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December 21, 2007


These aren't randomized controlled trials, and it's easy to think of reasons why sex might be correlated with other forms of well-being, so how do they infer causation?

Hilarious! Did it occur to your bayesian brain that one very simple explanation of the mentioned phenomena is that people have less sex because they have health problems and not the other way round?

Oh irony, your post brilliantly demonstrates new research findings: interpreting medical studies makes you stupid! Even the masters of rationality themselves fall prey to the infamous stupidity virus infecting every interpreter of medical studies! It's true, cause and consequence can only be this way, I have statistically significant humbug to prove it, double-blind!

Back in 2005, Tyler Cowen pondered Michael Vassar's pregnant observation: "there is an inexplicable shortage of sex." This remains, I think, one of the most neglected questions in social science. We should devote far more effort to diagnosing and fixing this problem.

The source of the problem should be traced to innate differences between the male and the female brain. Straight men express a desire for larger number of lifetime sexual partners and a shorter time elapse before seeking sexual intercourse far more than women do. These men would be willing to have more sex more often, but cannot find enough willing female partners. When female choice is not a factor, as in gay relationships, the frequency and diversity of sex goes up dramatically. A study conducted by the Kinsey Institute for Sex Research found that almost one-half of the male homosexuals had over five hundred different sex partners. As evolutionary psychologist Donald Symons notes, "heterosexual men would be as likely as homosexual men to have sex most often with strangers, to participate in anonymous orgies in public baths, and to stop off in public rest rooms for five minutes of fellatio on the way home from work if women were interested in these activities. But women are not interested."

So much for diagnosing the problem. As for fixing it, here is one promising approach.

Paul and Anon, yes of course our confidence should be low because direction of causation has not been clarified. There is far too little interest in doing a randomized trial.

Pablo, women of course claim that they love sex, when done right. The research question is: why is it so hard to arrange to do it right?

Prostoglandin, a hormone found only in semen

"Prostaglandins are found in virtually all tissues and organs."

While it's AFAIK well-documented that sex has some health benefits, that article looks really sloppy.

It seems to me that enjoyment of sex is seen as a "silly" topic, not worthy of "serious" researchers.

Makes me wonder: what other potentially important research topics are neglected as "silly"?

First off - Robin, I commend your effort to get us all to have more sex. I am not optimistic though.

You note that women claim they love sex, when done right. Well, they might love sex. But they don't love it as much as men do. In the book "The Female Brain" Louanne Brizendine noted the following distinction:
Thoughts about sex enter women's brains once every couple of days; for men, thoughts about sex occur every minute. See link to article about the book (I'm too lazy to find the cites to the research she's referencing). (The points Pablo S made above about the frequency of homosexual sex are perhaps even more compelling on this score).

You also ask why we can't increase the equilibrium amount of sex by responding to women's desire to have it "done right".

Brizendine presents more findings that seem relevant:
"Women excel at knowing what people are feeling; men have difficulty spotting an emotion unless someone cries or threatens bodily harm".......
It is not hard to imagine that this inability to sense what is going on with their female partners, could constrain mens' ability to get it "done right".

Maybe Santa will surprise you with a copy of the book - in which case I hope we can look forward to more posts on this topic.

You had to know that last comment was coming. . .

April, I agree reduced male empathy may be part of the story, but I find it hard to believe it is the main story. A related part is that women try less hard to be understandable, perhaps in part because that helps screen out uncaring or inattentive men.

The research question is: why is it so hard to arrange to do it right?

Well, why wouldn't it be? I can see why this is a possible research question, but not why it's a surprise/riddle. I don't see people asking "how come people choose to have so little True Love even though it makes them happy"; maybe this is sort of the same thing.


Fact-Checking "The Female Brain."

@ Robin:

Is there a reason you misspelled "exercise" in the title of this post?

Let's skip doing a study. Here's the reason why it's hard to arrange to do it right:

Sex for women comes with an additional set of needs that, left unfulfilled, can actually reverse the positive effects of sex (for some women). Casual sex can make some women feel wildly depressed because they're "not good enough for a relationship" even if no guy has directly rejected them. Sex with a partner for the first time can leave a woman unsatisfied because the guy has no idea how to please her - which is another reason why women seek long-term relationships. The necessary communication skills for good sex are also something that develops in a relationship.

Having sex can actively prevent a woman from FINDING a relationship, if she's doing it with someone who is uninterested in a relationship. It can feel like she's wasting her time - we all know she's on a clock - both biological and looks-wise.

In many situations, once two people have had sex, the question of whether and when they'll have it again is constantly present. Women may avoid this in order to not have to deal with being hassled for sex.

The dirtiest secret? People who are out of practice at sex are not as good. ESPECIALLY GUYS, though probably no woman will say that to your face. Sex is exercise, and requires a certain amount of stamina (which is another reason people don't have sex - they're tired). Most of the muscles a woman uses during sex can be maintained with special exercises, but men don't have equivalent exercises. Once a woman has figured this out, she generally wants to have sex with someone who will be around long enough for her to actually reap all the benefits mentioned above (ie. many of them don't happen without orgasm).

Let's be honest, sex is great, and in a long-term relationship, many women are happy to have lots of it. I think the question that needs to be researched is how men can be better one-time lovers. Cause being good at that would up their ability to get laid, and single women everywhere to have orgasms without having to work as hard on the winnowing process.

April: I remember seeing The Female Brain in a bookstore and considered buying it -- hey, what a better way to understand (trick?) women than to know their neurobiolgy, right?

Then, a few things raised red flags.

First, the "how often men think about sex" thing. I hit that passage when browsing the book, and IIRC it was uncited, and seemed to be repeating an urban legend that the author was unqualified to comment on or substantiate. She is, after all, an MD, not a PhD.

Second, her prose was more devoted toward finding metaphors than passing information. I read a passage that said something like "women have an eight-lane superhighway for processing emotion, while men have an abandoned dirt road". What practical things does emotional processing mean, that I can make use of? She doesn't clarify this long-cited difference between men and women.

Finally, on the teenage and mating sections, she again seemed deliberately vague and brief, like she wanted to avoid mentioning anything that could translate into better appealing to a woman's brain.

My assessment: A dumbed down book that churns up unsubstantiated popular wisdom.

I also want to comment on the "women want sex as much as men". Insofar as intersubjective utility comparisons are possible, this one is extremely hard to justify. There are several watermarks such a statement would have to satisfy to be true, and it fails them. Example: is it possible for a man to find a woman desirable enough to date, but not have sex with? Does the reverse hold for women?

The difference between male and female sex drives is a matter of elementary evolutionary psychology, but the idea that human women may not want as much sex as they could benefit from is a matter of more advanced evolutionary psychology. There are two forces at work here:

1) Female reluctance as a signal of trustworthiness, the old madonna/whore dichotomy. If she's reluctant to mate with you even though she seems to like you, hopefully she'll be reluctant to mate with anyone else after you're a couple. (Standard ev-psych.)

2) If it's an ancestral invariant that men are always pushing, women may evolve psychological desires to push back. Think of it as a kind of arms race. (My own idea.) This implies the startling notion that men would have sex more often than is optimal for reproducing, in the absence of womanly resistance; symmetrically around the idea that women would have less sex than the female reproductive optimum, in the absence of manly advances.

Then if women gain an ancestrally anomalous degree of power - are less likely to be forced into sex by male violence, or the need for support - if women generally assume the status of citizens rather than chattel - we should expect the amount of sex to drop below even the female reproductive optimum. As for the psychological optimum or medical optimum, I'm not sure that's a question that evolutionary psychology can answer directly, but it's not surprising that there isn't enough sex.

Other nonancestral forces at work include:

3) Video games.

4) Exhausting "day jobs".

5) Back in the old days, half the men killed themselves in fights over women (inside their own tribe, or trying to steal women from other tribes). Polygyny is an institution in most hunter-gatherer bands.

So I can't call the undersupply of sex "inexplicable".

I'm skeptical of the "6 minutes" or "1 minute" claims about men thinking about sex. I'm almost positive I don't think about sex while I'm reading say a Dennett book. It seems that any sort of poll or counting device would be self biasing. Secondly it's just this sort of titillating factoid people love to repeat regardless of its validity.

Kristen: Would you say general fitness has direct carry over to sexual performance? Say Man A lifts weights rigorously, is involved in a grappling sport and runs often. I would think the VO2 max, positional awareness from the grappling and the strength from the lifting would all transfer well. Man B who is sedentary or only runs may not have as much applicable skills and fitness.

Also, men do have specific exercises. http://en.wikipedia.org/wiki/Kegel_exercise#Benefits_for_Men

This isn't my idea of course but it is often said that "sex robots" may one day provide a lot of sex for men and women for the health benefits and the fun without the STDs or various emotional problems and sourcing difficulties.

One obvious problem with the "scarcity of sex" hypothesis is that much sexual activity occurs in unsafe ways which result in substantially increased STD load. Anecdotally, various kinds of risk- and sensation-seeking behavior seem to be correlated with sex drive and/or sexual attractiveness. I'm not dismissing the inefficiency claims outright, but the situation is more complex than it may at first appear.

All, I'm not saying that the various explanations offered are wrong, but since we don't seem to agree we could benefit from figuring out which explanations are really the main ones. The various "men are incompetent", emotionally or physically, theories would be quite surprising if true, as training would seem to offer a dramatic resolution.

Yes! More sex for all! Now, no health problem short of having my genitals severed would stop me from having sex. Secondly, women do love sex and think about it quite often. I don't know how this study that showed women thinking about sex once a day vs men thinking about it once a minute was done, but its a bunch of crap. I am a man (could you tell?) and I don't think about sex once a minute. It all depends on many factors - if my mind is occupied with work or allowed to idly wander, whether or not I had tossed one off recently, whether or not I have a new girlfriend... I guarantee you that a healthy woman that recently started going out with a healthy man she really likes is going to be thinking about sex at least every 5 minutes. Same goes for men, but men are more willing to engage in promiscuous activities, so they're more liable to daydream randomly about such stuff - such is their nature. So yeah, the right conditions must be present, but it doesn't change the fact that women love sex just as much as men do. The difference is in how they go about choosing a mate.

Also, if you have migraines - definitely get laid! I went out with a girl who had chronic migraines, and the only thing that seemed to help that was love's passionate embrace...

Very good joke! And like most really good jokes, it has that core of observed truth too. And then you get assailed by readers who took you seriously!

Would Jesus laugh or weep?

"I'm skeptical of the "6 minutes" or "1 minute" claims about men thinking about sex."

You're not the only one. To me, it is much akin to telling someone they are now breathing manually (which you now are hahahaha!). It's kind of self fulfilling. I'm thinking about sex right now, and I'll probably think about it frequently for at least the next few minutes since that's what this post was about. So, given that, I can see how it could seem like I think about sex a lot more often than I actually do.

While, I'm thinking about this, how would you even measure this? Much like trying to measuring the amount of time I spend breathing manually each day would be nearly impossible to measure because I would pretty much ALWAYS be breathing manually if I knew the measurement was being done, I would probably ALWAYS be thinking about sex if I knew I was supposed to write down every time I thought about it. I must confess I've never even looked at any studies on this sort of thing, are there any credible ones? And if so how did they manage to come up with numbers that didn't have this problem? Maybe there is some sort of technology that I'm not aware of that can detect sexual thoughts?

I don't put much stock in personal anecdotal evidence (since it can be made up on a whim), but I'm 99% certain I didn't think about sex at all when I was Christmas shopping today, and I was doing that for like 4 and a half hours! I don't even know how I could have gotten anything done if every minute or two I thought about sex. I'd like to think most other guys are the same way and I'm not the one lone weirdo who doesn't always have sex on the brain. Sure we'll think about sex if someone says the word or if an attractive woman walks by in a revealing outfit, but by and large I think we are plenty capable of focusing on something non-sexual for more than a minute.

Example: is it possible for a man to find a woman desirable enough to date, but not have sex with? Does the reverse hold for women?

One of the reasons intersubjective utility comparisons are impossible in principle and even approximations are hard in practice is that most of our preferences are multi dimensional.

For this question to be a useful heuristic, there have to a largely linear scales of desirability and date-ability and what we're interested in on dates that all mesh together pretty closely. I don't think this holds for either gender. Often I have been interested enough to ask someone out or chat them up before I could really know whether I would want to have sex with them. And yes, sometimes it has turned out that I do not wish to, so you have one example.

And I have known few women who would call a get-together a "date" unless they were at least considering a potential sexual encounter. I have almost certainly self-selected for companions with similar sexual appetites, but in my experience there has not been a great deal of difference between me and the women I have chosen to have relations with in our average levels of desire. What differences arise are usually due to circumstance (health, stress, etc.) and can swing the other way when circumstances change.

I'm reminded of "Only those with souls worry over whether or not they have them." Only those who aren't getting enough worry about how much they should (scientifically) be getting.

Michael - sounds like you have enough experience in the field to consider publishing a study soon!

Since this is partly an economics blog I'm surprised no one has mentioned that the fastest way to increase access to sex would be to let people pay for it. Legalised prostitution might disproportionately benefit men, since they seem to be overrepresented in the undersexed portion of the population; so, has anyone compared rates of diseases correlated with lack of sex in men (heart attack and stroke) in states that allow prostitution versus states that do not? I predict we would see lower rates of heart attacks and stroke among men in states in which it was legal.

As to Pablo Stafforini: "As for fixing it, here is one promising approach." It may be my warped imagination, but are you suggesting that we induce homosexuality in order to increase availability of willing sexual partners? If so I think you are equal parts brilliant and twisted.

Such a long post, and I've not said anything stupid. I like this topic.

I'm still firmly on the fence as to whether there is a national sex shortage....I hope there will be more blog entries and discussion on the topic.
As to whether there is a shortage of research on the subject.....I'm not sure we OB writer/ readers would know. I did a quick search on pubmed and found a few articles on sexual frequency. There do seem to be serious constraints related to data. Most research is based on household surveys that only collect data on marital (or cohabitating) sex. From those data sets there are some well established correlations - which may provide some ideas what is causing the (possible) sex shortage
Some, perhaps interesting, correlations: age; having small children; and, being unhappily married, all reduce sexual frequency.

Whereas, cohabitating; having cohabitated before marriage; and, being in a second or later marriage
all increase sexual frequency.
Link to article

Another interesting study on sexual frequency (with an admittedly tiny data set) among the very wealthy found that very wealthy women had a lot more (and better) sex than the non-wealthy. Men didn't show such a difference. (I originally found this piece via Marginal Revolution).

so, some (mostly humourous) ideas about how to bump us up to a higher equilibrium: tax marriage (or subsidize cohabitation), even better, tax at high rates bad marriages. and redistribute all the revenue brought in to women.


Sex with a partner for the first time can leave a woman unsatisfied because the guy has no idea how to please her - which is another reason why women seek long-term relationships. The necessary communication skills for good sex are also something that develops in a relationship.

As a man, I'm not sure why this marks women as particularly different. If I had sex with somebody and we had no idea of how to please each other, I'd sure be left unsatisfied as well. I had a "so why's this supposed to be so exclusive to women?" reaction to most of your other points, as well.

(I acknowledge that I'm hardly a typical male, but I find it difficult to assume that most men would be that different, at least in the example I quoted.)

Interesting question: not sure how you'd answer it. My first thought is that women (and some men) derive power/status from refusing sex.

The other comment about male homosexual sexual frequency brings up the obvious question: what's the lesbian frequency? I don't have access to PubMed. . .

I'll start with a disclaimer saying that I wouldn't be able to clearly explain what I'm saying and apologizing for broadly terming most of the responses as not addressing the actual issues.

I think of all the people referred to or written in the post, only what Eliezer says is a theory which actually addresses the real issue. I think he's talking about the disease while others are talking about the symptoms.

Bertrand Russell's 'Marriage and Morals' discusses the practical issues very well and Robert Wright's 'The Moral Animal' explains the issues in the light of evolutionary psychology superbly. These two books give the idea clearly on what I am unable to explain. The topic being one which would easily takes us in directions which wouldn't be fruitful, I think currently the way evolutionary psychology looks at it keeps it as scientific as possible.

Eliezer, your second point is interesting. Where did you get this idea from? Like, does it have a parallel with some other theory? But how is this different from feminism, which was the outcome of women's desire to push back?

Kinsey's work is admirable for how it destigmatized sexual expression, but his data-gathering was famously flawed. So while the results of his research may have dampened the good old carnal guilt in those prone to it, they also made a whole lot of people feel "below average" -- undeservedly, it appears.

The topic being one which would easily takes us in directions which wouldn't be fruitful, I think currently the way evolutionary psychology looks at it keeps it as scientific as possible.

Note that much of evolutionary psychology is a collection of "just so" stories with extremely dubious theoretical support.

For one thing, if the "madonna-whore dichotomy" was evolutionarily relevant one would expect impulsivity and untrustworthiness to be inversely related to sex drive, as agents with low future focus and impulse control would develop low sex drive as a crude commitment mechanism. Conversely if the reverse were true (which jives with existing evidence) then chastity would be socially desirable as a signal of responsibleness and self-discipline: but this would be a matter of social norms, not an evolutionary result.

All this talk about sex is making me hungry. But I have to say that April has hit the nail on the head.

Sex is dangerous, especially for women. At least, it has been through most of our evolutionary history, which has shaped our attitudes and behaviour. Anyone doubting this need only visit old graveyards, where there are large numbers of graves for women who died around twenty years of age. The main cause of death in that age group was childbirth. Modern medical practice has substantially improved the odds of surviving childbirth, to the point that most of those posting here seem ignorant of the historical risks.

I claim this is relevant in any analysis of the so-called inexplicable shortage of sex.

But isn't the question why there's a shortage of sex now, not why there was in the 19th century?

Nick: adaptation-executers, not fitness-maximizers.

But isn't the question why there's a shortage of sex now, not why there was in the 19th century?

You're missing the point. Sex has been dangerous to women for most of our evolutionary history. Even ignoring the metabolic costs of pregnancy and the various costs of taking care of a child alone, childbirth has been very risky for humans. Women are (on average) not designed to maximize their sexual encounters. Men (on average) are.

It's more complex than that, but it goes a long way toward explaining why people aren't having sex as often as they can.

Being a newcomer to the blog, I've been reading past posts. This is one that caught my attention, since my practice was limited to the field of sexual medicine for over 20 years. It seems inadequately discussed. Richard Feynman once defined "science" as belief in the ignorance of experts. With this in mind, I would say this post and the comments are pure science (I'd put a little smiley face here, but that's just not me).

The question addressed is "why we have too little sex". An implied question is "why have men evolved to desire sex more than women?"

First, the answer is not the physiology of achieving orgasm. Given equal arousal states, clitoral stimulation produces orgasm as quickly and reliably as penile stimulation. And why shouldn't it? The clitoris *is* the penis. And the mysterious "G-spot" is the clitoral crura. The penile crura are the reason that male perineal massage is pleasant, i.e., the "male G-spot". A blastocyst of totipotential stem cells has all the same stuff, save the sex chromosomes, no matter which gender it becomes. Here's a brief embryologic discussion. "There are no surprising facts, only models that are surprised by facts; and if a model is surprised by the facts, it is no credit to that model". - Eliezer Yudkowsky.

Second, male and female orgasms have different evolutionary roles. The male orgasm is tied to reproduction; the female orgasm is a vestigial male function (the reverse is nipples in men). In spite of the hundreds of references to increased fertility in orgasmic women, and the howling of feminist leaders, it just ain't so. Dr. Elisabeth Lloyd has made that abundantly clear in her research of evolutionary psychology here. In this discussion, she is the giving the answers about some "evidence" that female orgasm leads to fertility . Lloyd states: "We have many decades of sex research, most into reproduction, fertility, and their ties to sexuality, which failed to produce any evidence linking (female) orgasm to fertility." The American Society for Reproductive Medicine does not mention female orgasm at all.

My point is that orgasm, you know, the part that feels *really good* for both genders, has a genetic role for males and a memetic role for females. Ask Shere Hite. Richard Dawkins: "We are survival machines--robot vehicles blindly programmed to preserve the selfish molecules known as genes." How has that memetic evolution changed things? Paleontologist, Stephen J. Gould asked, “How can we possibly know in detail what small bands of hunter-gatherers did in Africa two million years ago?" Perhaps the best way is to look at the sexual customs of bonobos, where the females have more sex than the stronger males, primarily because they have it with other females as well, both for bonding and for specific pleasure. Look how "evolved society" has cheated us!

Richard Dawkins also has observed :"In a universe of blind physical forces and genetic replication, some people are going to get hurt, other people are going to *get lucky* (my emphasis), and you won't find any rhyme or reason in it, nor any justice. The universe we observe has precisely the properties we should expect if there is, at bottom, no design, no purpose, no evil and no good, nothing but blind pitiless indifference."

Here's hoping we "get lucky".

Above comment was screened as spam b/o too many links. Mr. Yudkowsky kindly put it back up.

I hope you post this excellent comment to your blog, too.

I don't think that the theory Elisabeth Lloyd promotes is credible. She writes a book about scientific bias - while claiming her own role is "continuing to fight for definitions of women that are not based on their reproductive roles" (pg. 237).

Ironically for a book with the subtitle “bias in the science of evolution,” The Case of the Female Orgasm is marinated in bias: against “adaptationism,” “androcentric thinking,” and heterosexuality, and in favor postmodernist “social constructivism” as well as anything ever written by Stephen Jay Gould.

- Let a Thousand Orgasms Bloom! A review of The Case of the Female Orgasm, by Elisabeth A. Lloyd. .

Sorry if I was unclear. I'm not the least interested in Dr. Lloyd's gender-biased ideas about psychologic evolution. I was using her as an example of a well-informed researcher who has reviewed the evidence and found none credibly supporting the idea of female orgasm enhancing fertility. With today's wonderful data-searching tools, anyone who understands the vocabulary can perform an equally convincing survey of the literature from Starbuck's. I would have used my own name as an authority, rather than hers, but I'm trying to back away from arrogance in the autumn of my life.

I don't know about "enhancing fertility" - but the idea that female orgasm is "a vestigial male function" (as you claimed) seems very unlikely. Orgasms are obviously expensive - whereas male nipples are not. That suggests that they have been retained because of the positive value they provide.

Assessment of male quality is one obvious possibility: e.g. see Female orgasm rate increases with male dominance in Japanese macaques.

Tim: At the risk of getting my name on the comment list too frequently, let me respond once more, and then perhaps we could discuss the issue on my blog, where there is no limit to the BS.

The article you referenced about Macaca fuscata concludes that female orgasms are most likely when a low-ranking female has sex with a high-ranking male, and least likely when a high-ranking female has sex with a low-ranking male. One wonders: did any grant money go into this research? We of the intelligentsia call this the "Donald Trump Syndrome". Conversely, impecunious janitors, however well-motivated toward their fellow humans, ain't gettin' any from Victoria Secret models.

Seriously, as was noted, we're all the same in the blastocyst stage. We've got everything they've got, and vice versa. From there on, it's just phenotypia. There's no extra expense for female orgasms at all. Because we have evolved a system of toti-potentiality in the early stages of embryonic development, it has to be hard-wired from the start. If the genes "want" it to be present in males, the embryologic device requires that it be present in females at no extra charge, even if it has no demonstrable genetic purpose.

If the genes "want" it to be present in males, the embryologic device requires that it be present in females at no extra charge, even if it has no demonstrable genetic purpose.

Right - but it can be present the same way that antlers are present in females - i.e. hardly at all.

Call me a panadaptationist, but male nipples don't seem like a good example of what a vestigal feature (which owes its existence to embryological developmental constraints) looks like, either. In rats, mice and horses, male nipple development is completely suppressed by male sex hormones. However many other male mammals have nipples - and they often contain a rich supply of sensory nerves and erectile tissue. Common sense suggests that they have a role in sensing, generating and signalling arousal.


Once a supposedly evidence-based discussant begins with, "Common sense suggests ... ", it's time to stop listening. Dr. Hanson's post invited discussion of the premise "there is an inexplicable shortage of sex," and the implied difference between male and female sex drive. I have strained, but I cannot find anything in any of your comments that addresses this issue.

As noted, I am new to blogs. Apparently there is some cliche about how many comments will be made before the word "Hitler" is used; am I remembering correctly? Has anyone ever posted an analysis on a sophisticated blog such as this one about how many comments it takes before there is no mention of the original subject, such as Mr. Tyler's? For instance, on this thread there are 41 (now 42) comments. Excepting this one, and three others, all discussants address some aspect of the original topic. The three that do not are all by the same author.

As to the question of current sexual research, our professional society is the International Society for Sexual Medicine, begun in 1982 as the International Society for Impotence Research, and broadened to include all male and female sexual issues. Here is the home page. Damn! I got back on topic!

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