HIV heretics

Although the evidence in favour of an association between HIV and Aids looks convincing (Books, THES, July 7), we know from history that in science the big battalions are often wrong.

For example during and after the 1918 influenza epidemic (which killed 50 million people) most authorities were confident that flu was caused by the bacterium Bacillus influenzae. But there was a growing minority of microbiologists who suspected the disease might be caused by a filterable bacterium or by a true virus. These dissenters were marginalised and ridiculed.

A similar situation occurred in the history of stomach ulcers and gastric cancers. Before the 1980s nearly every gastrologist could confidently state that ulcers were caused by stress, and yet a few years later a bacterium (Helicobacter pylori) was shown to be the true cause of this disease.

In both cases, the experts used the most up-to-date methods and were happy to ridicule anyone who took an opposing view - yet in the end they were plain wrong.

Such examples are so common that there appears to be a "law" operating, namely that when an idea supported by an establishment majority is criticised by a knowledgeable, persistent minority it is usually the minority view that eventually prevails.

The "law" seems to operate because establishment scientists have everything to gain (honours, grants, promotions) from continuing with their views, even when evidence indicates they are wrong. The minority dissenters, on the other hand, who are often ridiculed, gain little from maintaining their views. The degree of persistence often provides a good test of whether a minority view is likely to be correct, since when the dissenters realise they are wrong, they usually quietly fade away. But if a knowledgeable minority maintains its criticisms over a long period it is usually shown to be right.

Milton Wainwright Department of molecular biology and biotechnologyUniversity of Sheffield