156 GEOLOGICAL BIOLOGY. 



there left for us to investigate ? But in fact, while the muta- 

 bility of species was received and advocated, the idea of 

 species was still retained, as evidenced by the title of Darwin's 

 famous book, "The Origin of Species." 



New Conception of the Nature of Species. — The change was a 

 philosophical one ; no longer was the species considered to 

 be a permanent entity with definite boundaries, but in the 

 definition of organic species its time-relations and its geograph- 

 ical distribution were elements added to those of its morphol- 

 ogy and physiology. This was a great advance. The organism 

 came to be recognized as not a mere concrete being independ- 

 ent and standing by itself, constituted at the beginning what 

 it is and remaining so during its existence, but as a very de- 

 pendent part of a greater organism, nature itself, and related 

 intimately to its surroundings or environment, to the organ- 

 isms which preceded it or its ancestry-, and to those which are 

 to follow or its descendants, as a sensitive, slowly changing 

 reflex of all that has been and is. In the new conception 

 there is the dim outlining of the idea (an old idea, but one 

 which is day by day growing more distinct and of fuller com- 

 prehension) that nature itself is a greater organism in which 

 the species is but one of the organs. 



Remarkable Revolution of Thought started by Darwin's " Origin 

 of Species." — Darwinism, although not pure evolutionism, but 

 only one phase of it, has done more than anything else to 

 bring about these changed views of nature. Darwin took up 

 the general theory of evolution, and attempted to give an 

 account of the method of its working. The title of his work 

 clearly sets forth the essential scope of his theory: " On the 

 Origin of Species by Means of Natural Selection, or the Preser- 

 vation of Favored Races in the Struggle for Life." This defini- 

 tion of the origin of species implies two fundamental propo- 

 sitions, viz. : (i) That the species naturally varies in its 

 characters, for the natural selection is selection among char- 

 acters that differ; this is the idea of "mutation"; and (2) 

 that the reason why one character rather than another is pre- 

 served is its better adaptation to conditions of environment ; 

 this is the idea of " natural selection." 



Darwin brought out prominently the fact, that what we 



