Yves here. Around the globe, the impact of human activity is starkly evident, with evidence ranging from significant species extinction to the erratic weather patterns linked to global warming, as well as severe air pollution in major Asian cities and widespread microplastic contamination. Consequently, the decline in birth rates within high-resource nations should be seen as a positive trend that can be effectively managed. As advancements in robotics and AI are expected to significantly reduce labor demands, this may help alleviate, if not entirely eliminate, the age-old concern of increased dependency ratios—fewer workers supporting a growing population. However, achieving these objectives would require a robust industrial policy, something that developed economies have become reluctant to adopt.
Unfortunately, the Trump Administration, along with Health and Human Services Chairman RFK Jr., exhibits an alarming tendency toward promoting a “Make America Whiter” agenda that clashes with the reality of low reproduction rates among non-Hispanic populations and restrictive immigration policies. The U.S. was projected to experience a population decline as early as the 2000 census. It was, in fact, immigration throughout the 1990s and higher birth rates among Hispanic communities that led to an unanticipated population increase.
There’s also another layer to consider: advanced economies and even some middle-income nations, such as Thailand, are increasingly dependent on immigration for lower-wage labor and economic growth, especially as natural population increases plateau. Unlike the large waves of immigration seen in the U.S. during the late 19th to early 20th centuries, many developed nations are not facilitating effective assimilation. This leaves newcomers feeling noticeably foreign, contributing to a rise in tribalism and a rejection of outsiders. Additionally, businesses favor immigration to keep wages low, leading to a justified sense of grievance among workers unless robust protections are in place.
Furthermore, public expectations regarding healthcare are rising. The wide media coverage of fertility treatments and surrogacy suggests that more potential parents facing infertility are opting for medical interventions rather than adoption.
My critique of articles like this begins with their headlines, which often reflect Administration priorities. A fall in male fertility is indeed a significant health concern. It raises alarms about population-wide factors adversely affecting virility—such as depression (correlated with lower sperm counts), dietary choices, and pollutants. Occasionally, I’m shocked by reports indicating high levels of medications and recreational drugs in public water systems, yet there is little discussion regarding affordable methods to reduce their concentrations. This is indicative of a broader neglect in public health. Although easy solutions may not exist, the questions surrounding these issues remain largely unaddressed.
By Joshua Cohen, an independent healthcare analyst and freelance writer based in Boston, and the author of Undark’s Cross Sections column. Originally published at Undark
For decades, U.S. marriage rates have steadily declined while the average age at which Americans have children has risen. Alongside this, birth rates have plummeted—a trend that Health and Human Services Secretary Robert F. Kennedy Jr. deems a “national security threat.” Within the framework of Donald Trump’s Make America Great Again movement, pro-natalist advocates argue that the very sustainability of society is in jeopardy.
Kennedy recently raised alarms during a White House press briefing, stating that the current fertility rate is insufficient to maintain a stable American population. The rate dropped to a historic low in 2023 and continued to decline in 2024, resulting in a total fertility rate below 1.6 live births per woman. This figure falls significantly short of the replacement rate of 2.1. To address this, President Trump has proposed collaboration with a pharmaceutical company to provide fertility medications at reduced rates and facilitate easier access to fertility benefits through employers.
However, the administration has yet to publicly address specific treatments targeted toward men, and until recently, male infertility was regarded as somewhat taboo, despite accounting for nearly half of all infertility cases in women.
Factors contributing to male infertility include a man’s age, health, and weight. Research indicates that these factors can influence both sperm count and testosterone levels, which appear to be declining. Kennedy has frequently voiced concern over these declines, claiming exaggerated stats such as that “today, the average teenager has 50 percent of the sperm count and testosterone levels of a 65-year-old man.”
But what is the relationship between male biology and declining birth rates? Could addressing this help the administration achieve its fertility objectives? The answer is far more intricate than one might assume.
For years, researchers have investigated whether sperm counts are genuinely on the decline. Recent studies have advanced the “sperm count decline hypothesis,” which suggests that decreasing sperm counts indicate suboptimal health that could impede fertility.
A 2017 meta-analysis, analyzing data from North America, Europe, Australia, and New Zealand, discovered a staggering 52 percent decline in sperm counts from 1973 to 2011. A subsequent 2022 follow-up corroborated this trend across a broader range of countries. Clinician and researcher Rossella Cannarella from Italy expressed alignment with these findings, attributing the decrease in sperm counts to pollution and metabolic disorders, among other factors.
A recent report by Cannarella for the Health and Environment Alliance raises alarms about chemical pollution fuelling a “growing male health crisis,” including male infertility linked to harmful chemicals and endocrine disruptors. These substances—whether from natural or synthetic origins—are prevalent in plastics, food packaging, and pesticides, and can interfere with hormones such as estrogen and testosterone. Importantly, during the October White House briefing, Kennedy highlighted the potential role of endocrine disruptors in the observed decline in fertility rates.
Endocrine disruption can occur through exposure to chemicals present in food, air, and water, as well as through skin contact. These disruptors in food can affect the beneficial microorganisms in the gut. Germar Pinggera, a researcher from Innsbruck Medical University, explained that pollution, poor diets, and an unbalanced microbiome can negatively affect sperm production and quality, potentially complicating fertility issues.
However, Pinggera cautions that while some studies indicate a decline in sperm counts, “other data don’t confirm this.”
A recent press release from the lead author of a new meta-analysis suggests that for men in the U.S. without known fertility issues, “sperm counts are largely stable and haven’t changed significantly” in recent times. Additionally, it remains uncertain if sperm quality has deteriorated. A review published in 2022 in Nature Reviews Urology indicated that while some geographic areas show trends, the current evidence does not definitively support global or Western decline in semen quality.
Moreover, a reassessment of the 2017 meta-analysis pointed out measurement inconsistencies regarding sperm counts. Researchers proposed an alternative framework indicating that sperm count varies within a broad range, much of which may be considered normal.
Critics of the sperm count decline hypothesis argue that it implies that sperm count is a reliable predictor of male fertility. Experts contend that male fertility is influenced by a combination of factors, including sperm count, concentration, morphology, and motility, in addition to testosterone levels, age, and other characteristics. Male fertility cannot be viewed in isolation from female fertility, especially in couples trying to conceive either naturally or through assisted reproductive technologies. Analyzing the interaction among sperm, the female reproductive system, and the egg is essential.
Turning our attention to testosterone, the hormone pivotal in male puberty and reproduction, we observe a general peak in testosterone levels during adolescence and early adulthood. After age 30 or 40, men typically experience a gradual decline of about 1 percent annually.
Testosterone is critical for sperm production, though it is not the sole ingredient. Other hormones, including luteinizing hormone—which stimulates testosterone synthesis—and follicle-stimulating hormone also play significant roles, complicating the ability to determine each hormone’s specific impact on infertility.
While Kennedy claims that testosterone levels in young men have drastically declined over recent decades, scientific literature presents a more nuanced narrative. A 2021 study noted a 25 percent reduction in testosterone levels among young adult males from 1999 to 2016. Additionally, testosterone deficiency among adolescent and young men is now at 20 percent.
Yet, Geoff Werstuck, a professor at McMaster University, pointed out in an email to Undark that the “relative rate of decline is noteworthy.” An endocrinologist from Cleveland Clinic also connects the rapid decrease in testosterone to similar factors likely affecting sperm counts.
However, there is still some disagreement regarding the magnitude of the decline. Adith Arun, a researcher at Yale New Haven Hospital’s Center for Outcomes Research and Evaluation, expressed in an email that shifts in measurement methods over time make direct comparisons challenging. The outdated threshold for low total testosterone may contribute to overestimating the number of self-reported healthy individuals with low levels. In a follow-up email, he further noted that this discrepancy might lead to overstated fractions of healthy individuals
Werstuck added that due to a lack of comprehensive historical data, determining the onset of testosterone declines and their precise extent remains complicated. He believes there isn’t “robust evidence to either support or discount” the various suggested causes for this trend.
This leaves a tenuous connection between male biology and declining birth rates.
During a recent discussion hosted by the Harvard University T.H. Chan School of Public Health, a panelist suggested that much of the decline is due to teenagers and young women postponing childbirth. Margaret McConnell, an associate professor in Harvard’s Department of Global Health and Population, cautioned that overall family size over a woman’s lifetime has not decreased as significantly as the annual fertility rates.
Leslie Root, a fertility and population policy researcher at the University of Colorado Boulder, told Newsweek, “We are witnessing this as part of a continuous trend toward fertility delay. The U.S. population is still growing and experiences more births than deaths.”
This ongoing trend toward delayed fertility may reflect reproductive agency, wherein women make informed decisions about their reproductive choices influenced by factors like career trajectories, their ability to afford raising a family, and advances in technologies such as IVF and egg-freezing. These considerations impact marriage age, desired family size, and general reproductive behaviors among both men and women in the U.S.
In conclusion, amid the panic surrounding declining fertility and sperm counts, many complex questions remain unresolved, many of which traverse beyond scientific inquiry and delve into social factors.
