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 and other priorities have risen to the fore. If a pleasurable activity continued to be pleasurable for too long, we would be in danger of getting locked into doing it and therefore neglecting higher-priority needs. Our ancestors would not have survived long enough to become our ancestors if they had sunk into a state of enduring bliss every time they did something enjoyable. For pleasure to do its biological job as a motivational common currency, it must be short-lived. And so it is.
Everyday experience, backed up by a reassuring mass of experimental data, confirms that pleasure is indeed short-lived. We habituate quite rapidly to pleasurable sensations. No matter how earth-shaking it may be at the time, any given pleasure will fade and the moment will pass. William Shakespeare famously encapsulated this aspect of human nature in the opening lines of Twelfth Night:
If music be the food of love, play on;
Give me excess of it, that, surfeiting,
The appetite may sicken, and so die.
The ephemeral nature of pleasure has important practical implications, which we will explore later. Above all, it means that anyone who attempts to rely exclusively on pleasure to make them happy is likely to have a struggle on their hands. The present pleasures will inevitably dwindle, forcing the determined hedonist to keep increasing the dosage or switch to new ones. Socrates likened pleasure-seekers to the damned in Hell, who are condemned for ever to keep trying to fill leaky jars. Psychologists refer to this phenomenon as the hedonic treadmill.
Pleasure must be self-limiting to do its job. However, biological reasoning would suggest that displeasure and pain should not be self-limiting in the same way. Instead, they should persist for as long as the problem that gives rise to them. If the biological function of displeasure and pain is to protect us from harm, we would expect them to linger until the corresponding threat to our well-being has gone away. Again, the theory is borne out by reality. Unpleasant feelings such as anxiety, fear and pain are generally not as ephemeral as pleasure; we do eventually adjust to displeasure or pain, but more slowly and less completely than in the case of pleasure. As the essayist William Hazlitt put it, ‘pain is a bittersweet, which never surfeits’.
The simple idea that pleasure evolved to make us behave in biologically beneficial ways further implies that there should be a clear relationship between our current biological needs and our current experience of pleasure. As those needs change, so too should our response to pleasurable stimuli. Once again, the theory is in line with everyday reality and experimental evidence. Our response to potentially pleasurable stimuli does indeed vary according to our current internal state and needs. Drinking tepid, murky water from a chipped mug can be delightful when you have a raging thirst, but not otherwise. Similarly, sinking into a steaming hot bath is altogether more pleasant when you are cold and wet than it is after a day of sunbathing on a tropical beach. Experimental studies have confirmed that changes in our internal state affect the amount of pleasure or displeasure we experience in response to stimuli. In one typical experiment, hungry people were repeatedly given drinks of sugary water, which they had to spit out without swallowing. They continued to find the sweet taste pleasant each time they experienced it. But if, instead, they swallowed each drink when it arrived, the sweet taste became progressively more unpleasant. Sweet pleasure turned to cloying displeasure as their stomach filled with sugary liquid. The same physical stimulus could elicit pleasure or displeasure, depending on the individual’s current internal state.
The idea that pleasure and other emotions are reflections of our body’s physical state has a long pedigree. William James, the pioneering nineteenth-century psychologist (and brother of writer Henry), proposed that our emotions arise, at least in part, from an awareness of our physical reactions to stimuli.2 So, for example, we feel afraid because we have become aware that our heart is pounding and our hands are trembling, rather than the other way round. James realised that if emotions are linked to internal state then we might be able to alter our emotions by manipulating the signals reaching the brain from the rest of the body. He tested this hypothesis with a very simple experiment. He smiled. More specifically, he forced his facial muscles to form the shape of a smile, even though he did not feel in the mood for smiling. (William James suffered from depression – hence, perhaps, his particular attraction to smiling.) He found that the more he smiled, the jollier he felt. The physical act of smiling was enough to elicit the corresponding emotional state, as though the configuration of his facial muscles had somehow tricked his brain into believing that he must be feeling good.
The two-way relationship between facial expression and emotion has been substantiated by more systematic experiments. In one study, psychologists got people to hold a pencil between their teeth without it touching their lips. This made them smile, without being consciously aware of doing so. As William James would have predicted, the physical act of smiling lifted their subjective mood, even though the subjects did not know they were smiling. By comparison, sucking a pencil with their lips wrapped around it did nothing to lift their mood. Similar mood-enhancing effects have been produced by giving experimental volunteers detailed instructions to move particular muscles in their face, causing them unwittingly to smile. The effect is strongest when the smile is of the so-called Duchenne variety – the ‘genuine’ type of smile that involves the corners of the eyes as well as the mouth. One day, perhaps, the well-read pleasure-seekers among us will be recognisable from the tell-tale pencil clenched between their teeth.
Deliberately smiling really can lift your mood. Try it for yourself. Use a pencil if you must. So too can holding your head high or whistling a happy tune. In each case, a physical act that would normally reflect an underlying emotional state can also elicit that same emotional state. Of course, people who never stop smiling can irritate those of us in a less ebullient mood, especially if their smile is obviously fake. Some celebrities
