The fact that James Watson and Francis Crick were able to discover the structure of DNA is, in retrospect, somewhat shocking. By the early 1950s, it had become clear that the riddle of DNA's structure would be solved through X-ray crystallography, while Watson admits in the fourth chapter of The Double Helix that "I knew nothing about the X-ray diffraction techniques that dominated structural analysis" (Watson 31). Moreover, some of the best scientists who did have a knowledge of X-ray crystallography -- like Linus Pauling in America and Rosalind Franklin in the UK -- were consciously working on the structure of DNA at the same time that Watson and Crick got involved. Additionally, Watson was extraordinarily young at the time of the discovery. Although Crick was "thirty-five, yet almost totally unknown" at the time of their collaboration (Watson 7) but Watson was born in 1928 and in his early twenties while working on the structure of DNA. Watson was thus eight years younger than Rosalind Franklin, twelve years younger than Crick or Maurice Wilkins, and almost thirty years younger than Linus Pauling. Finally, Watson's scientific background before his arrival in England had been in zoology rather than chemistry: the fact that he would solve a problem involving chemical structure therefore seems utterly unlikely (Lecture Notes). However the account given by Watson in The Double Helix goes a long way toward demonstrating how this unlikely duo managed to discover the structure of DNA.
A large part of the discovery, however, was due to non-scientific factors -- particularly the social and cultural traditions that can have an effect on the pursuit of science, but which in this case were overcome, often by the sheer force of Watson's personality. Watson emphasizes the most particular aspect of the social environment of England in the second chapter of The Double Helix, by way of explaining why Crick had not concentrated on the structure of DNA before Watson's arrival: "it would have looked very bad if Francis had jumped in on a problem" that had already been under study by Maurice Wilkins (Watson 15). Watson specifies that this problem was specific to England, where "it simply would not look right," and it would not have arisen in France "where fair play obviously did not exist" nor in America, where different researchers would be at different institutions and thus engaged in competition (Watson 15-16). Watson's own account in The Double Helix emphasizes competitiveness, and casts the discovery of DNA almost as a race in which Watson and Crick managed to beat out other competitors like Pauling, Wilkins, and Franklin. However it is crucial to note that Watson was also taking advantage of a long-standing scientific tradition here, in which it is customary for a scientist to share his research with others working on the same problems: indeed, as The Double Helix makes clear, Watson and Crick would have been utterly unable to determine the correct structure without access to Rosalind Franklin's research. Moreover, as Watson describes in the twenty-third chapter, he got access to Franklin's photographs not through Franklin but through Wilkins, which violates this scientific etiquette of research sharing. Watson rather outrageously in this chapter suggests that he gets access to the photo of the B. structure because his own conflicts with Franklin meant he could bond with Wilkins over the "emotional hell he had faced during the past two years" while working with Franklin (Watson 167). However, it is these traditions of scientific etiquette -- regarding not impinging on another person's research area, and also regarding the ethics of sharing research with others -- that Watson and Crick had to finesse in order to make their discovery.
In terms of how Watson and Crick actually arrived at the discovery, however, it is clear that the traditional pattern of scientific discovery was not really followed in their quest for DNA's structure. For example, the necessary empirical research for explaining the structure of DNA had largely been done by others: the chief field of empirical research necessary was the X-ray crystallography, about which Watson admits he was almost completely ignorant, but which was the focus of Wilkins's and Franklin's laboratory research. (The inclusion of Wilkins when the Nobel Prize was awarded is presumably a recognition that Watson and Crick could not have arrived at their conclusions without the photographic evidence of crystallography they obtained through Wilkins: Franklin was, of course, dead by the time of the Nobel Prize award, so whether she would have been a more fitting third winner than Wilkins is ultimately a moot point.) Moreover, the theoretical approach that Watson and Crick did bring to their analysis was also more or less borrowed. Watson admits that they were largely following the example of Linus Pauling, who had the reputation at the time for being the greatest chemist then alive. Watson emphasizes in The Double Helix that, while Pauling was capable of understanding the findings in X-ray crystallographic photographs and deducing what they suggested about molecular structure, his major breakthrough in determining difficult structures of complex molecules, like the alpha-helix structure of the peptide chain, was accomplished through the use of physical models: as Watson puts it, for Pauling's discovery "in place of pencil and paper, the main working tools were a set of molecular models superficially resembling the toys of preschool children" (Watson 50). If there were any basic theoretical ideas at work in Watson and Crick's discovery, they were largely borrowed from Pauling -- who was aware of the simplicity and also the difficulty of determining helical structures in molecules -- but they also hinged upon the conscious use of Pauling's own methodology here. In the seventh chapter of The Double Helix, Watson admits this outright: the basic method in approaching the structure of DNA would be to "imitate Linus Pauling and beat him at his own game" (Watson 48). Watson also suggests that -- despite her access to the best relevant empirical data -- Franklin's inability to perceive the structure first was due to her unwillingness to try this approach, viewing it as beneath her dignity. As Watson puts it, "Of course Rosy knew of Linus' success but saw no obvious reason to ape his mannerisms…only a genius of his stature could play like a ten-year-old boy and still get the right answer" (Watson 69).
But what is crucial in their decision to follow Pauling's example is the appreciation that, for determining something like the structure of a molecule, the simple trial and error of playing with different model structures is more likely to result in a way of seeing the given data in an appropriate fashion. That is why it is crucial to understand that the one moment (in Chapter 23) which is effectively the climax of The Double Helix -- when Watson gets Wilkins to show him Franklin's photographs of the B-structure crystallography for DNA -- has been preceded by the disastrous error of their "three-chain model" (Watson 94). Franklin's disdain for modeling over the empirical evidence provided by crystallography is absolutely warranted in this earlier episode (from Chapter 13) because, of course, the failure of Watson and Crick's "three-chain model" is entirely due to their lack of relevant empirical evidence. If Watson had known correctly how much water would be surrounding a DNA molecule, then he would have realized the centrality of magnesium ions in the three-chain model would be insupportable -- Franklin is thus able to refute the three-chain model in a matter of minutes, as she has greater grasp of the empirical data. However, Watson's larger point in his account is that Franklin's grasp of the data renders her unable to see the forest for the trees -- she had seemingly ruled out a helical model in advance. But ultimately, the modeling approach (itself borrowed from Pauling) is useless without empirical data (ultimately borrowed from Wilkins and Franklin). In some sense, the most original science that Watson and Crick brought to the question was a gift for synthesis: they knew what to borrow from other scientists.
It is also worth noting the role played by sheer chance in the discovery of DNA. Perhaps the most salient example of this in The Double Helix is the question of why Linus Pauling himself did not beat Watson and Crick to the discovery. Pauling had come up with an incorrect model, a three-helix chain, but this was not far off from Watson and Crick's incorrect three-strand model also. But here, the inability of Pauling to get to London and thus have the same access to shared research -- detailed in Chapter 17, where it is revealed that he was subjected to "withdrawal of his passport" for making political comments -- may very well have been the factor that allowed Watson and Crick to beat him to the solution (Watson 133). In the judgment of history, Linus Pauling's own conscience was correct on this point -- and moreover, he remains the only person to have won a solo…