Darwin's correspondence, online.

Darwin exchanged letters with nearly 2000 people during his lifetime. These range from well known naturalists, thinkers, and public figures, to men and women who would be unknown today were it not for the letters they exchanged with Darwin.

Darwin's correspondence provides us with an invaluable source of information, not only about his own intellectual development and social network, but about Victorian science and society in general. They provide a remarkably complete picture of the development of his thinking, throwing light on his early formative years and the years of the voyage of the Beagle, on the period which led up to the publication of The Origin of Species and the subsequent heated debates.

Via Tinkerty Tonk.