AUTHOR'S PREFACE 



Ecological methods can be applied to many different branches 

 of animal biology. For instance, they may be employed in the 

 study of evolution and adaptation. Most of the work done 

 so far under the name of ecology has been concerned with 

 this side of the subject, and has been summed up to some 

 extent by Borradaile (The Animal and its Environment) and 

 Hesse (Tiergeographie auf Okologische Grundlage). Or they 

 may be appHed to the study of the normal and abnormal life 

 of cells in the bodies of animals, as has been so strikingly done 

 by Morley Roberts {Malignancy and Evolution) ; or again they 

 may be used in the study of man, when they form the sciences 

 of sociology and economics (as exemplified by Carr- Saunders 

 in The Population Problem)^ or of the relations between the two 

 sexes, as illustrated by the work of EHot Howard and J. S. 

 Huxley on bird-habits. The present book is chiefly concerned 

 with what may be called the sociology and economics of animals, 

 rather than with the structural and other adaptations possessed 

 by them. The latter are the final result of a number of pro- 

 cesses in the lives of animals, summed up over thousands or 

 millions of years, and in order to understand the meaning and 

 origin of these structures, etc., we must study the processes and 

 not only their integrated results. These latter are adequately 

 treated in the two works mentioned above, and although of 

 great intellectal interest and value, a knowledge of them throws 

 curiously little Ught on the sort of problems which are en- 

 countered in field studies of living animals. I have laid a good 

 deal of emphasis on the practical bearings of many of the ideas 

 mentioned in this book, partly because many of the best 

 observations have been made by people working on economic 



