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was subject to scientific evaluation. Nevertheless, it was some time after Copernicus and Galileo had produced convincing evidence that the Earth orbited the sun, rather than the more facile explanation, that the heliocentric view of the world became universally accepted.

      Today, many people buy ‘organic food’ in spite of the extra expense because they believe it is ‘better’ for them than food grown or produced ‘conventionally’. There is no evidence to support this belief. Its supporters have been persuaded by unsubstantiated propaganda, repeated by what they see as authoritative sources, such as Prince Charles, the Soil Association, many retailers, celebrity chefs and some self-serving nutritionists. They ignore the evidence and remain unconvinced by conclusions reached by bodies they would normally be expected to respect, such as Food Standards Agency, the Advertising Standards Authority and highly regarded nutritionists who have contributed to and examined the evidence. This has consistently failed to show any advantage in ‘organic produce’, which is in effect a trademark rather than a genuine entity. Insistence on buying organic food is based on belief, not on evidence, and is as irrational as the belief that the world is flat.

      The germ theory of disease

      Before the pioneers of microbiology proved otherwise, many infections were believed to be due to draughts, exposure to damp or cold – perpetuated in the term ‘catching a cold’ – or a miasma emanating from swamps (malaria). It was the perfection of better optical lenses for microscopes that led to the identification of bacteria and other microscopic organisms as the cause of these infectious diseases. Identification of viruses came later with invention of the electron microscope.

      The 17th–18th-century German physician Robert Koch, who identified the tubercle bacillus and proposed that it was the cause of tuberculosis, was disbelieved by many of his contemporaries. In order to prove his hypothesis Koch established three most important elements of proof of causation of disease by a toxic agent.

      Now known as Koch’s postulates, these are:

      1 the proposed cause of the disease must always be shown to be present in a person suffering the disease;

      2 removing the proposed cause cures the disease; and

      3 reintroducing the putative cause re-establishes the condition.

      Koch went on to fulfil these three requirements for proof in experimental animals. As a result of this evidence his hypothesis became a fact. ‘The Germ Theory of Disease’, to which Koch’s and others microbiologists’ work had given rise, was espoused by many practitioners as though it applied to all diseases whether caused by micro-organisms or not. Clearly, it is going to be difficult, and often ethically improper, to try to satisfy all three of Koch’s postulates in all cases, but the more that are met, the more likely the proposed causal mechanism is to be correct. A recent example to hit the headlines, but one that fulfilled none of Koch’s postulates, was the suggestion that the measles virus is a cause of autism.

      Causation versus coincidence

      Illnesses caused by exposure to noxious substances, such as arsenic, have long been recognised. Those that take many years of exposure before the illness becomes apparent are much more difficult to identify.

      Richard Doll, the 20th-century British epidemiologist, demonstrated a relationship between cigarette smoking and the risk of developing cancer of the lung. He suggested that smoking caused cancer of the lung after he had surveyed people’s smoking habits and found very little effect in those smoking fewer than five cigarettes a day, whereas above this level the frequency with which they developed cancer increased with the number of cigarettes they smoked. This dose-related phenomenon added considerable credibility to his findings. When he further demonstrated that people – doctors, it so happened – who voluntarily stopped smoking reduced their risk of cancer dramatically, he had sufficient evidence to convince all but the most sceptical of a causal rather than chance association between the two. Without the supporting evidence the relationship between smoking and cancer of the lung would have remained a tentative hypothesis.

      Failure to seek evidential confirmation can produce half-baked theories, often presented in the media as ‘new scientific evidence’, that can be very misleading.

      Some years ago there was an epidemiological study that showed that the residents of the island of Okinawa, in the Pacific, lived longer on average than those on neighbouring islands. It was claimed that this was due to their high consumption of yams. The researchers clearly demonstrated that they did eat more yams and they did live longer. To have turned this hypothesis into proof they would have needed to show that the lives of the residents of Okinawa were shortened if they gave up eating yams and that by eating yams those living on nearby islands increased their life expectancy. They did not do this and the hypothesis remains unproven. It is highly probable that the conclusions are wrong and that the observations are better explained by the high proportion of the inhabitants of Okinawa who are of Japanese descent. Japanese have, in general, a longer expectation of life than almost all the other people living in the Pacific.

      Just as important as producing evidence to support a particular theory is the ability to demonstrate that any alternative explanation is wrong. It was this concept that led the distinguished 20th-century philosopher Karl Popper to propose that science advances by disproof. He pointed out that, if you made the hypothesis that ‘all swans are white’, it did not matter how many white swans you found, or how much evidence you gathered to support your theory, as soon as a black swan was found, the theory becomes untenable. However, it is always possible that the black swan was a white one that had been painted black or an odd genetic freak.

      In order to demonstrate the validity of the disproof, it would be necessary to show that it was a swan and that it was naturally black and bred other black swans. It is just as important to support any disproof with evidence as it is for proof. Popper pointed out that disproof is much more potent as an evidential weapon than proof. One element of disproof will dispel ideas supported by volumes of positive evidence. A tablecloth with a dirty stain in one corner is ‘dirty’ regardless of the fact that 99.9% of it is clean!

      This book

      This book is about evidence. It challenges some of the assumptions that we have come to accept as fact. It presents evidence that either supports the hypothesis or indicates that it is not necessarily the only, or even the best, explanation of observed events. In some instances, even the best analysis of present dogmas is unable to answer concerns about future uncertainties. Austin Williams points out in this book how mankind has, in the past, survived by overcoming the problems posed by nature while the doomsday soothsayers advocate a retreat into a primitive world of doing less, having less and achieving less. On the other hand, few would question the view put forward by Vincent Marks, in his chapter on population, that there must ultimately be a limit to unbridled population growth and consumption. However, no one knows what that limit is or how it will be affected by new technology and by world events.

      We live in an uncertain and unpredictable world – but none of us enjoys uncertainty. Nevertheless, we have to make decisions, and do so on the ‘balance of probabilities’ when we know what the alternatives are. Some scares, such as the probability that we will suffer a human bird flu pandemic sometime in the future, are justified by scientific evidence; some, such as the effect of unlimited growth, depend upon unpredictable future developments; while yet others are patently wrong. The millennium-bug scare was groundless. So were prophecies that AIDS and new-variant Creutzfeldt–Jakob disease (CJD) would decimate the population. Similarly, the prediction, made in the 1970s, of the coming of a new ice age and the authoritative forecast in 2006 that rainfall in England would decrease to a point where drought would be usual. All were pronouncements that made headline news but all have proved to be wrong.

      The paradox that many of the world’s great scientists are or were (religious) believers will not have escaped our readers’ attention. The ability to accommodate a belief system at the same time as a rigorous scientific inquisitiveness, in the same brain, is far from rare. Few things in life are certain

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