Books
Browne, E. J., and Brown, Janet. Charles Darwin: Voyaging: A Biography. Princeton University Press, 1996.
Darwin, Charles. The Origin of Species. First published in 1859, available in many editions.
Darwin, Charles, and Barlow, Nora. The Autobiography of Charles Darwin: 1809-1882. Norton, 1993.
Milner, Richard. Charles Darwin: Evolution of a Naturalist (Makers of Modern Science). Facts on File, 1994.