262 Comments

Are people masturbating more these days? Or more precisely: are men ejaculating more frequently these days? I feel like there must be some data on this. It's not immediately obvious to me that the increased availability of porn necessarily makes it so.

Expand full comment

For sperm counts to seem lower, it doesn't need to be that the average man ejaculates more. It is enough that those who agree to participate in a study on sperm counts masturbate more. And what kind of people are willing to participate in such a study? Presumably men who have nothing against masturbating in a public setting. That is, men who are used to masturbating.

In the pre-internet era, men who had the habit to masturbate had to use their imagination, or the same old pornographic magazine all over again. Today those men have quadrillions of pornographic films to choose from. If that didn't make them masturbate more, it would have been a market failure of proportions.

Expand full comment

They make men masturbate in public? I assumed they would have given the men and tube and told them to go home and collect the semen themselves.

Expand full comment

Interesting question! Answering it requires reading the fine print of a number of studies and I haven't done that. I guess that if researchers allow people to handle their sperm themselves, people would refrigerate it at different temperatures during different amounts of time, making the whole experiment less accurate.

At least I know that for fertility treatments hospitals have a small room with a stack of porn magazines which are supposed to help hopeful future fathers to masturbate successfully. A man who had children that way told me about it.

Expand full comment

I recently took a fertility test in the UK. I think it varies, but if you live close to a hospital they allow you to produce a sample at home. You're required to drop it off within a short time window after production, and to keep it close to your body to maintain the temperature.

Alternatively, they offer private booths at the hospital where a drop off isn't feasible.

Expand full comment

Slightly different interpretation, but to participate in this study, you have to be comfortable with someone knowing you masturbate, even if it's a private room.

A highly religious or shy person, for example, might masturbate in private, but would not "admit" to it as easily as someone who is more comfortable with masturbation in general.

Expand full comment

Scott mentioned samples potentially coming from people who had been selected for infertility issues. Which seems to imply it's not a self selecting sample

Expand full comment

Yes, basically we have two groups who are likely to give their sperm away for research:

1. Men with fertility issues who are eager to get those fertility issues investigated.

2. Men who think "masturbate in a cup - get paid ten dollars" sounds like a good deal.

Expand full comment

only ten? what kind of cheap w**** do they think I am? I demand $25

Expand full comment

Make it 0.0001 cents per sperm cell, and the trend in the data will go away rather quickly.

Expand full comment

No, it would be a lot stronger.

"Sorry, it seems sperm counts are declining fast. Here's a nickel."

Expand full comment
Feb 18, 2023·edited Feb 18, 2023

I don't know what "w****" stands for.

Expand full comment

From context I'm guessing the missing letters are hore.

Expand full comment

I'd imagine (hope?) these were couples that came in due to infertility and the issue was found to be with the other partner. Still not completely free of self-selecting taint, but not as bad as first blush.

Expand full comment

"In the pre-internet era, men who had the habit to masturbate had to use their imagination, or the same old pornographic magazine all over again. Today those men have quadrillions of pornographic films to choose from. If that didn't make them masturbate more, it would have been a market failure of proportions."

Speaking for a friend: The friend said his earlier masturbation--say, in college in the 1970s--was done usually without "photographic assistance", and sometimes multiple times per day . . . Youth! Now in his sixties, the friend's masturbation has ready access to "photographic and video assistance" as desired . . . as needed?? The college-age masturbation was quicker, and "simpler." The young geriatric masturbation during the age of the internet is an up-and-down, "edging" experience which can go on for 90 minutes or more. I'm not sure how that effects sperm count.

Expand full comment

We have a very important confounding factor here: age. Isn't it very common that it takes older men much longer to get off compared to younger men?

Expand full comment

Speaking as someone who was once a young man who gained and lost access to pornography at various times, I'd say that statement was accurate irrespective of age (for at least some people).

Expand full comment

I seem to recall a study saying it was the other way around.

Expand full comment

I don't think porn per se is very significant - imagination is frankly better, since it's almost definitionally more tailored to one's personal taste - but different societal expectations around masturbation certainly might be.

Expand full comment
Feb 17, 2023·edited Feb 17, 2023

I don't think porn addiction is as big a thing or issue as some media make it out to be, but it is _a_ thing and I can believe that milder forms of it are somewhat common, which should have an impact on masturbation frequency in at least part of the population.

Addiction aside: I'm sure people occasionally masturbated out of mere boredom (and that is definitely a thing, in women as well as in men) even before porn became widely accessible, but porn certainly facilitates that.

Expand full comment

I don't think it's the porn alone (see below). Rather I'd point to the decreased moral approbation of masturbation. When my dad went to catholic school he was taught it was a sin, when I went to catholic school they didn't say that but there was still a sense it was kinda unclean. Now you don't get much of that at all.

Now many ppl who were taught this later reject the idea that it's wrong but it's alot harder to purge a sense of guilt/shame when doing it especially if you think of it as something only ppl w/o partners do (I used to hear bragging about not needing to masturbate). So such ppl might be quite willing to agree to a study (besides, even on the old don't waste seed teaching this was ok) but masturbate less frequently at home.

--

And re: porn it's not necessarily about addiction. I mean my wife thinks nothing of firing up porntube and having a quick orgasm if she's having trouble falling asleep. I suspect some men do the same now while they wouldn't have bothered without the easy porn.

Expand full comment

Anecdata: I spent about 18 months in a "therapeutic boarding school" with no internet and no porn allowed (a non-zero but fairly small quantity of porn made its way on campus regardless). If anything, I think there may have been *more* masturbation simply because there was nothing better to do.

Expand full comment

Yes, at some point boredom will increase masturbation especially in the young and horny but I think since the advent of TV most adults have long had sufficient entertainment to minimize the boredom effect.

Expand full comment

Prediction #2 assumes reproduction works exactly the same in twenty years/has the same biological limitations. Totally putting aside various 'other' timeline-related concerns people have been animated about lately, this is a longer timeline than many reasonable-enough predictions for when human in vitro gametogenesis is 'viable enough', which would radically change the context of that and other problems.

Expand full comment

The hope would be that the market converges well before twenty years.

If the singularity happens, friendly or unfriendly, it shouldn't have any effect on the market one way or the other in forecasts, because there is no sperm count if everyone is dead - or alternatively, if everyone lives in a beautiful upload utopia, I don't think we'll leave child health and development up to random DNA carrier tadpoles.

Expand full comment

Your image of "the Singularity" is different from mine. E.g. I don't expect uploads to happen, except, perhaps, at the point of death. ISTM that even after a Singularity event, detailed mind readout will be a destructive process. Simulated uploads, however, may be quite common.

So for this argument the question would be "What effect will highly developed virtual reality have?". That might well result in reduced sperm count from many different variables, but the effect on reproduction would be due more to the lack of physical access. (I don't remember "The Machine Stops" addressing that point.)

Expand full comment

Prediction 2 also allows less time for consensus to form - if sperm counts continue to decline, there's 20 years before market resolution for studies to prove it. if fertility only begins to sharply decline in X years, there's only 20-X years for studies to find it. Science is slow - it is quite plausible to believe that fertility will begin to decline in eg 15 years and there won't be scientific consensus on it in 20 years.

Expand full comment

I had the good fortune to be in a room with fertility doctors not long ago, and here a few random takes:

- fertility almost always an egg problem, not a sperm problem - plenty enough sperm left for fertility at this point

- declining counts may or may not be real, but they tend to argue against it. Why, because sperm count varies a lot from day to day. Personally this make me inclined to believe that masturbation frequency / "porn addiction" may have more to do with it than medical reality

- vitamin D is a very real factor in egg quality. Egg quality can be shown to relate to the amount of body coverage in Middle Eastern women (!!) and current egg quality in 25 year olds in the middle East is more like what used to be seen in typical 40 year olds. Indoor life with a/c and body covering to blame. What does that mean for sperm, well, not so outlandish that similar factors may be at work.

- increasingly off topic, overall fertility: once again Middle Easterners these days seem to get married (often arranged) and then head straight to the IVF center. No one even tries to have sex anymore.

YMMV.

Expand full comment

This is fascinating info, and not readily accessed by those not in the know. Do you have any other ideas that you picked up during this meeting?

Expand full comment

Let me see... more on the details. The decline in Middle Eastern egg quality also has to do with endemic cousin marriage. And, evidence on the body-covering angle was given by a published paper that compared the exact shape and size of women's face and body coverage by country, with egg quality.

Expand full comment

Very interesting! Thank you. It's always useful to see a problem from another perspective, in this case a cultural one.

Expand full comment
Feb 17, 2023·edited Feb 17, 2023

"The decline in Middle Eastern egg quality also has to do with endemic cousin marriage."

That is surprising. I thought cousin marriage has been the norm there for at least the last millenium - my intuition would be that either effects of that on egg quality should have plateaued by now, or egg quality should have reached abysmal levels a long time ago. But seeing how many middle eastern countries have a high population growth, it obviously hasn't?

Expand full comment

Same thought crossed my mind. I can only speculate that the Vitamin D issue created by indoors living due to A/C, might have exacerbated a pre-existing problem. But really... I don't have any data here.

Expand full comment

It was, but historically, there was revolution/warfare every 3/4th of a century in Arabia, leading, to, let's say, 'women reallocation', which had the fortunate side effect of preventing runaway inbreeding.

See Ibn khaldun, scholar's stage. Arabs weren't blessed by geography.

Expand full comment

Without having seen any of this research, I note that this sounds like it could largely be explained by the bias of those reporting the issues if there isn’t a careful design and agreed standard before gathering the data. For example, a society that is more biased against women will produce medical staff more inclined to blame ‘the egg’ rather than ‘the sperm’, especially where this is being reported to the clients (where ‘poor sperm quality’ might be taken as an insult or threat, as might ‘poor egg quality’ but I doubt the staff will worry about that). And this is likely to correlate with requiring women to cover up more, and allowing them outside less.

Which isn’t to say that it sounds implausible: it does sound plausible. But it could also be very easily confounded, especially if it has been gathered by surveying people involved in fertility clinics rather than by testing egg and sperm quality themselves.

Expand full comment

This wasn't from a survey, these were qualitative comments by people running these clinics. It came unprompted during a session where a technology provider was demoing a device to improve the odds on the male side. They started saying, noted, this may work, but it's irrelevant because it is nearly never a sperm problem. From then on a discussion developed and the rest of the viewpoints came out. As to the atmosphere in the room, everyone talked about this like it's plumbing. They are commercial operators and get paid for successful fertilization. No incentive to bias science because of society or religion. It would hurt their business.

Expand full comment

Ah! I was thinking especially of you saying

> evidence on the body-covering angle was given by a published paper

because I do think commercial operators discussing this are likely to be biased, especially when having a relaxed conversation. They get paid by people who decide to use their services, and continue using their services: that is their financial incentive. And they are ordinary humans, subject to all the normal biases of humans, choosing to live in particular societies.

If the solution to “sperm problem”, “egg problem”, “both problem”, and “neither is a problem, but I make money if you use me” is “use my IVF services”, then it doesn’t really matter if you default to recording “egg problem” for anything where it isn’t obviously and only a sperm problem, except that maybe recording that makes it more likely that clients use your services and continue to use them. And we know (as seen in Scott’s investigation of research into telepathy) that the beliefs of the person running a study can affect the results, even when you cannot see how they could possibly do so, even when they are totally honest.

Hence, while I completely agree it is plausible, I also think it is easily confounded, and would be interested in seeing the study you referred to, if either of us happen across it.

Expand full comment

I'd guess that if anything, cousin marriage was *more* endemic in the past than today, not vice versa?

Expand full comment

The sunshine deprivation hypothesis brings to mind the higher latitudes, which should accordingly suffer from horrible problems with egg quality. During the cold seasons women walk around totally covered, and even if they have some parts of the face sticking out, there won't be much sun anyway, at least where I live. UV levels way low.

Expand full comment
Feb 17, 2023·edited Feb 17, 2023

Is it possible that the wedding->IVF thing might be to do sex selection? I know India went the full mile and criminalised sex selection because everyone was selecting for boys and they were worried about demographic collapse.

Expand full comment

it might. The doctors were more inclined to say that it had to do with pressure from parents to conceive ASAP, and that the couples were often arranged marriages between cousins, so, umm, the passion may be lacking too.

Expand full comment
Feb 17, 2023·edited Feb 17, 2023

> - fertility almost always an egg problem, not a sperm problem - plenty enough sperm left for fertility at this point

Swan argues against this in Count Down:

>The recent decades have seen a substantial change in perspective, at least in the scientific community, as it has become increasingly recognized that men contribute to a greater proportion of infertility cases than previously believed. Male reproductive issues are currently thought to cause approximately one-quarter to one-third of infertility cases, equal to the proportion of female reproductive challenges. The remaining cases of infertility stem from a combination of male and female factors—perhaps a woman is slightly subfertile (because she has irregular ovulatory patterns, for example) and her male partner is also a bit subfertile (due to reduced sperm motility), so they have trouble conceiving.

I don't have the expertise to say who's right but it doesn't seem to be as clearly settled as those doctors made it sound.

Expand full comment

I can only report what I hear. They were MDs that had become IVF clinic owners/operators and some were active researchers. So they were clearly practitioners. Their guesstimate was, 95% is an egg quality issue. Of course they're in IVF so they tend to focus on issues occur with the gametes, sperm and egg. Say if you have infertility due to chronic ED on the male side, lowered sex drive, or what have you, that's not a sperm problem but "epidemiologically" a male problem. Perhaps that explains the discrepancy. Maybe one should reword it as "usually not a sperm issue but an egg issue, or else, a wider relationship issue".

Expand full comment

Is there a chance they meant "rarely a sperm problem for the clinic"? It possible an IVF clinic can do a lot more with a few thousand sperm than nature can; however in either case there's only a few eggs involved.

Expand full comment

I wonder if this won't depend in part on how long people try before going to get help. You could easily imagine that there's a fair frequency of sperm related fertility lowering but that it rarely reduces the rate by more than 80% and most people just try long enough to overcome that before seeing a doctor. Thus, depending on how you define your study population or the willingness of a population to see a fertility doc you get different values.

Expand full comment

>plenty enough sperm left for fertility at this point

So what is the minimum amount required before the odds of successful fertilization drops significantly? I vaguely remembering hearing or reading somewhere that immune cells get some of the sperm as they travel, but when even the minimal count is still in the millions, and you only need one to reach the egg. I have a hard time believing white blood cells make that much of a difference...or are there other factors that can prevent sperm from reaching the egg?

Expand full comment

Don't be too sure "you only need one to reach the egg". I've read some articles that implied that sometimes sperm need to cooperate for any of them to be successful. Not only during the swimming, but there's a barrier around the egg that (at least) one sperm breaks to allow another sperm to penetrate.

Well, this could be wrong. It was in (IIRC) Science News, so it was popularized. OTOH...

Expand full comment

"The Arab world has one of the highest rates of genetic disorders globally" - to quote Wikipedia. Should affect eggs/sperm. Ofc, it is those cousin-marriages over generations in the same tribe , due to inheritance-rules. https://en.wikipedia.org/wiki/Genetic_studies_on_Arabs#:~:text=The%20Arab%20world%20has%20one,%2C%20and%20Niemann%2DPick%20disease.

Expand full comment

Interesting that you attribute the vitamin D link to indoor living and air-conditioning, rather than shifts in cultural norms around covering up - the shift from covering hair to covering everything but the face to covering the face too would seem to drastically reduce the amount of sunlight a body is exposed to. If one were inclined to investigate the relative contributions of the two effects, I'd expect the "aircon" explanation to be mostly gender neutral while the "culture" explanation is strongly gendered, so one could compare the relative declines in male and female vitamin D levels

Expand full comment

Perhaps that came across so later, but in my initial post I mentioned the paper I saw, which did indeed attribute much of the change covering up everything in women.

Expand full comment

Porn might affect sperm counts but not fertility rates -- since couples who are trying hard to conceive might be foregoing porn in favor of the real thing.

Expand full comment

What happens if you change X axis to study quality instead of year, and Y axis to difference in count from comparison cohort?

Have someone neutral grade each study by quality, and see if there’s correlation to claim and effect. If the poorer the study, the bigger change in sperm count is found, that might indicate bias , likely unintentional.

Expand full comment

What about the similar decline in testosterone?

Expand full comment

Also, the “taint” distance studies while we’re at it.

Expand full comment

Ever since I heard about these on Joe Rogan's podcast, I've really wanted Scott to do a deep dive on the topic.

Expand full comment

"Taints, much more than you wanted to know" really sounds like the next hit piece.

Expand full comment

Is that like the popehat rant version of digit ratio?

Expand full comment

That is partly because men are smoking less and cigarettes increase testosterone.

Expand full comment

do we know that this is the case and not just that men with higher test start smoking?

Expand full comment

>cigarettes increase testosterone

If this is really the case, given how there seems to be a "bro science" trend around anything that has even the slightest anecdotal evidence towards it increasing testosterone (I remember when raw onions were big a few years back), I'm surprised "tobaccomaxxing" hasn't become a thing yet.

Expand full comment

There are bootleg movements like that on certain bodybuilder forums, but they don't catch on much because of two opposing forces.

1. Smoking is a very strong societal taboo. Zizec calls it the ultimate sin next to pedophilia in current society, and while that is a bit hysterical it is reality that there are a lot of very ardent anti smokers who shit up every thread about benefits of tobacco on fitness forums.

2. Smoking shoots your stamina to hell and back. Apart from being generally terrible for your health it also immediatly collapses your stamina, and t-maxxing gymbro culture is very focussed on perceivable benefits in the iron temple. Technically this aspect can be overcome with snus, as snus and other oral tobacco products are a lot less bad for your health and stamina, and snus and other oral tobacco sorts tend to come up in fitness forums, however oral tobacco is a lot less socially viable than smoked tobacco because the smoking circle is a huge reason smoking became so big in the first place.

Expand full comment

Anecdotally I have seen bro science people promoting cigarettes recently, although it seems half joking a lot of the time. I think it started when there was some evidence that they reduced the chance of catching COVID.

Expand full comment

What about the similar decline in testosterone?

Expand full comment

Are there studies about the amount if sperm ‘wasted’ vs ‘deposited’ into proper receptacles?

Will there be studies on ‘the size of the woman’s vagina’ or ‘the desiring affect women have on men’? These might have affect on the amount of sperm a man produces/ejaculates.

Expand full comment

> It feels wrong to me to model this linearly, although I can’t explain exactly why besides “it means sperm will reach precisely 0 in thirty years, which is surely false”.

How about "it means sperm counts will be negative after thirty years, which is surely false"?

Expand full comment

If I tell you that you're driving towards a cliff and will reach it in 20 minutes given your current speed and direction, would it be a valid argument for you to say "that can't be true, because it implies that in 21 minutes I will be floating in air, which is obviously silly"?

Obviously there's going to be some discontinuities once you reach the cliff. That doesn't mean my prediction up to that point can't be correct.

Expand full comment

Obesity could be causing a decline in sperm count, but a decline in sperm count (well, testosterone) could also be causing some amount of obesity. Lower T -> harder to build muscle mass -> less calories being burned at rest.

Expand full comment

It could also be caused by warmer buildings. If you're warm all the time, you convert your brown fat to white fat. Brown fat can burn lipids to produce heat, so you can burn calories just sitting or sleeping in a cold room.

When there's a whole bunch of possible causes, it's often wrong to select just one and say "That's the cause!". E,g, multiple pesticides all at sub-effective doses, can interact to produce drastic population drops. Yet each one of them when measured is at a safe level.

Expand full comment

That's true! I'm not sure it disagrees with anything I said, though...I used the phrase "causing some amount of obesity", I never said "the cause!".

Expand full comment

Lea, R., Byers, A., Sumner, R. et al. Environmental chemicals impact dog semen quality in vitro and may be associated with a temporal decline in sperm motility and increased cryptorchidism. Sci Rep 6, 31281 (2016). https://doi.org/10.1038/srep31281

Expand full comment

I think you underweight how likely this is to be the result of decreased censure of porn/masturbation. Go back 30-40 years and lots of people still felt vaguely guilty about masturbating (even if intellectually u think it's ok feeling guilty and sad can be a buzz kill).

Yes, the doctors tell you to abstain but I can't even always remember to fast the day before my physical so ofc some of the subjects forget.

When I was younger I tried to donate sperm (liked idea of someone using it and could get some money) and I certainly forgot to refrain from masturbating for those days (ended up rejected bc not enough sperm)

And if you forget you won't want to sound like someone who couldn't even refrain from masturbating. I sure as hell didn't mention it when I came in. And how good is the evidence the effect is literally zero for everyone if you wait a few days?

--

And re: porn it's not that it's all porn addicts or something but I know ppl who think nothing of opening up porntube for a quick walk whenever they are having trouble falling asleep. Back in the day that would have been more work and probably less likely to be something so casual.

Expand full comment

Wholeheartedly agreed. Plus there's an additional porn effect: the material that sperm clinics provide are usually DVDs, sometimes from the 90s. That can't keep up with modern porn, and sperm count feels like it should be related to intensity of ejaculation. (speculation based on 10 minutes of googling)

Expand full comment

I'm not sure that matters. I doubt they stop you from bringing your phone in with you. I don't think many ppl use the provided materials anymore.

Expand full comment

Ohh, nevermind. I guess back in the day most ppl didn't look at porn all that much so seeing it in the collection room was probably more exciting.

Expand full comment

I think that maybe the main reason.

Expand full comment

People keep talking about masturbation-related guilt in the past tense. This is still very much a thing and IMO we can’t expect very many people to be utterly and completely transparent, much less accurate, about when and how often they masturbate.

Expand full comment

Well yes, but it's likely much less than it was in the past and we are looking at the differences. But yes, I agree that bc it's not exactly something ppl are proud of we can't always expect them to admit when they didn't follow the rules. I sure as hell didn't.

Expand full comment

> Partly because the decline could stop - either because we identify the cause and correct it, or for more mysterious reasons. But partly it’s just an unjustifiable penalty for something that it seems very hard to imagine happening.

And partly it is a justified penalty for the most likely outcome being «be us damned if we have any idea either way, given all the confounders we had not even considered recording ten years ago»

Expand full comment

Porn might not affect sperm count, but I wonder if it explains the recorded rise in erectile dysfunction and decline in sex frequency among young men. Seems like a plausible hypothesis, but the only study I found seems to debunk it.

https://www.nature.com/articles/s41443-022-00596-y

Expand full comment

Seeing how the "social networks" are addictive, and how people who install them on smartphones turn to zombies, I don't think we need to look hard for explanations of "why young people spend less time doing X".

Expand full comment

Probably yes for ED, but I'd bet sex frequency has more to do with how much the social environment has changed.

Expand full comment

If the population declines and I believe it is sperm rates will be a small factor in that equation.

Expand full comment

Disappointed the "other things" section didn't include "extremely fast evolution".

Expand full comment

How would that work? Surely there's an inherent selection effect towards spark quality, almost by definition

Expand full comment

Yes, but selection pressure might be decreasing in the modern era.

Expand full comment

So in the olden days, people would have lots and lots of children, as many as possible often, and many of the children would die. So high sperm count would be useful.

But now many people decide how many children they want. So say a couple decide they want 2 children. With high sperm count that might happens in say 2 years, and with low sperm count it might happen in say 3 years. So the sperm count isn't that important, they end up with 2 kids either way.

Now it does matter somewhat, the guy might die after 2 years, and then the low sperm count guy would only end up with 1 child. But the selection pressure is probably less now than in the olden days.

But I don't think evolution is fast enough that this is a big factor yet.

Expand full comment

I also think we'd only see this happen quickly if there was some big cost imposed by having high sperm count. Assumedly this wouldn't just be a "drift" sort of thing; for it to happen quickly there would need to be some sort of gain from evolving to produce lower sperm counts. I'm not a biologist, but if anyone with expertise wants to weigh in on the costs of having high sperm count, I'd be really curious

Expand full comment

Could be something that seems completely unrelated. Like one gene gives high sperm count but also increases the chance of heart failure.

Expand full comment

The filter-- which still might not be very fast-- would apply if a couple delays having children until the woman is late in her fertile years. At that point, if conception has become more difficult, she might have one or two fewer children than the couple was hoping for.

Expand full comment

Even if we don't correct it, I think most potential causes listed there would level off (e.g. we're using more plastics than fifty years ago, but I don't think the rate of plastics use is still increasing), so if the problem is caused by one of the listed explanations we should be fine.

(Unless it's the porn one and AI-generated superporn makes it worse, I guess)

Expand full comment

I wonder when that's coming out. I'm rather sure it will, but also that it will be expensive, so I'll never see it. (I'm a cheapskate.)

Expand full comment

I should probably say here that before this blog post, I had thought this issue - that sperm counts had been declining - was, as a simple fact, completely uncontested, with no serious counterarguments even presented against this basic thesis. I've seen comments like "Sure, they're declining, but this is not a serious problem" or "Sure, they're declining, but why panic about it? Too many babies anyway" and so on, but this was probably the first thing I've seen that indicated they might *not* be declining, actually.

Is this just discussed differently in Finland and Finnish media than elsewhere?

Expand full comment

Nope, same here. Score another point for "'Trust The Science' is not so easy because for a layperson there's no easy way to find out what The Science is actually saying, and the media through which you get your information, even if you're reading reasonably high-quality mainstream media and not the Daily Mail or whatever, are not guaranteed to give you a good overview".

Expand full comment

The "reasonably high-quality mainstream media" can be the worst. The NYT is controlled by the US State Dept. and the Washington Post is controlled by the CIA. And both the State Dept and the CIA are captured by big corporations like Pfizer and the major defense contractors, so propaganda all-around. That leaves substacks--like this one--and there are a lot of them to parse.

Expand full comment

No, no, you silly person: I have it on good authority that Pfizer is controlled by the NYT, the CIA is controlled by the State Dept, and all major defense contractors are controlled by the Washington Post.

Expand full comment

People rag on the Daily Mail a lot because they don't like its politics, but I don't think it's especially problematic as regards science.

Expand full comment

It's still a tabloid with a penchant for sensationalism, no? The Daily Telegraph and the Times have similarly right-leaning politics AFAIK (speaking from across the pond) but I'd take a science article I saw a link to in either of those far more seriously

Expand full comment

C'mon, Science is full of politics. Okay, "Gravity" isn't very political. "Physics," and "Astronomy" aren't, but Medicine and Technology--for example--are!

Expand full comment

This was a great article! Now something I've been wondering about is the supposed decline in testosterone over time in healthy adults. Do you guys think this trend is real? I haven't done much research, just read a few abstracts, wondering if anyone has gone through the literature.

Expand full comment

haven't testosterone levels declined precipitously since then?

Expand full comment

If these studies aren't controlling for age wouldn't aging populations, and later age having children, explain it fairly well? That would for why developing countries and China seem to have it worst.

Expand full comment

We could check for correlation if we want. https://www.worlddata.info/average-age.php

With Japan showing a lower decline than China, I would think no.

Expand full comment

Japans population is older than China.

Expand full comment

Is this even a problem? As is hinted in the article human males overproduce sperms on a massive scale, probably a legacy from more polyandrous times when males were actually competing sperm to sperm. Anyway, the bottomline is that lower sperm count, if it is even real, should not translate into a general fertility problem until it gets way worse than today. The fact that this rather obscure subject is so popular in the news media probably has more to do with fragile male egos than actual science. (It is still a good thing of Scott to sort it out, of couse.)

Expand full comment

The decline is continuing. So maybe.

Expand full comment

Well, *if* the decline is continuing. Which is the point of the article.

FWIW, I think other factors will dominate. Which other factors depends on decisions that we make in the next decade (and ones I don't know about from the last decade). One that was suggested above was "AI generated super-porn". I'm not sure that won't be a problem. Certainly I don't understand (or realize the degree) to which people are attached to "Social Media". This despite the fact that I'm posting here. But if that limits human physical interactions, that could have a very strong effect of reproductive success.

Expand full comment
author

It wouldn't surprise me if whatever issue causes declining sperm causes other bad things too.

Expand full comment

I think both this and declines in testosterone are considered important not because of 'fragile male egos' but for their status as canaries in the sociological coal mine, possibly downstream of larger issues like water source contamination or unknown health effects from electronic devices.

Also, they're seen as possible causes of a worldwide decrease in traditional masculine values and behaviors. It seems extremely reasonable to be concerned.

Expand full comment

You don't mention it, but there's supporting evidence. Not only are sperm counts going down, so is testosterone, and these are obviously related. Next up, rates of testicular cancer are increasing. And surveys show that masculinity is decreasing. These all fit together, and it seems difficult to not posit a general common cause or set of causes. I would guess improved clothing and heating is a major player and the causal evidence for heat stress to sperm quality is strong. As in, they literally put monkeys in hot baths and checked their sperm quality.

https://kirkegaard.substack.com/p/secular-genetic-phenotype-paradoxes

Masculinity surveys, note these are pre-Woke takeover

https://today.yougov.com/topics/society/articles-reports/2016/05/23/decline-manly-man

Expand full comment
author

I was interested in including something about this, but I found a few studies saying that sperm count didn't really correlate with testosterone. Obviously this isn't true at the extremes (if you have zero testosterone ever, I guess you are a woman and don't have sperm) but it seems to be true at the margins. I only looked into this superficially; let me know if you've investigated more and found I'm wrong.

Expand full comment

This could be very good news.

The biggest threat to this civilization can be expressed in this equation:

violent men + knowledge explosion = game over

It would be great if we could keep the many peaceful men while getting rid of the minority of violent men, but no society in history has figured out how to do that. Thus, the best thing that could happen to this planet could be a world without men, that is, without male humans.

Or far fewer men at least. A tiny number of men can impregnate huge numbers of women, and would be happy to do so. Or, science is learning how to make sex cells from skin cells. Works in mice, but not yet in humans. Point being, we can maintain the species with far fewer men, or at some point, no men.

Violent men are responsible for 90%+ or more of the violence which so afflicts many millions of innocents all over the planet. It's an unspeakable horror show. In addition, they are a HUGE expense. Removing them from the population would solve a great many very important problems, save this civilization from collapse, and lead to a state of affairs which can reasonably be labeled world peace.

I'm making this argument in some detail in 13 pages of analysis here:

https://www.tannytalk.com/p/world-peace-table-of-contents

Here's our situation in a nutshell.

1) In the 21st century face a choice between the knowledge explosion and violent men.

2) We can have either, but not both.

3) If we don't solve this problem, there's not really a point in discussing much else, as we're racing towards a cliff. So, forget about AI, curing cancer, progress in general, the NFL, the Internet, and whatever else matters to you, because if we don't get rid of violent men, sooner or later they will erase it all.

4) If we do get rid of violent men, we can have world peace, the next miracle in human evolution.

Declining sperm counts could be very good news.

Expand full comment

Do you think that sperm only produces men, and the more of it the more violent the men?

Expand full comment

Better challenges will yield better responses.

Expand full comment

"Save humanity by killing half of it" is the villain plan of multiple stories. "Save humanity by killing all the men" is straight out of The Vampire Chronicles: Queen of the Damned.

What I'm saying is, this line of thought will end in you getting your organs eaten by psychics.

Expand full comment

If you had actually read the articles I've pointed you to, you would already know that I've not proposed killing anybody. What I'm saying is, your line of thought is not actually a line of thought. It's a lazy social media gotcha burp.

Better challenges will yield better responses.

Expand full comment

Your line of thought barely exists. You didn’t answer my question. Do you think lower sperm counts leads to fewer men or less violent men? Because it seems like you do and that’s incorrect.

Expand full comment

Lower sperm counts would seem to be taking us in the direction of fewer humans, which seems a good thing. Lower testosterone might be lowering the violence level of men, again a good thing if true.

If you're interested in lines of thought, I have 13 pages of that already up on my blog. See the prominently displayed world peace section. I welcome intelligent thoughtful challenges. If that interests you, you might start here:

https://www.tannytalk.com/p/world-peace-is-possible-part-11

And here:

https://www.tannytalk.com/p/world-peace-is-possible-part-2

Expand full comment

Isn't there a relationship between testosterone and risk-taking? And thus, driving society forward?

Expand full comment

Is there a relationship between testosterone and risk taking? Seems likely, but not sure. There is a well documented relationship between male humans and violence, which is possibly related to your question.

Does risk taking drive society forward? That would seem to depend on the scale of the risk being taken and the potential benefit involved. Some risk taking would seem advisable, while other risk taking would seem insane.

If testosterone levels fall would that reduce violence? That seems a reasonable theory worth exploring. Your question does open a new door for me, so thanks for that. If we could biologically alter men so that they committed violence at the same rate as women, then that would accomplish the goal of world peace (a radical reduction of violence) and it then wouldn't be necessary to remove the male gender.

What the article on this page might suggest is that nature may already be at work on this plan. Species are always attempting to adapt to a changing environment. The invention of nuclear weapons changed our human environment in a radical manner. Maybe we're already adapting to the new environment biologically? Don't know, but that's an interesting line of inquiry to explore.

Expand full comment

It seems clear to me that societal progress and economic growth requires risk taking. Developing new technologies and making important investments are never sure bets, and those overall tend to be done by men (although obviously not exclusively so). So if there's a tradeoff between economic growth and levels of societal violence, I'm willing to tolerate some level of violence to maintain growth. (Does that sound a bit like Omelas? Maybe.) We probably find them negatively correlated in real life, though.

Also, I'd like to point out that we've had nuclear weapons for almost 80 years, and they haven't been used since their invention. So I'm not as fearful of the inevitability of catastrophe given technological advances as you.

Expand full comment

Imho, economic growth depends on successfully managing social violence. You know, there's not much economic growth happening today in Ukraine.

I'm not fearful, I'm rational. I'll be 71 in a few days, I'm sorta dead man walking anyway, no matter what happens. I have little reason to fear whatever is coming on this Earth, as I'm scheduled to be elsewhere.

So, you think we can keep nuclear weapons around forever and they'll never be used? And conflicts like Ukraine will never spin out of control? Ever? Are you aware that on multiple occasions we've come within minutes of having global nuclear war BY MISTAKE?

Progress is only meaningful in a stable environment where we don't have to worry about everything we're building being swept away in a matter of minutes.

Expand full comment

It's quite possible that nuclear weapons will be used, but not used on a grand scale. They might be comparable to conventional wars and other disasters.

Expand full comment

Quite true. In the case where they were used, in WWII, two of them were used.

Phil Tanny's whole concern seems misplaced to me. Sure, there is violence tied to specifically male psychology and biology. There are roughly 17,000 homicides per year in the USA, and roughly 90% of the killers are male. This doesn't threaten to bring down civilization. The sorts of events with huge death tolls - wars, Mao's great leap corpseward, etc. are not matters of momentary anger and poor impulse control. They are matters of institutional structure and game theory and ideology. If every national leader were female I doubt that they would change much.

Expand full comment

That is indeed possible, agreed. In fact, a nuclear weapons accident could almost be called a plus, in that it might blast us out of denial without starting another war. As far as one or more nukes used in anger, there's no telling how that might go.

Expand full comment

There's a relationship, but showing it's causal is difficult. There's also a relationship between emptying cat litter boxes and risk-taking.

FWIW, men generally take more risks of encountering violence than do women, so if you survey humans, there is naturally a relationship to level of testosterone. This doesn't prove that it's causal, as there are LOTS of other differences. You run into this problem even among sub-groups of men. Smaller men often are perceived as taking fewer risks, but the risks they take aren't the same as those that would be encountered by a more muscular man (and muscles ARE related to testosterone level).

Your argument COULD be right, but proving that it's causal in the implied direction would be quite difficult.

Expand full comment

"If there were no men, we'd all be still living in huts." -- Camille Paglia

Expand full comment

If violent men continue to be further empowered by an accelerating knowledge explosion, we'll soon all be living in huts again. As you know, the technology to make this happen already exists and is ready to go on a moment's notice.

We face a choice between violent men and the knowledge explosion. We can have either, but not both.

Expand full comment

Men have also been responsible for >95% of the science, technology, mining, construction, and industry that have created the modern world of health and abundance, where the average worldwide life expectancy is 72 instead of 30. You want to talk about unspeakable horror shows? How about a world where parents lose a child every other year?

Expand full comment

Men have been responsible for the STEM fields because women have been ruthlessly prohibited from participating until pretty recently, basically one lifetime.

Expand full comment

And how about mining and construction, aka actually building the physical world we live in every day? All the STEM in the world isn't worth anything if you can't make stuff with it.

Expand full comment

All the STEM in the world won't be worth anything after the violent men blow it all up. Please bring your A game, this can't be it. Try this:

https://www.tannytalk.com/p/world-peace-is-possible-part-11

Expand full comment
founding

Women have been just as ruthlessly prohibited from participating in the violence fields until pretty recently, basically one lifetime. If you're going to assume that relaxing the restrictions on women (and taking male competition out of the equation) will result in women achieving male-equivalent performance in science, technology, etc, then it seems only fair to assume that it will also result in their achieving male-equivalent performance in crime, insurrection, and war.

Expand full comment

John, I'm headed back to my blog. See ya there if you wish to continue. Have a good one!

Expand full comment

They are still responsible for most of everything that matters, despite women being preferred 2:1 in STEM.

Expand full comment

If you're concerned about world peace, you might be interested to know that European queens have historically waged war 27% more often than European kings: https://www.economist.com/europe/2017/06/01/who-gets-into-more-wars-kings-or-queens

War has nothing to do with a playground fistfight. Just because girls don't usually punch each other in the face in grade 4, doesn't mean that women are better at unentangling the complex web of ideology, economic interests, balance of power dynamics, and domestic political concerns that lead to war.

Expand full comment

Many Thanks! That is very helpful evidence.

Expand full comment

That's the "Margaret Thatcher and Hillary Clinton" effect. Both of them were careerists who thought they needed to compensate for being women by being MORE warlike than men . . . Thatcher (Falkland Islands); Hillary Clinton: (Qaddafi) https://www.youtube.com/watch?v=6DXDU48RHLU

Expand full comment

That's a just-so story. An equally plausible just-so story is that Thatcher and Clinton were simply warlike for the same reasons that men are warlike, which in turn is because war is the result of a complex web of ideology, economic interests, balance of power dynamics, and domestic politics, and those factors often make war desirable in the eyes of a country's leaders.

Expand full comment

"violent men + knowledge explosion = game over"

The knowledge explosion already happened, rates of violence are down by extraordinary amounts, and we are still here.

As for eliminating men, there is no "we." The idea that human civilization is run by a single person who can unilaterally decide what's best for it is utopian nonsense. You can only get rid of men in the corner of the world you control, at which point that corner of the world would be thoroughly subjugated by societies that still have men. Even if you had superior military technology as a deterrent, societies with men would not only surpass you, but your society would be too afraid to use it, maintain it, or keep developing it.

Expand full comment

This is why it amuses me that almost all of the people who love to speculate about genetic causes for differences in racial crime rates are men.

Expand full comment

Nothing amusing there. We're all fully aware that men commit most crimes, but there's a big difference between removing men from your society (which is a wee bit difficult) and pushing back against utopian lies about race.

Plus, if you got rid of all the men, you'd have nobody left to think about--and address--harsh truths like the above, and the fact that a certain demographic of women commit even higher rates of murder than a certain demographic of men.

Expand full comment

Even assuming environmental pressures are driving this, there's such a straightforward evolution mechanism to counteract it that "sperm count goes to zero" strikes me as extremely unlikely.

Expand full comment
author

Evolution doesn't operate that quickly.

Even supposing that ten people currently have some rare mutation that allows them to keep natural sperm count, evolution would have to go through "everyone except those ten people fail to reproduce" -> "those ten people's descendants repopulate the earth", which doesn't really seem like a "business as usual, no need to worry" scenario.

Expand full comment

Most traits are polygenic! Natural selection can act on the diversity that is already present, it doesn't depend on "rare mutations", there are already hundreds of polymorphic loci. Thinking in terms of "rare mutations" is appropriate for novel traits (where did wings come from?), but not here.

My prediction is that after the first generation where a significant enough minority gets into the problematic range, the trend will slow down, with a delay of one generation. Eventually it might even revert.

Expand full comment

Surprised there was no mention (that I can see) of the world becoming more peaceful since WWII, especially in daily interactions, probably in part by the removal of high-testosterone men into prisons. (This presupposes that high testosterone is correlated with both higher sperm counts and higher violent tendencies, which quick research indicates that it is.) Norms have changed significantly over these 70 years, removing high-T guys into prisons, or self-segregating them into violent sports. The decline in everyday violence (eg bar fights) also creates an environment whose cues, to the extent they influence T production, are more relaxing, so whatever the environmental contribution to T is should have declined.

Obv this is a hypothesis (or two hypothesis with a link) and empirical studies are needed, but I hesitate to suggest any; the sheer number of countries/regions, over time, over norms, creates too many confounders for me.

Expand full comment

It's not mentioned because it's an orthogonal hypothesis with only a tenuous relationship to what's being discussed. In short, it's not germane. I fail to see why you are surprised.

Expand full comment

The hypothesis that we've removed the high-T men from the gene pool through policing might be wrong, but it isn't orthogonal.

Expand full comment

I would advocate strongly for a "impact of plastics on the human body: much more than you wanted to know" post from our fearless leader.

Expand full comment

seconded

Expand full comment

What does "community-dwelling" mean in this context? Does it mean people who are not institutionalized (i.e. in long-term medical care or prison)?

Expand full comment
Feb 17, 2023·edited Feb 17, 2023

What a hilarious timing, to publish it one day after the meta-analysis:

"Worldwide Temporal Trends in Penile Length: A Systematic Review and Meta-Analysis"

https://wjmh.org/DOIx.php?id=10.5534/wjmh.220203

(Spoiler: the analysis concludes that the erect penile length increased 24% over the past 29 years.)

Expand full comment
Feb 17, 2023·edited Feb 17, 2023

Is that self-reported length or did some researcher have to stand there with a tape measure as the subject watched porn?

If it's self-reported, I think the ubiquity of porn where (I assume) the male actors are well-endowed, and assumptions that "the average size is supposed to be X so I better say I'm at least X", might be at work there.

Expand full comment

They excluded all studies with self-reported measurements.

Expand full comment

So somebody *did* have to stand there with a tape measure. Dedication to science! 😂

Expand full comment

I think you have to use a ruler rather than a tape measure if you want reliable results. Otherwise it's not clear where the baseline is. (not accounting for this fact apparently casts a lot of doubt on the 24% figure)

Also they sometimes get it up by injecting vasodilators rather than more artisanal methods.

source: doi:10.1038/s41443-017-0013-3

Expand full comment

Penile dimensions co-evolve with the female organ based on female mate selection which is coupled and amplified by promiscuity:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4484975/

Dixson, A.F. (2009). Penile morphology, sexual selection and human evolution. Sexual selection

and the origins of human mating systems.

Witness from dung beetle to chimpanzees.

Expand full comment

How many of these potential causes point to continued decline? E.g. it seems like plastics and pesticides have more or less reached market saturation at this point -- will we really see significant further increases in exposure to them going forwards?

Expand full comment
author

I agree with this, but remember that Levine et al say the decline has intensified in the past 20 years; I would have thought we were at saturation for those things 20 years ago. Maybe there are other developing countries where we hadn't, and the intensification is concentrated there?

Expand full comment
Feb 18, 2023·edited Feb 18, 2023

Or maybe we're measuring the sperm counts of people who got a lot of plastics/pesticide exposure when they were babies? Basically the numbers appear to be increasing because people who grew up with less exposure are dying?

The possibility I'm most worried about is epigenetic changes that get passed from father to son.

Expand full comment

"It feels wrong to me to model this linearly, although I can’t explain exactly why besides “it means sperm will reach precisely 0 in thirty years, which is surely false”"

It seems to me that biology generally isn't linear. There are s-curves, there are sudden breaks, and there's random things having an effect.

As for vitamin D, there's more to sunlight. Humans have nitric oxide precursors under the skin that are activated by sunlight. It definitely affects blood pressure, it might affect sperm production.

Expand full comment

Speaking to the plastics issue -- seems important to note that at least for the map shown it's measuring plastic waste *emitted to the ocean* per capita.

I've lived for extended periods in both the USA and South America, and it has always felt like if anything I had less contact with plastics in South America than in the USA, but that the disposal of plastic waste in South America was less effective.

It's common to see lots of trash on streets, beaches, etc to an extent that I don't really see in the USA -- I would suggest that it's possible that we have more contact with plastics in the USA but they are disposed of in such a way that less of it ends up in the ocean.

Admittedly i have no data to support this apart from my own observation and vibes

Expand full comment
Feb 17, 2023·edited Feb 17, 2023

My understanding is that countries that emit more plastic in the oceans do so because of poor waste management infrastructure. If a truck comes around every week to haul off trash, people will use that service. Absent waste disposal options, people have no choice but to find another outlet to keep the garbage from piling up, and the river runs 24/7.

That may still translate to higher environmental exposure, from waste upstream, especially if population centers tend to be on the rivers. However you'd also expect that to translate into lower animal sperm counts, but maybe that's confounded by selective breeding.

Expand full comment

That makes sense. At least in my experience there were plenty of waste disposal services, the issue I think was more of a combination of more stray animals getting into the trash and scattering it and less taboo on littering. Would not be the case possibly in other less developed south American countries though. Unless you're getting your water directly from the river though -- which I never heard of happening (city water did come from the river, but with plants in the mountains before the river ran through any population centers and therefore with little plastic) -- I can't see this having a bigger effect than everyday contact in the USA would. This obviously would be different in other countries though; would be interesting to see a comparison of some sort within latam

Expand full comment

Yeah, it would be great to see a comparison story of phthalates and other plastics of concern in communal areas (river, playground) across countries.

Were there smaller communities upstream that had fewer government services? (trash, water, electric, free wifi on mass transit vehicles)

Expand full comment

Not really -- a couple close to the capital, but it was mostly just mountains

Admittedly not a situation that would apply in other countries

Expand full comment

I mean it's very possible that a strong correlation exists between societies that can't collect garbage effectively and societies that can't keep it out of their drinking water effectively.

Expand full comment

If you are familiar with the curve of population against time in a fixed-resource culture, say, bacterial colonies in a petri dish, you will be familiar with the exponential growth, slowing down as resources dwindle and waste-products accumulate, eventually leading to a slight reduction in population then a catastrophic crash. Well, what would that look like if we consider ourselves in the situation of those bacteria? We know that over-crowding and stress cause a rise in non-functional behaviours (self-injury, homosexuality - no offense to gay people who were always that way!, paraphilias, aggressive behaviours etc) in both animal populations (eg pigs in a factory farm) or humans in an artificial environment such as a crowded prison. Stressful overcrowding is, I'm sure I have been taught somewhere, a cause of low sperm counts (unless, oddly, you are overcrowded among men alone, in which case elevated testosterone accounts for rises in aggression and sperm counts).

Seen in that light, perhaps some of the odd behaviours we see, especially those that prevent reproduction - asexuality, transgenderism, homosexuality, bizarre genders - might fit in with where we are on that curve. Likewise, we delay having children and have fewer of them as economic conditions get harsher. Now we can add a falling sperm count to the list of physiological ways we unconsciously try to stave off the collapse. We may be at the stage of population contraction and perhaps these are parts of the mechanism.

Expand full comment

Economic conditions aren't getting harsher though.

Expand full comment

For people who want to learn more about sperm biology, I wrote this post last year: https://denovo.substack.com/p/know-your-sperm

I don't think fertility will actually decrease due to declining sperm count.

Expand full comment

I've observed a number of morphological differences between the older generations and modern generations; modern generations have smaller and more delicate hands, for example, as a result of the fact that we're (collectively, on average) not smashing and vibrating the shit out of ours hands on a regular basis as much.

Even if sperm count is decreasing, it isn't obvious to me that this necessarily represents a decrease from a "correct" number of sperm. It could simply be that people are less exposed to environmental conditions that were previously increasing the number of sperm.

For example, as I understand it, selenium, which may increase sperm count, used to be a major pollutant in our waterways, but we've greatly improved our treatment of wastewater to eliminate this pollutant - and over the past couple of decades, selenium deficiencies have started to become more prominent an issue; perhaps the odd thing isn't modern sperm levels, but the sperm levels we are attempting to make a comparison to. Mind, it's hard to find exact details, so don't take this as advocacy of this idea, but merely using it as an example of something else that might be confounding our data - we don't know what the "correct" value should be, and things can increase as well as decrease sperm count, so it's entirely possible that the issue is a -decrease- in key pollutants.

Expand full comment

This is a good point, and I hope future studies manage (thought surely there are cultural barriers) to measure counts from pastoral and hunter-gatherer groups with very limited contact with the pollutants of today and the early 20th century.

Expand full comment

An anecdote point: in 1979 (solid date, it was summer after my freshman year in college), I recall an industrial chemist friend of my dad's remarking, "that new-car smell, that's plasticizers, phthalates [he used the word], out-gassing. They're everywhere, if we ever find out they're bad for us, that'll be a big problem".

So, 1979, an industrial chemist in the aerospace industry believed that they were already everywhere, and worried-but-did-not-know if they were bad for us. And also, there may be a difference between "new" (flexible, new-car-smell) plastic and "old" (brittle) plastic in the amount/rate of plasticizers that they leak into the environment.

Expand full comment

they are bad for us, most are carcinogens.

Expand full comment

Everything is a carcinogen.

Expand full comment
Feb 17, 2023·edited Feb 17, 2023

I'm surprised you seem so skeptical of the obesity explanation. We know obesity rates are going up, and that obesity is associated with reduced sperm counts, so wouldn't it be pretty surprising if rising obesity weren't causing at least some of the decrease? (even if obesity being the only cause doesn't perfectly match the noisy regional variation).

It makes me wonder if there might be some cognitive bias in play, favoring exciting solutions (e.g. toxic environmental plastics are endangering us!) over mundane solutions (e.g. obesity is already known to be associated with reduced sperm counts).

Expand full comment

> We know obesity rates are going up, and that obesity is associated with reduced sperm counts, so wouldn't it be pretty surprising if rising obesity weren't causing at least some of the decrease?

It wouldn't be surprising if both obesity and reduced sperm counts are caused by the same thing. For example, testosterone levels. It's a classic case of "correlation is not causation".

Expand full comment

Here is a randomized study suggesting that the effects of excess weight on sperm count are causal. Also, Scott didn't offer evidence against such a causal connection, and in fact his own link and wording on obesity/diet assumed a causal relationship w/ sperm count, even if he doubted its role in the long term trend. (note diet could be a "shared" cause here, but that is hard to separate from obesity and Scott just lumped them in the same category - diet and obesity).

https://academic.oup.com/humrep/article/37/7/1414/6587152

Expand full comment

At the moment (2/17/2023, 10:22 EST) substack is saying this was posted "11 hr ago", but I thought I saw it (days?) earlier. Is there a glitch in the reported time for posts?

Expand full comment

There was a subscribers-only "sneak peek" posted a while ago.

Expand full comment

Ah, that explains it. Many Thanks!

Expand full comment

There is at least one dissertation / thesis. prior to 1975 that penis size is decreasing as well, and the proposed cause was pesticides. The author was my favorite Aunt although she left KS abruptly after marrying my uncle. I was told she returned to southern CA. Her name was Joanne (SP?) Gaston or Joanne Gaston-Pressgrove. I have been unable to find her and would ask that if someone is able to find her thesis or any indication of a Berkly grad with a similar name, I would appreciate you sharing any information. Unk passed a few years back and I would really like to let her know. TIA

Expand full comment

Actually, the largest contributor - assuming the fall is real - is probably just age.

Look at the sperm count by age decile and compare vs. the average age of the "donors". Increasing life expectancies = older men = older men contributing sperm count numbers.

I am 99% sure sperm counts decline with age, period, and an aging population would certainly yield lower overall sperm counts just because of the aging.

The other things are probably much more minor factors, relatively speaking, but are far more alarmist hence useful to dumbass narratives. See climate change.

Expand full comment
author

Everyone realizes this and has controlled for it.

Expand full comment

Approximately a perfect reply. And close to providing an acronym (Ertahcfi or Ertacfi) for future use.

Expand full comment

While your at it, can we do the declining testosterone levels claim as well? Interesting post!

Expand full comment

What about exercise?

Expand full comment
Feb 17, 2023·edited Feb 17, 2023

"Harvard Gender Science Laboratory paper [...] mostly just says that it sounds sexist to say something bad might be happening to men (it also adds that since some studies have found the decline is higher in Europe, it’s racist for saying something bad is happening to white men)."

I read some of the paper, and the closest I could find to a claim of sexism was a paragraph mentioning that MRAs and Alex Jones have referenced declining sperm counts to complain about soy boys. The main point seems to be that even if sperm counts have declined, it doesn't seem to be pathological, there's no reason to think the levels in the 70s were natural or optimal, and high sperm count is not particularly a marker of general health.

It does use a lot of disapproving air quotes about dividing countries into """Western""" and """Other""" and points out that pollution of plastics and pesticides tends to be worse in poor countries, which doesn't really fit with declining sperm counts in western countries.

Expand full comment
author

Aside from that paragraph, there's the one saying "Narratives about the decline of men have been taken up by white supremacist and misogynist groups who claim that men in the Global North are

victims of their liberal feminist environments", the one saying "The results have been framed in terms of a crisis for Western men and masculinity", the one saying "representations of sperm are ‘deeply contextually situated within a crisis of masculinities’", etc. See also https://news.harvard.edu/gazette/story/2021/05/fears-over-falling-human-sperm-count-may-be-overblown/

The "how do we know the levels in the 70s were optimal"? question seems like concern-trolling - there are many pollutants and illnesses that we know lower sperm count, very few that raise it, and we should have a prior that we're getting further away from the EEA over time. It also seems naturally concerning that there's a level at which people stop being fertile, and we're approaching it apparently linearly. While it's always possible to have a galaxy-brained take where sperm count seesaws in a U shape forever for unclear reasons and everything will be fine, I think it's fair to not have that as your base model, and when someone starts suggesting it should be I start looking for ulterior motives.

Expand full comment

It's a fair point that most pollutants would lower sperm count, not raise it (Thegnskald above mentions selenium as a counterexample, although most of the studies seem to link it to motility rather than total count).

Still, if our main concern is that maybe "whatever issue causes declining sperm causes other bad things too" then it seems like we should be looking for evidence of that correlation, not just imagining it. On the other hand, if our main concern is that a large fraction of men will be unable to have children, shouldn't we already be able to see an increase in problems at the low end of the bell curve?

Expand full comment

Disclaimer: N=1, personal experience, YMMV.

I tried to have children with my (now ex-) wife for ±5 years using IVF in France. The cause of infertility was my sperm count being too low (as low as <1m/mL at the worst.) Since I spent plenty of time around doctors and other patients, here are a few points I thought I could share:

- There is a global concensus among professional that the global sperm count is lowering worldwide (they might be biaised since they only see infertile patients though)

- My sperm count varied dramatically (20× factor) over a period of 5 years. Some can be attributed to the surgeries I had, but in between surgeries, I still experienced a 5× change. It didn't seem corelated with any other variable (health, eating habit, alcool consumption or smoking)

- Sperm count is usually corelated with sperm quality. So sperm count and fertility don't have a linear relationship, and it might skew some studies quite a lot:

- Low quality sperm can be very short-lived and when the lab performs a sperm count, they only count the effective sperm found (discarding dead, or imobile ones), making the timing between production and analysis very crucial which it is not.

I made a few samples at home and brought them to the lab for analysis about 30" later. I didn't check at what time they made the count, but I had 30% less than the week before. I paid a little extra for a more in-depth analysis and went to a different lab where I needed to produce the sample there, and they would check periodically over a period of 24h.

Just after producing I had my 30% more, and ~80% were dead (thus not counted) after 24h. The high variability of the result might just be the different collection methods used.

Expand full comment

Look I realize a lot of people are putting effort and thought into this hypothesis.

But frankly, I find it crazy to see an idea entirely based upon surveys of non-random, non-representative samples of the population being so widely discussed as though it has solid scientific backing. The media really need to chill on this topic.

These meta analyses are mostly GIGO. The fact that this obvious problem with the data is only listed as limitation #3, and then is so easily dismissed by the authors of these studies, is something of a cosmic joke.

Scott your analysis of the issue was legitimate and helpful to frame the topic.

But you forgot to mention what I see as the most likely possibility: Based upon my observations of other fields of epidemiology that receive far more funding and research interest, I estimate a 90% probability that in 20 years we still will not have any truly useful data to either strongly support or falsify this hypothesis.

Likely instead this will continue to be among the topics to be debated endlessly among friends at a pub while enjoying a flight of good beers…

Expand full comment
author

In 20 years it should reach the point where fertility goes way down; if nobody has noticed this by then, it's been (at least partly) disproven.

(or it's sublinear, I guess)

Expand full comment

But I don't think we're comparing like with like; if you compare today with twenty years ago, fertility has gone way down. Is that due to declining sperm count or to people avoiding childbearing, not wanting more than one or two kids, and the rest of the question we argue over when we discuss replacement rates?

If the baseline remained the same over a hundred years (i.e. no contraception or abortion, no limiting family size to 'just two will do', and people want to have babies as soon as they're married, people get married in their early twenties), then you could compare 'how many kids did grampa father to how many kids did grandson father' and see if fertility was affected by decline in sperm quality. But since we don't have that kind of steady underpinning, we can't see if "are we at the point when fertility goes way down due to declining sperm", not even in developing countries because there have been huge campaigns to reduce population numbers there, from giving women access to contraception to paying poor men to have vasectomies (and of course things like China's One Child policy):

https://timesofindia.indiatimes.com/city/indore/50-more-incentives-for-male-vasectomy-across-state/articleshow/89613490.cms

"In all districts of state, male undergoing vasectomy will get Rs 3000 as incentive money instead of Rs 2000 paid earlier. Similarly, females will get Rs 3000 for post-delivery tubectomy and Rs 2000 for post abortion sterilisation under revised incentives, showed records."

https://qz.com/india/1414774/the-legacy-of-indias-quest-to-sterilise-millions-of-men

"In 1976, men across India were drastically changing their behaviour. Some were abandoning the beds inside their homes to sleep in fields; others were skipping major festivals and public gatherings. Those who in the past had taken the train freely, without a ticket, were finding alternative routes. They were all trying to avoid government officials. On trains, inspectors were suddenly cracking down on ticketless passengers with heavy fines, but they would give fare dodgers a break on one condition: that they agreed to be sterilised.

Government workers, from train inspectors up to the top brass, were working to sterilise as many men as possible. Some even had monthly quotas for how many men they had to convince to get vasectomies. In turn, poor men in rural villages were doing everything they could to avoid government officials, because any such encounter might end with the villager on a dingy operating table where his genitals would be cut—whether or not he wanted the operation, whether or not he already had children."

Without knowledge of such campaigns, attributing "wow, sudden drop in fertility rates in India during the late 70s" to "declining sperm count/quality" would be mistaken.

Expand full comment

I'm apparently the top "NO" holder on Manifold, so I suppose I should say something.

My estimate (based solely on this post, and no other research) is about 30% for "In twenty years, will the best evidence available suggest that sperm counts have been substantially declining across most of the world?" That's, roughly, 25% that there is a non-trivial phenomenon (beyond simply "people are getting older", which Scott said doesn't count), and 5% "there is no decline, but the scientific establishment in 20 years is fundamentally broken, probably because of scientists who do bad research to get headlines and/or tenure".

The key is Figure 2, along with "approximately every study makes a ton of compromises for longitudinal data". As other people have mentioned, Garbage In Garbage Out. And "sperm production of a healthy male" (by height? by weight? by mL of seminal fluid?) ... well, maybe it does vary by 50% depending on the population, depending on what metric you are using. Which just means the differences in populations surveyed (which Scott notes) make a simple linear regression problematic.

( there is also my meta-heuristic of "after years of reading this blog, I believe Scott consistently over-estimates the likelihood of phenomena like this being real" )

Expand full comment

With any luck.

Somehow people are still arguing over what causes obesity after 40 years. So I’m not holding my breath.

Expand full comment