Origin of the thesis: At the bottom of Darwin's garden

His Galapagos voyages are legendary, but Charles Darwin made many of his greatest breakthroughs at the bottom of his own garden. By Simon Usborne

There he is, on the back of the £10 note – a stately gentleman with a majestic beard and earnest eyebrows, gazing across the paper rectangle at a tableau of a life devoted to science. Laid over a giant compass, there is a hummingbird feeding on exotic yellow blooms and, sailing on the azure waters of the Galapagos, HMS Beagle, one of the most famous ships that ever set sail.

This is the popular image of Charles Robert Darwin (1809-1882), the Victorian naturalist whose observations and theory of evolution helped crack the code of life. But the voyages to the equator and the exotic birds that are the staple of biology textbooks formed only a small part of the life of the man on the money. Darwin's real laboratory was not the Galapagos, nor below the decks of the Beagle, but in the lawns, borders and orchards of his beloved Kent garden, where he liked nothing more than to potter, plant and observe nature surrounded by his family.

Michael Boulter, a professor of palaeobiology, has set out to reveal the real Darwin in Darwin's Garden, which separates the man from the legend. "Darwin is an icon and it's difficult to imagine icons as real people," Boulter says. "His image has become so wrapped up in Victorian mythology we've lost a sense of who he was."

Two years after Darwin returned from his five-year voyage on the Beagle, he married his cousin Emma Wedgwood (they shared as a grandfather the potter Josiah Wedgwood). The couple moved into a small north London house, but the hubbub of the capital suited neither Darwin nor his growing family so he looked to the countryside. They settled on a house in Downe, Kent, with a large garden. Darwin described Down House as "unattractive, bleak and desolate" and quickly set about making improvements. He turned the 16-acre estate of Down House into a place of study, where he could think in peace and test his nascent ideas. Boulter writes: "What first appeared to be an isolated and quite Victorian retreat would turn out to be the proving ground for revolutionary change."

Darwin is perhaps most famous for his finches. The variations in the closely related species of the birds he collected from isolated islands in the Galapagos – most notably their different-shaped beaks – would help to show how the animals adapted to food sources and thus drive evolution. But the image of Darwin realising this at the time is false. "It wasn't until many years later that they became the textbook example of evolution in action," Boulter says.

In the meantime, at Down House, it was the less exotic pigeon that fascinated Darwin. "He enjoyed the birds and the challenge of trying to work out what the hell was going on to produce all these funny shapes of feathers and other variations," Boulter says. Darwin asked the local carpenter to build an aviary against the wall of the orchard beside his greenhouse. On the rare occasions he returned to London, Darwin loved swapping notes with pigeon fanciers in the pubs of Borough Market at London Bridge.

For years, Darwin bred his pigeons to show what Boulter calls "an example of quick evolutionary experimentation"; by crossing birds with different characteristics, he attempted to discover the key to the adaptation of the Galapagos finches. Darwin's love of his pigeons was so great that when, one morning in 1860, his daughter Etty's cat invaded the aviary and killed some of Darwin's prized specimens, the fancier ordered the cat be killed. It was a reaction, suggests Boulter, not to the damage to his experiment, but to the loss of a life; Darwin was still mourning the death, nine years earlier, of his "favourite daughter", Annie, 10. Two other of Darwin's 10 children had died in infancy. "He was continuing to suffer and here was one of the surviving children being involved in the death of more of his 'babies'," Boulter says. "This time it was pigeons but, what the hell, a life was a life."

It was an uncharacteristic act of cruelty by Darwin, whom Boulter describes as "a friendly father with a good sense of humour, who loved to go on walks with his wife and was adored by his staff." Perhaps the most endearing image of Darwin the garden scientist came when he turned his attention to earthworms. Not much thought had been given to the lowly burrowers, but Darwin saw method in their apparently pointless existence. He devised a way to measure their activity, which he suspected played a key role in shaping the earth beneath his lawns and borders. He built a "wormstone" – a disc of stone whose slow sinking caused by the displacement of earth by worms Darwin could measure. In this and other worm experiments, Darwin would encourage the wrigglers to move by playing music with his daughters. Boulter writes: "Emma played loudly on the piano indoors, Francis played the bassoon and Darwin whistled."

The wormstone was among many gadgets Darwin used in his garden, but the naturalist was happiest pottering rather than tinkering. At least once a day he would take a stroll through the copse he had planted in his garden when he moved to Down House. He called it the Sandwalk. It was during these walks that Darwin observed subtle variations in the species of plants that dotted the wood floor, and those he saw beside the lanes that led to Orpington, from where he would catch the train to London. "He had this eureka moment," Boulter says. "He wondered, maybe the plants have migrated down the hill of Downe and adapted to the slightly different environment there. And maybe this is what drives evolution forward. And, of course, he was right – taken on a global scale, the movement of flowers down the hill replicated the distribution of species across continents, which is the driving force of environmental change and the evolution of population."

And all this in Darwin's back garden. In 1859, almost 20 years after Darwin moved to Downe, he published his life's work: On the Origin of Species. Earlier in his career, Darwin had been a nervous scientist. "He was conscious that, without any professional training as a biologist, he was speaking out of turn with his extravagant views," Boulter says. "So he silenced his pen. It was only the observations he made in his garden that gave him the confidence to publish."

Boulter says the aggressive theories of "the survival of the fittest" were forced upon the scientist in the macho Victorian era of empire-building and grand discovery.

"It's misleading, because Darwin's theories weren't necessarily like that," Boulter says. "He showed that species were, very cunningly and quietly, taking advantage of situations that were available. I guess Darwin was doing the same with his garden – he was quietly moving forwards, often at a snail's pace, but eventually he got the answer."

Darwin's Garden by Michael Boulter is published by Constable & Robinson, priced £16.99. To order this book at the special price of £15.29, call Independent Books Direct on 0870 079 8897 or visit www.independentbooksdirect.co.uk