Natural Selection

Wallace wrote "Note on the Theory of Permanent and Geographical Varieties" as a refinement of the approach outlined in "On the Law which has Regulated The Introduction of New Species". He noted in the opening paragraph of "Note" that his intent was only to present facts, not to "advocate either side of the question." However, his actual position on the matter was evident in private notes he kept during the expedition.

"Note" attempted to differentiate between species and variety. At that time, both biologists and theologians considered "species" as having arisen as an independent creation, and fixed permanently. A variety was not so permanent, possibly reverting back to the parental form. Wallace argued that if only the degree of variation separated one species from another, the actual point where one population was a different species than another would be too arbitrary to be useful. Wallace developed this line of thought to propose no difference in nature between the origin of species and of varieties with the intent of discrediting the concept of species as fixed. The problems inherent in formulating a include the lack of a satisfactory definition of species.

The expedition to the Malay Archipelago yielded the data Wallace needed to support the proposition made in his 1855 paper (On the Law..). Wallace's paper, On the Natural History of the Aru Islands, published in late 1857, exemplified the Law as put forth in the 1855 paper. The above-mentioned papers may have laid the foundation for a third paper published in 1859, On the Zoological Geography of the Malay Archipelago, which described the biogeography of Wallace's Line. The line Wallace drew as a result of his analysis of the data he collected in the Archipelago has been disputed and redrawn by other exploring naturalists and has come under as much discussion as the theory of natural selection - a hot topic of debate between Wallace and Darwin himself.