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IF THERE’S ONLY one fact you know about the structure of DNA, it is probably that it was first described by Watson and Crick. This is true, we learn from Unravelling the Double Helix, in that it was they who came up with the final imaginative leap. It is also true that Watson and Crick never worked with DNA in the lab and relied on data from others’ experiments. Unravelling opens with a quotation from Rosalind Franklin, a peer of Watson and Crick whose images of DNA they had found useful and who may not have been far herself from deducing the structure when it was announced: “We all stand on each other’s shoulders.”

Knowing DNA’s chemical structure with certainty allowed access to the mechanisms of life itself, and we’ve come a long way since 1953. But it is the past Unravelling is interested in. Watson and Crick’s deduction of DNA’s structure can be seen as the culmination of work done by scores of researchers over the previous century. The book tells their story, using that moment in 1953 to shine a light back through time. Many of these men and women are forgotten, or at least, poorly remembered; many of them had no idea their work would be useful in the ways it ended up being useful. That may just be how the enterprise of science works, so it’s a good thing we have science writing to help us remember and reckon.

The book’s narrative structure seems inspired by DNA—two threads that circle each other. One of these, dealing with the physical stuff of cells, begins in 1833, with Robert Brown looking through a microscope at orchids and finding that each cell had a bit that would later come to be called the nucleus. In the late 1860s, it was Friedrich Miescher, working first with pus from soiled bandages and later with the testes of salmon from the Rhine, who isolated from the nuclei of cells a ‘fluffy grey precipitate’ (largely what we’d call DNA today) and went on to find out its chemical composition. The German microscopist Walther Flemming spent four decades figuring out what happened inside cells when they divided and described the deeply staining bits that we now know as chromosomes.

The pioneer of the other thread is better known: Gregor Mendel. Until he came along it wasn’t understood exactly how traits were handed down from parents to children, or how a trait could skip a generation. Mendel’s laws of inheritance came in 1866 from seven years of studying pea plants. While he worked out the rules, he did not know exactly what material carried traits from parents to children. The two threads began to come together only at the turn of the 20th century. Walter Sutton showed that it was chromosomes that contained the ‘unit of inheritance’ and could provide a physical mechanism for Mendel’s laws. By 1910, the words ‘gene’ and ‘genetics’ had been coined. But it wasn’t until 1944 that it was established that genes are made of DNA.
By then, advances in X-ray crystallography had begun to provide images with clues about the structure of DNA. Researchers in the US, England and Europe were racing to be the first to get it right. Leading in the final stretch were two groups who worked a short train-ride away: Watson and Crick in Cambridge, and Wilkins and Franklin in King’s College, London. It’s an exciting, dramatic story, and Unravelling tells it well.

Beyond its immediate subject, Unravelling turns out to be a fascinating book about how science works. The value of institutions, mentorship and collaboration are evident all through. Yet, the researchers we meet in its pages are markedly human, not immune to pettiness and squabbling. For everyone who gets something right, there are a dozen who get it wrong. Some were ahead of their time, their life’s work neglected in some library or the other for decades. Some were blinded by the scientific orthodoxy of the day and could not see clearly what lay in front of them. Still, despite all the jostling, they clambered onto each other’s shoulders and got there in the end.

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