by James Morris
I’m a list-maker. I keep all kinds of lists. I have lists of books I want to read, movies I want to see, things I need to do, projects that are unfinished, things I don’t want to forget to tell someone, ideas for classes I am teaching.
I am not alone. Many people keep lists, from shopping lists to bucket lists. Students memorize spelling and vocabulary lists. David Letterman is well known for his Top Ten lists. There are even apps these days to help you manage your lists: keep track of tasks, prioritize them, or be reminded of them.
Charles Darwin too was a list maker. Thankfully, we have much of his writings, and not just his major works like On the Origin of Species or The Descent of Man. We also have his notebooks, diaries, and letters. We even have his student bills! Much of this wonderful collection can be found here.
We also have several of his lists. Two have become quite famous. The first, in Letterman fashion, is a list of the top reasons why he should not go traveling around the world on the H.M.S. Beagle as a naturalist. The reasons are numbered from 1 to 8, beginning with “1. Disreputable to my reputation as a clergyman hereafter” (he was training to be a member of the clergy at the time) and ending with “8. That it would be a useless undertaking” (he had already dropped out of medical school).
This may come as a surprise to those of you who know that he did indeed make this voyage, and it was the turning point in his life. Darwin later wrote, “The voyage of the Beagle has been by far the most important event in my life, and has determined my whole career.”
The list is written by Darwin, but is actually his father’s objections to the voyage. His father, Dr. Robert Darwin, was obviously not keen on the idea. Earlier, he wrote to his son, “You care for nothing but shooting, dogs, and rat-catching, and you will be a disgrace to yourself and all your family.” Not exactly words of support or encouragement.
But Darwin eventually decided to accept the offer. In a letter to his father, Darwin begins, “My dear Father, I am afraid I am going to make you again very uncomfortable…”
There is another one of Darwin’s lists that is well known. When he was trying to decide whether or not to marry Emma Wedgwood, he jotted down a list of pros and cons. It reads like many lists we might make around big decisions, like which college to attend, classes to take, or job to accept. I don’t think he thought it would be saved and widely read, and I am sure he could not have imagined it being posted on the Internet. But it is, and we can all read it.
He divides a sheet of paper in two. On the left, he writes “Marry” and on the right “Not Marry.” Under the two headings is a list of all the pros and cons of getting married. Between the two headers he writes and circles, “This is the Question.”
In the Marry column is, for example, “Children” and “Constant companion” and in the Not Marry column is “Freedom to go where one liked” and “Not forced to visit relatives, & to bend in every trifle.”
He ends with the words “Marry. Marry. Marry. Q.E.D.” as though he just completed a mathematical proof. If only our own decisions could be resolved so convincingly. He got married a few months later and remained married until his death – a total of 43 years.
Like Darwin, I went to medical school, and was happy to learn that lists also show up in medicine. When considering what is wrong with a patient, for instance, physicians come up with what is called a “differential diagnosis,” or “differential” for short. This is essentially a list of possible diagnoses a patient might have.
There are many ways to generate a differential, but one involves writing down a list of systems of the body (nervous, cardiovascular, renal, etc.). Another is to consider processes, like trauma, inflammation, inheritance, etc. The idea is to come up with a system that you can turn to for any kind of complaint or symptom that you come across. It’s deliberately thorough, so that nothing is missed.
Most of the time, a differential diagnosis is not a laundry list. Instead, it is prioritized in some way. For example, if a patient comes in complaining of chest pain, there is a long list of possibilities, but there is one that requires immediate attention: a heart attack (or myocardial infarction). Therefore, this possibility goes to the top of the list. It is so high that physicians often write down a diagnosis of “R/O MI,” which stands for “rule out a myocardial infarction.” It expresses the idea that you should rule out the worst-case scenario before turning to other, less worrisome possibilities.
Another rule of thumb is, “When you hear hoofbeats, think horses not zebras.” This reminds medical students to consider common explanations before unusual ones. In medical school, you learn all kinds of rare diseases. These should not be forgotten, but common conditions should be considered first. So, if you see a patient with a headache, think common cold, migraine, or sinus infection before brain tumor.
Some signs and symptoms are so specific that they don’t require a differential diagnosis at all. These are what physicians call “pathognomonic.” In these cases, a symptom points to one diagnosis, not several. For example, a bull’s eye rash is pathognomonic for Lyme’s disease, Koplik’s spots for measles, and a third heart sound for congestive heart failure (the “lub-dub” of the heart counts for the normal two heart sounds). These are all quite different from chest pain, abdominal pain, or headaches, all of which have long, complex differentials.
Sometimes, after all diagnoses are considered, the physician is left empty-handed. For example, when I was a teenager, I had optic neuritis. This is inflammation (“-itis”) of the optic nerve, which sends signals from the eye to the brain. There are many worrisome diagnoses, including multiple sclerosis and a brain tumor. In my case, after investigating and ruling out each possibility, the physicians were left empty-handed. Physicians have a name for this too – they call it “idiopathic.” This simply means that they don’t really know what caused it. So, I had idiopathic optic neuritis.
Physicians then have a way to bring closure when there really is none. In our daily lives, we also have lists that we can’t really finish, that remain open-ended. Laundry is one of them. I sometimes say something like, “I am glad we are done with the laundry,” to which my wife replies, “We are never done with laundry.” Or it’s like painting the Golden Gate Bridge – as soon as you are “done,” it’s time to start over. Or e-mail – there’s always more.
But, for those of us who like lists, it’s comforting to know that there are some things that can’t ever be truly crossed off.
© James Morris and Science Whys, 2014