Charles Darwin relied on his notebooks. In them, he jotted private ideas, questions, fragments of conversations, and sketchy drawings related to his thinking on “transmutation”—what we now call “evolution.” The notebooks reveal a great mind homing in on a great idea: Plants and animals are not fixed and unchanging. Instead, all species are related through common ancestry, and they change over time.
Many of these notebooks are now accessible through the Darwin Manuscripts Project, an effort at the American Museum of Natural History to digitize Darwin’s scientific writings in close collaboration with Cambridge University Library. These high-resolution and color images include manuscript pages, drawings, book abstracts, Darwin’s children’s drawings, and other work, complete with transcriptions that decipher the naturalist’s sometimes hard-to-read handwriting. By June 2015, the Museum will post more than 30,000 digitized documents written by Darwin between 1835 and 1882, the year of his death.
Once Darwin started thinking seriously about evolution, he grasped its essentials with astonishing speed. Only a month or so elapsed between the time he opened the first full transmutation notebook, in about July 1837, and the time he drew this crude—but unmistakable—evolutionary tree.
For Darwin such sketches were likely a way of thinking out loud. And sure enough, above his tree Darwin wrote: “I think.” With the most ancient forms at the bottom and their descendants branching off irregularly along the trunk, the tree reveals that Darwin understood all plants and animals are related.
Below is the full notebook page, with a transcription of the text:
Case must be that one generation then should be as many living as nowa
To do this & to have many species in same genus (as is). REQUIRES extinction.
Thus between A. & B. immens gap of relation C & B. the finest gradation, B & D rather greater distinction
Thus genera would be formed.— bearing relation
aCase must…now] added in balloon in same brown ink as figure
bTo do this…extinction] added in second balloon in grey ink