ACADEMY OF SCENES] BIOGRAPHY 11 



The fact that Wallace in his classic, Geographical Distribution of Animals (1876), adopted 

 the faunal regions proposed by Sclater, gave Doctor Allen an additional incentive to prove 

 the incorrectness of faunal boundaries which are not based primarily on climatic zones. " One 

 of the reasons given by Mr. Wallace for adopting Doctor Sclater's regions," he writes, "is that 

 'it is a positive, and by no means unimportant advantage to have our regions approximately 

 equal in size and with easily defined, and therefore easily remembered boundaries, ' " to which 

 Doctor Allen adds: "These arguments can be scarcely characterized as otherwise than trivial, 

 since they imply that truth, at least to a certain degree, should be regarded as secondary to 

 convenience." 



Wallace, commenting on the criticism of Sclater's faunal regions made by Doctor Allen 

 in 1871, said: " The author continually refers to the 'law of the distribution of life in circumsolar 

 zones,' as if it were one generally accepted and that admits of no dispute. But this supposed 

 'law' only applies to the smallest details of distribution — to the range and increasing or 

 decreasing numbers of species as we pass from north to south, or the reverse; while it has little 

 bearing on the great features of zoological geography — the limitation of groups of genera and 

 families to certain areas. It is analogous to the ' law of adaptation ' in the organization of animals, 

 by which members of various groups are suited for an aerial, an aquatic, a desert, or an arboreal 

 life; are herbivorous, carnivorous, or insectivorous; are fitted to live underground, or in fresh 

 waters, or on polar ice. It was once thought that these adaptive peculiarities were suitable 

 foundations for a classification, — that whales were fishes, and bats birds; and even to this 

 day there are naturalists who cannot recognize the essential diversity of structure in such groups 

 as swifts and swallows, sun-birds and hummingbirds, under the superficial disguise caused 

 by adaptation to a similar mode of life." 



Doctor Allen was not slow to accept this challenge of the correctness of his fundamental 

 principles, replying: 



I unblushingly claim, in answer to the main point, that the geographical distribution of life is by necessity 

 in accordance with a "law of adaptation," namely, of climatic adaptation; that such a law is legitimate in this 

 connection, and that the reference to the "superficial disguise" adapting essentially widely different organisms 

 to similar modes of life is wholly irrelevant to the point at issue — a comparison of things that are in any true 

 sense incomparable; furthermore, that the "law of distribution of life in circumpolar zones" does apply as well 

 in a general sense as to details — "to groups of genera and families" as well as to species. 



He then advances the theory of dispersal of life southward from the arctic which has since 

 been so ably developed by Matthew, writing: 



In this connection it may be well to recall certain general facts previously referred to respecting the geo- 

 graphical relations of the lands of the northern hemisphere and their past history. Of first importance is their 

 present close connection about the northern pole and their former still closer union at a comparatively recent 

 date in their geological history; furthermore, that at this time of former, more intimate relationship, the cli- 

 matic conditions of the globe were far more uniform than at present, a mild or warm-temperate climate prevailing 

 where now are regions of perpetual ice, and that many groups of animals whose existing representatives are 

 found now only in tropical or semitropical regions lived formerly along our present Arctic coast. We have, 

 hence, an easy explanation of the present distribution of such groups as Tapirs, Manatees, many genera of 

 Bats, etc., in the tropics of the two hemispheres, on the wholly tenable assumption of a southward migration 

 from a common wide-spread northern habitat, to say nothing of the numerous existing arctopolitan and semi- 

 cosmopolitan genera. . . . The succeeding epochs of cold caused extensive migrations of some groups and the 

 extinction of others; with the diverse climatic conditions subsequently characterizing high and low altitudes 

 came the more pronounced differentiation of faunae, and the development, doubtless, of many new types adapted 

 to the changed conditions of life — the development of boreal types from a warm-temperate or semi-tropical 

 stock. The accepted theories respecting the modification of type with change in conditions of environment — 

 changes necessarily due mainly to climatic influences — render it certain that if animals are so far under the 

 control of circumstances dependent upon climate, and emphatically upon temperature, as to be either exter- 

 minated or greatly modified by them, the same influences must govern their geographical distribution. 



Further study induced Doctor Allen to modify somewhat the views advanced in his Museum 

 of Comparative Zoology essay of 1871, "especially in relation to the divisions of the Australian 

 Realm, and to unite the South African Temperate with the Indo-African, as a division of the 

 latter, and also to recognize Madagascar and the Mascarene Islands as forming together an 

 independent primary region, in accordance with the view of Sclater, Wallace, and others." 



