If you’ve ever wondered whose addresses Charles Darwin was sure to keep tabs on—or even a few rat poison recipes—you’re in luck. A digitized edition of the famed naturalist’s personal address book is available online for the first time. But despite the collection’s roughly 15,000 letters to and from Darwin, the recently digitized address book still manages to contain previously undocumented individuals, businesses, and subject matter. Page 3 in Charles Darwin’s address book mentions ‘Rarytes carbonate for Rats.’ Credit: National University of Singapore Jackie LeaMultiple entries concern previously unknown pigeon breeders, for example. Interestingly, the address book’s first entries come from Darwin’s wife, Emma, not long after the couple married in January 1839.