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that was when I told them something factual—that irradiation with X rays dramatically reduced the viscosity of a solution of DNA. I would dearly love to know exactly what I said on that occasion. I think I know what I would have said, but the memory is so overlaid with the ideas and developments of later years that I feel I can hardly trust it. Nor, as far as I know, have my notes for the talk survived. However, what I probably discussed was the importance of genes, why one needed to discover their molecular structure, how they might be made of DNA (at least in part), and that the most useful thing a gene could do would be to direct the synthesis of a protein, probably by means of an RNA intermediate.
    After a year or so I went to Mellanby to report progress. I told him that I was getting results on the physical properties of cytoplasm but that I had spent much of my time in trying to educate myself. He looked rather skeptical. “What does the pancreas do?” he asked. I had only the vaguest ideas about the function of the pancreas but I managed to mumble something about it producing enzymes, hastily adding that my interests did not lie so much in organs as in molecules. He seemed temporarily satisfied.
    I had visited him at a fortunate moment. On his desk lay the papers proposing the establishment of an MRC unit at the Cavendish to study the structure of proteins using the method of X-ray diffraction. It was to be headed by Max Perutz, under the general direction of Sir Lawrence Bragg. To my surprise (because I was still very junior), he asked me what I thought about it. I said I thought it was an excellent idea. I also told Mellanby that now that I had a background in biology, I would like to work on protein structure, since I felt my abilities lay more in that direction. This time he raised no objection, and the way was cleared for me to join Max Perutz and John Kendrew at the Cavendish.

3

The Baffling Problem
    I T IS TIME to step aside from the details of my career to consider the main problem. Even a cursory look at the world of living things shows its immense variety. Though we find many different animals in zoos, they are only a tiny fraction of the animals of similar size and type. J. B. S. Haldane was once asked what the study of biology could tell one about the Almighty. “I’m really not sure,” said Haldane, “except that He must be inordinately fond of beetles.” There are thought to be at least 300, 000 species of beetles. By contrast, there are only about 10, 000 species of birds. We must also take into account all the different types of plants, to say nothing of microorganisms such as yeasts and bacteria. In addition, there are all the extinct species, of which the dinosaurs are the most dramatic example, numbering in all perhaps as many as a thousand times all those alive today.
    The second property of almost all living things is their complexity and, in particular, their highly organized complexity. This so impressed our forebears that they considered it inconceivable that such intricate and well-organized mechanisms would have arisen without a designer. Had I been living 150 years ago I feel sure I would have been compelled to agree with this Argument from Design. Its most thorough and eloquent protagonist was the Reverend William Paley whose book, Natural Theology — or Evidence of the Existences and Attributes of the Deity Collected from the Appearances of Nature , was published in 1802. Imagine, he said, that crossing a heath one found on the ground a watch in good working condition. Its design and its behavior could only be explained by invoking a maker. In the same way, he argued, the intricate design of living organisms forces us to recognize that they too must have had a Designer.
    This compelling argument was shattered by Charles Darwin, who believed that the appearance of design is due to the process of natural selection. This idea was put forward both by Darwin and by Alfred Wallace,