Darwin's theory is still the fittest: Steve Connor asks why we still find natural selection so difficult to come to terms with

What is it about Darwin? More than a century has elapsed since his theory of evolution, in which time a wealth of scientific research has demonstrated its validity. Yet seemingly intelligent people still find it difficult to swallow.

The latest anti-Darwinist crusade started with a prominent news story in the Sunday Times at the end of August with the headline 'Scientist threatens to make Darwin extinct'. The article lionised a book called The Facts of Life - Shattering the Myth of Darwinism, written by one Richard Milton.

As it happens Mr Milton is not a scientist but an amateur geologist and journalist, who answers readers' queries for the computer magazine What Micro?. Yet the book struck a chord. Several newspapers followed the Sunday Times story. The Times ran an editorial saying the book 'could shake the 'religion' of evolution'. New Statesman and Society gave the book a 2,000-word lead review by Richard Dawkins, an Oxford University zoologist, who agreed to write lest the paper commission someone else who would treat it as a serious scientific treatise. Oxford students wanted to invite Dr Dawkins and Mr Milton to lead a re-run of the famous 19th-century debate on evolution between Bishop Wilberforce and T H Huxley.

The book presumably got such attention because it came from a serious and reputable publisher, Fourth Estate. Yet, as Dr Dawkins put it, it would be about as silly to publish a book claiming that the Romans never existed and that Latin was 'a cunning Victorian fabrication to keep schoolmasters employed'. No doubt Fourth Estate judged that there is a market for scientific iconoclasm. But, as Dr Dawkins says in his book The Blind Watchmaker, people rarely take on Einstein in the way they tackle Darwin.

This is because few people presume to understand theories of relativity but almost everyone thinks they understand Darwin's theory of natural selection and gradual change. It says (they think) that all species, including such advanced forms as Homo sapiens, have evolved by blind chance. This sounds ridiculous: a Creator sounds far more plausible.

People have several difficulties with Darwinism. First, they cannot grasp how there can be enough time for random mutation to throw up complex and successful life forms. We are used to dealing with events that take place in minutes, days or years. But many species live, reproduce and die at prolific rates, and evolution takes place over hundreds of millions of years, periods difficult to imagine.

We see a form of selection taking place in our own lifetimes: flies, resistant to insecticides, have thrived because they have an obvious selective advantage. Small genetic changes of this sort, giving slight advantages over competing forms of life, accumulate over millions of years. Eventually, life- forms become sufficiently different from their distant ancestors to be considered a new species. Contemporary cousins with common ancestors become so genetically divergent - perhaps by being geographically isolated - that they can become two or more different species. Chance is involved, certainly, but not blind chance because natural selection operates so that the fittest - those best adapted to their environment - survive.

A second difficulty is understanding the evolution of complex structures such as the vertebrate eye. What intermediate stages, people ask, could have led to something so seemingly wellengineered and how could they have arisen randomly? But a single light sensitive cell, the result of a single mutation, could give an organism an advantage over its competitors. Two light sensitive cells would be even better. If further mutations enabled these primitive eyes to focus, even greater advantage would ensue. And so on, and on.

Another problem for Darwinism is that it cannot be proved in a laboratory. But this does not disqualify it as science. The last and biggest difficulty is that people do not want to believe Darwinism. It reduces Homo sapiens to a bit player in Earth's history, a species that has a long way to go before it rivals the dinosaurs' record as lords of the Earth. Mr Milton - though he claims not to be a Creationist - puts Man back in the lead role. Most scientists estimate the Earth's age at 4.5 billion years. Mr Milton suggests it could be anywhere between 10,000 and 170,000 years old. Thus, Man has been around, if not for the whole time, at least a large chunk of it. As Dr Dawkins says, such claims fly in the face not just of biology, physics, cosmology and geology, they also make 'a complete nonsense of history and archaeology'.

The reality is that there are far more interesting debates about evolution than Mr Milton has raised. For example, Stephen Jay Gould, the American biologist, has described in Wonderful Life the huge diversity of marine fossils found in the Burgess Shale in Canada. Vast numbers of these creatures, apparently well-adapted, simply disappeared. He has suggested that, were the evolutionary tape to be re-run, we would not necessarily see the same organisms evolving successfully. Homo sapiens, perhaps, was just lucky. This is the real challenge to conventional ideas about Darwin. Evolutionists are constantly debating and fine-tuning their theories. But they are building on Darwin, not overturning him; it will take more than a few journalists and a maverick book to make him extinct.