134 STUDIES IN LIFE AND SEXSE. 



unquestioned, it was of all logical processes the most natural that 

 a " special centre " of creation should be sought and found for each 

 species. This theoretical "specific centre" was allocated, cateris 

 panbus, in the region where the species was found to be most 

 abundantly represented. The diffusion of a species beyond its 

 centre was due, it was held, to such favouring influences as con- 

 tinuous land surfaces, the presence of food in surrounding regions, 

 favourable temperatures and climates, and like conditions. The 

 limitation of a species to its centre or original area was held, 

 conversely, to depend upon an absence of the conditions favouring 

 migration and dispersion. The presence of rivers, lakes, or seas, the 

 existence of land-barriers in the shape of mountain chains, extremes 

 of temperature and vicissitudes of climate and other causes, were 

 regarded as the means whereby a species was confined more or 

 less strictly within its area. 



But the growth of the idea that the existing species of animals 

 and plants were the descendants, by ordinary generation, of pre- 

 existing species, wrought a wonderful and sweeping change in biolo- 

 gical opinions concerning distribution, as in every other department 

 of natural-history science. The theory of the separate and detached 

 placing of animals and plants here and there over the surface of the 

 earth, in obedience to no ascertainable law, was soon driven to the 

 wall as a weak invention possessing no logical standpoint whatever. 

 Affording no reason for. ; the marvellous diversities of life's distribution, 

 the doctrine of " specific centres " wa,s soon consigned to the limbo 

 reserved for the myths and traditions of biology. To say that provi- 

 dential reasons namely, the necessity of a fatty dietary on the 

 part of the Esquimaux accounted for the presence of seals and 

 whales in the Arctic regions, or similarly, that farinaceous plants grew 

 most plentifully in the tropics because the inhabitants thereof fed 

 upon their products, might indeed satisfy primitive minds, preferring 

 to bring scientific facts under the sway of dogma rather than to test 

 dogma by the logic of facts. Moreover, all such apologetic attempts 

 at correlating the facts of distribution with theoretical interpretations 

 of the designs of Providence missed their mark, because in placing 

 man in the first place, and the distribution of life in the second, they 

 reversed not merely the chronological order of affairs, but subverted 

 the real aspect of the case. Thus, clearly, no explanation of the 

 "whys" of distribution was forthcoming from former aspects of this 

 study, just as the "hows" of the science were equally neglected. 

 The newer era of research inaugurated by the publication and growth 

 of Mr. Darwin's opinions, derived no small share of its power and 

 progress from its ability to explain the " how " and " why," not 

 merely of distribution, but of other departments of biology. Evolu- 

 tion, for example, gave a reasonable explanation of the metamorphosis 



