cause the end of the world’, ‘will kill hundreds of thousands’ and ‘time is running out’ should alert readers to the probability that they are being mentally bullied and manipulated. It should warn them of the need to examine the evidence carefully to see whether the case is indeed proven ‘beyond reasonable doubt’.
Defining our terms
Beliefs are authoritative statements that have not been subjected to testing or are incapable of being tested. They rely on anecdotal evidence and the power of authority.
Hypotheses are tentative beliefs that are subject to proof or disproof and consequently a step beyond ‘belief’.
Facts are measurable and reproducible events. There is no known or current evidence that casts doubt upon their truthfulness. They are therefore ‘beyond reasonable doubt’, although new evidence may emerge to question their accuracy in the future. Such is the nature of progress.
To illustrate the importance of separating these three categories let us consider some examples.
Before the 16th century it was universally believed that the sun orbited the Earth. This was a consensus opinion. Not to accept this idea was regarded as heresy. It was an authoritative dogma promulgated by the Church and could not be questioned. The authority of the Bible was invoked as evidence to support the claim – if, indeed, evidence was required, since it was ‘self-evident’ from everyone’s personal daily experience. The idea that the Earth spun at an incredible speed as it orbited the sun seemed as improbable as it was blasphemous. Unlike many beliefs, this one 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
