112 GEOLOGICAL BIOLOGY. 



shall find that organisms present as close a relationship to the 

 conditions of the environment into which they are born. 



The Importance of the Study of Geographical Distribution, — 

 Geographical Distribution is a subject which no one has studied 

 more thoroughly and with keener appreciation than Alfred R. 

 Wallace, and a quotation will, in a few words, express the 

 importance of the subject. He says: "So long as each 

 species of organism was supposed to have had an independent 

 origin, the place it occupied on the earth's surface, or the 

 epoch when it first appeared, had little significance. It was, 

 indeed, perceived that the organization and constitution of 

 each animal or plant must be adapted to the physical condi- 

 tions in which it was placed ; but this consideration only 

 accounted for a few of the broader features of distribution, 

 w^hile the great body of the facts, their countless anomalies 

 and curious details, remained wholly inexplicable; but the 

 theoiy of evolution and gradual development of organic forms 

 by descent and variation (some form of which is now univer- 

 sally accepted by men of science) completely changes the 

 aspect of the question, and invests the facts of distribution 

 with special importance." "The time when a group or a 

 species first appeared, the //c?c"r of its origin, and the area it 

 now occupies upon the earth become essential portions of 

 the history of the universe. The course of study, initiated 

 and so largely developed by Darwin, has now shown us the 

 marvellous interdependence of every part of nature. Not 

 only is each organism necessarily related to and affected by 

 all things, living and dead, that surround it, but every detail 

 of form and structure, of color, food, and habits, must, it is 

 now held, have been developed in harmony with, and to a 

 great extent as a result of, the organic and inorganic environ- 

 ments. Distribution becomes, therefore, as essential a part 

 of the science of life as anatomy or physiology. It shows us, 

 as it were, the form and structure of the life of the world 

 considered as one vast organism, and it enables us to compre- 

 hend, however imperfectly, the processes of development and 

 variation during past ages which have resulted in the actual 

 state of things. It thus affords one of the best tests of the 

 truth of our theories of development [evolution] ; because the 



