Sex, Drugs and Chocolate: The Science of Pleasure. Paul Martin

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.

       FOUR Drugs

      It is a custom with some people to blame, without limit, those who indulge in nervous stimulants of a nature differing from their own, while serving the same purpose.

      MORDECAI CUBITT COOKE,

      The Seven Sisters of Sleep (1860)

      We all use psychoactive drugs, by which I mean chemicals that alter the functioning of the brain by acting on its internal communication mechanisms. Among the more familiar examples are caffeine, nicotine and alcohol, but the term also encompasses illegal recreational drugs like cannabis, ecstasy and cocaine. We take these substances because they make us feel better – or, at least, different. They are capable of delivering intense pleasure and causing great harm. The paradox of drug use was encapsulated by Louis Lewin, a pioneering German pharmacologist who wrote in the 1920s that they ‘lead us on the one hand into the darkest depths of human passion, ending in mental instability, physical misery and degeneration, and on the other to hours of ecstasy and happiness or a tranquil and meditative state of mind’.

      Why do we do it? The brain systems that underlie pleasure, desire and reward evolved hundreds of million years ago and are found, in at least some basic form, in all mammals, birds, reptiles, amphibians and fishes. A long time ago, we humans discovered how to manipulate these brain systems artificially with drugs. We use psychoactive drugs because they produce pleasure, or because they alleviate unpleasant feelings of anxiety and stress, or both. We always have and we always will.

      Getting on for half of all young British adults admit to having used an illegal drug during their lifetime, and one in six say they have used a Class A drug such as cocaine or heroin.¹