The creationist movement, and its cloak of “intelligent design” theory, is usually seen in Britain as a peculiarly American phenomenon. Most of us are relieved that our schools have not had to fight off a lobby seeking to deny the facts of evolution and enforce teaching of theocratic dogma in its place.

A recent poll for the BBC’s Horizon programme, however, suggests that Britons of a scientific bent would be unwise to be complacent. A surprising four people in ten, it found, think that religiously inspired alternatives to evolution should be taught in the science classroom.

The survey probably overestimates support for creationism, but on the eve of Darwin Day — the 197th anniversary of the great man’s birth is tomorrow — it is a reminder that Britain is not immune. Whether it is city academies adding God to science lessons, or columns pushing intelligent design in The Daily Telegraph, creationism is seeking to establish a British foothold.

This must be resisted, chiefly because introducing faith to science, a discipline based on experiment and evidence, undermines the critical thinking that education should promote. But the practical consequences of evolution denial are worth considering, too. Prominent among them is the effect it has on health. It is impossible to understand biology, and therefore medicine, without a good grasp of evolution.

Darwin’s natural selection has transformed medical science. Its contribution to health stands comparison with Jenner’s vaccine, Pasteur’s germ theory of disease and Fleming’s antibiotics.

Infectious diseases are a prime example. Influenza and MRSA show natural selection in action. These pathogens mutate and those variants that acquire an ability to evade immune systems, or to resist antibiotics, are the ones that thrive. Flu pandemics and superbugs arise because of an evolutionary arms race between germs and their human hosts.

An understanding of how pathogens evolve, and how our immune systems evolve

to counter them, enhances greatly medicine’s ability to fight back. It is critical to tracking new diseases — our surveillance of bird flu is largely a matter of monitoring the evolution of the H5N1 virus. It highlights weaknesses in the defences of viruses and bacteria, which can be used to improve drugs. It also assists immunisation, allowing vaccines to be redesigned in response to emerging resistance. The development of an Aids vaccine will probably rest on establishing how HIV evolves so rapidly to evade antibodies.

The importance of evolutionary insights is not limited to infections. Genetic conditions make sense only when considered in light of evolution. Sickle-cell anaemia is a case in point: it is an unfortunate by-product of an evolutionary adaptation. When people inherit one copy of the sickle-cell mutation, they acquire a beneficial resistance to malaria that has ensured the gene’s survival. When they inherit two, the result is a nasty disease.

Cancer is the result of another evolutionary trade-off — the ability of tissues to repair themselves also allows for uncontrolled cell division when certain genes go wrong. Obesity and type 2 diabetes are linked to evolution, too. Through most of human history, food has been scarce, favouring bodies that store fat readily and shed it reluctantly. This beneficial trait, however, becomes malign when a high-calorie diet combines with a sedentary lifestyle.

Recognising the origins of these conditions, of course, is the first step towards understanding and treating them, and evolution is fundamental to this goal. Its importance has been proven at the coalface of medical research, where creationism has contributed, and can contribute, absolutely nothing. The forthright defence of Darwin’s legacy is of far more than intellectual significance. It is also critical to effective medicine.

Mark Henderson is the Times science correspondent