The Polymerase Chain ReactionJames D. Watson When, in late March of 1953, Francis Crick and I came to write the first Nature paper describing the double helical structure of the DNA molecule, Francis had wanted to include a lengthy discussion of the genetic implications of a molecule whose struc ture we had divined from a minimum of experimental data and on theoretical argu ments based on physical principles. But I felt that this might be tempting fate, given that we had not yet