Something alarming is happening between our legs.

Sperm counts have been dropping; infant boys are developing more genital abnormalities; more girls are experiencing early puberty; and adult women appear to be suffering declining egg quality and more miscarriages.

It’s not just humans. Scientists report genital anomalies in a range of species, including unusually small penises in alligators, otters and minks. In some areas, significant numbers of fish, frogs and turtles have exhibited both male and female organs.

Four years ago, a leading scholar of reproductive health, Shanna H. Swan, calculated that from 1973 to 2011, the sperm count of average men in Western countries had fallen by 59 percent. Inevitably, there were headlines about “Spermageddon” and the risk that humans would disappear, but then we moved on to chase other shiny objects.

Now Swan, an epidemiologist at Mount Sinai Medical Center in New York, has written a book, “Count Down,” that will be published on Tuesday and sounds a warning bell. Her subtitle is blunt: “How our modern world is threatening sperm counts, altering male and female reproductive development, and imperiling the future of the human race.”

Swan and other experts say the problem is a class of chemicals called endocrine disruptors, which mimic the body’s hormones and thus fool our cells. This is a particular problem for fetuses as they sexually differentiate early in pregnancy. Endocrine disruptors can wreak reproductive havoc.

These endocrine disruptors are everywhere: plastics, shampoos, cosmetics, cushions, pesticides, canned foods and A.T.M. receipts. They often aren’t on labels and can be difficult to avoid.

“In some ways, the sperm-count decline is akin to where global warming was 40 years ago,” Swan writes. “The climate crisis has been accepted — at least by most people — as a real threat. My hope is that the same will happen with the reproductive turmoil that’s upon us.”

Chemical companies are as reckless as tobacco companies were a generation ago, or as opioid manufacturers were a decade ago. They lobby against even safety testing of endocrine disruptors, so that we have little idea if products we use each day are damaging our bodies or our children. We’re all guinea pigs.

Aside from the decline in sperm counts, growing numbers of sperm appear defective — there’s a boom in two-headed sperm — while others loll aimlessly in circles, rather than furiously swimming in pursuit of an egg. And infants who have had greater exposures to a kind of endocrine disruptor called phthalates have smaller penises, Swan found.

Uncertainty remains, research sometimes conflicts and biological pathways aren’t always clear. There are competing theories about whether the sperm count decline is real and what might cause it and about why girls appear to be reaching puberty earlier, and it’s sometimes unclear whether an increase in male genital abnormalities reflects actual rising numbers or just better reporting.

Still, the Endocrine Society, the Pediatric Endocrine Society, the President’s Cancer Panel and the World Health Organization have all warned about endocrine disruptors, and Europe and Canada have moved to regulate them. But in the United States, Congress and the Trump administration seemed to listen more to industry lobbyists than to independent scientists.

Patricia Ann Hunt, a reproductive geneticist at Washington State University, has conducted experiments on mice showing that the impact of endocrine disruptors is cumulative, generation after generation. When infant mice were exposed for just a few days to endocrine disrupting chemicals, their testes as adults produced fewer sperm, and this incapacity was transmitted to their offspring. While findings from animal studies can’t necessarily be extended to humans, after three generations of these exposures, one-fifth of the male mice were infertile.

“I find this particularly troubling,” Professor Hunt told me. “From the standpoint of human exposures, you could argue we are hitting the third generation just about now.”

What if anything does all this mean for the future of humanity?

“I do not see humans becoming extinct, but I do see family lines ending for a subset of people who are infertile,” Andrea Gore, a professor of neuroendocrinology at the University of Texas at Austin, told me. “People with impaired sperm or egg quality cannot exercise their right to choose to have a child. That may not devastate our species, but it is certainly devastating to these infertile couples.”

More research is necessary, and government regulation and corporate responsibility are crucial to manage risks, but Swan offers practical suggestions for daily life for those with the resources. Store food in glass containers, not plastic. Above all, don’t microwave foods in plastic or with plastic wrap on top. Avoid pesticides. Buy organic produce if possible. Avoid tobacco or marijuana. Use a cotton or linen shower curtain, not one made of vinyl. Don’t use air fresheners. Prevent dust buildup. Vet consumer products you use with an online guide like that of the Environmental Working Group.

Many issues in headlines today won’t much matter in a decade, let alone in a century. Climate change is one exception, and another may be the risks to our capacity to reproduce.

The epitome of a “low blow” is a kick to the crotch. And that, friends, may be what we as a species are doing to ourselves.