The placebo effect is the ultimate in evolutionary self-help. It has been used to explain everything from miracle cures to dying of a broken heart. How does it work and are we getting any closer to harnessing its power? The bizarre name placebo comes from the Latin chant of funeral mourners in the Middle Ages who were hired to sing vespers for the dead, beginning 'Placebo Domino ....' It is appropriate, then, that the pilgrim destination of Lourdes is the site of what some psychologists consider a demonstration of one of the world's most spectacular placebo effects. Every year, scientists there corroborate recovery from diseases for which there is no possible medical explanation. Something close to the reverse effect has been noted among Chinese-American cancer patients whose birth year - according to Chinese medical theory - fates them to an early demise. They die sooner than non-Chinese of a similar age: from one to several years earlier. Some speculate that similar forces are behind the phenomenon of dying of a broken heart. We have all heard of less dramatic stories, and many of us have had personal experience of the placebo effect, even if unknowingly. Doctors know that patients commonly feel the effects of medical treatment as soon as they leave the surgery - long before any prescribed medication has entered their bloodstream. As early as 1572, essayist Michel de Montaigne noted, 'the mere sight of medicine is operative'. Nowadays, psychologist Richard Bootzin calls this the 'hello-goodbye' effect. Just going for help and having the expectation of relief seems to do the trick. And no one, studies show, is immune. On the other hand, the experience, competence and level of optimism of the health-care provider have a profound influence on the effectiveness of the phenomenon. Kindness, touching, caring and encouragement may alone halt or slow further deterioration, perhaps by a rush of stress-reducing endorphins. This might help account for the initially 'miraculous' effectiveness of new drugs and why formerly effective treatments stop working when publicly discredited. Not everyone is convinced. John Dodes, as president of the New York chapter of the National Council Against Health Fraud, pointed out that 'even serious diseases have periods of exacerbation and remission'. Placebo results may simply coincide with spontaneous remission. However, a high-profile 2001 statistical report in The New England Journal of Medicine concluded placebos brought benefits, especially in subjective outcomes and for the treatment of pain. So, how does a placebo actually work? How does the mind instruct the body to heal itself? It seems that there are more intimate connections between the nervous system and the immune system than was once thought, and that the chemical pathway between them may provide a kind of lingua franca for mind-body interaction in relation to healing. This may explain the nuts and bolts of the mechanism. But it still does not explain why, if the body can cure itself, it doesn't do so as soon as a person falls ill or is injured? Why wait for a visit to the church or surgery? This is where the fashionable field of evolutionary psychology comes in. Psychologists of this persuasion suggest that over the very long term, humans have developed a sort of internal health-management system, which makes executive decisions about how the body will handle incoming threats such as injury and disease. But now that humans have inherited this system, with all its networking capacities, the environment has suddenly changed, in evolutionary terms. Our internal health managers have had to learn to interpret signals that are very different from the behaviour of wild animals and weather conditions. Not without justification, they have concluded that the best survival strategy is to be around doctors, hospitals, medicines and whatever other health-care apparatus our cultures have taught us to associate with getting better. The effects of placebos are not universal. There are significant cross-cultural differences, which might suggest that our internal health executives are commanding operations based on very detailed information received from the surrounding environment. What we need to know, for example, is why stomach ulcer placebo treatments work so well in Germany, with a 60 per cent cure rate, while they flop in Brazil. Such huge cultural differences in the effectiveness of placebos could give us a clue as to how our minds translate circumstances into meaning, and meaning into response. Understanding this chain of 'meaning response' could lead us to ways of more accurately targeting the phenomenon and turning it on and off as required. We can and do heal ourselves, it seems, but are only beginning to understand how and why. Jean Nicol is a Hong Kong-based psychologist and writer everydaypsychologist@yahoo.com