Darwin, manuscript page
This original manuscript page for On the Origin of Species shows how Darwin agonized over every sentence in the book. He worried that his writing might be too boring or too abstract. He thus asked friends to read his text for clarity and interest, and he had his wife Emma help edit and proofread it. Unfortunately for us today, no one seems to have helped him with penmanship, as his handwriting is notoriously hard to read.
Charles Darwin (1809–1882). Manuscript page for On the Origin of Species, c. 1858.