Natural Selection: The Law

Tentative Explanations

Wallace wrote "On the Law which Has Regulated the Introduction of New Species" while in Sarawak, Borneo during February of 1855. This paper was published in Volume 16 (2nd Series) of the Annals and Magazine of Natural History in September 1855. In this paper, Wallace discussed the geological history and proposed the geological history of an area as a factor in the flora and fauna inhabiting the region:

"Now, taking this as a fair statement of the results of geological inquiry, we see that the present geographical distribution of life upon the earth must be the result of all the previous changes, both of the surface of the earth itself and of its inhabitants. Many causes no doubt have operated of which we must ever remain in ignorance, and we may therefore expect to find many details very difficult of explanation, and in attempting to give one, must allow ourselves to call into our service geological changes which it is highly probable may have occurred, though we have no direct evidence of their individual operation."

Drawing of a Wallace's hut by Wolf, from a photograph by Woodbury. Scanned from The Malay Archipelago, Alfred Russel Wallace.

Wallace's knowledge of geology was based on his readings of Charles Lyell and other uniformitarians. Geology was still a very young science. In his paper, "On the Law..." Wallace took 4 propositions from geography and 5 propositions from geology to support the idea he began to formulate during his work in the Amazon. These propositions are summarized in a 4-part law:

"Every species has come into existence coincident both in space and time with a pre-existing closely allied species. This law agrees with, explains and illustrates all the facts connected with the following branches of the subject:--1st.The system of natural affinities. 2nd. The distribution of animals and plants in space. 3rd. The same in time, including all the phænomena of representative groups, and those which Professor Forbes supposed to manifest polarity¹. 4th. The phænomena of rudimentary organs. We will briefly endeavour to show its bearing upon each of these."

British naturalist Edward Forbes had stated that palentological evidence, because there was more fossil evidence from very early times and more recent times with none from intermediate times, indicated a maximum formation of generic forms at those times. This was consistent with a creation that would fit divine ordination. Wallace deemed Forbes' paper absurd and set about refuting it with his own ideas.

Wallace's position was that during periods of geologic stability, there would be little change in living things from generation to generation as the conditions were already suitable for their existence. During times of more rapid geological change, changes in living conditions could become less favorable for many individuals and some species would become extinct while other, newer species might be created. While Forbes assumed fossil knowledge was complete, Wallace was certain more facts were needed. Wallace knew much about the Galapagos, for in his 1855 paper On the Law which has Regulated The Introduction of New Species, he maintained that the differences among species found on these tiny, isolated islands could not be explained by a creation theory.

Comparative anatomy played a role in Wallace's new law. Georges Cuvier, a pioneer in this field, is not listed on this site as having significant influence on Wallace's work. It is known that Wallace was familiar with Cuvier's work on comparative anatomy as he argued that a classification system should be based on a combination of both internal and external structural traits rather than superficial traits.

Wallace's "law" would undergo further modification. He intended to test it with data from another expedition, this time to the Malay Archipelago.