JD Vance, Elon Musk are right about falling birth rates — here’s where they get it wrong
President Trump’s return to the White House has made pro-natalists more influential than ever. Vice President Vance says he wants “more babies” in America. Elon Musk has claimed that declining fertility could lead to “mass extinction.”
Their efforts are noble, but Vance and Musk both underappreciate the role of genetics in determining fertility. Without a proper understanding, their efforts will fail.
In his 1930 book “The Genetical Theory of Natural Selection,” seminal geneticist Ronald Fisher observed a substantial correlation between the fertility of parents and their descendants. Fisher noted that the granddaughters of large families tended to have more children than those from small families. Fisher concluded that “about 40 percent of the total variance” in fertility was attributable to genetics.
Importantly, Fisher didn’t just conclude that fertility varied between individuals because of different genetic abilities to have children. Instead, Fisher argued that the most important cause of variation was different genetic desire to have children.
In this, Fisher found reason for optimism. Observing the rate at which genetic inheritance led some families to have more descendants than others, Fisher theorized that “more fertile strains” with a greater desire for children could become more common "within a span of ten generations," or approximately 250 years.
In other words, cultural and economic features of modernity may lower birthrates. But the question of why modernity lowers birthrates is less salient than that genetic selection can counteract the parts of modern civilization responsible.
Why does this matter? Falling fertility is often attributed to social factors. Vance has mentioned car-seat mandates and high parenting costs. Musk has pointed to secularization and cultural malaise. But put to the test, none of these explanations are sufficient to explain global birthrate falls.
Also, Western cultural malaise can’t account for Japan’s demographic collapse. Irreligiosity can’t explain why Islamic Bahrain has a lower birthrate than mostly atheist Czechia. The high cost of child-rearing in developed countries can’t clarify why Americans are more fertile than Mexicans.
The genetic theory, on the other hand, is supported by wide bodies of both academic and practical evidence.
Twin studies from the U.S. and Britain, Denmark and Sweden have shown that as much as 50 percent of variation in fertility is genetically derived, supporting Fisher’s earlier estimate. DNA sequencing has supported this, highlighting individual genes that are strongly associated with fertility.
Similarly, studies from Denmark and Quebec have shown that the role of genetics in determining fertility has increased in Western populations, supporting the idea of ongoing selection for the desire to have children. Genes have been identified that correlate with earlier age of first birth, later age of last birth, total children ever born, and later menopause.
Perhaps most importantly, several real-world examples have emerged in support of Fisher’s thesis.
In Europe, France was the first nation to experience significant modern birthrate declines. Yet today, France has the highest birthrate in all of Europe. France’s high fertility can’t be explained by immigration (regions with few immigrants lead the country in fertility), culture (French-speaking areas of neighboring Belgium and Switzerland don’t have elevated fertility), or policy (France is below the OECD average for family aid). But it may be explainable through genetics. France’s fertility transition occurred in the 1750s, matching Fisher’s calculation that it would take approximately 10 generations for genetic shifts to substantially increase birthrates.
Likewise, Japan was once notable for its low fertility. But today, Japan’s birthrates are the highest in East Asia — exceeding peers such as South Korea and Singapore and much poorer China. Japan’s regionally elevated birthrates may also be the product of genetic selection, because the greater steepness of Japan’s fertility decline could have accelerated the normal timeline for genetic shifts to have a substantial effect.
Given that genetics do play a substantial role in determining fertility, two conclusions stand out.
First, one-size-fits-all proposals to raise birthrates while ignoring genetics won’t work. Vance has argued for increasing the child tax credit, while Musk has called for giving medals to increase the social status of motherhood. But as we’ve seen in Hungary and Norway, which both generously subsidize births, solutions that focus on extrinsic motivations are ineffective at raising fertility.
Instead, policies to counter population decline will be most effective if they consider genetics by subsidizing those with demonstrated fertility desires. For example, governments could offer increased tax credits for larger families, rather than evenly distributing incentives per child.
Second, falling rich-world birthrates will likely be less of a problem than they appear, because countervailing genetic pressures may lead to a fertility resurgence. Models that consider evolutionary pressures already suggest likely rebounds in European and North American birthrates not reflected in other estimates.
History has always been shaped by shifts in populations. Ancient Greece’s power rose in a world in which every 15th person was Greek and waned with demographic stagnation. Today, falling birthrates pose even greater risks to global economies and geopolitical stability.
But although cultural and economic factors have been extensively considered, policymakers including Vance and Musk appear to underestimate the influence of genetics on fertility. Incorporating a proper understanding will be crucial to navigating the demographic shifts that will shape the 21 century, and offer a path for the West to recover from its fertility crisis.
Jacob Hornstein is an undergraduate student at the University of Austin.
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