Book 43: The Traveling Anatomist by Nuno Castel-Branco (All Souls College, Oxford)
The power of interdisciplinary interests and friendships in the evolution of science
This week is a small exception. We usually discuss books of the past, but I sat down with a friend to talk about a book published in October 2025, about a scientist most people have never heard of, whose principles are still taught in most introductory geology courses around the world.
The Traveling Anatomist tells the story of Nicolaus Steno, a seventeenth-century Danish scientist whose work reshaped anatomy and laid the foundations of modern geology. Steno is far less famous than Galileo or Newton, but Castel-Branco argues that his career offers one of the clearest windows into how modern science was actually made.
Dr Nuno Castel-Branco is a Research Fellow at All Souls College. All Souls admits its Examination Fellows through what has been called the hardest exam in the world, two days of papers featuring questions like “Why are some jokes funnier than others?” and “Is boredom unfairly maligned?” If you fancy challenging yourself this weekend, the past papers are here.
Nuno’s career has followed a path his subject would recognise. He trained as a physicist in Lisbon, published on the accelerated expansion of the universe, and then walked away. The frontier of cosmology, he told me, had narrowed to a choice between programming models and presenting research that only five people in the world could follow. History of science offered the same rigour with a wider door. A PhD at Johns Hopkins followed, then a fellowship at Harvard’s Renaissance villa in Florence, then All Souls. He is in Chicago on July 7, launching the book. If you happen to be there, go say hello.
You should listen to his Network Capital podcast and check out his Substack.
The Traveling Anatomist
Steno was born in Copenhagen in 1638 and trained as a physician at Leiden. His real passion, however, was mathematics, and his mentors had steered him towards medicine because it promised a steadier career. Instead of abandoning mathematics, Steno brought it into anatomy. He described the glands as filters of the blood and used simple arithmetic about blood flow to explain how the body produces tears, correcting older ideas that imagined the brain as a reservoir of water. He also developed a new mechanical model of how muscles move. In each case, he was applying quantitative, mechanical reasoning to the human body at a time when this was highly unusual.
His career took a turn in Florence, where he worked at the Medici court after turning down a position at the newly founded Paris Academy of Sciences. Asked to dissect a large shark caught in the Mediterranean, Steno noticed that its teeth closely resembled the strange stones people kept finding on mountain tops, far inland from any sea. Others had observed the likeness and dismissed it. Steno set out to prove that these stones really were the teeth of ancient sharks. To explain how such objects could come to rest inside solid rock high above the ocean, he worked out how layers of sediment are deposited over time, one upon another, and how the history of the earth can be read from its strata. These conclusions became the principles of stratigraphy still taught in geology courses today.
Later in life, Steno underwent a religious conversion, became a Catholic priest, and eventually a bishop in northern Germany, shifting his career from anatomy to geology and finally to theology.
Castel-Branco uses this remarkable life to advance several larger arguments, and each one pushes against a familiar assumption about how science works.
The first concerns method. Castel-Branco describes Steno’s genius as focused interdisciplinarity, and he is careful to distinguish this from the loose modern celebration of people who do many things. The seventeenth century is often called the golden age of the polymath, and the temptation is to place Steno in that gallery beside Newton and Leibniz and leave it there. Castel-Branco resists this. Newton, he points out, wrote more on theology than on physics, and worked on mathematics, chemistry and scripture across a long life, but these pursuits largely ran in parallel channels that did not feed one another. His chemistry was not driving his mathematics, and his theology was not shaping his optics. Leibniz represents a different ambition again, a genuine desire to bring all knowledge together into a single universal science. Steno did neither of these things. He held a broad training in mathematics, mechanics, chemistry and theology, all of it standard for a well-schooled physician in Lutheran Denmark, and then he collapsed the whole of it onto one narrow problem after another. First the glands, then the heart, then the muscles, then the ovaries, then the earth. The breadth was the inheritance of his education. The discipline lay in refusing to let that breadth scatter him. For Castel-Branco this is the more useful model for anyone with many interests, because it treats breadth as a resource to be aimed rather than a temptation to be indulged. Steno himself felt the strain of it, describing his later research as a hydra whose heads multiplied faster than he could cut them, and his answer was simply to choose one problem, follow it, and choose again.
The second argument concerns friendship. The standard history of early modern science is written as a contest, Newton against Leibniz over the calculus, priority disputes conducted in bitter pamphlets, men who despised one another racing to publish first. Castel-Branco tells the story that rarely gets told, a history of friendship, collaboration and co-authorship. Steno is an ideal witness for it. Everywhere he settled, in Leiden, London, Paris and Florence, he sought out the leading mathematicians, because mathematics was his first love, and he made friends of them and worked alongside them. Castel-Branco shows that Steno influenced these men and was influenced by them in turn. Friendship also changed the character of competition itself. When you discover that a friend is working on the same question, the dispute over who arrived first loses its sharpness and becomes something more horizontal, a matter of courtesy rather than combat, an acknowledgement that had you known, you would have credited one another. Ideas then multiply and travel across Europe through these networks of affection. Underpinning all of it is travel. Steno’s contemporaries typically journeyed abroad and then returned home to write, but Steno produced his work on the move, and Castel-Branco argues this is precisely why his disciplines cross-pollinated so freely. The library you sit in and the people beside you shape the questions you think to ask.
The third argument concerns the people history forgets, and it emerges from the book’s final chapter. Steno converted to Catholicism in Florence, and Castel-Branco set out to understand why. The trail led to a devout noblewoman who had a real influence on him, whom Steno met through a physician friend. That struck Castel-Branco as a puzzle worth pursuing. How does a noblewoman in Florence come to shape the course of a visiting intellectual of Steno’s stature? Reading the correspondence more closely, he began to find other women, in Paris, in Leiden, in Copenhagen, moving through the same scientific circles, corresponding and persuading and shaping, and almost wholly absent from the historical record. This became a wider preoccupation. Castel-Branco points out that the first woman to hold a university professorship taught in eighteenth-century Bologna under the sponsorship of Pope Benedict XIV, who also supported a professor of mathematics and a professor of anatomical design at the same university, and that almost no one has heard the story. The southern European world in particular, he argues, holds a rich and largely untold history of women in science and education.
The Traveling Anatomist rewards anyone drawn to the history of science, but its real reach is broader. Anyone who juggles too many interests, or wonders whether their scattered curiosity is a flaw, will find in Steno both a warning and a permission.
