There must be something in the water here in Lanesboro, Minnesota, because last night I dreamt of an encounter with a very muscular African-American centaur, an orgiastic experience with – gasp – drunken members of the opposite sex and (as if that weren’t enough) then being asked by my hostess to wear a white wedding dress while giving a scientific keynote presentation. “Does it make me look too feminine?” “Not at all,” she assured me, “it’s a man’s dress.”

Now Freud might raise his eyebrows at such a lurid dreamscape, but if these images represent my repressed sexual yearnings, then there’s a side of me that I apparently have yet to discover. But I doubt that this is the case. Dreams with erotic undertones are like most other dreams during REM sleep—runaway trains with a conductor who is helpless to do anything about the surrealistic directions they take. Rather, if you really want to know about a person’s hidden sexual desires, then find out what’s on his or her mind’s eye during the deepest throes of masturbation.

This conjuring ability to create fantasy scenes in our heads that literally bring us to orgasm when conveniently paired with our dexterous appendages is an evolutionary magic trick that I suspect is uniquely human. It requires a cognitive capacity called mental representation (an internal “re-presentation” of a previously experienced image or some other sensory input) that many evolutionary theorists believe is a relatively recent hominid innovation.

When it comes to sex, we put this capacity to very good—or at least, very frequent—use. In a now-classic, pre-Internet-porn (I’ll get to that later on) study by British evolutionary biologists Robin Baker and Mark Bellis, male university students were found to masturbate to ejaculation about every 72 hours, and “on the majority of occasions, their last masturbation is within 48 hours of their next in-pair copulation.” If they’re not having intercourse every day, that is to say, men tend to pleasure themselves to completion no more than two days prior to having actual sex.

Baker and Bellis’s quite logical argument for this seemingly counterintuitive state of affairs (after all, shouldn’t men try to stock up as much sperm as possible in their testes rather than spill their seeds so wastefully in a rather infertile swath of toilet paper or a dirty sock?) is that because there is a “shelf-life” for sperm cells – they remain viable for only 5-7 days after production – and because adult human males manufacture a whopping 3 million sperm per day, masturbation is an evolved strategy for shedding old sperm while making room for new, fitter sperm. It’s quality over quantity. Here are the adaptive logistics.

The advantage to the male could be that the younger sperm are more acceptable to the female and/or are better able to reach a secure position in the female tract. Moreover, once retained in the female tract, younger sperm could be more fertile in the absence of sperm competition [sexually monogamous relationships] and/or more competitive in the presence of sperm competition [in which the woman is having sex with other men]. Finally, if younger sperm live longer in the female tract, any enhanced fertility and competitiveness would also last longer.

Unconvinced? Well, Baker and Bellis are clever empiricists. They also apparently have stomachs of steel. One way that they tested their hypotheses was to ask over 30 brave heterosexual couples to provide them with some rather concrete samples of their sex lives: the vaginal “flowbacks” from their post-coital couplings, in which some portion of the male’s ejaculate is spontaneously rejected by the woman’s body.

The flowback emerges 5-120 min after copulation as a relatively discrete event over a period of 1-2 min in the form of three to eight white globules. With practice, females can recognize the sensation of the beginning of flowback and can collect the material by squatting over a 250 ml glass beaker. [And here comes a useful tip, ladies…] Once the flowback is nearly ready to emerge, it can be hastened by, for example, coughing.

As the authors predicted, the number of sperm in the girlfriends’ flowbacks increased significantly the longer it had been since the boyfriend’s last masturbation -- even after the researchers controlled for the relative volume of seminal fluid emission as a function of time since last ejaculation (the longer it had been, the more ejaculate was present). If only the parents of teenage boys had these findings available for the first hundred thousand years of our history, think of all the anxiety, guilt and shame that might never have been.

In fact, even the father of adolescent psychology research, G. Stanley Hall, had a particularly nasty thorn in his paw when it came to the subject of masturbation. Hall accepted that spontaneous nocturnal emissions (that is, “wet dreams”) in adolescent boys were “natural,” but he viewed masturbation as a “scourge of the human race … destructive of that perhaps most important thing in the world, the potency of good heredity.” In Hall’s view, the offspring of teenage masturbators would show signs of “persistent infantalism or overripeness.” Boys will be boys, Stanley, and how wrong you were.

Now back to masturbation fantasies and cognition—and this is where it gets really interesting. Baker and Bellis’s theory may be peculiarly true for human beings, because from all appearances, under natural conditions, we are the only primate species that seems to have taken these seminal shedding benefits into its own lascivious hands. Unfortunately, there have been a paltry handful of studies tracking the masturbatory behaviors of nonhuman primates. Although some relevant data is probably buried in some mountain of field notes, I didn’t come across any targeted studies on the subject in wild chimpanzees , and even the prolific Jane Goodall doesn’t seem to have ever gone there. But nevertheless by all available accounts, and by contrast with human beings, masturbation to completion is an exceedingly rare phenomenon in other species with capable hands very much like our own. As anybody who has ever been to the zoo knows, there's no question that other primates play with their genitalia; the point is that these diddling episodes so seldom lead to an intentional orgasm.

In a 1983 study from the International Journal of Primatology , the sexual behaviors of several groups of wild gray-cheeked mangabeys were observed for over 22 months in the Kibale Forest of Western Uganda. There was plenty of sex, particularly during the females’ peak swellings. But just two incidents of male masturbation leading to ejaculation were observed. Yes, that’s right. Whereas healthy human males can’t seem to go without masturbating for longer than 72 hours, two measly cases of masturbating mangabeys were observed over a nearly two-year period.

University College London anthropologist E.D. Starin didn’t have much luck spying incidents of masturbation in red colobus monkeys in Gambia, either. In a brief 2004 article published in Folia Primatologica , Starin reports that over a 5.5-year period of accumulated observations totalling more than 9,500 hours, she saw only 5–count ‘em, five –incidents of her population of five male colobus monkeys masturbating to ejaculation, and these rare incidents occurred only when nearby sexually receptive females were exhibiting loud courtship displays and copulations with other males.

Intriguingly, Starin says that although females weren’t in the immediate vicinity, it is possible that the females could still be seen or heard by the masturbating male while the incident at hand occurred. (In other words, no mental representation required.) In fact, the author’s descriptions of these events strike me as producing accidental, rather than deliberate, ejaculations. Not that they weren’t happy accidents, but still. “During each observation,” Starin writes, “the male sat and rubbed, stretched, and scratched his penis until it became erect, after which additional rubbing produced ejaculate.” I know what you’re thinking: What did the monkeys do with the “product”? Well, they ate their own ejaculate—and in one case, a curious infant licked it off the adult’s fingers. Also, out of the 14 female colobus monkeys observed during this time span, “three different females were observed possibly masturbating” by self-stimulating their genitals—only possibly because none of these episodes culminated in the telltale signs of colobus orgasm: muscle contractions, facial expressions or calls.

Perhaps the most colorful report of nonhuman primate masturbation—or rather the astonishing lack thereof, even in subordinate males that aren’t getting any—comes from a 1914 Journal of Animal Behavior study by a primatological colleague of Robert Yerkes named Gilbert Van Tassel Hamilton, who apparently ran something of a monkey research center-cum-sanctuary on the lush grounds of his Montecito, California estate. Hamilton was clearly a pioneering sexologist, or at least had especially liberal attitudes for his time, defending the naturalness of homosexual behavior in the animal kingdom, among other things. In justifying his research, which meant getting up close and personal with his monkeys’ genitals, Hamilton opines:

The possibility that the types of sexual behavior to which the term ‘perverted’ is usually applied may be of normal manifestation and biologically appropriate somewhere in the phyletic scale has not be sufficiently explored.

In fact, he seems to have expected to find rampant masturbation in his animals, but to his surprise only one male (named Jocko) ever partook in such manual pleasures:

Of all my male monkeys only Jocko has been observed to masturbate. After a few days confinement he would masturbate and eat part of his semen. I have reason to believe that he lived under unnatural conditions for many years before I acquired him. In view of this fact that not one of seven sexually mature monkeys masturbated after several weeks of isolation under conditions that favored a fairly healthy mental and physical life (close proximity to other monkeys, large cage, warm climate) I am inclined to believe that masturbation is not of normal occurrence among monkeys.

Granted, Hamilton seems to have been a tad eccentric. Earlier in the article he reports that one of his female monkeys named “Maud” liked to be mounted (and entered) by a pet male dog out in the yard until one day poor, horny old Maud offered her backside to a strange mongrel that proceeded to bite off her arm. More disturbing is Hamilton’s description of a monkey named “Jimmy” who one sunny afternoon discovered a human infant lying in a hammock: “Jimmy promptly endeavoured to copulate with the infant,” observes Hamilton matter-of-factly. It’s unclear whether or not this was the author’s own child, nor is there any mention of the look on said human infant’s mother’s face when she saw what Jimmy was getting up to.

In any event, though he may have had some questionable child supervision skills, the candor by which Hamilton reports on the sex lives of his monkeys lends his non-observations of masturbation that much more credence.

So why don’t monkeys and apes masturbate even nearly as much as humans? It’s a rarity even among low status male nonhuman primates that frustratingly lack sexual access to females–in fact, the few observed incidents seem to be with dominant males. And why haven’t more researchers noticed such an obvious difference with potentially enormous significance for understanding the evolution of human sexuality? After all, it’s been nearly 60 years since Alfred Kinsey first reported that 92 percent of Americans were involved in masturbation leading to orgasm.

The answer for this cross-species difference, I’m convinced, lies in our uniquely evolved mental representational abilities—we alone have the power to conjure up at will erotic, orgasm-inducing scenes in our theater-like heads … internal, salacious fantasies completely disconnected from our immediate external realities. One early sex researcher, Wilhelm Stekel, described masturbation fantasies as a kind of trance or altered state of consciousness, “a sort of intoxication or ecstasy, during which the current moment disappears and the forbidden fantasy alone reigns supreme.”

Go on, put this article aside, take a five minute break and put my challenge to the test (don’t forget to close your office door if you’re reading this at work): Just try to masturbate successfully—that is, to orgasmic completion—without casting some erotic representational target in your mind’s eye. Instead, clear your mind entirely, or think of, I don’t know, an enormous blank canvass hanging in an art gallery. And of course no porn or helpful naked co-workers are permitted for this task either.

How’d it go? Do you see the impossibility of it? This is one of the reasons, incidentally, why I find it so hard to believe that self-proclaimed asexuals who admit to masturbating to orgasm are really and truly asexual. They must be picturing something , and whatever that something is gives away their sexuality.

Empirically capturing the phenomenology of masturbation fantasies is no easy matter. But some intrepid scholars have indeed tried to do so. A British physician named N. Lukianowicz, in a 1960 issue of the Archives of General Psychiatry , published one of the most sensational scientific reports I’ve ever had the pleasure of reading. Lukianowicz personally interviewed 188 people (126 males and 62 females) about their masturbation fantasies. An important caveat: all of these people were psychiatric patients with “various complaints and different neurotic manifestations,” so their masturbation fantasies aren’t necessarily typical. Nevertheless the details provided by these patients about their erotic fantasies give us an extraordinary glimpse into the rich internal imagery accompanying human masturbation. Consider the self-report of a retired civil servant, age 71, being treated for obsessive feelings of guilt on account of his “excessive masturbation”:

I see in front of me naked beautiful women, dancing and performing some most exciting and tempting movements. After the dance they lean back, and keeping their legs wide apart, show their genitals and invite me to have sexual intercourse with them. They appear so real, that I can almost touch them. They’re in a setting of an oriental harem, in a large oval room with divans and a lot of cushions around the walls. I can clearly see the wonderful gorgeous colours and the beautiful patterns of the tapestry, with an unusual vividness and with all the minute details.

Or consider Lukianowicz’s account of a 44-year-old schoolmaster’s fantasies, which reads like some Bacchanalian, morphine-dappled scene ripped from the pages of William Burroughs’s Naked Lunch (1959):

In them he “saw” naked adolescent boys with their penes stiffly erected, parading in front of him. As he progressed in his masturbation, the penes of the boys increased in size, till finally the whole field of his vision was filled with one huge, erect, pulsating penis, and then the patient would have a prolonged orgasm. This type of homosexual masturbatory fantasy started shortly after his first homosexual experience, which he had had at the age of 10, and it persists unchanged hitherto.

Now, obviously, there are pathological cases of chronic masturbation where it actually interferes with the individual’s functioning. In fact, it’s not an uncommon problem for many caretakers of adolescent and adults with mental impairments, whose charges often enjoy masturbating in public and making onlookers squeal and squirm in discomfort. (Not unlike some captive primates housed in miserable conditions such as laboratories or roadside zoos, where self-stimulation sometimes becomes stereotypical.) But one thing that clinicians dealing with this problem may wish to consider is that the individual’s cognitive limitations may not allow them to engage in more “appropriate” private masturbation because of difficulties with mental representation. In fact, frequency of erotic fantasies correlates positively with intelligence. The average IQ of Lukianowicz’s sample was 132. So perhaps public masturbation, in which other people are physically present to induce arousal, is the only way that many with developmental disorders can achieve sexual satisfaction. Sadly, of course, society isn’t very accommodating of this particular problem: Between 1969-1989, for example, a single institution in the United States performed 656 castrations with the aim to stop the men from masturbating. One clinical study reported some success in eliminating this problem behavior by squirting lemon juice into the mouth of a young patient every time he pulled out his penis in public.

In any event, Lukianowicz argues that erotic fantasies involve imaginary companions not altogether unlike children’s make-believe friends. But unlike the more long-lived latter, he concedes, the former is conjured up for one very practical purpose: “… as soon as the orgasm is achieved the role of the imaginary sexual partner is completed, and he is quite simply and quickly dismissed from his master’s mind.”

And, perhaps not surprisingly, men seem to entertain more visitors in their heads than do women. In a 1990 study published in the Journal of Sex Research , evolutionary psychologists Bruce Ellis and Donald Symons found that 32 percent of men said that they’d had sexual encounters in their imagination with more than 1,000 different people, compared to only 8 percent of women. Men also reported rotating in from their imaginary rosters one imagined partner for another during the course of a single fantasy more often than women did.

In their excellent 1995 Psychological Bulletin article on sexual fantasy, University of Vermont psychologists Harold Leitenberg and Kris Henning summarize a number of interesting differences between the sexes in this area. In their review of research findings up to that date, the authors concluded that, in general, a higher percentage of men reported fantasizing during masturbation than did women. It’s important to point out, however, that neither “fantasy” nor “masturbation” were consistently defined across the studies summarized by Leitenberg and Henning, and some participants likely interpreted “masturbation” to mean simply self-stimulation (rather than orgasm-inducing ) or had a more elaborate conceptualization of “fantasy” than we’ve been using here, as some form of basic mental representation. For uncertain reasons, one dubious study compared “Blacks” and “Whites,” so it’s definitely a mixed bag in terms of empirical quality. They didn’t find much of a difference, by the way.

A side note: both sexes claimed equally to have used their imaginations during intercourse. Basically, at some point, everyone tends to imagine someone—or something—else when they’re having sex with their partner. There’s nothing like the question, “What are you thinking about?” to ruin the mood during passionate sex.

Here are some other interesting tidbits. Males report having sexual fantasies earlier in development (average age of onset 11.5 years) than do females (average age of onset 12.9 years). Females are more likely to say that their first sexual fantasies were triggered by a relationship, whereas males report having theirs triggered by a visual stimulus. For both men and women, straight or gay, the most common masturbation fantasies involve reliving an exciting sexual experience, imagining having sex with one’s current partner and imagining having sex with a new partner.

It gets more interesting, of course, once you step a little closer to the data. In one study with 141 married women, the most frequently reported fantasies included “being overpowered or forced to surrender,” and “pretending I am doing something wicked or forbidden.” Another study with 3,030 women revealed that “sex with a celebrity ,” “seducing a younger man or boy,” and “sex with an older man” were some of the more common themes. Men’s fantasies contain more visual and explicit anatomical detail (remember the giant, pulsating penis from Lukianowicz’s study?) whereas women’s involve more story line, emotions, affection, commitment and romance. Gay men’s sexual fantasies often include, among other things, “idyllic sexual encounters with unknown men,” “observing group sexual activity,” and here’s a shocker: images of penises and buttocks. According to one study, the top five lesbian fantasies are “forced sexual encounter,” “idyllic encounter with established partner,” “sexual encounters with men,” “recall of past gratifying sexual encounters,” and—ouch!—“sadistic imagery directed toward genitals of both men and women.”

One of the more intriguing things that Leitenberg and Henning conclude is that, contrary to common (and Freudian) belief, sexual fantasies are not simply the result of unsatisfied wishes or erotic deprivation:

Because people who are deprived of food tend to have more frequent daydreams about food, it might be expected that sexual deprivation would have the same effect on sexual thoughts. The little evidence that exists, however, suggests otherwise. Those with the most active sex lives seem to have the most sexual fantasies, and not vice versa. Several studies have shown that frequency of fantasy is positively correlated with masturbation frequency, intercourse frequency, number of lifetime sexual partners, and self-rated sex drive.

The Psychological Bulletin article on sexual fantasy is chockfull of interesting facts, and those with a more scholarly interest in this subject should read it themselves. Leitenberg and Henning also provide a fascinating discussion about the relation between sexual fantasy and criminality, including a clinical study in which deviant masturbatory fantasies were paired with the foul odor of valeric acid or rotting tissue. Now that’s enough to put a crimp in anybody’s libido, I’d say. But Leitenberg and Henning’s piece was written over fifteen years ago, summarizing even older research. The reason this is important is because it was still long before the “mainstreaming” of today’s Internet pornography scene, where zero is left to the imagination.

And so I’m left wondering … in a world where sexual fantasy in the form of mental representation has become obsolete, where hallucinatory images of dancing genitalia, lusty lesbians and sadomasochistic strangers have been replaced by a veritable online smorgasbord of real people doing things our grandparents couldn’t have dreamt up even in their wettest of dreams, where randy teenagers no longer close their eyes and lose themselves to the oblivion and bliss but instead crack open their thousand-dollar laptops and conjure up a real live porn actress, what, in a general sense, are the consequences of liquidating our erotic mental representational skills for our species’ sexuality? Is the next generation going to be so intellectually lazy in their sexual fantasies that their creativity in other domains is also affected? Will their marriages be more likely to end because they lack the representational experience and masturbatory fantasy training to picture their husbands and wives during intercourse as the person or thing they really desire?

I’m not saying porn isn’t progress, but I do think that over the long run it could turn out to be a real evolutionary game-changer.

In this column presented by Scientific American Mind magazine, research psychologist Jesse Bering of Queen's University Belfast ponders some of the more obscure aspects of everyday human behavior. Sign up for the RSS feed, visit www.JesseBering.com, friend Dr. Bering on Facebook or follow @JesseBering on Twitter and never miss an installment again. For articles published prior to September 29, 2009, click here: older Bering in Mind columns. Jesse's first book, The Belief Instinct (Norton) [The God Instinct (Nicholas Brealey) in the U.K.], will be published early February, 2011.



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