Waterville, County Kerry, Ireland

We're sitting around a peat fire, while rain batters the windows of the cottage and a howling gale blows in from the Atlantic. Five of us are here for a workshop on the placebo effect, Anne Harrington (historian of science), Howard Fields (neurobiologist), Dan Moerman (anthropologist), Fabrizio Benedetti (neurphysiologist), myself (psychologist). It's the latest in as series of interdisciplinary workshops under the auspices of the Harvard Mind Brain Behaviour Initiative. We've set ourselves the goal of writing a joint paper by the end of the summer "How to think well about the placebo effect". We've decided to organise it around Niko Tinbergen's four "Whys?": proximate causation, developmental history, biological function, evolutionary history.

My own interest is especially in the question of evolutionary design. When a person recovers from illness as a result of placebo treatment, it must of course be his own healing system that is doing the job. Placebo cure is self-cure. But if the capacity for self-cure is latent, then why is it not used immediately? If a person can get better by his own efforts, why doesn't he just get on with it as soon as he gets sick—without having to wait, as it were, for outside permission? Why should the mind be allowed to influence the body in this way—when the net result is, if anything, to put a brake on healing?

The paradox can, I think, be resolved by considering the placebo effect in a broader biological context.

Long before medicines or doctors came on the scene, we should assume the ancestors of human beings had already developed a fine capacity for looking after their own health: by mounting defences such as pain and fever, by actively attacking infections, by repairing bone and tissue damage, by indulging in sickness behaviours, and so on. However none of these measures would ever have been free of cost (immune resources are expensive, pain is debilitating, acting-sick is time-wasting, etc.). So it must always have been essential to have some kind of internal "health management system" in place, to ensure that the way the body responded to any particular threat was nearly optimal.

Sometimes, for example, it would have been best for a sick person to get well as rapidly as possible, throwing off defences such as pain and mounting a full-scale immune response; but at other times it might have been more prudent to remain unwell and out of action and to conserve resources for later use. As a general rule (and of crucial importance for the story of placebos): the brighter the prospects for a rapid recovery, the less to be gained from playing safe and remaining sick.

But this must have meant that the health management system would have needed to take account, so far as possible, of any intelligence available to the sick person about what the future held. Relevant information would have included the nature of the threat, the costs of the defensive measure, the prospects for spontaneous remission, evidence of how other people were faring, the presence of social support, and so on. The mind therefore must have had to become an adjunct to the healing system—precisely so as to gather this intelligence.

In the past all kinds of environmental information would have been be brought to bear. And no doubt they still are. But today, the medicalisation of sickness has changed the picture. For it means nowadays that there will often be a novel and even overriding piece of information to take into account. People have learned—their culture has taught them—that nothing is a better predictor of how things will turn out when they are sick (whether the pain will ease, whether the infection will abate, whether they will be nursed back to health . . ) than the presence of doctors, medicines, and so on.

Yet human beings remain tied to their evolutionary heritage. And so, today, the very prospect of medical attention—the patient's belief in it—works its magic for the simple reason, stemming from the general rule above, that for most of human history, once a sick person has had cause to think that he will soon be safe and well, he has had just the excuse he needs to bring on his own recovery as fast as possible.

(Fabrizio Benedetti, Nicholas Humphrey, Anne Harrington, Howard Fields, Dan Moerman)

At least this is the story I've been pushing! Are my colleagues convinced? It's such a different way of thinking for them—especially the two neuroscientists—that I'm afraid they haven't yet taken it on board.

Max Planck said "A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it." I like my friends in this group much too much to hope that this is true.

Nick