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

he argued that society’s disapproval of anal sex stemmed from an irrational antipathy towards pleasure, especially sexual pleasure. Bentham even tried to devise an objective method for calculating exactly how much ‘felicity’ any particular action would unleash, but this proved too difficult. Indeed, it remains the case to this very day that no one is entirely sure how best to quantify happiness or pleasure.

      Strong echoes of Bentham’s philosophy are evident in current thinking that national governments should pursue policies and enact laws that are specifically intended to maximise national happiness, in contrast with their conventional preoccupation with maximising national wealth. However, it is often unclear what the proponents of such policies really mean by ‘happiness’, which they sometimes seem to equate with pleasure, or just feeling good. As we shall see later, pleasure and happiness are two quite different entities.

      What does hedonism look like in the early twenty-first century? Much the same as in Georgian London or imperial Rome, it would appear. A far wider variety of mind-altering drugs is now available, but the familiar mainstays of sex, alcohol, food and gambling remain as popular as ever. In the UK, for example, the average household devotes about 4 per cent of its total expenditure to those two ancient and deeply entrenched drugs, alcohol and tobacco. Psychological research and social surveys consistently find that people around the world continue to derive most of their pleasure from having sex, eating, drinking, relaxing and socialising with family and friends. In private, many of them also seek chemical pleasure from illicit drugs, which is why drug trafficking is estimated to account for around 8 per cent of all international trade. But enough of the social history: it is time now for a little science.

       TWO What Is Pleasure For?

      Pleasure is the only thing worth having a theory about.

      OSCAR WILDE,

      The Picture of Dorian Gray (1891)

      What is pleasure for? That is the sort of question biologists ask. What they mean is: how did this feature of our biological makeup help our ancestors to survive and reproduce, and therefore to become our ancestors? To put it another way, why did evolution equip us and other animals with the capacity and appetite to experience pleasure in so many varied and delightful ways, including perhaps some that are still undiscovered?

      The simplest answer is that pleasure and its dark counterpart, pain, are there to encourage us to do the right things. Pleasure entices us to behave in ways that are likely to be biologically beneficial, while pain discourages us from doing ourselves harm. The ever-shifting balance between pleasure and pain is, to quote the philosopher David Hume, ‘the chief spring or actuating principle of the human mind’.

      The idea that pleasure and pain direct our behaviour has been circulating in various guises for thousands of years, dating back at least as far as Epicurus and like-minded philosophers of ancient Greece. Psychology, as it came to be known, built upon this simple concept in the nineteenth century. In 1880, for example, Herbert Spencer advanced a specific psychological theory that all human behaviour is underpinned by the twin motivating forces of pleasure and pain.¹

      Sigmund Freud pursued the theme with his psychoanalytic Pleasure Principle. In his characteristically doubt-free style, Freud asserted that he had no hesitation in assuming that all mental activity was ‘automatically regulated’ by the Pleasure Principle – by which he meant that all mental activity was directed towards the production of pleasure or the avoidance of displeasure. Freud decided that pleasure and displeasure were reflections of a mental phenomenon that he called ‘unbound excitation’; pleasure supposedly acted to reduce this excitation, while displeasure did the reverse. In another of his works, an even less hesitant Freud proclaimed that ‘It is simply the programme of the pleasure principle that determines the purpose of life.’

      What has science, as distinct from Freudian conjecture, revealed about pleasure? One basic conclusion is that the behaviour of humans and other animals is self-evidently motivated by stimuli that are associated with pleasure. Pleasurable rewards (or ‘reinforcers’) tend to increase the frequency of the behaviour that produced them, whereas unpleasant stimuli do the reverse. The long-suffering experimental pigeon will peck energetically at a button if its efforts are rewarded with food, but it will rapidly stop pecking and avoid the button if instead it receives a mild electric shock.

      A second basic conclusion is that the sorts of activities we find pleasurable could mostly be viewed as biologically beneficial, in the sense that they would generally have helped our ancestors to survive and reproduce in their natural environment. As we saw earlier, people consistently report that socialising, having sex and eating are their main sources of pleasure. These activities are also biologically beneficial, in the right circumstances. Even the simplest pleasures of life, like warming yourself in front of a fire or tending a garden, make good biological sense if you imagine yourself as one of your hunter – gatherer ancestors.

      The capacity to respond to pleasurable stimuli emerged very early in evolution and is detectable, in one form or another, in animals ranging from flies and shellfish to dogs and gorillas. Pleasure almost certainly plays a bigger role in the lives of other species than we humans often tend to assume. The neuroscientist Jaak Panksepp has even uncovered evidence that rats are capable of experiencing playful joy which they express in the form of high-pitched ‘laughing’. When a rat has a joyful experience, such as playing with another rat, it emits a series of ultrasonic (50-kilohertz) chirps. Panksepp contends that these vocalisations are biologically related to the joyful laughter that children emit when they are playing. The thought that rats enjoy a giggle with their mates is a reminder that life for other species can amount to more than just a grim struggle for survival.

      If pleasure did evolve to guide our behaviour, then how does it perform this biological function? The task is not quite as straightforward as it might seem. At any given moment we could be doing many different but mutually exclusive things, each of which would be biologically beneficial. We might, for example, be faced with the choice of cooking dinner, sleeping in a cosy bed or having vigorous sex. How do we decide what to do next? Humans and other animals must continually choose between competing requirements. We therefore require some form of mechanism for weighing the conflicting motivations against each other and choosing the best option at the time. To help us choose, we need some form of measuring stick or common currency. According to the physiologist Michel Cabanac, that common currency is pleasure.

      The essence of Cabanac’s theory is that pleasure enables the brain to compare the strengths of current motivations to perform different activities. When choosing between, say, eating, staying warm or avoiding danger, we may, of course, make a conscious, rational judgement about our priorities. But even an apparently conscious decision will be influenced by an unconscious weighing of the options in terms of how much pleasure or displeasure each would produce. We are drawn towards the most pleasant, or least unpleasant, course of action. This simple form of hedonism encourages us to behave in ways that, on average, will be in our best biological interest.

      Pleasure is the hidden force behind what might be called ‘gut instinct’; it guides our choices even when we think we are using our conscious mind to make rational decisions. Experimental tests have lent support to this simple theory, confirming that humans and other animals behave in line with its detailed predictions. We make unconscious but surprisingly precise trade-offs between the amount of displeasure we are prepared to experience and the amount of pleasure we anticipate in return. The evidence suggests that something akin to pleasure is used to prioritise actions in other species as well. Even a lizard will be guided by the unconscious trade-off between, say, physical discomfort and the attractiveness of food.

      If evolution has equipped us with pleasure as a mechanism to help guide our behaviour then we would expect those feelings of pleasure to be inherently transient and self-limiting. Faced with competing priorities, we will choose the most pleasant or the least unpleasant course of action. But in order to survive and thrive, we must stop performing that activity and switch to something else as soon as our current needs have been satisfied