1. Annan, Noel. 1955. “The Intellectual Aristocracy.” J.H. Plumb (ed.), Studies in Social History; a Tribute to C. M. Trevelvan. London, New York: Longmans, Green, pp. 243–287.
2. Agassiz, Louis. 1874. “Evolution and the Permanence of Type.” The Atlantic Monthly 33: 92–101.
3. Artificial Selection and Pangenesis [Review]. 1868. “The Popular Science Review.” John van Wyhe (ed.), The Complete Work of Charles Darwin Online, vol. 7. London: Robert Hardwicke, pp. 176–180. darwin-online.org.uk . Accessed 22 February 2013.
4. Beatty, John. 2006. “Chance Variation: Darwin on Orchids.” Miriam Solomon (ed.), Philosophy of Science. Proceedings of the 2004 Biennial Meeting of the Philosophy of Science Association, Part II, vol. 73(5). Lansing: Philosophy of Science Association, pp. 629–641.
5. Brewer, William Henry. 1868. The Variation of Animals and Plants Under Domestication; by Charles Darwin, M.A., F.R.S. American Journal of Science and Arts 46(136): 140–143.