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It is truly amazing just how much you can put up with when you are getting regular sex.

NIGEL SLATER, Toast (2004)

Sexy beasts

Sex may be blissful, but biologists are still not sure why it evolved in the first place. It is, after all, a strange way for animals to reproduce themselves, if you think about it. In their efforts to understand the evolution of sexual behaviour, biologists have paid surprisingly little attention to the role of pleasure. This may be because, in the natural world, sex is mostly about procreation rather than fun. Even among the big-brained mammals, most females are interested in sex only when they are fertile, around the time of ovulation. They may copulate frequently and energetically during these fertile phases, but sex is unlikely to be the main source of pleasure in their lives. Much the same must be true of many male mammals, for whom the sexual act can be remarkably brief. Rabbits and rams, for example, usually ejaculate within a few seconds of starting intercourse.

We humans belong to a small coterie of species in which sexual behaviour is not biologically shackled to reproduction. Our willingness or desire for sex has little to do with female fertility. We may have sex more or less throughout the menstrual cycle and carry on doing it during pregnancy and after menopause. Most human sexual activity takes place when reproduction is impossible, and in that sense it is largely recreational. Dolphins share this unusual characteristic with us, as they too continue to have sex throughout the female’s reproductive cycle. Dolphins are also enthusiastic practitioners of masturbation, as we shall see in chapter 10. However, our main rival for the title of sexiest beast on the planet is the bonobo (Pan paniscus), a species of African ape that looks very similar to the chimpanzee.

Bonobos are our closest biological relatives. They live in the dense and inaccessible rainforests of the central Congo basin, which makes it difficult for biologists to study them in the wild. One of their many attractive characteristics, besides being very intelligent and highly sociable, is that they have a lot of recreational sex. Several times a day is normal, under the right conditions. Like us, they remain sexually active regardless of whether the female is fertile and they have an extensive sexual repertoire. In addition to conventional male – female intercourse, bonobos go in for male – male and female-female couplings, group sex, masturbation, oral sex and kissing with tongues. Female bonobos often have close encounters with other females: after embracing each other, one female lies on her back, the other climbs on top and they vigorously rub their genitals together. Biologists refer to this as ‘g – g-rubbing’, as in genital – genital. Just about the only form of sexuality that bonobos do not regularly indulge in is copulating with their own children.

Bonobos are not the only primates to engage in girl-on-girl action. Female stump-tailed macaques also achieve orgasms through female-female couplings, just as they do from having sex with males. We know this thanks to scientists who secreted miniaturised radio-telemetry equipment in hard-to-reach places in the monkeys’ anatomy. Measurements obtained in this way from stump-tailed macaques while they are having sex have revealed that their orgasms involve much the same profile of physiological changes as those observed in human females, including intense uterine contractions and sharp increases in heart rate. Other female primates have their own ways of enhancing sexual pleasure. For instance, female sooty mangabeys, a species of monkey from West Africa, sometimes use their hands to stimulate their own genitals while they are having sex.

In bonobo society, females often dominate males, initiate sex and form powerful coalitions. Female bonobos exercise a lot of control over when, how and with whom they have sex. They use sex as a social tool as well as a source of pleasure. When two unfamiliar tribes of bonobos encounter each other in the forest, females from each tribe will often initiate sex with males from the other tribe as a way of breaking the ice. Perhaps as a result of all this pleasurable sex, bonobos are generally friendly towards each other. There is little overt conflict. Biologists have pointed out the contrast between these sexy, peaceful apes and their closest biological relative, the chimpanzee. Chimps have less recreational sex than bonobos and their society is more male-dominated. They are also more aggressive. When two chimpanzee tribes meet in the wild, they are more likely to make war than make love. The outcome is often violent and bloody. All of this has led the bonobo’s admirers to regard them as the hippies of the ape world. One observer described them as equal parts dolphin, Dalai Lama and Warren Beatty.¹ Sadly, only a few hundred thousand of these wonderful animals are left on the planet. So how do we humans compare?

We belong to a very sexual species that is capable of being even more lustful and inventive than the bonobo. Sex is self-evidently a prominent feature of human life, albeit one that is expressed (or repressed) in many different ways. A national survey conducted in the UK at the end of 2005 found that people rated sex as the second most important source of pleasure in their life, after socialising with friends and family, although many men put sex in first place.² The average person reported having sex seven times a month, with a small minority claiming a monthly tally of more than twenty. Nine out of ten people said they found sex more pleasurable with a longstanding partner (not to be confused with a long, standing partner). A common theme to emerge from studies of human sexuality is that many people say they would prefer to have sex more often than they do. The ideal frequency is usually higher for men than for women.

Pleasure begets pleasure, when it comes to sex. The enjoyment of sex creates a virtuous circle, in which good sex improves mood and good mood in turn gives rise to more sex. This mutually reinforcing relationship was highlighted by a study in which researchers tracked the sexual behaviour of middle-aged women. The results showed that when a woman had good sex with her partner she was more likely to be in a good mood the following day. Being in a good mood made her, in turn, more likely to have sex the day after that.

Low mood usually dampens sexual desire, although it can have the opposite effect on some individuals. Research has found that a significant minority of men become more interested in sex when they are depressed, anxious or stressed. This may be because they have unconsciously learned to use sex as a form of self-medication, exploiting its combination of pleasure, intimacy, distraction and relaxation to lift their mood. In women, a correlation has been found between low mood and a greater desire to masturbate.

The lure of sexual pleasure is so powerful that people will find ways of obtaining it even in difficult situations like prisons. Pleasure can also be derived from fantasising about sex. Almost everyone has erotic fantasies, often while they are having real sex. Perhaps surprisingly, research has revealed that men’s sexual fantasies tend to focus more on the desire and pleasure of their partner than do women’s fantasies.

The sheer diversity of human sexual behaviour is impressive, even for an intelligent ape. Small but significant minorities of humanity engage in a wide range of practices such as sadomasochism and bondage. Some individuals develop a fetish, in which their sexual pleasure becomes linked to an inanimate object which would not commonly be regarded as erotic. Among the many such fetish objects recorded in the psychosexual literature are feet, fire, clothes, rubber, shoes and spectacles. Transvestic fetishists are sexually aroused by cross-dressing. Researchers in Sweden found that almost 3 per cent of men had experienced this form of erotic pleasure at least once.

Far more people enjoy anal sexuality in its many different forms. The fact that humans and other animals find anal stimulation pleasurable is unsurprising: the anus and rectum are richly endowed with nerve endings, making them highly sensitive to stimulation. Moreover, the genital and anal regions share some of the same nerve connections to the brain, creating the possibility of ‘cross-talk’ between pleasurable sensations originating from either region. Humans have always responded to this aspect of their architecture. Anal intercourse and other forms of anal stimulation are, and always have been, commonplace among heterosexuals and homosexuals. Research in the USA and Sweden shows that between a quarter and half of adults have tried anal intercourse and a small but substantial minority practise it regularly. The use of enemas for sexual pleasure, a practice known as klismaphilia, is also more common than might be assumed. Very few forms of behaviour are unique to humans, and anal sexuality is not one of them. For example, male rhesus monkeys have been observed to have penetrative anal sex with other males.

The diversity of human sexuality may be remarkable but it is certainly not new. Historical records show, for example, that the ancient Egyptians explored every known variation in the sexual repertoire, including masturbation, anal sex, male and female homosexuality, exhibitionism, incest, bestiality and necrophilia. The Romans were also great sexual explorers. They used a bewildering range of aphrodisiacs to boost their libidos, including bone marrow and cuttlefish. Sex in pre-Christian Rome seems to have been a pleasurable and largely guilt-free form of recreation, in an era when there was no expectation that marriage must be strictly monogamous. Attitudes were much the same elsewhere in the ancient world. Herodotus, who wrote his epic Histories in the fifth century BC, recorded these observations on the sexual practices of tribes inhabiting the lands east of the Mediterranean:

When a Nasamonian man gets married, it is the custom first for the bride to have sex with all the guests, one after another, on her wedding night; every man she has sex with gives her something he has brought with him from his house as a gift.… Gindanes women each wear many leather anklets; it is said that they tie on an anklet for each man they have had sex with. The woman with the largest number of anklets is considered to be the most outstanding because she has been loved by the largest number of men.

Recreational sex for its own sake later came to be regarded with severe disapproval, as religious belief clashed with hedonism. We shall return to this theme in chapter 13.

The dazzling variety of sexual pleasures available to our species has been augmented by the application of technology and pharmacology. The use of psychoactive drugs to enhance sexual pleasure is an ancient tradition. Many different drugs, including alcohol, cannabis, amphetamine, amyl nitrite, ecstasy and cocaine, are said by some users to enhance sex, although the evidence is mixed. The actor Errol Flynn, of whom more later, liked to apply a pinch of cocaine to the tip of his penis. Mechanical technology also has its place, with vibrators and other sex toys forming the basis of a large global industry. A national survey in the UK found that almost half the respondents had used sex toys to enhance the pleasure of sex and one in six had taken drugs for the same reason.

The vibrator was invented in the late nineteenth century by a British doctor named Joseph Mortimer Granville. He had been searching for a better way to treat ‘hysteria’ – the quasi-medical term that was applied then to what we would now regard as suppressed female sexuality. A common remedy for hysteria at the time was for the doctor to massage the woman’s genitals until she experienced a ‘hysterical paroxysm’, or what we would now recognise as an orgasm. This practice, which was known as ‘medical massage’, had been used by doctors since the time of Hippocrates to give relief to female patients. Administering a ‘medical massage’ could be tiring work for the doctor, and Granville was keen to find a modern, technological way of speeding it up. In 1883 he published a book entitled Nerve-Vibration and Excitation as Agents in the Treatment of Functional Disorder and Organic Disease, in which he described the use of his new ‘Percuteur’ electrotherapeutic device. It was the original vibrator.

Within a few years, cheap electromechanical vibrators were being widely advertised to the general public. Their ostensible purpose was the relief of muscle pains, headaches, poor circulation, wrinkles, or indeed almost anything that had no explicit link to sex or pleasure. By the 1920s, however, the public connection had been made between vibrators and sexual pleasure, with the result that they rapidly became shameful and virtually disappeared from view until the second half of the twentieth century.

The use of penis-shaped sex toys to enhance sexual pleasure has a very long history. The antiquities section of any good national museum should contain at least a few artefacts decorated with images of dildos. References to dildos can also be found in the literature of ancient Greece; for example, the anti-war comedy Lysistrata, written by Aristophanes around 411 BC, contains a scene in which Lysistrata and her women friends complain that their husbands are always away fighting wars, leaving them feeling sexually frustrated:

And not so much as the shadow of a lover! Since the day the Milesians betrayed us, I have never once seen even an eight-inch dildo to be a leathern consolation to us poor widows.

The ‘Milesians’ were the inhabitants of Miletus in Asia Minor; they were renowned in Aristophanes’ day for manufacturing a tip-top type of leather-covered dildo known as an olisbos, which was used with olive oil as a lubricant. Two thousand years later, William Shakespeare made this thinly veiled reference to the sexual function of dildos in The Winter’s Tale:

He hath songs for man or woman, of all sizes; no milliner can so fit his customers with gloves: he has the prettiest love-songs for maids; so without bawdry, which is strange; with such delicate burdens of dildos and fadings, ‘jump her and thump her’.

The innocent reader could choose to interpret Shakespeare’s words as an allusion to music, since ‘dildo’ also meant the chorus of a song. However, ‘fading’ was contemporary slang for orgasm and ‘jump and thump’ was innuendo for the process by which ‘fading’ is usually achieved. Shakespeare’s real intention is clear, even if his words are deliciously ambiguous.

Detailed practical advice on hardware for enhancing sexual pleasure could be found in the Kama Sutra, a Sanskrit treatise dating from the fourth century AD. Among other things, it suggests that a man may improve his partner’s pleasure by fitting devices, or Apadravyas, to his penis to supplement its length or thickness. These devices, it says, should be made of gold, silver, copper, iron, ivory, buffalo horn, tin or lead; they should also be ‘soft, cool, provocative of sexual vigour and well fitted’. In the absence of expensive raw materials, various makeshift alternatives are recommended, including the tubular stalk of the bottle gourd or reeds softened with oil and tied to the waist. The Kama Sutra also explains how a man can insert solid objects into the shaft of his penis to stimulate his partner. The ancient practice of using penile nodules continues to this day in parts of Southeast Asia, central Europe and the Middle East. In the 1990s, a medical journal recorded the case of a Fijian man who had got into difficulties after whittling his own penile nodules out of a plastic toothbrush handle.

One of the most imaginative applications of technology in the service of sexual pleasure has to be the Anal Violin. This ingenious contraption is featured in a nineteenth-century anthropological treatise written by a French army surgeon under the pseudonym of ‘Dr Jacobus X’. The good doctor, who spent much of his career in Asia, encountered the Anal Violin whilst visiting a Chinese male brothel in what is now Vietnam. He described it as long, thin and oval-shaped, about five inches in length and just over an inch in diameter at its widest. It was hollow and made of very thin silver, with the back end open and flared outwards, like a child’s trumpet. A thin metal cord, like a piano string, was fixed inside the front end and extended out of the open back for about three feet, terminating in a handle. The device was deployed by inserting it into the anus of the kneeling ‘erotic melomaniac’. The Anal Violinist then proceeded to play the instrument by rubbing the string with a metal bow to create pleasant harmonies and good vibrations. According to Dr X, ‘this Chinese symphony produces the most peculiar physiological sensations, and is certain to cause an erection in the old, worn-out debauchee who uses it.’

Pleasure, distilled

Sexual pleasure obviously amounts to more than just the creation of orgasms. That said, orgasms do have a lot to recommend them. An orgasm is one of the most intense, if regrettably brief, forms of pleasure a human can ever experience. It is pleasure, distilled. Every one of the 6.6 billion or so humans currently alive on our planet was the result of at least one orgasm, and between us we notch up several hundred million new orgasms every day. Even allowing for the pitifully short duration of an orgasm, this still amounts to a fabulous quantity of pleasure.

How long does an orgasm last? Scientists have attempted to answer this question objectively, confirming along the way that women’s orgasms generally last longer than men’s. Researchers in one study monitored young women who gave themselves orgasms in the laboratory. Measurements of their vaginal blood flow indicated that these lasted on average 20 seconds, although half the women felt subjectively that their orgasms were of shorter duration. Incidentally, Meg Ryan’s legendary fake orgasm in the film When Harry Met Sally also lasted 20 seconds, making it convincing even in its duration. Many women experience longer orgasms. According to physiological measures and women’s own subjective estimates, these longer orgasms may last between 30 and 60 seconds, with some going on for up to two minutes. Much depends, of course, on where you judge an orgasm to start and end. Even so, a 60-second full-on orgasm would make most men’s year. The typical male orgasm is much shorter, at around 10–15 seconds.

Some women are able to reach orgasm using mental imagery alone, without any physical stimulation. Scientists have verified this by demonstrating that imagery-induced orgasms are accompanied by more or less the same physiological reactions as mechanically induced orgasms, including the characteristic increases in heart rate, systolic blood pressure, pupil diameter and pain threshold. The ability to have an orgasm without the help of mechanical stimulation is not as remarkable as it might seem, since most men and women are quite capable of having orgasms during their dreams. However, the evidence indicates that fewer than one in a thousand men are capable of achieving orgasm when they are awake without some mechanical assistance.

Many women also experience the delights of multiple orgasms, something that few men even pretend they can do. Of the few men who are capable of multiple orgasms, most do not ejaculate until the final orgasm in the sequence. There has, however, been at least one documented case of a man who could achieve multiple orgasms, each of which was accompanied by ejaculation. The man in question demonstrated this extraordinary ability to scientists in a laboratory, ejaculating six times in 36 minutes while maintaining an erection throughout.

The changes in brain activity that accompany orgasm are similar in many respects to those observed during other forms of highly rewarding or pleasurable activity, including the consumption of recreational drugs. Many different parts of the brain are activated during orgasm, among them the nucleus accumbens and the anterior cingulate. As we shall see later, these two brain regions play prominent roles in mediating the experience of pleasure. We know that these areas of the brain are more active during orgasm because doughty volunteers have been willing and able to push back the frontiers of knowledge by masturbating to orgasm inside a functional magnetic resonance imaging (fMRI) machine.³

Orgasm is accompanied by involuntary muscle contractions in the perineum and rectum. Needless to say, scientists have measured these as well. In one study, researchers at the University of Groningen in the Netherlands persuaded twenty-three healthy women to have a measuring instrument inserted into their rectum to record these muscle contractions. The women were then monitored while having real orgasms, produced by clitoral stimulation, and also when faking orgasms. The data revealed that when a woman has a genuine orgasm – as opposed to a fake one – her rectum palpitates at a frequency of between 8 and 13 hertz (cycles per second). Fluctuating rectal pressure in the frequency band 8–13 hertz was an accurate indicator of genuine clitoral orgasm. Faking an orgasm, or masturbating to just short of orgasm, did not generate this signature response.⁴

Orgasm also triggers the release of the hormone oxytocin, a substance which is perhaps better known for stimulating the flow of milk from the breasts. Oxytocin contributes to the formation of the pair-bond between sexual partners. Some of the clearest evidence for this comes from research on voles. In monogamous prairie voles, an adult male forms a strong pair-bond with one female and helps her care for their offspring. When they first get together, the male and female have sex twenty or more times in a day, which makes them very fond of each other. These animals have high oxytocin levels and large numbers of oxytocin receptors in their brain. If a female’s oxytocin receptors are artificially blocked, she does not pair-bond with a partner. By contrast, a closely related species of vole behaves promiscuously; the males of this species, who mate with many different females, have lower oxytocin levels and fewer oxytocin receptors in their brain. This and other evidence implies that oxytocin plays an important role in pair-bonding, probably by acting on reward centres in the brain.⁵ One interpretation is that monogamous males become hooked on the pleasure of having sex with their mate. Recent research on humans has shown that spraying oxytocin up someone’s nose makes them more trusting towards other people. We shall return to the subject of trust in the final chapter, in view of its curious relationship with pleasure.

Oxytocin may have some bearing on the anecdotal observation that human drug addicts find it easier to quit their drug habit if they fall in love. Experiments have shown that giving oxytocin to rats or mice reduces their voluntary consumption of heroin and makes them more resistant to becoming tolerant to morphine and alcohol. Oxytocin also alleviates the symptoms of morphine withdrawal and reduces the behavioural effects of cocaine, especially the hyperactivity and stereotyped movements.

Orgasm in human females is usually achieved through direct or indirect stimulation of the clitoris – the only biological structure in the known universe whose sole function is the creation of pleasure. The anatomical structure of the clitoris, as distinct from its much more obvious pleasurable effects, was discovered in the mid-sixteenth century by an Italian professor of anatomy called Matteo Realdo Colombo. His discovery led to him being accused of heresy, blasphemy and Satanism, among other things. A century later, in the more liberated environment of Restoration England, one Jane Sharp felt free to write in her 1671 publication The Midwives Book that the clitoris ‘will stand and fall as the yard [penis] doth and makes women lustful and take delight in copulation’.

The clitoris, for all its awesome pleasure-giving powers, is only part of the story, however. In many women, mechanical stimulation of the vagina or cervix can generate orgasms in the absence of direct clitoral stimulation. This common experience has been confirmed under laboratory conditions in several studies. Many sexologists believe that women are equipped with other anatomical structures that are capable of generating orgasms in their own right. Perhaps the best known of these is the G spot.

According to one version of history, humanity discovered the G spot in 1950. In that year a German gynaecologist called Ernst Gräfenberg published an academic paper in a medical journal, in which he described a ‘distinct erotogenic zone’ on the anterior (front) wall of the vagina. When stimulated, this zone could produce a distinctive type of orgasm. In fact, descriptions of a G-spot-like entity date back much further than the 1950s. References to an erotically sensitive area on the front wall of the vagina can be found in Indian texts dating from the eleventh, thirteenth and sixteenth centuries. These texts also describe how stimulating this zone causes some women to ejaculate a clear liquid. An explicit account of female ejaculation can be found in the work of a seventh-century Indian poet.

Gräfenberg’s research was not of the highest quality; his findings were based on a small sample of women, only some of whom displayed signs of erotic sensitivity in this area. Nonetheless, his observation has been backed up by more solid research. In the early 1980s, sex researchers Beverly Whipple and John D. Perry reported that mechanical stimulation of deep-lying tissue in the front wall of the vagina could induce orgasm. They named this erogenous zone the G spot in honour of Gräfenberg. Their eponymous book became a best-seller, the spot itself became an accepted fact and the rest, as they say, is history. Few writers of sex manuals now doubt the existence of the G spot and an industry has grown around its erotic potential, selling instruction manuals, DVDs and specially shaped G spot vibrators to pleasure-seekers around the world. And yet, the G spot is still not mentioned in most medical textbooks and some scientists are openly sceptical about whether it actually exists. One academic who reviewed the published research likened the G spot to UFOs: much searched for and much discussed, but unverified by objective means. The truth is a little more complex, although still broadly good news.

Evidence from numerous scientific studies leaves little doubt that the front wall of the vagina is erotically sensitive to some degree, and that a majority of women can achieve orgasm with sufficient stimulation of this area, whether manually or during penetrative sex. This was shown, for example, in a laboratory study in which women had the front and back walls of their vagina stimulated. All the women reported that certain areas of their vagina were more erotically sensitive than others, and most of them were able to reach orgasm by stimulating these sensitive zones. Although most women normally achieve orgasm through clitoral stimulation, three out of four women in one study said that vaginal stimulation could also produce orgasm. Most reported that the front wall of their vagina was more sensitive to erotic stimulation than the rear wall. Several other studies reached similar conclusions. That said, there is little solid evidence for the existence of a discrete anatomical structure or erogenous hotspot that corresponds to the ‘G spot’ as it is sometimes portrayed in the popular media.

The fact that the lower front wall of the vagina is to some extent erotically sensitive is unsurprising. Our primate ancestors would presumably have had sex in the rear-entry (‘doggie’) position, which naturally tends to stimulate this part of the vagina. Another possible explanation for at least some ‘G spot orgasms’ is that they are, in fact, indirect clitoral orgasms. Most vaginal orgasms involve at least some indirect stimulation of the clitoris. Rubbing the lower part of the vaginal front wall can have the effect of moving the clitoral hood back and forth across the clitoris, as though the clitoris itself were being massaged. Stimulating the front wall of the vagina can therefore be pleasant and produce orgasms, whether or not that part of the vagina is an erogenous hotspot in its own right. Either way, I see no problem in continuing to call this friendly region the G spot, even if it is neither a spot nor an anatomically distinct organ.

What of the related belief that ‘G spot orgasms’ can bring about female ejaculation? Again, the reality is a little more muted than the popular image of ‘gushers’ would suggest. Many, if not most, women emit some fluid from their genitalia at orgasm or when they are at a peak of sexual arousal. One study found that women who were aware of their G spot were twice as likely to be ‘ejaculators’. In most cases, however, the amount of fluid emitted is too small to be easily noticeable.⁶ Moreover, its release does not depend on having a ‘G spot orgasm’. Experiments have shown that when the front wall of the vagina is stimulated, some women have an orgasm but do not ejaculate, some women ejaculate but do not have an orgasm, and some do neither.

Since Ernst Gräfenberg first unveiled what became known as the G spot more than half a century ago, the quest for new erogenous zones has continued. More recent erotic explorers have laid claim to discovering the A spot, the U spot and the X spot. What and where are these alleged pleasure troves? In reverse alphabetical order, the X spot is an erotically sensitive spot on the cervix. According to the American sexologist who ‘discovered’ it, the X spot is even better than the G spot and easier to find. The U spot is a small sensitive area just above, and on either side of, the opening to the urethra. Finally, the A spot, or anterior fornix erogenous zone, is a sensitive patch at the inner end of the vagina, just above the cervix. Stimulation of the A spot is said to produce violent orgasmic contractions. In addition to the G, A, U and X spots there is, of course, the clitoris – that fabulously sensitive organ whose visible tip contains many thousands of nerve endings, all of them dedicated to the production of pleasure. Meanwhile, not one single new flag of discovery has been planted on the male genitalia. The general assumption appears to be that the male organ, like the male psyche, is a simple thing, altogether lacking in mystery.

All of these glaring gender disparities in sexual pleasure call to mind the ancient Greek myth of Tiresias, a priest who had been transformed from male into female then back to a man again. Tiresias became embroiled in an argument between the goddess Hera and her husband Zeus about whether men or women derived the most pleasure from sex. As someone who had been both a man and a woman, Tiresias would have known. His considered opinion was that, on a ten-point scale, men enjoy only one part in ten whereas women enjoy all ten in full.

As well as possessing a larger collection of erogenous hotspots than the average man, the average woman’s potential for orgasmic pleasure is much greater. Not all women fulfil this potential, however. Individual women differ considerably in the frequency with which they have orgasms. Research has shown that part of this individual variation is linked to genetic differences.

Scientists at St Thomas’ Hospital in London investigated the influence of genes on orgasmic function by gathering data from pairs of identical and non-identical twins.⁷ A large sample of adult female twins provided information about their sexual histories. Virtually all the women had been sexually active, with an average of four or five sexual partners each. The data revealed a striking variability in the ease with which they had orgasms. One in three women said they reached orgasm during sexual intercourse either infrequently (less than a quarter of the time) or never, and one in five reported the same for masturbation. Overall, one in seven women never had an orgasm, not even when masturbating. At the other end of the scale, one in seven women always had an orgasm during intercourse.

By comparing data from identical and non-identical twins, the scientists were able to estimate that 34 per cent of the individual variation in reaching orgasm from intercourse was genetically inherited, while for orgasm from masturbation the heritability was 45 per cent. In other words, somewhere between 34 and 45 per cent of the individual differences between women in their ability to have orgasms could be explained by genetic differences. Other twin studies have produced similar findings.

Genetic factors could affect a woman’s orgasmic potential in many different ways, both direct and indirect, ranging from subtle influences on anatomy to variations in how the brain responds to sensory stimuli or perceives pleasure. Genetic predispositions aside, most sexologists would argue that an overwhelming majority of women are ultimately capable of reliably achieving orgasm, provided they have suitable circumstances, the right attitudes, a little knowledge and enough time.

Research has highlighted the role of one particular gene in human sexuality. The gene in question, which is called DRD4, affects how the brain responds to the neurotransmitter substance dopamine.⁸ As we shall see in chapter 6, dopamine plays a central role in the perception of pleasure and desire. Most people carry one of two different variants of the DRD4 gene: about 70 per cent of us have one version and about 20 per cent have the other. Individuals with the less common version of the gene score higher on self-reported measures of sexual desire, sexual arousal and sexual function than those who have the more common variant.

As you may have noticed, the pleasure of orgasm does not stop abruptly when the exquisite peaks of the orgasm itself have passed. It lingers on in a different and more subdued form. The pleasant feeling of satiated relaxation that follows a good orgasm stems from the sudden release into the bloodstream of the hormone prolactin. This post-orgasmic surge in prolactin, which occurs in men and women, has the effect of damping down sexual arousal. (Scientists have yet to investigate whether it also stimulates the desire for a cigarette.) However, not all orgasms are equal in this regard. Research has discovered that the prolactin surge is four times bigger following orgasms that result from sexual intercourse than following orgasms achieved through masturbation. This helps to explain why having good sex with a partner tends to produce a more satisfying wave of post-orgasmic relaxation than having sex with oneself.

What are orgasms for? The delightful capacity to experience orgasms is built into our biological makeup and should therefore have some form of biological function. But how might orgasms have helped our evolutionary ancestors to survive and reproduce? The answer is not quite as obvious as it might seem. The male orgasm coincides with ejaculation, which is essential for making babies. But ejaculating semen and having an orgasm are two different things. There is no inherent reason why males should not be built to ejaculate without experiencing the accompanying spasms of orgasmic pleasure. Indeed, some men with spinal cord injuries are capable of ejaculating without being able to feel the sensations of orgasm.

In females, the connection between orgasm and reproduction is even less obvious. A fertile woman is biologically capable of conceiving without ever having an orgasm. And, as we saw, a substantial minority of women rarely or never have orgasms during sex. Furthermore, this difficulty in achieving orgasm has a strong genetic component, implying that the female orgasm is unlikely to have been crucial for human survival and reproduction. This line of thinking led the biologist Elisabeth Lloyd to conclude that the female orgasm may have no biological function at all, but may instead be an evolutionary by-product of the male capacity for orgasm. Lloyd has likened the female orgasm to the male nipple, which serves no biological purpose but exists because it is constructed at an early stage in embryonic development. Similarly, Lloyd argues, women are equipped with a clitoris, and hence the capacity for orgasm, as an evolutionary by-product of constructing the male penis. She believes this is why most women only have an orgasm if their clitoris is stimulated and why some women find it hard to have orgasms at all.

The female orgasm may not be essential for conception, but that does not mean it is entirely irrelevant. Having an orgasm could influence a woman’s chances of conceiving, possibly as a result of the muscular contractions helping to draw semen into the uterus. This theory is supported by research evidence that women who have a strong desire to become pregnant are more likely to have an orgasm after, rather than before, their partner ejaculates, other things being equal. Somewhat more controversial evidence indicates that women who have an orgasm after their partner ejaculates retain more of his sperm in their vagina and are therefore more likely to conceive. Having an orgasm at the right time could make a difference. Having an orgasm with the right partner at the right time could make even more of a difference. We are therefore drawn back to the simplest and most compelling explanation, which is that the primary function of orgasm in both sexes is to give pleasure. This pleasure encourages men and women to keep having sex in the right way with the right mate.

Pleasure is not the only benefit bestowed by recreational sex and orgasms. They can also relieve stress, reduce the risk of heart disease and prostate cancer, and may even protect pregnant women against premature delivery. Several studies have found that sexual arousal and orgasm activate elements of the immune system. In one investigation, eleven healthy young German men masturbated to orgasm (though not all at the same time) while their blood composition was monitored. Sexual arousal and orgasm were accompanied by a rise in the number of white blood cells circulating in their blood – particularly white cells of a type known as natural killer cells, which are able to destroy some tumour cells and virus-infected cells. Another study found that men and women who had more active sex lives tended to respond better to stress, as measured by their blood pressure reaction to mildly stressful tasks. Individuals whose sexual pleasure came mainly from masturbation, or sexual contact without intercourse, displayed a substantially bigger (that is, worse) blood pressure reactivity to stress than those who were having regular penile – vaginal intercourse.⁹

The proof of the pudding is that people who have more orgasms live longer. A long-term study of middle-aged men found that those who had two or more orgasms a week had a mortality rate that was 50 per cent lower than men who had orgasms less than once a month. This relationship between a higher frequency of orgasm and a lower risk of death held true even when confounding factors such as age, smoking habits and social class were taken into account. For anyone who might need any additional encouragement beyond the pleasure, findings such as these pleasingly reinforce the conclusion that sex and orgasms are good for us. From sex we turn now to drugs.