Adams, A.B. 1969. Eternal Quest: The Story of the Great Naturalists. G.P. Putnam's Sons, New York.
Darwin, C. 1859. On the Origin of Species. First edition. John Murray, London. (Facsimile reprinted 1964, Harvard University Press.)
Darwin, C. 1861. "An historical sketch of the progress of opinion on the Origin of Species, previously to the publication of this work." Appended to third and later editions of On the Origin of Species.
Eiseley, L. 1958. Darwin's Century: Evolution and the Men who Discovered It. Doubleday, New York.
Packard, A.S. 1901. Lamarck, the Founder of Evolution: His Life and Work. Longmans, Green, and Co., New York.