Rosalind Franklin had seen the helix: A forgotten photograph rewrites the history of DNA’s structure

For decades, one of the best-known stories in science was told like a movie. In 1953, at the age of 23, James Watson visited Maurice Wilkins’s laboratory at King’s College London. There, Wilkins showed him a photograph of DNA taken by Rosalind Franklin, and Watson had an epiphany. “The instant I saw the picture my mouth fell open and my pulse began to race,” Watson wrote in The Double Helix: A Personal Account of the Discovery of the Structure of DNA, the book in which he recounted, 15 years later, how he and Francis Crick unraveled the structure of DNA.

That account emphasized the brilliance of its narrator and the inability of the woman who took Photograph 51 to grasp its significance, despite having had it before her for months. Watson, Crick and Wilkins were awarded the Nobel Prize in Physiology or Medicine in 1962, four years after Franklin’s death. Now, a paper published in the Journal of the History of Biology and first reported by Science challenges that narrative. Her notes show she had indeed seen the helix.

One argument used to cast doubt on Franklin’s ability to interpret her own image was that, unlike her usual practice, she made almost no notes on Photo 51 commenting on its result. Alistair Sponsel, from the Institute for the History of Science in Philadelphia, and Brian Sutton, from King’s College, argue that she did not do so because she had already recognized DNA’s helical structure in an earlier image, Photograph 49, taken on May 2, 1952.

According to her notes, the authors explain, Franklin identified the pattern in the image as consistent with a helix and calculated that the structure completed one turn every 3.4 nanometres and contained about 10 layers of bases “per turn of the helix (if it is a helix),” as she wrote. But the quality of the image was not good enough, and so, using the same DNA sample and the same experimental conditions, she went on to take Photograph 51. She was aiming for a better-centred image of publishable quality. The very reason the new photograph was so clear was that Franklin already knew the phenomenon she was trying to capture.

However, the article also clarifies that this does not mean Franklin, on her own, had discovered the full double-helix structure. Although by May 1952 she knew DNA had that shape, she had not yet determined exactly how the two strands were arranged or how their components fit together.

Watson and Crick went further, building a model of the molecule that brought together clues from the photographs with what was known about DNA chemistry. The 10 layers of bases Franklin calculated for each helical turn were in fact 10 pairs of opposing bases. In that model, the two strands ran in opposite directions and the bases on one strand paired specifically with those on the other: adenine with thymine and guanine with cytosine. Thus, each strand contained the information needed to reconstruct the other.

This made it possible to explain something that a photograph alone could not reveal. The great achievement of Watson and Crick was not simply identifying a helix, but discovering an architecture that simultaneously accounted for the molecule’s shape, its chemical properties, and its ability to store and replicate information. In short, they showed how DNA could copy itself and, therefore, how genetic information could be passed from one cell to its descendants.

In 2023, Brian Sutton, one of the paper’s authors, had already argued that Rosalind Franklin came close to making the discovery herself. By early 1953, her notes show that she was explicitly considering a two-stranded helix and had written that a helical structure was highly likely, probably with 10 bases per turn, with the phosphates on the outside and the bases on the inside — the classic description later given by Watson and Crick.

Memoir

One of the main sources of the historical confusion surrounding Rosalind Franklin’s role is the power of Watson’s first-person account in The Double Helix. Watson makes clear that it is his version of events and, in the book’s original foreword, Lawrence Bragg, director of the Cavendish Laboratory and supervisor of Watson and Crick, cautions that the book “is not a history” but rather “a record of impressions rather than of historical facts.” He notes that events were more complex and the motivations of the protagonists “less tortuous” than Watson understood at the time.

These impressions make clear the contempt Franklin faced from her colleagues. Watson refers to Rosy as “the problem” and appears obsessed with her appearance — noting that she was plain and did not wear lipstick or style her hair to highlight her beauty. He also describes her as “incompetent in interpreting X-ray pictures,” even though she was an expert whose photographs, according to other experts, were the best of the time.

Watson writes that “the best home for a feminist was in another person’s” and recalled the conflict between Franklin and Wilkins, which stemmed in part from Wilkins’s assumption that Franklin would work as his assistant, while she believed she would have the independence to run her own research project.

The Double Helix was controversial from the outset. Watson had reached an agreement with Harvard University Press to publish the book, but Crick and Wilkins objected to the way they were portrayed, and the press ultimately declined to publish it. Crick wrote to Watson that the manuscript was “misleading and in bad taste” and argued that, rather than illuminating the scientific discovery, it distorted it. Wilkins complained that it was unfair to almost everyone mentioned in its pages except Watson himself, and especially to Franklin, whose death was not even acknowledged. The book was revised following objections from those portrayed in it, but Franklin was no longer alive to defend herself.

In the book’s epilogue, Watson reflects on Franklin’s death and revises part of his earlier portrayal. He admits that many of his initial impressions, both scientific and personal, had been mistaken, and praises her courage and integrity, particularly the determination with which she continued working while seriously ill. He also acknowledges the quality of her crystallographic work. For many readers, however, these concessions do not offset the dismissive tone of much of the rest of the book, which remains one of the most controversial memoirs in the history of science.

Sign up for our weekly newsletter to get more English-language news coverage from EL PAÍS USA Edition