My Eureka Moment ; Fifty Years Ago Tomorrow, Two Young Scientists Finally Solved Science's Greatest Mystery: The Structure of DNA. Here, One of Them, JAMES WATSON (Left), Describes the Moment He and Francis Crick Cracked the Code of Life
Watson, James, The Independent (London, England)
As was normal for a Saturday morning, I got to work at Cambridge University's Cavendish Laboratory earlier than Francis Crick on 28 February 1953. I had good reason for being up early. I knew that we were close - though I had no idea just how close - to figuring out the structure of a then little-known molecule called deoxyribonucleic acid: DNA. This was not any old molecule: DNA, as Crick and I appreciated, is the chemical structure that holds the very key to the nature of living things. It stores the hereditary information that is passed on from one generation to the next, and it orchestrates the complex world of the cell. Figuring out its three-dimensional structure - the architecture by which the molecule is put together - would, we hoped, provide a glimpse of what Crick referred to only half-jokingly as "the secret of life".
We already knew that DNA molecules consist of multiple copies of a single basic unit, the nucleotide, which comes in four forms: adenine (A), thymine (T), guanine (G), and cytosine (C). I had spent the previous afternoon making cardboard cut-outs of these various components, and now, undisturbed on a quiet Saturday morning, I could shuffle around the pieces of the three-dimensional jigsaw puzzle. How did they all fit together? Soon, I realised that a simple pairing scheme worked exquisitely well: A fitted neatly with T, and G with C. Was this it? Did the molecule consist of two chains linked together by A-T and G-C pairs? It was so simple, so elegant, that it almost had to be right. But I had made mistakes in the past, and before I could get too excited, my pairing scheme would have to survive the scrutiny of Crick's critical eye.
It was an anxious wait. But I need not have worried: Crick realised straight away that my pairing idea implied a double-helix structure with the two molecular chains running in opposite directions. Everything known about DNA and its properties - the facts we had been wrestling with as we tried to solve the problem - made sense in light of those gentle complementary twists.
Most importantly, the way the molecule was organised immediately suggested solutions to two of biology's oldest mysteries: how hereditary information is stored, and how it is replicated. Despite this, Crick's brag in the Eagle, the pub where we habitually ate lunch, that we had indeed discovered that "secret of life", struck me as somewhat immodest, especially in a country such as England, where understatement is a way of life.
Crick, however, was right. Our discovery put an end to a debate as old as the human species: Does life have some magical, mystical essence, or is it, like any chemical reaction carried out in a science class, the product of normal physical/chemical processes? Is there something divine at the heart of a cell that brings it to life? The double helix answered that question with a definitive No.
Charles Darwin's theory of evolution, which showed how all of life is interrelated, was a major advance in our understanding of the world. The breakthroughs of the early bacteriologists, Theodor Schwann and Louis Pasteur, during the second half of the 19th century, were also an important step forward. But despite these advances, various forms of vitalism - the belief that physiochemical processes cannot explain life and its processes - lingered on. Many biologists, reluctant to accept natural selection as the sole determinant of the fate of evolutionary lineages, had invoked a poorly defined overseeing spiritual force to account for adaptation. Physicists, accustomed to dealing with a simple, pared-down world - a few particles, a few forces - found the messy complexity of biology bewildering. Maybe, they suggested, the processes at the heart of the cell go beyond the familiar laws of physics and chemistry. …