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In March, 1868, Moritz Wagner read a paper before the Royal Academy of Sciences at Munich on "The Law of the Migration of Organisms," and in 1873 an English translation of a fuller paper by him entitled "The Darwinian Theory and the Law of the Migration of Organisms" was published by Edward Stanford, of London. It was through this pamphlet that I became acquainted with his theory concerning the impossibility of the production of new species except when and where migration establishes a colony geographically isolated from the original stock. In this paper we read: "The constant tendency of individuals to wander from the station of their species is absolutely necessary for the formation of races and species" (p. 4). "Where there is no migration, that is, where no isolated colony is founded, natural

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selection can not take place" (p. 59). These and many other passages of similar import indicate how fully he recognized the importance of isolation, and how at the same time his theory was a denial of some of the facts in the origin of species. The following are some of the facts with which his general theory as well as his special statements were in conflict.

That, through change of climate and of other conditions due to geological changes, the whole fauna and flora of an island like Iceland might be subjected to new forms of selection producing a complete change of many species into new species, without any chance for migration. After the publication of my article in Nature, July 18, 1872, in which I emphasized the importance of isolation, I met Darwin at his home, and he called my attention to Wagner's theory, and suggested that it did not correspond with the facts of nature, especially on this point.