In Anthony Burgess's novella (and Stanley Kubrick's film) A Clockwork Orange, Alex, an unrepentant psychopath, has his eyes pried wide open and is forced to watch violent images. Like Pavlov's dog, Alex is being programmed to respond with nausea to violence and sex. This scene remains shocking, but, like most science fiction, it has aged. The behaviourist psychology it drew on has long expired, and the fear that science will be used to make people morally better now sounds old-fashioned.
But science fiction has a long afterlife. Over the past decade, psychologists, neuroscientists and evolutionary biologists have been busy trying to uncover the neural "clockwork" that underlies human morality. They have started to trace the evolutionary origins of pro-social sentiments such as empathy, and have begun to uncover the genes that dispose some individuals to senseless violence and others to acts of altruism, and the pathways in our brain that shape our ethical decisions. To understand how something works is also to begin to see ways to modify and even control it.
Indeed, scientists have not only identified some of those brain pathways that shape our decisions but also chemical substances that modulate this neural activity. A recent study has shown that the antidepressant citalopram can change the responses of individuals to hypothetical moral dilemma scenarios. Individuals given the drug were less willing to sacrifice an individual to save the lives of several others.
Another series of studies has shown that, when the hormone oxytocin is administered via nasal spray, it increases trusting and co-operative behaviour within social groups but decreases co-operation with those perceived as outsiders. Neuroscientists have even magnetically "zapped" people's brains to influence their moral judgments in surprising ways - making it easier to lie, for example.
Of course, no one is developing a "moral" pill that will transform us into saints. But the research is advancing fast, and it's almost certain to suggest new ways to reshape our moral intuitions, sentiments and motivations.
Should we use our growing scientific understanding of the basis of human morality to try to make people morally better?
A Clockwork Orange was accused of glorifying violence, and some of its scenes are still hard to watch. But as Anthony Burgess himself argued, the novella has an almost Christian message: What makes us human is our freedom to choose both good and evil, and for society to crush individuals into servile conformity is as wicked as, and perhaps even worse than, the sadism of psychopaths like Alex.
I suspect many will agree with the view that our ability to distinguish right from wrong is something precious we should safeguard, not a broken clock that scientists should fix.
Of course, most of us don't need to be conditioned to feel repulsed by rape or torture. But this does not mean we are morally good, or good enough. As you read this, perfectly ordinary people are doing unspeakable things to others. Even in the most advanced and affluent societies, a concentrated effort is needed to preserve even minimal decency: Think of locks, security alarms, police, courts and prisons. And it's doubtful we really care enough about others, or give enough to the less fortunate.
Humans are born with the capacity to be moral, but it's a limited capacity ill-equipped to deal with the modern world's ethical complexities. For thousands of years, humans have relied on education, persuasion, social institutions and the threat of real (or supernatural) punishment to make people behave decently. We could all be morally better, but it's clear this traditional approach can't take us much further. It's not as though people would begin to behave better if we just gave them more facts or better arguments.
So we shouldn't be too quick to dismiss the suggestion that science might help - in the first instance, by helping us design more effective institutions, more inspiring moral education or more persuasive ethical arguments. But science might also offer more direct ways of influencing our brains.
Science fiction sometimes limits our sense of what is possible. It would be self-defeating, or worse, to try to promote morality through brutal coercion. Governments must not be given the power to control their citizens' moral code - we know that if they had such power, they would misuse it.
It would be ideal if individuals could freely explore different ways to improve themselves, whether by practising mindfulness, reading moral philosophy or, yes, by taking a "morality" pill. But it's also true that, although some people are eager to take pills that make them feel better, it's not so obvious that people would want to take pills that would make them morally better. It's not clear people really want to be morally better. And those who, like the psychopathic Alex, need the most help are probably those who would want it least.
We don't yet know, of course, what's possible. But it's better to begin the ethical discussion too early than too late. And even if "moral" pills are just science fiction, they raise deep questions. Will we want to take them if they ever become available? And what does it say about us if we won't?
Guy Kahane is deputy director of the Uehiro Centre for Practical Ethics at the University of Oxford.