One of the earliest pictures of Darwin’s theory of common descent is a doodle.
It sits on the upper-left of a page in a small leather-bound notebook in Cambridge University Library, catalogued as DAR 121. Above the sketch, in Darwin’s hurried handwriting, are two small words: “I think.” Below them, a stubby branching tree fans out across the page, the kind of thing a child might draw of a stick with twigs. It is an early visual hypothesis of common descent. The date is around July 1837. The book is Notebook B. Darwin was 28 and still working through the implications privately, while discussing parts of his thinking with a small circle.
Darwin’s notebooks are not tidy, and they are not especially eloquent. That is what makes them useful. They show what it looks like to think a hard thought slowly, on paper, in private, over many years. He spent more than two decades developing the argument that became On the Origin of Species (1859), using pocket notebooks, margins, lists, correspondence, and loose notes. Much of the archive is digitized at Darwin Online. Scroll through Notebook B and the uncertainty is still visible on the page.
This post is about what those notebooks reveal, and what we can borrow from them. Most of us have ideas we are not ready to defend, decisions we do not know how to make, and observations we might otherwise forget. Darwin kept giving those things somewhere to go.
1. The Beagle Diary: A Five-Year Habit of Looking Hard at Things
Before there was a tree of life, there was a young man with a notebook on a small ship.
When the HMS Beagle left Plymouth in December 1831, Darwin was 22 and had no real career. He had drifted through medicine at Edinburgh, then theology at Cambridge. He sailed as a “gentleman’s companion” to Captain FitzRoy and as an unpaid naturalist. What he produced over the next five years, documented in Janet Browne’s biography Charles Darwin: Voyaging, is one of the most thorough field-observation records of the 19th century: about 770 pages of diary, 1,750 pages of zoological and geological notes, and 5,436 specimen labels.
If the voyage notebooks make you want to try the same thing on a smaller trip, here is how to keep a travel journal, with a one-page format you can finish on a train.
Darwin did not confine his records to polished reflections after the voyage. His field notebooks contain observations, specimen information, geological sections, and questions recorded as the expedition moved. The habit was not “I will journal when inspired.” It was closer to “I will keep looking, and I will keep a record of what I see.”
This is the part of Darwin that gets skipped when we tell the story. We jump from “young man on a boat” to “evolution.” We miss the sustained observation and note-taking that gave his later theorizing something concrete to work with.
Darwin’s example is a useful correction to the idea that a notebook is only for special thoughts. Much of the record is descriptive: specimens, locations, geological features, questions, and details that became meaningful later. The larger ideas had a foundation because the smaller observations had been kept.
“I worked on true Baconian principles, and without any theory collected facts on a wholesale scale.” – Darwin, in his Autobiography, looking back on the Beagle years.
That line, “facts on a wholesale scale,” is the whole game. If you want to know what to put in your notebook today, start there.
You can browse the Beagle diary in Darwin’s own hand at Darwin Online. I’d suggest spending 10 minutes scrolling. It will change what you think a journal can be.
2. Notebook B and the “I Think” Sketch: The Smallest Drawing That Changed Biology
The Beagle returned in October 1836. Nine months later, in July 1837, Darwin opened a small notebook with a brown leather cover and labeled it “B” on the spine. It became a private place to work through questions about how species change.
Notebook B was the first of what scholars now call the “transmutation notebooks” – B, C, D, and E, running from July 1837 to mid-1839. The originals are at Cambridge University Library (DAR 121, DAR 122 and the rest of the sequence). The standard scholarly edition is Charles Darwin’s Notebooks, 1836-1844, edited by Paul H. Barrett and colleagues (Cambridge University Press, 1987). Read the modern transcripts, then go look at the manuscript scans, and you understand that Darwin was working at the edge of what he could say.
On page 36 of Notebook B, he wrote two small words and drew a sketch:
“I think.”
[Then a small branching tree, with letters A, B, C, D, marking endpoints of branches. Below the sketch:] “Case must be that one generation then should be as many living as now. To do this & to have as many species in same genus (as is) requires extinction.”
This is the first known visual argument for common descent. Note the hedge: “I think.” Not “I have proved.” Not “Eureka.” Just the smallest possible commitment in writing. Two words and a drawing.
I find that incredibly liberating. Most of us don’t write down our biggest ideas because we feel we have to defend them. Darwin gave himself permission to write “I think” and move on. The notebook was a workshop, not a courtroom.
Try this: open a fresh page. Write “I think” at the top. Then sketch the dumbest possible diagram of an idea you’ve been afraid to commit to. You are not publishing. You are starting.
This is the same instinct you can see in Leonardo da Vinci’s observing journals – the willingness to draw before you understand, to use a picture as a question rather than an answer.
3. The Five-Year Silence: What Darwin Did Between Privately Knowing and Publicly Saying
Here is the part of Darwin’s story that I keep teaching myself.
By September 1838, Darwin had read Thomas Malthus on population and the last piece clicked. He had a mechanism: natural selection. He wrote it into his notebooks. He had, by any honest reading, the core of On the Origin of Species.
He published the book in November 1859.
That is more than twenty years of working privately. Not because he was lazy. He filled volumes. In 1842, five years after the “I think” sketch, he wrote a 35-page “pencil sketch” of the theory. In 1844, he expanded it to 230 pages and instructed his wife Emma, in a letter, to publish it if he died. Then he kept it in a drawer for another fifteen years.
What he was doing in those years, as Janet Browne documents in Charles Darwin: The Power of Place, was extending the work through studies of barnacles, pigeons, orchids, earthworms, and much more. The evidence became extensive, although the argument remained controversial when he published it.
I am not suggesting you sit on your idea for twenty years. The useful distinction is between postponing an idea and developing it. Darwin wrote the idea down, returned to it, tested it against new evidence, and gradually made the argument strong enough to publish.
The notebook was the holding pattern that made the patience possible. He didn’t have to remember. The book remembered for him.
If you are sitting on a creative project, ask yourself: am I avoiding it, or am I building it slowly in a notebook? The two look identical from the outside. They are not the same.
“How odd it is that anyone should not see that all observation must be for or against some view if it is to be of any service.” – Darwin, in a letter to Henry Fawcett, 18 September 1861.
4. The “Old and Useless Notes”: Permission to Think Heretical Thoughts
Filed alongside the transmutation notebooks is a small bundle Darwin himself labeled “Old & Useless Notes about the moral sense & some metaphysical points.” He started it around 1838.
It is the part of Darwin almost nobody talks about. In it, he is working out what evolution would mean for the soul, for morality, for God, for free will. He scribbles half-thoughts about how a sense of guilt might evolve. He doodles around the edge of belief. The handwriting is messier than the species notebooks. The thinking is rawer.
He did not publish these notes. The label “useless” does not tell us exactly how seriously he meant it, but the pages gave him somewhere to explore questions that did not yet belong in a finished argument.
One practical idea to borrow is a sub-notebook, or a section of your journal, that you have officially declared useless. The deal is simple: “I am allowed to think anything here. None of this needs to be defended.” That permission can make room for thoughts that are not ready for a destination.
You might call it a “fragments” page. Nothing on it has to lead anywhere. Half-formed worries, odd questions, and sentences without a home are allowed to remain unfinished. Read it back occasionally and see whether anything has begun to connect.
You can read Darwin’s “Old & Useless Notes” in full at Darwin Online. They are short. They are strange. They are very human.
5. The Marry / Not Marry List: A Decision Journaled in Two Columns
In July 1838, under two years after returning from the Beagle and one year into Notebook B, Darwin was thinking about whether to propose to his cousin Emma Wedgwood. He did what a notebook keeper does. He took a piece of paper, drew a line down the middle, wrote “Marry” on one side and “Not Marry” on the other, and made a list.
It survives. It is one of the most famous artifacts of decision journaling in history.
Under “Marry,” he wrote:
“Children – (if it Please God) – Constant companion, (& friend in old age) who will feel interested in one, – object to be beloved & played with. – better than a dog anyhow. – Home, & someone to take care of house – Charms of music & female chit-chat. – These things good for one’s health. – Forced to visit & receive relations but terrible loss of time.”
Under “Not Marry”:
“Freedom to go where one liked – choice of Society & little of it. – Conversation of clever men at clubs – Not forced to visit relatives, & to bend in every trifle. – to have the expense & anxiety of children – perhaps quarelling – Loss of time. – cannot read in the Evenings – fatness & idleness – Anxiety & responsibility – less money for books &c.”
At the foot of the Marry column, he wrote a single conclusion: “Marry – Marry – Marry Q.E.D.”
I love this for three reasons.
First, the categories are wonderful and absurd. “Better than a dog anyhow” is going on his side of the marriage column. We forget that 28-year-old Darwin was just a guy.
Second, the format works. The two columns force him to stop arguing in circles in his head and put it on paper. The moment “loss of time” appears on both sides, you can almost feel him realizing the question is not really about time.
Third, the artifact is preserved. He didn’t throw the list away. He filed it. It is the same instinct as the species notebooks: write it down, even when it is embarrassing, because the page is honest in a way the head is not.
The format is older than Darwin. Benjamin Franklin’s “moral algebra” used the same two-column logic, and it shows up later in Bruce Lee’s planning journals too. Try it the next time you cannot decide something. Not on a screen. On paper. With pen.
(He proposed to Emma in November 1838. They were married in January 1839. In later decades, many of his working notes moved from pocket notebooks into loose papers and subject portfolios.)
6. A Working Habit on a Moving Ship, Then at Down House
When Darwin moved with Emma to Down House in Kent in 1842, he created what we would now call a writing routine. Walks in the morning. Reading aloud after lunch. Letters in the afternoon. Notebooks always within reach. He maintained an enormous correspondence (about 15,000 letters survive) and used the letters themselves as a kind of distributed notebook, asking specific questions of breeders, gardeners and scientists all over the world, and pasting the answers into his files.
I think this is one of the most underrated features of his system. Darwin did not just keep a journal. He kept an infrastructure. The notebook was the central node, but the letters were tributaries, and the bookshelf was a memory bank, and the garden was a laboratory. Each one fed the others.
It is the same architecture you see, on a smaller scale, in Thomas Edison’s structured notebooks, where the journal is the spine and the lab is the lung. Darwin built one of these, slowly, over forty years.
You don’t need 15,000 correspondents. But it is worth asking: what feeds my notebook? Where do my notebook entries come from? Conversations? Books? Walks? Patients? Customers? If your notebook is starving, the answer is upstream.
7. Drawing to Reason: Why the Tree Mattered More Than the Words
There is something specific about a drawn diagram that pure prose cannot do.
When Darwin sketched the branching tree in Notebook B, he was not illustrating a theory he already had. He was using the sketch to think. The page is the cognition. Look closely at the manuscript and you can see he is testing the diagram: writing “case must be that…” next to it, working out what the picture would have to imply if it were true. The image is doing the work.
Across the journals of scientists and artists, “drawing to reason” appears again and again. We type. We bullet. We outline. We draw less often, and when we do, we tend to apologize for it.
This is one place where Einstein’s notebooks and Picasso’s sketchbooks meet Darwin: in all three, the page is full of arrows, shapes, schematic figures. Richard Feynman, much later, would do the same thing. The hand-drawn image is faster than language and more honest than a formula.
Try this. The next time you are stuck on a problem, instead of writing a sentence about it, draw a picture of it. The picture can be terrible. You are not making art. You are making a hypothesis you can see.
8. Darwin’s Wife Kept a Journal Too
This is the detail I think about most often.
Emma Wedgwood Darwin, Charles’s wife, kept pocket diaries across more than seventy years, although the surviving sequence has gaps. They are terse records of appointments, expenses, family illnesses, and remedies. Three of Charles and Emma’s children died in childhood: Mary Eleanor at three weeks in 1842, Annie at ten in 1851, and Charles Waring at eighteen months in 1858. Darwin wrote a private memorial of Annie on a few loose sheets soon after she died. It runs to about 1,700 words and reveals a kind of attention very different from the transmutation notebooks.
The Darwin household, in other words, included two parents who kept records for very different purposes. Charles’s scientific notes and Emma’s domestic diaries preserve different views of the same family life.
We sometimes treat journaling as a solitary, dramatic act. In the Darwin family, writing things down was also ordinary household practice. The surviving records show scientific work, appointments, illnesses, expenses, grief, and daily life sharing the same historical frame.
If you want a quietly radical experiment, ask the person you live with whether they would keep a journal in the same room with you for thirty days. You don’t need to read each other’s. Just write near each other.
9. How to Borrow Darwin’s System This Week
Pulling it all together, here are seven practical lessons from Darwin’s notebooks:
- Write boring observations on a wholesale scale. Most of your notebook should be small, daily, ordinary. The big ideas need an underlay of small facts.
- Allow yourself to write “I think.” Don’t wait until you can defend an idea. Commit it to the page with the smallest possible verb.
- Sketch, even if you cannot draw. Trees, arrows, columns, blobs. The page is a thinking tool, not an art gallery.
- Keep an “old and useless” section. A page where heretical, embarrassing, or unfinished thoughts are allowed to live.
- Two-column hard decisions. When stuck, draw the line down the middle. Force the trade-offs into the open.
- Be patient on paper. A notebook lets you hold an idea for years without losing it.
- Build the infrastructure. Notebook plus letters plus reading plus walks. Don’t expect the notebook to do all of it alone.
None of this requires a leather notebook or a sea voyage. It requires that you write today, and then again tomorrow, and that you let the page see what you actually think.
I run the Journaling Habit newsletter for exactly this kind of slow, patient practice. I send out one essay on the journals of a single person (Darwin, Martin Luther King Jr., Einstein, Edison, and others) and one small experiment you can try in your own notebook that week. If that sounds useful, you can join free.
You can also browse the full archive of journals of historically remarkable people for more case studies in how serious thinkers actually used a notebook.
A Closing Note
Notebook B does not look like a polished monument to genius. It shows a young man, in messy handwriting, hedging. “I think.” Then a small sketch. Then more pages. Then years of more work.
That is one reason journaling is worth taking seriously. A foundational theory in modern biology appears in this notebook as a tentative sketch. It became a published argument through sustained observation, testing, correspondence, and revision.
There is something encouraging in that small beginning. A page does not have to look important while you are writing it. It only has to give the next thought somewhere to land.
Featured image: Page 36 of Darwin’s Notebook B, Transmutation of Species (1837). Public domain, via Wikimedia Commons.
