At lunchtime on the 8th of February fifty-odd years ago, two young men rushed into a pub in Cambridge and told anyone who would listen that they had discovered 'the secret of life'. Not surprisingly, most of the other customers just stared into their pints... Today, everyone has heard of DNA. It shouts in capital letters from newspaper headlines: it helps to solve ancient mysteries, it brings hope to the ill and frees people accused of crimes they did not commit. But the uses of DNA that have developed over the last few decades fuel some of the greatest moral debates we've ever faced. DNA is often a double-edged helix. So, what's so special about DNA? A hint is given by the first double helix model, reconstructed in London's Science Museum. It stands alongside other objects from the 1950s -- a prototype jet-powered car, a hand-cranked calculator and a box of parts for testing how quickly factory workers could assemble things. The 1950s was a mechanical age of chrome, metal, wood and varnish. There were few plastics, a limited range of colours and no modern electronics. The room-sized computers of the time stored their data in mecury-filled tubes through which pulses of sound were passed -- an echo of wartime sonar. Take apart any of these old machines and you can begin to understand how they work -- quite unlike a mobile phone or a flat-screen TV today. And the 'secret of life' stands there, made from steel plates, brass screws and old laboratory stands; a metal sculpture that's quite at home in mechanical surroundings. Study this model and just like the machines around it you can start to picture how DNA might work -- how life itself might work. Knowledge of the structure of DNA revealed almost at once a mechanism for the replication, mutation and expression of genes. This is why the double helix was so important; it was a discovery that changed our world and our understanding of our place in it. | 
