In a recent conversation that went viral on X, Washington Post columnist Shadi Hamid and University of Chicago philosophy professor Martha Nussbaum illuminated two contrasting approaches to the question of modern sustainability. Nussbaum said that “no one should be having children right now unless they really think about it in a global sense” and take into account what effect their children could have on the global food supply. Hamid pushed back against this and argued that, for many countries, a much more pressing concern is underpopulation rather than overpopulation.
Nussbaum’s warning about overpopulation speaks to the concerns of many activists (especially on the Left) during the 20th century. Much of the “population bomb” environmentalism of the last century was haunted by the figure of extraction: Constraints on natural resources would mean that the growth of the human population would cause increasing misery, culminating in famine. The 1973 science-fiction film Soylent Green — where people have to power lights by bicycles and live on some bizarre green food — embodies that anxiety. This is the context in which Nussbaum argues that a growing population inevitably taxes the globe’s underlying material resources.
While it is an empirical fact that certain minerals are indeed limited, this kind of eco-pessimism may obscure the power of human ingenuity. New technologies have been found, either to make use of new resources or to stretch old resources further. The shale revolution has, for instance, dramatically challenged the “peak oil” hypothesis of the 20th century.
If this concern with overpopulation sees extraction as a challenge for modern sustainability, another challenge has grown more prominent in the 21st century: internal reproduction. While the crisis of extraction fixates on a lack of material resources to sustain a decent society, the crisis of reproduction instead relies upon a worry about the ways that contemporary social and economic arrangements may undercut the ability of a society to foster a successor generation. This in part is what Hamid was getting at, and it speaks to a bigger epochal change. During the industrial takeoff period of the 20th century, the global population exploded. It is still growing in some places (most notably Africa and parts of the Middle East), but birthrates have collapsed in many areas, especially Asia. South Korea’s fertility rate (the average number of children a woman gives birth to) has dropped to 0.72, well below the 2.1 replacement rate. The United States and many European countries have also seen their fertility rates drop below 2.1.
A drop in fertility of this magnitude causes major sociological disruption. It means shrinking populations and poses an existential threat to many national retirement programs, which rely upon a continued infusion of payments from new workers to pay for retirees. It is also something with major geopolitical stakes. As Nicholas Eberstadt documented in a recent Foreign Affairs article, the projected population drop in East Asia will affect the balance of power in that region.
To respond to this bigger challenge of reproduction, many industrialized nations have witnessed more interest in pro-family efforts (whether affirmatively natalist or trying to unwind anti-natalist policies). Immigration has sometimes been proposed as a remedy to below-replacement birthrates, but that is an incomplete solution at best. It’s all well and good to welcome hopeful aspirants into a country, but the inability of a population to sustain itself speaks to a much deeper civilizational challenge. According to polls, most people want children — potentially more than they actually end up having. A society in which people cannot afford to have children or are socially discouraged from having them is a much poorer one on a very deep level.
The crisis of reproduction is an old one in modernity. In the 1600s, the Puritans worried that material success would corrode the personal virtue that made this success possible in the first place; Alexis de Tocqueville famously fretted that American democracy could undermine itself. While different from the past, current challenges to family formation indicate a much broader theme. They might also remind us that the hearth is an important bulwark for a free society.