Projected butterflies cover the hand of an employee at the Darwin Center at the Natural History Museum in London in September 2009. (Peter Macdiarmid/Getty Images)

I’ve always wondered about the doubts the geniuses of old felt about their work. Or the notes they scribbled alongside the manuscripts that would become our classics.

Kubla Khan, the classic poem written by Samuel Taylor Coleridge about an opium-inspired dream, was written in 1787 but readers didn’t get the full story until a copy of the poem called Crewe Manuscript was discovered, linking the Kubla Khan’s origins to Coleridge’s stay at a place called Ash Farm.

Now, we are getting more insight about the man behind the theory of evolution through the notes he wrote to himself. Three hundred thirty of Charles Darwin’s most heavily annotated titles were just put online at the Biodiversity Heritage Library, a project to digitize natural history information. ScienceNOW’s Elizabeth Pennis writes about one of the best annotations Darwin made: After he finished reading Charles Lyell’s “Principles of Geology,” Darwin scribbled on the last page, “if this were true[,] adios theory.”

Darwin’s comments appear in the margins of about half of his 1,480 books, and are often telling of the naturalist’s opinions. For example, the story goes that Darwin did not like the butterfly. On the side of a book he co-wrote on biodiversity, Darwin scribbles a note which could have been a jab at the winged insect: “The differently colored caterpillars produce the same form of Butterfly.”

Darwin’s scribbles also reveal how thoughtful, and often almost philosophical, he was. On a journal written about his own work, Darwin writes in the margin:

“The more perfect the organism the less evolution.”