Americans are having fewer babies. In 2018, age-controlled fertility may fall to near the lowest level in our history. We aren’t alone in this: fertility rates have fallen across much of the western world, despite widespread economic expansion.
The main reasons for this are sociological: declining marriage, rising cost of childbearing, and related factors that amount to cultural norms and practices.
Recently, scientists have raised a different alarm bell: human biology may be changing. For decades, some scientists have been arguing that men are producing less sperm than they used to, but these studies were plagued by small sample size, non-randomly selected men, or other methodological problems.
Last summer, however, a research team in Israel (the country at the forefront of reproductive technology) assembled a massive dataset, combining hundreds of prior studies, creating a sample of tens of thousands of men across decades. They found that male sperm counts are indeed in decline.
While their findings aren’t universally accepted, they have succeeded in persuading a large number of former skeptics. The sample sizes are sufficiently large, the extra checks for possible counterarguments sufficiently robust, and the findings sufficiently clear in the data that it’s time to take seriously that men really may be losing some degree of their biological fertility.
Their key takeaway graphs are here:
That looks quite dire. Notably, the decline is continuing to the last year: there’s no bottom in sight. If these trends continue, men could lose the ability to sire children by the end of the 21st century.
This paper doesn’t illuminate causes of this decline. But the article reviewing it, which went viral yesterday, provides a lot of possibilities, which boil down to “chemicals.” Many reproduction researchers believe that the increased human exposure to various complex chemical compounds over the last century has negatively affected reproductive potential.
The list of candidates is long: BPA, its replacement BPS, pesticides, chemical fertilizers, air pollution, and more. Some chemicals have been conclusively shown to lower fertility, like lead. A recent study persuasively showed that spikes of lead in water, like the crisis in Flint, cause fetal death, miscarriage, and prevented conceptions.
More than that, lead in the air from gasoline in the 20th century, and its residual content in soil today, lowered fertility by about as much as abortion or contraception did, and is continuing to suppress fertility today. It should surprise nobody that lead is toxic, and particularly influential on the reproductive system, which is one of the most sensitive systems in the human body.
In other words, the argument that 20th century, and probably 21st century as well, exposure to more chemicals and compounds that are unfamiliar to the human biology has reduced fertility is almost certainly true. We know conclusively that lead is one such dangerous compound; it is almost certain that there are others. Multiple studies have found linkages between air pollution and fertility as well.
Given how many environmental factors seem to matter, it is more than plausible that male sperm count may be sensitive to environmental chemical exposure as well. Since laboratory study supports the idea that certain chemicals, like BPA, alter the hormonal systems responsible for sperm production, the specific theory that industrial plastics alter fertility is entirely credible. We have grounds to be concerned, and rational grounds to reduce plastic usage and exposure.
However, some of the apocalyptic rhetoric may be overblown. For example, it is well-known that male obesity reduces sperm count and worsens sperm quality. Because both obesity and chemical exposure are outcomes of economic development and modernization, they will produce nearly identical correlations across time and place, so are difficult to disentangle. Other behavioral factors, like smoking, alcohol consumption, lack of exercise, or substance abuse, also impact fertility.
Thus, while it’s possible that exposure to plastic is lowering fertility (indeed highly likely), it is implausible that the whole observed effect of falling sperm concentration can be attributed to chemical exposure. It is almost certain that rising obesity and sedentarism, and various forms of substance abuse, can account for much of it. Those problems are, in principle, fixable.
Declining biological fertility for men, and for women as well, is a very real public health issue, and deserves more study. Right now, the bias of the evidence is that sperm counts are declining, and that environmental exposure to pollutants probably has some role to play. But it will take much more research to disentangle how much of a role, and to what degree ongoing declines can be prevented, or historic declines reversed.