To some extent, Darwin's theory was a product of its time. Another great naturalist-explorer, Alfred Russell Wallace, simultaneously arrived at very similar notions after travels in South America and Indonesia. Both he and Darwin were influenced by Thomas Malthus, who argued that human population growth was limited by struggles to survive.

In broad terms, the evolutionary theory they described involved individuals of a species varying from one another - and if the variations helped them survive they had more chance of passing on these traits, which could lead to species changing over time.

Like all scientific theories, Darwinism has been tested wherever possible. Among scientists it has held up well. But this has not prevented attacks, chiefly from outside the scientific community.

On 11 November, this newspaper published one such attack in a letter from reader Kevin Ma. To my mind the letter featured leaps in logic, such as apparently suggesting there is no "struggle for existence", and so natural selection cannot produce higher forms: "Therefore lower organisms including primates such as monkeys cannot evolve into human beings."

Ma also claimed there was greater trouble for Darwin's theory in the form of soft sponge embryos in Precambrian rocks, asserting: "Through scientific evidence alone, one can clearly see that evolution cannot produce the wonderful complexity that we see in all life and in our own bodies."

These are bold claims indeed. But it was also revealing that Ma described himself as a "former atheist" - so surely his main leap is a leap of faith, into a realm away from science. For science abounds with evidence natural selection can produce astonishing complexity - and is not content with concluding something hard to explain must be the work of one or more supernatural beings.

Fossils are a key source of evidence for evolution. While Darwin referred to the fossil record, he also noted it was incomplete.

One period proved especially puzzling to Darwin. Soon after the onset of the Cambrian age about 542 million years ago, it appeared there had been an "explosion" in the diversity of life. Summarising what became known as Darwin's Dilemma, he wrote: "To the question why we do not find rich fossiliferous deposits belonging to these assumed earliest periods prior to the Cambrian system, I can give no satisfactory answer."

Creationists - aka intelligent design proponents - seized upon this period as if it demolishes evolutionary theory, implying that one day the supernatural being waved a magic wand and said "let there be shellfish, trilobites and crustacean-like critters." The soft-sponge fossils referred to by Ma suggest processes forming older rocks did suit fossilisation, but ancestral Cambrian life forms were mostly absent.

Yet recent research suggests that while the Cambrian was special, there is no real dilemma. Mechanisms for driving the burst of diversity have been suggested, such as increased calcium levels in oceans as the sea eroded immense areas. Though fast, the "explosion" took far longer than a day.

"We found that with improved dating and correlation of rock sequences, the short burst of appearances goes away," said Susannah Porter of the University of California Santa Barbara, US. "Instead, appearances of the earliest skeleton-forming animals were drawn out over more than 20 million years."

Even as evidence for evolution by natural selection accumulates, creationists argue more strongly for their supernatural designer. Religion-inspired pseudoscience is tenacious. Yet there is one thing all should agree on - particularly if you believe man was given dominion or stewardship over nature. The diversity of life is magnificent, and we should do all we can to safeguard it.