Written by Olivia Nater | Published: August 8, 2025
A new book by economists Dean Spears and Michael Geruso warning of rapid depopulation driven by low fertility rates has been gaining a lot of media attention. The authors argue that reduced population pressure is not beneficial, and that more people means a better quality of life for all. Here we debunk some of their core claims.
Spears’ and Geruso’s book, After the Spike: Population, Progress, and the Case for People, has been promoted in The New York Times, Wall Street Journal, The Guardian, TIME, and on NPR, among other high-profile outlets.
Dean Spears is an economics professor and director of the Population Wellbeing Initiative (PWI) at the University of Austin, Texas. PWI was founded with a $10 million grant from the world’s most inflammatory pronatalist, billionaire Elon Musk — a key fact that has not been mentioned in any recent media coverage of Spears’ work.
Spears is an adherent of a bizarre utilitarian philosophy that argues that a larger population equals higher collective well-being. In an op-ed about depopulation published in The New York Times in September 2023, he lamented the “tens of billions of lives not lived over the next few centuries — many lives that could have been wonderful.” He does not seem to consider that these lives could also be anything but wonderful, especially in light of the hundreds of millions of people still being born into poverty and lacking the freedom to fulfil their basic human rights, as well as escalating environmental crises.
The 2023 op-ed also featured a population curve graphic that shows an alarmingly steep drop-off and, due to lack of a clear timeline, apparent human extinction shortly after the UN’s projected peak of just over 10 billion. The article reports on Spears’ research on possible population trajectories past 2100 under below-replacement fertility — the paper reveals that the projected decline actually extends over 2,000 years.
According to the authors’ models if, in the next century, global fertility converges to a total fertility rate of 1.66 (which was the fertility rate of the US in 2020), then by 2400, the global population will have shrunk to around two billion people.
Two billion is a noteworthy number because it’s in the range that has been estimated to be a sustainable population size (see e.g. Daily et al., 1994 and Pimentel, 1999) if everyone lived a decent quality of life (but consumed a lot less than today’s average American). It wasn’t even that long ago, around 1930, that our population last stood at two billion. A sustainable population is obviously what we should aspire to, so a slow contraction over 375 years driven by people voluntarily choosing smaller families would be a very positive development, not one to fear. And if fertility declines faster and converges at an even lower level, then we would reach a more sustainable population size sooner, which would arguably be even better.
The usual arguments against depopulation focus on socioeconomic concerns, such as shrinking workforces, a growing proportion of elderly dependents, reduced economic growth, and Social Security and Medicare insolvency. Dean Spears focuses on more esoteric arguments, however.
Spears argues that a smaller population will not solve our environmental problems, citing examples of environmental success stories that occurred despite ongoing population increase: improvements in particulate air pollution, as well as the phase out of stratospheric ozone depletion and acid rain. The reason for these victories, however, is that these issues had simple, low-cost, and readily available solutions. They involved replacing particularly harmful substances with less damaging ones, improving filtration, and financial incentives for reducing pollution. These problems could be solved fairly quickly with small changes to industry regulation, and were followed by a comfortable return to business-as-usual.
Our most critical environmental crises — climate change, biodiversity loss, and resource depletion — have no such quick fix. Innovation alone cannot cancel out the devastating impacts of overconsumption and overpopulation. Our most pressing crises are still escalating, and can only be solved through profoundly transformative changes to how we live on this planet. Despite one in ten people still living in extreme poverty, we are collectively consuming natural resources almost twice as fast as the Earth can regenerate them, and we’ve already breached six of nine vital planetary boundaries.
While Spears is correct that population is “a big ship, slow to turn,” this doesn’t mean empowering population solutions aren’t worth pursuing. Yes, we must rapidly implement all other available solutions, but the more we manage to rein in our population size, the higher the likelihood that we can achieve a sustainable future and a decent quality of life for all.
Dean Spears argues that everyone benefits from a populous world, because more minds lead to more innovation, and because “whenever people need and want things, they make it more likely that you will get what you need and want.”
Regarding humanity’s ability to innovate, this is not actually a function of how many of us there are. If this were true, then surely, at our current gigantic population size, we would have done a better job at solving our greatest challenges. Spears seems to think that everything has improved since our population started growing, but this is just not the case. In fact, we are sliding backwards on several key Sustainable Development Goal (SDGs) indicators. Even the number of people suffering from hunger and malnutrition has been increasing in recent years. It is not a large population size that yields brilliant ideas and innovations. Rather, it is investments in education and ensuring children (and adults) are equipped with what they need to learn and thrive.
The fastest population growth is happening in the poorest regions, where the outcome is stagnating development and widespread suffering, not lots of innovation.
Regarding the argument that a higher number of people creates demand for things that other people also benefit from, sure, this is true, but it is also true that higher population pressure leads to more competition for jobs, more pollution and traffic, less nature, faster resource depletion, a higher potential for conflict, more pressure on services and infrastructure, etc. Yes, a bigger population can bring improvements to certain aspects of quality of life, but it also brings significant detrimental effects to other aspects.
What we appreciate about Spears is that he is honest about the dangers of right-wing pronatalism, that he promotes free choice when it comes to family planning, and that unlike his patron Elon Musk, he doesn’t call on people to have lots of babies. He notes that he is not advocating for endless population growth, but stabilization. That’s a goal we can agree on.
Surprisingly, Spears claims that he does not know of any solutions to the issue he is so focused on: “No one yet knows how to avoid depopulation — not researchers, not policy experts, not politicians. The issue is still too new.”
In fact, surveys have repeatedly suggested that the majority of people desire to have two children — exactly the number needed to achieve a stable population. Population Connection conducted one such survey last year. We found that people feel constrained in their childbearing decisions by concern over the state of the world and finances. Other research has brought up very similar findings. Unsurprisingly, it appears that investments in social welfare and a better future will allow more people to fulfil their desired family sizes (and could ultimately lead to population stabilization).
Depopulation at a global level is still at least 60 years away, when our population will contain around two billion more people than it has now. The UN projects we will stay above 10 billion through the end of the century. No one alive today will likely experience a global population that is smaller than today’s 8.2 billion. And even if our population does eventually shrink to a much smaller size as a result of people’s choices, this could be very beneficial for the planet and humanity.
There is really no reason to start fretting about global depopulation now, when we are still facing the opposite problem, alongside an increasingly unstable environment. We should instead worry about the areas that are experiencing rapid population growth combined with extreme climate vulnerability. An estimated 257 million women worldwide still have an unmet need for contraception — empowering them to choose if and when to get pregnant should be a global priority.
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