How Darwin changed the world

What was so new about his theory?

Religious fundamentalists today rail against Charles Darwin for challenging the account of creation in Genesis, but this was not in fact a major issue at the time of his seminal work, On the Origin of Species, published in 1859. Long before Darwin, the Victorian geologist Charles Lyell had debunked the idea of seven days of creation; indeed, 19th century scholarship encouraged Christians to see the early Bible stories as metaphors rather than literal accounts. Many theorists before Darwin had endorsed the idea of evolution - though to most it was a divinely ordained linear evolution, a march to ever greater perfection, with Man as the pinnacle. What was new and deeply unsettling about Darwin's idea was that it seemed to do away with the need to invoke divine authority or any sense of purpose or design.

And what were the ingredients of Darwin's Big Idea?

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It rests on three fundamentals: the observation that the offspring of plants and animals naturally vary from their parents by random mutation; the assumption that those variations are passed down through the generations; and the hypothesis that in a world where population growth outstrips the increase in available resources, any individual with a genetic variation that confers a competitive advantage in the struggle for resources is more likely to survive to breed and pass that variation on – eventually leading to a new species. Darwin referred to this process as "natural selection", though even that was not entirely novel.

Who else had speculated on those lines?

His grandfather, Erasmus Darwin, among others. Long before his grandson, the noted polymath and free thinker had outlined his view – in works such as The Origin of Society (1803) – that life had evolved as a result of natural variation influenced by the "three great objects of desire": sex, sustenance and security. Long before his grandson, he had earned the wrath of conventional thinkers. The idea that "the whole human species is accidentally descended from a remarkable family of monkeys" is absurd, said the author of Rip van Winkle, Washington Irving, while Samuel Taylor Coleridge scoffed at the idea that man had descended "from some lucky species of baboon".

Was Darwin an infant prodigy?

Far from it. He was kicked out of school in Shrewsbury; he dropped out of medical studies in Edinburgh; and when sent up to Cambridge to study for Holy Orders - to prepare him for the Anglican priesthood - he spent his time on shooting trips and foraging for beetles. "You care for nothing but shooting, dogs and rat-catching, and you will be a disgrace to yourself and your family," said his exasperated father, a wealthy society doctor and financier. It was only because Darwin had befriended a botany professor at Cambridge that he was invited on a surveying trip to Tierra del Fuego on board the Beagle, as a gentleman naturalist and companion to the captain. And it was only after his uncle, Josiah Wedgwood, persuaded Darwin's reluctant father to pay for the jaunt, that he set off in 1831 on his five-year odyssey around the coasts of South America.

Did he arrive at his theory on this trip?

No, but the observations he made and specimens he collected set him on the path. The variations in the closely related species of finch he found on isolated islands in the Galapagos (notably their different-shaped beaks) would help show how animals evolved as they adapted to food sources and gave him the first inkling of his big idea. But the fully developed theory did not take its final shape for another quarter of a century. What took him so long to publish?

Partly because he hated controversy (he once said that explaining his beliefs was like "confessing to a murder") and was fearful about the effects on his devoutly Christian wife, Emma (daughter of Josiah Wedgwood). When he did publish, he confined his account of evolution to animals and plants, avoiding the tricky issue of human origins as "surrounded with prejudices". He also knew that if his ideas were to be accepted, he had to present a meticulously supported case. So he used the intervening years to add "great quantities of facts" to his Beagle observations, turning his kitchen garden into a lab and developing a far-flung network of correspondents - friends, pigeon fanciers, nurserymen, colonial officials, missionaries, game keepers, gardeners. He wrote out his theory in some detail in 1844, but was still hesitating to publish when, in June 1858, one of his correspondents, the explorer Alfred Russel Wallace, wrote to him outlining a mechanism for species change identical to his own. Ashamed of his "trumpery feelings" of disappointment that his "priority" of discovery was compromised, Darwin went public with his big idea in 1859. So did his theory make Darwin an atheist?

Darwin claimed only to be agnostic, and it was personal tragedy rather than science that made him doubt – notably, the death of his beloved daughter Annie, at the age of 10. After her death, he no longer attended the village church and his failure to find spiritual comfort in his grief seems to have strengthened his trust in natural laws.

And his impact on science?

Origin gave to biology its key guiding principle. When Mendelian genetics, accompanied by the discovery of chromosomes, became established in the early 20th century, it explained many of Darwin's observations about heredity. When the DNA helix was unravelled 50 years later, it served to underpin the molecular basis of genetic variation on which the forces of natural selection act. Even the Pope had to declare in 1996 that Darwin's theory of evolution was now "more than a hypothesis". Even so, in a 2006 BBC poll, only 48 per cent of the British public accepted the theory of evolution as the best description for the development of life.