ANYONE doubtful about Darwin should do a little homework on flu. There is no intelligent design in a virus — only the mindless force of natural selection.

Darwin realised that random errors in reproduction will automatically ensure successive generations become adapted to their environments. Viruses are the speeded up version of evolution — the whole process is happening before our eyes.

The fact that flu is caused by a virus was a British discovery, made in 1933 by scientists of the Medical Research Council (MRC). The MRC still plays a central role in the global fight against flu.

Its National Institute for Medical Research at Mill Hill, north London, houses the World Health Organisation’s World Influenza Centre, the hub of a network of laboratories that analyses virus samples from around the world, following the evolution of new strains. Their advice guides the production of vaccines.

The swan washed up on a beach in Fife is just the latest story in the evolution of flu. We now know it was infected with the dreaded H5N1 virus, raising fear of a deadly pandemic.

We are reminded of the Spanish flu of 1918, the most devastating plague in history. One billion people, half the world’s population, were infected; one in 20 died.

Sir John Skehel, the director of the MRC institute at Mill Hill, analysed the structure of the 1918 virus and found it was a bird virus that had changed to enable it to transmit readily from person to person.

The crucial step that triggers a pandemic is probably a process known as reassortment, which could occur in an animal infected with two different strains of flu. The genes of the two viruses could combine to create a novel virus with the ability to spread easily from person to person. This might occur in a person, or any species that can catch both bird flu and human flu, perhaps a pig, a cat or a ferret.

How worried should we be? Given the historical record, we can be sure there will be flu pandemics in the future. But we must get the threat into perspective. H5N1 has been in circulation for nearly 10 years without the crucial change. It is currently a disease of birds.

H5N1 has infected almost 200 people in southeast Asia and Turkey and more than half of them died. But, so far, virtually all cases seem to have occurred in people in very close contact with heavily infected poultry.

Wild ducks are playing a sinister role in the evolution of H5N1. They can be infected with H5N1 and spread the virus to other birds but do not develop symptoms or die. This means H5N1 is likely to circulate for years to come.

Threat is the engine of innovation. Medical agencies are researching how H5N1 affects the body, how it spreads, and how to develop new anti-viral drugs — for poultry as well as humans. But research will take time. We have to hope evolution will be kind to us and that containment will buy us that time. The future holds a competition between time, chance and science.

Colin Blakemore is chief executive of the Medical Research Council

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