Sclater mentions the relationships of natural areas, a concept that was to appear over a century later (see Hennig 1950, 1966; Brundin 1966), but was never explored further in his 1858 essay. Sclater’s regions were adopted by Wallace (1876), who shared similar sentiments regarding arbitrary lines:
The divisions in use till quite recently were of two kinds; either those ready made by geographers, more especially the quarters or continents of the globe; or those determined by climate and marked out by certain parallels of latitude of by isothermal lines. Either of these methods was better than none at all; [but] it will be evident, that such divisions must have often been very unnatural, and have disguised many of the most important and interesting phenomena which a study of the distribution of animals presents to us … The merit of initiating a more natural system, that of determining zoological regions, not by any arbitrary or a priori consideration but by studying the actual ranges of the more important groups of animals, is due to Mr. Sclater (Wallace 1876, vol. 1, pp. 52–53).
Wallace’s revision of Sclater’s regions is perhaps the most significant of all the geographical classification of the 19th century as it unified zoogeography under a single classification. Even though there were certain disagreements over terminology (see Ebach 2015), the areas have withstood the test of time, with the same divisions appearing in the 21st century studies (e.g. Holt et al. 2013; Morrone 2015). Regardless of its popularity today, the Sclater–Wallacean areas and the whole notion of topographical zoogeography were challenged as “essentially static” and “wrong”. “Instead of thinking of fixed regions, it is necessary to think of fluid faunas” (Mayr 1946, p. 5). For the newly developing field of population genetics and the Modern Synthesis, “zoogeography has had a similar fate very much like taxonomy. It was flourishing during the descriptive period of biological sciences. Its prestige, however, declined rapidly” (Mayr 1944, p. 1). Taxonomy apparently had run its course.
