INTRODUCTION TO THE AMERICAN REVISED EDITION xi 



along the more classic lines based on historical distributions of species 

 in which the homologies will be emphasized rather than the physi- 

 ological aspects. The mastery of the implications of the present dis- 

 cussion appears essential for the preparation of such a treatise. 

 Zoogeography as developed by Wallace and by Heilprin underempha- 

 sized the physiological or ecological factors. They were dealing pri- 

 marily with the distribution of birds and mammals; these homoio- 

 thermal animals are largely independent of such an important 

 climatic factor as temperature, and hence the conclusion became 

 widespread that climate is not clearly correlated with animal dis- 

 tribution. Appreciation of the importance of relative humidity and 

 rainfall lagged even when the value of temperature began to be more 

 fully appreciated, while the importance of such climatic factors as 

 the composition and intensity of sunlight is only now beginning to be 

 investigated actively. 



All our experience to date has taught us that it is impossible to 

 organize local or geographic animal ecology upon the basis of struc- 

 tural adaptations, and yet it is impossible to disregard these. We must 

 at the same time avoid the conclusion that appearance of adaptation 

 necessarily means that the adapted structure originated as a response 

 to the special conditions which it now fits. The structure may really 

 be older than the habitat feature for which it appears to be an adapta- 

 tion. Students of adaptation should be warned that, although they will 

 find close adjustments described in the following pages, and although 

 a sense of the fitness of organisms underlies the whole discussion, the 

 immediate emphasis lies elsewhere. 



Throughout the book attention is focused on the distribution of 

 communities of animals rather than upon the more readily observed 

 distribution of vegetation or on the still more easily measured ele- 

 ments of the non-living environment. These are discussed, but only 

 as a background for the distribution of animals. 



Any work on animal geography, if it is to be carefully studied, 

 should be read with an atlas near at hand. Only an atlas can give a 

 sufficient number of detailed maps, hence we have made no effort to 

 include maps other than the suggestive outline ones found in the 

 original edition. For casual use we recommend Goode's School Atlas 

 (1933), which shows the world distribution of temperature, rainfall, 

 vegetation, and other factors. Bartholomew, Clarke, and Grimshaw's 

 Atlas of Zoogeography (1911) gives the world distribution of animals 

 of different sorts. The Times Atlas has good maps which show localities 

 with English nomenclature, while Stieler's Hand Atlas (tenth edition) 

 gives even better maps; the German edition of the latter (1928-1930) 



