Moritz [or Moriz] W. Wagner was a well-known German geographer and naturalist who travelled widely. He is known among geographers and historians for publications of his travels in North, Central and South America and the Caribbean, as well as North Africa, Persia, Armenia, Georgia and Iraq. See also: http://en.wikipedia.org/wiki/Moritz_Wagner
From an evolutionary biologist's point of view, Wagner is most famous for having developed a theory he variously called "Migrationstheorie," "Law of Migration," or "Separationstheorie." He corresponded with Darwin, who received his ideas cooly. In 1868, he argued that Darwin's ideas of speciation were incomplete, and proposed what he felt was an important addition: that small colonies, containing a subset of the existing variation, migrated to a new region, whereupon the changed conditions would cause Lamarckian evolution of new species. He felt that "Absonderung" (or dispersal, followed by geographic isolation) was essential for the formation of new species by preventing intercrossing.
Wagner's model was acknowledged as a forerunner by Ernst Mayr to his own "founder effect" model of allopatric speciation (1954). Careful reading indicates that Wagner (1868) felt that Darwin hadn't explained the source of initial divergence, or the source of variation, that led to speciation. Lamarckian evolution of traits caused by novel conditions in a new location after migration was Wagner's answer to the problem. Geographic isolation aided this process by preventing intercrossing, so allowing the Lamarckian evolution to continue without being swamped by the parent form.
Wagner's ideas were strongly resisted by Darwinists, particularly August Weismann, Ernst Haeckel, Alfred Russel Wallace, John Thomas Gulick, as well as by Darwin himself. It seems likely that Darwin found these views annoying because many of Wagner's published ideas on geographic isolation could also be found in his own Origin of Species, but were insufficiently acknowledged by Wagner, and that most of his novel ideas were poorly supported or demonstrably wrong. Darwin scribbled "most wretched rubbish" across one of Wagner's papers (1875, published in Ausland -- see Sulloway 1979 for this story). Wagner felt that his idea was a major advance: "Those who with Darwin deny the necessity of isolation for natural selection, and only admit its advantage, must indicate another cause for the first stimulus to increased variation, and other conditions upon which the preservation of the new characteristics depend." (from the 1873 translation of Wagner 1868).
In later years, particularly 1880, Wagner hardened his stance against Darwinism, arguing that his own Migrationstheorie was not only an essential improvement ofDarwin's theory of evolution as he had stated in 1868, but also incompatible with Darwin's theory of natural selection (he effusively thanked Weismann for clearing this matter up). Having been criticised on the basis that mimicry could not be explained by Separationstheorie, Wagner argued that actually mimicry was explained better by Separationstheorie than by natural selection. In his view, variants within populations, finding they had the wrong colours to adapt to local situations, were impelled innately to move to areas, substrates, and habitats where their colours hid them from their natural enemies (including living among others having the same colours, as in Muellerian mimicry). Having got there, the new varieties would also be protected from intercrossing with the ancestral species by geographic distance, and would form a new species. Thus it was movement of the pre-adapted forms to better habitats, not selection of varieties in the new habitats, that permitted evolutionary progress.
He doesn't seem to have noticed the profound changes in his own theory, which initially required a change of conditions to induce the variation in the geographically isolated population. In 1880, he instead argued that the variants already in the parental population, having migrated, required an absence of intercrossing due to isolation from the parental population. This allowed the novel variation to become fixed, and species to form.
He equated the movement of twig-like caterpillars by night towards leaves, and the movement back down towards the bark, in terms of Separationstheorie. The reason why caterpillars are twig mimics, apparently, is that variants which happened to be camouflaged on twigs choose suitable twigs on which to rest. This is supposedly a more parsimonous explanation than the Darwinians', which requires caterpillars resting on twigs to be selected against if they do not resemble twigs. Needless to say, Separationstheorie could explain everything.
Ernst Mayr frequently alluded to Wagner's theories as important forerunners of his own views on geographic isolation. However, Mayr ignored the abundant criticism of Wagner from that time, as well as Wagner's odd views and extreme anti-selection stance. There is a good discussion of this aspect of Mayr's thinking, as well as of Wagner's theories, by Sulloway (1979).
In a review of Wagner's 1889 post mortem book, Charles S. Minot (1890) writes:
"Wagner's essays show the journalist's [talents]. They are all discursive and pleasant, it is easy to read along in them, but there is a complete absence of that formidable marshalling of, facts and unconquerable logic which is the stamp of Darwin's work. Wagner nowhere compiles all the facts of geographical isolation, nor enumerates those which conflict with his theory, either to acknowledge their force or explain them away."
It is of historical interest to note that Wagner's ideas, which blended evolutionary ideas with social science and geography, had some far reaching effects. An important disciple, Friedrich Ratzel, who was influenced by Wagner in Munich, developed the social Darwinist theory that 'fitter' nations (such as Germany) would expand their borders at the expense of less successful nations. He coined the term 'Lebensraum' and his work led to the invention of the idea of 'Geopolitik.' Ideas such as these were to culminate in certain expansionist ideas that led to much suffering during the 20th Century. See: http://en.wikipedia.org/wiki/Friedrich_Ratzel. Ratzel also wrote an important biography of Wagner (Ratzel 1896).
Below, I make available some fragments of Wagner's evolutionary publications, as well as some references to his work.
Mayr, E. 1954. Change of genetic environment and evolution. Pp. 157-180 in J. Huxley ed. Evolution as a Process. Allen and Unwin, London.
Minot, C. S. 1890. Book review. Die Entstehung der Arten durch räumliche Sonderung. Von Moritz Wagner. Basel, 1889. Science 15:305-306.
Ratzel, F. 1896. Wagner: Moritz W. Allgemeine Deutsche Biographie 40:532-543. [PDF] 2.4 MB
Sulloway, F. J. 1979. Geographic isolation in Darwin's thinking: the vicissitudes of a crucial idea. Studies in the History of Biology 3: 23-65.
Wagner M. 1868. Darwin'sche Theorie und das Migrationsgesetz der Organismen. Duncker & Humblot, Leipzig.
Wagner M. 1873. The Darwinian Theory and the Law of the Migration of Organisms.
Translation by J.L. Laird of Darwin'sche Theorie und das Migrationsgesetz
der Organismen, published in 1868. Edward Stanford, London.
[PDF of whole book] 15.5 MB
Wagner M. 1889. Die Entstehung der Arten durch räumliche Sonderung. Gesammelte Aufsätze. Benno Schwalbe, Basel. Published after Wagner's death by suicide by his friends and nephew. Confusingly this nephew was also named Moritz Wagner. [The Origin of Species through Geographic Isolation. Collected Works]. Some contents:
Front matter 1.6 MB
Foreword, by the Editor 4.4 MB
Biographical sketch. By Dr. Karl von Scherzer, 12.1 MB
Der Naturprozess der Artbildung 4.6 MB
[The natural process of species formation, originally published in Ausland 1875]
Über die Entstehung der Arten durch Absonderung 21.4 MB
[On the origin of species through spatial separation, originally published in Kosmos 1880]
Leopold von Buch und Charles Darwin 1.4 MB
[originally published in Kosmos 1883]