When I talked to Alex Rich and Jack Dunitz, who were Pauling’s postdocs at the time, both agreed that had Pauling seen Rosalind Franklin’s X-ray photograph 51 of the B form of DNA, he would have realized immediately that the molecule possessed a two-fold symmetry, pointing to a double-stranded rather than a three-chain structure. As we have seen, however, Pauling made no special effort to see Franklin’s photographs.

In January 2011, I asked James Watson how surprised he was when he saw Pauling’s erroneous triple-helix model. Watson laughed. “Surprised? You could not have written a fictional novel in which Linus would have made an error like this. The minute I saw that structure, I thought, ‘This is wacko.’ ”

A close examination of the many potential causes for Pauling’s calamitous model raises a series of questions at a deeper level: How can we explain the haste, the apparent lack of exertion, the forgetfulness, and the disregard for some of the basic rules of chemistry?

On the face of it, the haste is particularly puzzling if we accept Peter Pauling’s testimony that there never was a “race” to solve the DNA structure. In the same entertaining account in which he noted that to his father DNA was just another interesting chemical, Peter added, “The story of the discovery of the structure of DNA has been described in the popular press as ‘the race for the double helix.’ This could hardly be the case. The only person who could conceivably have been racing was Jim Watson.” Peter explained further that “Maurice Wilkins has never raced anyone anywhere,” and that Francis Crick simply liked “to pitch his brain against difficult problems.” I asked Alex Rich and Jack Dunitz about it, and neither of them thought that there was a race as far as Pauling was concerned. Why, then, did he hurry so much to publish? “Because he was always competitive,” Rich suggested. This is certainly true, but it can be only part of the explanation, since Pauling had shown so much more caution and patience in the case of the alpha-helix. Ironically, his triumph with the alpha-helix had no doubt contributed to his defeat with the triple helix, since Pauling assumed, based on his success with the former, that he could reproduce the accomplishment with the latter. In this sense, this was a classical case of inductive reasoning: the common strategy of probabilistic guessing based on past experience—taken way too far.

Everyone engages in inductive reasoning all the time, and usually it helps us make correct decisions based on relatively little data. Suppose I ask you, for instance, to complete this sentence: “Shakespeare was a uniquely talented ___.” Most people would probably answer “playwright,” and they would be perfectly justified in doing so. While there is nothing illogical with completing the sentence with “cook,” or “card player,” chances are that the word sought for was indeed “playwright.” Inductive reasoning is what allows us to use our cumulative experience to solve problems through the choice of the most likely answer. Like experienced chess players, we do not typically analyze every possible logical answer. Rather, we opt for what we think is the most probable one. This is an essential part of our cognition. Psychologist Daniel Kahneman described the process this way: “We can’t live in a state of perpetual doubt, so we make up the best story possible and we live as if the story were true.” However, because inductive reasoning involves probabilistic guesswork, it also means that sometimes it gets things wrong, and occasionally, it can get things very wrong. Pauling thought that he could take a shortcut, because past experience had shown him that all of his structural hunches turned out to be correct. In the DNA failure, the blunderer was a victim of his own previous brilliance.