Don’t worry about your sperm count A testy book fails to explain why mankind is doomed

Let’s imagine that you think the world is facing a real problem, and it’s not paying enough attention to that problem. Say you think, I don’t know, that grazing deer kill young trees and damage ecosystems, and that we ought to reintroduce apex predators in order to reduce their populations and restore natural forests. 

Obviously, you don’t think this is the only problem in the world, and you don’t think that all of humanity’s resources and ingenuity should be dedicated to finding ways of getting lynx and wolves released into north-west Scotland; we should still worry about carbon emissions and so on. But you think some of humanity’s resources and ingenuity should be devoted to it. Say you think that 0.01% of society’s time and effort should be spent thinking about lynx, instead of none at all.

But you’re only one person, representing one 70-millionth of the British population. Shifting society’s behaviour even by that small amount means convincing thousands of people to agree with you. You would need to dedicate all of your time, all of your effort, if you are to have any chance whatsoever of moving the dial even a little bit. 

So you end up looking obsessive and weird – “why are you shouting about lynx all the time? Don’t you know there are other problems in the world?” – even if you’re completely right that the lynx-shortage is a bad thing. Scott Alexander calls this the “fallacy of reversed moderation”. The lynx-advocate might even be tempted to overstate the scale of the problem and the efficacy of the solution: “Deer overpopulation is causing children’s brains to shrink; only introducing lynx can restore normal-sized cortices to our nation’s young!”

This is, I think, part of what is going on in Count Down: How Our Modern World Is Threatening Sperm Counts, Altering Male and Female Reproductive Development, and Imperilling the Future of the Human Race, by Shanna Swan and Stacey Colino.

In 2017, Swan, along with other scientists, published a meta-analysis, an aggregation of existing research. It said that since 1973, the average sperm count among men in Western countries had fallen by 59%, and by somewhat less in the developing world. It seems to have been a well-carried-out study, and it caused quite a stir.

The question, of course, is what caused (or is causing?) this decline. Swan and her co-authors suggested that it is, in large part, the modern chemical industry, and in particular a family of products called “endocrine-disrupting chemicals” (EDCs), which interfere with hormonal processes in the body, especially those involved with development and reproduction. One group of EDCs found in plastics, known as phthalates, are the particular enemy. They get into the water system, they’re in our takeaway containers, they’re in our cosmetics, and they’re damaging our precious bodily fluids. 

Count Down is essentially the book of that study. It expands on the problem, to talk about fertility in general, not just sperm counts; it talks about other causes, like smoking and obesity; and it offers individual advice and policy recommendations for how to ameliorate it. 

All of which probably sounds pretty sensible. Swan thinks we have a growing fertility problem; she thinks she has identified the main cause; and she wants to help solve it.

But the book does not seem sensible. Because for Swan, everything causes fertility problems, not just phthalates. Sugar, beef, cycling, stress, watching TV, doing too much exercise, doing too little, eating the wrong diet; you can barely get out of bed in the morning without sabotaging your chance of having a baby. Undergoing stress and trauma will not only make you less fertile, they’ll affect your children’s fertility (should you remain capable of having them). You ought to “ban plastic from your microwave” and throw out your non-stick pans because they’re killing your sperm. I half expected her to say we ought to wear ray-shielded underpants.

And phthalates and other EDCs don’t just damage your chance of having a baby – they seem to be the cause of everything wrong in the world. Declining bird and fish populations. Abnormal development in alligators and sea snails. Reproductive failure in dolphins and grey seals. The apparent worldwide decline in insect populations is, for Swan, the fault of chemical pollution. She even suggests that the growth in intersex conditions and perhaps the rise of gender dysphoria, and even changes in gender identity, could be because of EDCs (and taking paracetamol in pregnancy!). She does say, in what feels a bit like an act of arse-covering, that it has led us to become more open-minded towards gender expression, which is a “silver lining”.

What’s more, she hints, it’s causing the worldwide slowdown in human reproduction. The world’s “fertility rate” has dropped, she says; halved, in fact. And “the average twenty-something Danish woman today is less fertile than her grandmother was at thirty-five”.

And — and this is the big one — this could literally drive humans extinct. Our sperm could wither and die; we will become unable to have children. She refers several times to Children of Men and The Handmaid’s Tale, even saying that modern gestational surrogacy is a “consensual version of the [Handmaid] scenario”. (I feel like the non-consensual nature of the Handmaid scenario was fairly central to the story, whatever your opinions about surrogacy, but that’s by the bye.)

I can’t confirm all these different claims¹, and perhaps many of them are entirely true; it is hardly as though chemical pollution hasn’t caused many environmental catastrophes in the past. Leaded petrol and asbestos are two obvious candidates that took decades to be fixed. And a few quick glances do suggest that there is something real here: EDCs seem to be implicated in the collapse of bald eagle populations, and in an apparent rise in intersex conditions, for instance.

But some parts seem on shakier ground. As it happens I’ve been speaking to entomologists recently for some other work. They thought that insect populations probably were declining (although the data was shaky), some much more than others; and they thought that pesticide pollution was probably a driver, and many pesticides are indeed EDCs. But they also mentioned climate change, eutrophication, light pollution, invasive species, habitat loss. Swan doesn’t outright say that EDCs are the main cause of insect loss (or of declining seabird populations), but she certainly implies it.

There’s also the fact that, as she says, smoking in pregnancy seems to be a huge cause of infertility in male offspring, but expectant mothers smoke much less now than they did even 15 years ago and that is dropping all the time. You’d hope that would go a long way to offsetting environmental influences.

And her take on the human fertility issue just seems entirely backwards to me. The Danish woman being less fertile than her grandmother sounds dreadful, until you realise that fertility is literally measured by how many children you have. The Danish study found that 20-somethings in the 2000s have fewer children than 35-year-olds in the early 1900s. But that’s because Danish women, like women almost everywhere in the world and especially the developed West, are just having fewer children and having them later. The study had nothing to say about whether these women (or their partners) were less capable of having children.

In fact, the decline in total fertility rate – that is, the number of children born per woman — has indeed been going down worldwide; from more than five in 1950 to less than 2.5 last year. But usually I see that portrayed as a good thing. As Swan acknowledges, it correlates with, and is normally said to be partly driven by, female education: the more years of schooling women get in a country, the fewer children the average woman has. 

Fertility also correlates with child mortality: as the number of children dying in childhood goes down, so does the number of children born. There’s also the fact that women still tend to have more, rather than fewer, children than they would ideally like (although I should admit that the data all comes from poorer countries, which have more children and which are less affected by sperm-count decline). That doesn’t mean there isn’t a fertility problem, but it does suggest it’s hardly time to start making comparisons with Children of Men.

Swan says that this reduction in global birth rates will lead to a “demographic crisis”, and she’s probably right: having lots of old people and fewer young, working people will make it harder to support pension schemes, raise taxes, and so on. But unless you want to keep growing the population forever, you’re going to have to go through it at some point. More important, whether it’s good or bad, I don’t think you can reasonably blame it on phthalates or EDCs. You could easily convince me that there is a growing problem of infertility in the developed world, but I doubt it’s the main cause of declining family size, or that it’s mainly caused by EDCs, given the tendency to have children later.

Most important, though, it seems bizarre to suggest that this is going to lead to human extinction. This isn’t me over-interpreting Swan: she really drums it home. Scientists suggest, she says, that fertility decline “could threaten the survival of the human race”; she quotes a researcher saying it is “possible” it could lead to “extinction of the human species”. Her last chapter ends with the phrase “we and other species could end up marching toward the brink of extinction”.

And she says that humanity should be considered an “endangered species”, by the US Fish and Wildlife Service’s definition of the term: “Of five possible criteria for what makes a species endangered, only one needs to be met; the current state of affairs for humans meets at least three.” (Those three criteria are destruction of habitat, inadequate regulatory mechanisms, and man-made factors affecting our existence.)

But there are at least 7.7 billion of us. Our population has increased by more than 10% in the 10 years since I wrote this. You can argue about whether or not we’re damaging our habitat or inadequately regulating ourselves, but surely the key criterion for whether a species is endangered must be that there aren’t very many of them.

Sure, Swan might reply, but the main reason the population is still going up is because we’re living longer. If the world fertility rate drops below replacement, then the population will decline, and eventually we’ll run out of people.

But that is, still, obviously nonsense. We’ve all learned about R in the last year. Of a virus, it’s the average number of new infections that one infected person will cause. If R>1, exponential growth and epidemic; if R<1, disease dies away. But it can apply to anything that reproduces itself: yawns, computer viruses, internet memes. Or humans.

A fertility rate of 2 would be an R of 1 (two people creating two new people), if we ignore deaths in childhood for now. So if the world’s fertility rate dropped below 2, the population of the world will indeed decline, just as the virus does.

But there are different strains of the virus, some of them more infectious — with a higher R — than others. They spread more easily. So the more infectious ones become more common in the population, and even if the “average” virus has an R below 1, it only takes one strain with an R above 1 to eventually become the dominant version and then cause a new wave of the epidemic.

Similarly, there are different fertility rates around the world. Even if R is below one, on average, worldwide, some countries will have higher rates of reproduction. Unless the phthalates are literally rendering us all infertile, which so far they don’t seem to be doing, then humans will continue to reproduce, and those human groups which have the most children will end up being the most common. The future is Amish!

(Plus, if we really do get a Children of Men situation, total global infertility, then efforts to create viable gametes from somatic cells will be increased pretty damn quick; they’re almost there now. We may go extinct some day, but it won’t be fertility loss that does it.)

This hyperventilating about human extinction, and rolling everything bad into a ball labelled “fertility and phthalates”, makes no sense if you think Swan (a respected epidemiologist) is trying to give a dispassionate assessment of fertility issues. But she’s not. This is a polemic. Swan thinks the world doesn’t pay enough attention to the problems of EDC-influenced fertility loss and environmental damage: so she’s upping the stakes as much as she can, making it as big a deal as she can, trying to shift the dial a little bit. The fallacy of reversed moderation declares that you can only do so by dedicating your whole being to the problem (and perhaps overstating it here and there) and looking like a crank.

In a way, I hope she’s right, and that phthalates and other EDCs really are as big a problem as she says. If they are, then — just as we did with leaded petrol, asbestos and CFCs — it is possible that we could simply ban them, find some non-harmful replacement, and watch our alligator, dolphin and sperm populations spring back (although she does point out that the chemical industry, when some harmful chemical is banned, often replaces it with some not-banned but equally harmful equivalent). If all these problems are actually caused a huge, interwoven web of habitat loss, overfishing, air pollution, climate change, diet, and EDCs, then while getting rid of EDCs will help, we’ll still be staring at a severely depleted, damaged world with a lot of complicated problems to fix.

And in one important sense, her book is a success. I’m not going to follow all the advice in her book and replace my shower curtain or my pans — the convenience of non-stick pans seem to me to be worth it for a presumably small risk of reduced fertility (if it weren’t small, we’d have noticed it).

But I am going to turn the little dial in my head, the one labelled “Importance of endocrine-disrupting chemicals”. She has convinced me that they may be a real problem, and I hope someone more dispassionate and less polemical takes a long look at the risks (and benefits) to humanity of using them, and decides whether and where they are worth it. I’m still going to use Tupperware in the microwave, though. 

---

Tom Chivers is a science writer. His second book, How to Read Numbers, is out now.

TomChivers