co-author of a 2021 paper on avoiding a "ghastly future"(co-authored with, among other researchers, the Ehrlichs). Population and consumption patterns are intertwined, he says, and together are causing multiple environmental problems, some of them irreversible.

Blumstein points out that the innovations in agriculture that Malthus and the Ehrlichs failed to account for have allowed our population to swell far beyond our ecological niche — with unintended consequences. Pesticides, for example, are killing the bees necessary for pollinating crops. The big picture: Buildup of waste, especially carbon dioxide, along with the destruction of habitat for wild plants and animals, are now threatening humans more than a shortfall in the global supply of food. These changes are contributing to valid concerns about the creation of climate refugees.

People aren't selfish for choosing smaller families. We are powerfully programmed by Darwinian evolution to want to have offspring, or at least to have sex, but women are also endowed with the instinct to limit reproduction to the number who can be raised with a high probability of success in life. When women have large numbers of children, it's often a result of high child mortality or lack of power over their own lives.

Those warning that a population drop could decrease collective brain power and hurt the economy overlook a better solution than producing more babies: Taking better care of the ones we have.

About 22% of children under 5 today are too short for their age because they don't get enough of the right kinds of nutrients to grow, and because worms and infections compete for the inadequate food they do get, Cohen said. That can affect not only the body, but the brain. And Eberstadt worries about future mismatches between skilled jobs and an undereducated population.