By HANS GADOW, M.A., Ph.D., F.R.S.
Strickland Curator and Lecturer on Zoology in the University of Cambridge.
The first general ideas about geographical distribution may be found in some of the brilliant speculations contained in Buffon's "Histoire Naturelle". The first special treatise on the subject was however written in 1777 by E.A.W. Zimmermann, Professor of Natural Science at Brunswick, whose large volume, "Specimen Zoologiae Geographicae Quadrupedum"..., deals in a statistical way with the mammals; important features of the large accompanying map of the world are the ranges of mountains and the names of hundreds of genera indicating their geographical range. In a second work he laid special stress on domesticated animals with reference to the spreading of the various races of Mankind.
In the following year appeared the "Philosophia Entomologica" by J.C.
Fabricius, who was the first to divide the world into eight regions. In 1803 G.R. Treviranus ("Biologie oder Philosophie der lebenden Natur", Vol.
II. Gottingen, 1803.) devoted a long chapter of his great work on "Biologie" to a philosophical and coherent treatment of the distribution of the whole animal kingdom. Remarkable progress was made in 1810 by F.
Tiedemann ("Anatomie und Naturgeschichte der Vogel". Heidelberg, 1810.) of Heidelberg. Few, if any, of the many subsequent Ornithologists seem to have appreciated, or known of, the ingenious way in which Tiedemann marshalled his statistics in order to arrive at general conclusions. There are, for instance, long lists of birds arranged in accordance with their occurrence in one or more continents: by correlating the distribution of the birds with their food he concludes "that the countries of the East Indian flora have no vegetable feeders in common with America," and "that it is probably due to the great peculiarity of the African flora that Africa has few phytophagous kinds in common with other countries, whilst zoophagous birds have a far more independent, often cosmopolitan, distribution." There are also remarkable chapters on the influence of environment, distribution, and migration, upon the structure of the Birds!
In short, this anatomist dealt with some of the fundamental causes of distribution.
Whilst Tiedemann restricted himself to Birds, A. Desmoulins in 1822 wrote a short but most suggestive paper on the Vertebrata, omitting the birds; he combated the view recently proposed by the entomologist Latreille that temperature was the main factor in distribution. Some of his ten main conclusions show a peculiar mixture of evolutionary ideas coupled with the conception of the stability of species: whilst each species must have started from but one creative centre, there may be several "analogous centres of creation" so far as genera and families are concerned.
Countries with different faunas, but lying within the same climatic zones, are proof of the effective and permanent existence of barriers preventing an exchange between the original creative centres.
The first book dealing with the "geography and classification" of the whole animal kingdom was written by W. Swainson ("A Treatise on the Geography and Classification of Animals", Lardner's "Cabinet Cyclopaedia" London, 1835.)in 1835. He saw in the five races of Man the clue to the mapping of the world into as many "true zoological divisions," and he reconciled the five continents with his mystical quinary circles.
Lyell's "Principles of Geology" should have marked a new epoch, since in his "Elements" he treats of the past history of the globe and the distribution of animals in time, and in his "Principles" of their distribution in space in connection with the actual changes undergone by the surface of the world. But as the sub-title of his great work "Modern changes of the Earth and its inhabitants" indicates, he restricted himself to comparatively minor changes, and, emphatically believing in the permanency of the great oceans, his numerous and careful interpretations of the effect of the geological changes upon the dispersal of animals did after all advance the problem but little.
Hitherto the marine faunas had been neglected. This was remedied by E.
Forbes, who established nine homozoic zones, based mainly on the study of the mollusca, the determining factors being to a great extent the isotherms of the sea, whilst the 25 provinces were given by the configuration of the land. He was followed by J.D. Dana, who, taking principally the Crustacea as a basis, and as leading factors the mean temperatures of the coldest and of the warmest months, established five latitudinal zones. By using these as divisors into an American, Afro-European, Oriental, Arctic and Antarctic realm, most of which were limited by an eastern and western land-boundary, he arrived at about threescore provinces.