As new data emerge, however, many scientists now believe sperm counts have indeed fallen—and continue to fall. As a story in GQ noted earlier this year , a widely cited study published in 2017 by researchers from the Hebrew University and Mount Sinai’s medical school found that among nearly 43,000 men from North America, Europe, New Zealand, and Australia, sperm counts per milliliter of semen had declined more than 50 percent from 1973 to 2011. And not only that, “but total sperm counts were down by almost 60 percent: We are producing less semen, and that semen has fewer sperm cells in it,” wrote the GQ contributor Daniel Noah Halpern. When Halpern asked several scientists why, they presented a united front: It was the unprecedented amount of chemicals now routinely entering the human body. “There has been a chemical revolution going on starting from the beginning of the 19th century, maybe even a bit before,” one biologist told Halpern, “and upwards and exploding after the Second World War, when hundreds of new chemicals came onto the market within a very short time frame.”

Halpern went on to explain that many chemical compounds that are used to make plastic hard (like Bisphenol A, or BPA) or soft (like phthalates) can mimic estrogen in the bloodstream—so men with lots of phthalates in their system are likely to produce less testosterone and fewer sperm (though the U.S. Food and Drug Administration stated earlier this year, somewhat controversially, that its research continues to support its claim that the authorized amounts and uses of BPA are safe for consumers). Plus, chemicals like BPA and phthalates can alter the way genes express themselves, making some of the conditions these chemicals cause inheritable. “Your father passes along his low sperm count to you, and your sperm count goes even lower after you’re exposed to endocrine disruptors,” Halpern wrote. “That’s part of the reason there’s been no leveling off even after 40 years of declining sperm counts—the baseline keeps dropping.”

Sharpe, however, now a professor at the University of Edinburgh’s Medical Research Council Center for Reproductive Health, isn’t totally convinced by the BPA-and-phthalates theory. While there’s a much more cohesive consensus throughout the field of reproductive medicine these days than there may have been 10 or 20 years ago that sperm counts are indeed falling, he says, “the controversy and lack of agreement continue regarding what has caused the fall and when in life has the effect been induced.” Though many consider environmental chemicals to be the primary cause of declining sperm counts, Sharpe says he’s “increasingly skeptical” of that hypothesis: “I would favor that it results from our huge dietary and lifestyle changes, both by pregnant women and by young men.”

Studies like the new ones presented by ASRM, in other words, increasingly serve as bolstering evidence to what many scientists already believe. As scientists reach a consensus that something is happening to men’s sperm in the Western world, the next phase will be to figure out exactly what, and why.

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