Nature 27 April 2000

Dear Mr Mbeki ...

We are writing in response to your recent letter to world leaders, including US president Bill Clinton and United Nations secretary general Kofi Annan, expressing your concern about the horrific situation that your country faces over the spread of AIDS, and your desire to see the situation approached in the most rigorously scientific way possible (see page 911). We share this goal; AIDS will not be defeated or contained without access to the best treatment that modern science has to offer. But we are also concerned that, in your admirable enthusiasm to ensure that a wide spectrum of scientific views is heard, you appear tempted to give greater weight to some voices than the scientific process justifies.

No one who has been impressed by your success in what many claimed impossible — the peaceful transition to democracy in South Africa following the long struggle against the iniquities of apartheid — will reject the argument that there are times when the voice of those challenging the existing order must be heard. Your own colleagues have referred to the astronomer Galileo in this context. But this does not mean that all dissidents and 'heretics' can claim equal legitimacy merely on the basis of their persecution; democratically endorsed procedures exist through which their ideas can be put to the test, and viable heresies separated from those that, after close scrutiny, deserve to be placed aside.

Politics has developed one set of such procedures: the ballot box, parliamentary debate and constitutional law. Science has developed its own, very different, set. Contrary to the impression given by your letter, science thrives on the ideas of heretics. But heretical hypotheses only become widely accepted in science if they prove useful and effective in understanding and interacting with the natural world. The peer-review system is little more than a way of speeding up the process of sorting out those ideas which have a greater chance than others of surviving intellectual scrutiny and testing through experiment.

One hypothesis that has survived this process is that the idea that there is a direct, causal relationship between infection with the human immunodeficiency virus (HIV) and the onset of AIDS. We are well aware of the arguments of those who challenge such a direct relationship. Our columns have been — and remain — open to anyone offering evidence to the contrary, but on one simple condition: that their evidence passes the same rigorous tests of scientific robustness that are applied to any scientific paper that we receive. So far this has not happened. Those who have experienced rejection may choose to castigate this as 'censorship', but the vast majority of authors of the scientific papers that we reject on technical grounds accept the process as valid and necessary for the health of science.

You yourself admit in your letter to President Clinton and the other world leaders that your comments about the treatment being given to heretical ideas on the nature of AIDS may be "extravagant"; you justify this on the grounds that in the recent past you have had, in your own words, "to fix our eyes on the very face of tyranny". But as Koïchiro Matsuura, the new head of Unesco, said at a meeting in Nigeria this week: "Without a scientific capacity of its own, Africa will not be able to tackle and overcome its endemic diseases".

Mr Mbeki, we ask you, in the spirit of Matsuura's comment, not to ignore the advice of your own leading scientific and medical experts, nor to reject those aspects of science that offer your country the greatest hope for the future. A respect for vigorous scientific debate is one of these aspects that we endorse. Giving excessive credence to populist hypotheses that fly in the face of established evidence and fail to survive rigorous peer review is not.