Charles Darwin's theory of evolution by natural selection - and the modern world view of the origins of man - might never have come about if the eager young naturalist from Shrewsbury had not taken a coach journey at just the right time.
His father, Dr Robert Darwin, had already barred the Shropshire lad from joining the HMS Beagle expedition to South America in 1831. Only after Charles's uncle, Josiah Wedgwood, had made the doctor change his mind did the 22-year-old rush down to London to claim his berth on the voyage. But his procrastination meant his place had already been awarded to another candidate. By a stroke of luck, his rival had just withdrawn from the voyage. So Charles put himself forward and was accepted at the last gasp: survival of the luckiest or a case of random selection?
"It's true to say that On the Origin of Species would never have been written unless Darwin had arrived at the Admiralty at that moment," said Jon King, director of Shrewsbury's annual Charles Darwin Festival, which runs from Thursday to 28 February. "The voyage was essential to him developing his theories.
"The accepted view is that the Beagle voyage was the start of his life of discovery. But it started long before that with digging for worms in the garden of The Mount - his father's house - scouring the banks of the Severn, even shooting and fishing, walking among the fantastic geological formations of Shropshire, and in conversation with the brilliant mind of his grandfather Erasmus. He'd rejected medicine and the church and developed a passion for the natural world long before the Beagle trip was even thought of."
Such perspectives are typical of the approach to the great 19th-century scientist taken by his home town, which has focused on his youth since it started the festival five years ago. The Beagle anecdote is one of many that Jon tells on his guided walk around the 10 Darwin sites in Shropshire's beautiful county town. He also slips in the fact that Darwin was - like any gap-year student - forever asking his father for money.
Every year at the Bellstone, a granite boulder thought to have been brought here during the Ice Age, a toast is drunk to the great man on his birthday, 12 February. Visitors are also shown the spot where a young Charles was duped into believing that if he wore his friend's "magic hat" at an angle he could take any food he wanted from the Pailin cake shop.
The Darwin Gate, a sculpture installed in 2004, uses Gothic arch shapes that make visual sense only when seen at a distance - symbolic apparently of how the naturalist saw life in a fresh way. Despite the strong family Unitarian connections, he was baptised in the Church of England St Chad's, whose establishment status maximised his chances of getting into Cambridge.
Darwin attended Shrewsbury School, whose original 16th-century building is now the town library. Because the school taught only Latin and Greek, Darwin wrote later that "nothing could have been worse for my development than Shrewsbury school". His keenness for conducting out-of-hours scientific experiments earned him the nickname Gas. Perhaps it's apt that the statue of him has its back to the school.
It is planned to open The Mount, Darwin's imposing birthplace (and, bizarrely, in the property portfolio of the Office of the Deputy Prime Minister) to the public in time for both the 2009 bicentenary celebrations of his birth and the 150th anniversary of the publication of On the Origin of Species.
Since its inception, the annual festival has grown in stature. Each year has had a theme - among them genetics, climate change, artificial intelligence and, this year, geology. Celebrity speakers have included David Bellamy, Colin Pillinger and Richard Dawkins.
This year will feature a geological walking tour, led by experts, along Wenlock Edge, to view the legendary fossilised coral reef, which was once connected to Antarctica. There will be talks on the 19th-century botanist Joseph Hooker and his friendship with Darwin. Professor James Moore, Darwin's biographer, will deliver the Charles Darwin Memorial Lecture, "Darwin, Sex and Slavery", to mark the 200th anniversary of the parliamentary abolition of the transatlantic slave trade. For all the misrepresentation of his works in the 20th century, in particular the mistaken link with the theory of eugenics, Darwin himself was an abolitionist.
Ever mindful of maintaining as wide a remit as possible, the organisers have invited Alistair McGrath, a professor of theology, to talk on "Atheist Interpreters of Darwin: Richard Dawkins on the God Delusion". Shropshire and the Galapagos Islands will also be the subject of talks and exhibitions and there will be a dramatic interpretation of Darwin as a family man at St Julian's Church.
"The issues that Darwin throws up are still being debated and we try to reflect current thinking," said Jon King. "But there's a fun side to the festival, too, with many activities for the whole family."
Children can experience what it's like to be a snail or a slug by creating their own slime at the Shropshire Hills Discovery Centre, which over the years has come up with a secret recipe for recreating primordial ooze. Snail races are followed, in slow succession, by "Tweet, Tweet" in which kids learn how to make a nest box and play the Beak Evolution Game. This involves matching certain kinds of birds' beaks to habitats and foods. The Shropshire Wildlife Trust is holding a fossil-making day and the Ludlow Resource Centre offers creative activities around dinosaurs and prehistoric mammoths found locally.
Even music gets a look-in, courtesy of the town's concert band which will play works with a Darwin theme, including a choral piece composed specially for his funeral at Westminster Abbey in 1882 - "Happy is the man that findeth wisdom". The composer Ralph Vaughan Williams was Darwin's great-nephew, and the concert will feature some of his music too.
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Robert Nurden stayed at the Prince Rupert Hotel (01743 499955; prince-rupert-hotel .co.uk) and was a guest of Shrewsbury Tourist Office (01743 281200; visit shrewsbury.com), where double rooms cost from £105 per night b&b. He travelled from London Euston to Shrewsbury with Virgin Trains (08475 222333; virgin.com/trains) and Central Trains (0845-302 2022; centraltrains.co.uk). Return fares cost from £41.
The Darwin Festival runs from 1 to 28 February in Shrewsbury. For details contact Destination Shrewsbury (darwinshrewsbury.org).