Secrets of the Human Body. Andrew Cohen

      What I never got used to was the vast complexity of human anatomy. I passed my exams like everyone else. I even went on to teach anatomy at Cambridge for a term. But the sense of how hard it must have been for my predecessors to make the original anatomical discoveries stayed with me. I was doing what they, the early anatomists, had done: cutting up dead bodies. But those plastic models in the doctor’s office? It doesn’t look like that at all. It’s a confusing jumble of tubes and sinews. The question for me has stopped being ‘how is the body put together?’ and is now ‘why is it put together that way?’

      The early anatomists – the important Italians, for example: Eustachius, Vesalius, Malpighi – had to dissect, observe and catalogue with no knowledge of what the liver did or what a nerve was for. It is hard to imagine a contemporary equivalent. Perhaps mapping the outer reaches of the Solar System? Though the astrophysicists do not face either the smell of decomposition or illegality of obtaining scientific material that the anatomists did. They were in a very real sense uncovering secrets. Secrets that the church did not want them to know, that many older doctors did not want them to know and that the bodies themselves did not want them to know. No one in Renaissance Italy left their body to medical science.

      When I want to feel better about my inability to tell one part of the body from another, I think of Leonardo da Vinci. Possibly the greatest draughtsman that ever lived and one of the greatest minds. A phenomenal observer of the human body in every way. And yet, he never entirely figured out how the heart and circulation worked. This is probably the only human organ whose function you can understand from simple macroscopic inspection. It still works after death to some extent: if you go to the butcher’s shop and buy a beef heart and fill it with water from the tap, it will still pump blood in the right direction if you squeeze it. But even the great da Vinci could not quite work out the order of valves and chambers such is the stringy, fleshy complexity of it.

      Andreas Vesalius (1514–64). De humani corporis fabrica libri septum. The last section of the Fabrica is devoted to the brain. Here, the dura mater has been peeled away, exposing the brain with its thin membrane and vessels. Vesalius drew such exquisite charts for his students that he became famous enough that the judges of Padua ensured a steady supply of cadavers from the gallows.

      Learning anatomy with the cadavers was a geography lesson: the rivers and mountains of the body all labelled and connected. It was a vast quantity of information. In the foot there are 26 bones. Taken out of the foot and held in the hand, they look like pebbles on a beach: they do not have a particularly discernible function. And yet assembled, you can see that they sit together the way that a stone bridge holds together: in your foot you have a keystone, the navicular bone. A miraculous example of biological engineering. I felt like I had acquired a lot of secret knowledge that first year, and all in Greek and Latin, so it felt doubly secret. I had begun to speak a language that my non-medical friends could not. And if you can draw the chambers of the heart and the valves and label the flow correctly, as most GCSE biology students can, then you’re doing better than the smartest man in seventeenth-century Florence. In studying anatomy you feel like you are approaching a complete catalogue of the secrets of the human body: after all, if you know every road and house and place of interest in London, then you know London right? Of course not. There are other kinds of knowledge that are far more secret.

      Doctors are in the business of keeping secrets. We keep them about our patients. All the details of a medical consultation, no matter how mundane, are confidential except in very unusual circumstances. Patients rarely confess to murder or plan to deliberately spread their deadly diseases so, although these potential dilemmas are popular among medical students determined to imagine that their careers will be difficult in exciting ways, the secret-keeping pretty much boils down to not talking about what you heard. Why is this so important? Because knowledge makes us vulnerable in many ways. Secrets must be kept not because they are illicit or shameful but because they can be exploited. Your business competitors, employers, insurers, bank and maybe even relatives are all in a position to exploit knowledge about your body: your fertility, your risk of future illness, your health fears and the limits of your abilities. Medical confidentiality isn’t just about privacy, shame or discretion. It’s about vulnerability to exploitation. That is why this book is not an anatomy book: the secrets we’re interested in lie deeper. Your body is in the business of keeping secrets from everything that wants to exploit it: bacteria, viruses, fungi, parasites, larger predators and, crucially, other people. All these things are constantly probing our bodies, looking for weaknesses and opportunities. We survive by not giving anything away that we don’t absolutely have to. This book is about those secrets, how we keep them and the people who uncover them.

      The scientists who study the human body are not stargazers or map-makers, charting the features and dimensions of some territory in ever greater detail. They have to have the mindset of detectives or spies or tabloid journalists: they are digging for things that are deliberately concealed, information of life and death importance to those who keep it and those who seek it. This is what makes the stories in this book so thrilling: they are about stuff we are not meant to know. The important scientific discoveries about our bodies have both the deliciousness of gossip about who slept with who, and the heft of state secrets about where the nuclear submarine fleet is stationed. Let me explain.

      There are two things you have to understand if you want to expose a secret. First, that a secret is a thing that is known, but only to a few. Secrets are not simply mysterious things that we can’t explain; they aren’t just obscure facts, or stuff that’s too complicated to understand. They are hidden, deliberately, and they are ‘knowable’.

      The second important thing to understand about a secret is that it is a hole in the truth. A missing piece of a jigsaw. We notice secrets in their absence: a non-explanation; a story that doesn’t make sense.

      The last secret I was involved in keeping was pregnancy: my son was on the way. Like most people we kept it secret from just about everyone until the 12-week scan. But to keep this secret you can’t just not mention that you’re pregnant. You’ll need to conceal or explain changes in your habits. So if people are watching you closely and consider your age, relationship status, recent weight gain and refusal of blue cheese and booze at the company picnic, they won’t struggle to figure out the missing piece of the puzzle. To keep a secret you either have to lie or conceal a much wider array of facts. Whether you’re pregnant and trying to keep it to yourself, or you’re a government intelligence agency hiding their knowledge of the location of that fleet of nuclear submarines, the tactics must be the same: dissemble and confuse. And the tactics of anyone wanting to discover either secret take this into account: gather as many of the facts as possible until you can see the exact shape of the hole in the truth. Only the secret can fit in that hole. This is how much of biological science works. Using the facts you know to tell a story and then seeing if new facts are consistent with that story and revising it to make them fit.

      The human body keeps secrets for the same reason that companies and states and you, as an individual, keep secrets: we live in an environment of relentless competition and exploitation. All of life is exploitation. In most cases this exploitation is about who eats who; occasionally about who eats what. This might sound dramatic if you live in the UK. We don’t seem to be in competition with much of what we eat or at much risk of getting eaten. But we all have an extensive set of defences to prevent us being eaten or exploited. Some of these things are complex behaviours, some of them work at a cellular level via antibodies and the killer cells of the immune system. But without all of them constantly functioning, we would be consumed within hours.

      The relentlessness of the attacks on your body becomes clear when a person stops fighting them, even briefly. I used to work in the Bone Marrow Transplant Unit at King’s College Hospital. In order to give someone a new bone marrow (this might be done because they have a bone marrow cancer like leukaemia), you have to kill their original one with radiation and chemotherapy, and this completely wipes out most of their immune system: they lose their ability to make antibodies or white blood cells. Sustaining life without a functioning immune system can be done for a short period of time. Our patients lived in positive pressure rooms, with minimal human contact and