18 INTRODUCTION. 



other creature is a condition of existence. Even in 

 the lowliest world of plants the labors of Maternity 

 begin, and the animal kingdom closes with the crea- 

 tion of a class in which this function is perfected to 

 its last conceivable expression. The vicarious prin- 

 ciple is shot through and through the whole vast web 

 of Nature; and if one actor has played a mightier 

 part than another in the drama of the past, it has 

 been self-sacrifice. What more has come into human- 

 ity along the line of the Struggle for the Life of 

 Others will be shown later. But it is quite certain 

 that, of all the things that minister to the welfare and 

 good of Man, of all that make the world varied and 

 fruitful, of all that make society solid and interesting, 

 of all that make life beautiful and glad and worthy, by 

 far the larger part has reached us through the activi- 

 ties of the Struggle for the Life of Others. 



How grave the omission of this supreme factor from 

 our reckoning, how serious the effect upon our whole 

 view of nature, must now appear. Time was when 

 the science of Geology was interpreted exclusively in 

 terms of the action of a single force — fire. Then 

 followed the theories of an opposing school who saw 

 all the earth's formations to be the result of water. 

 Any Biology, any Sociology, any Evolution, which is 

 based on a single factor, is as untrue as the old Geol- 

 ogy. It is only when both the Struggle for Life and 

 the Struggle for the Life of Others are kept in view, 

 that any scientific theory of Evolution is possible. 

 Combine them, contrast them, assign each its place, 

 allow for their inter-actions, and the scheme of Nature 

 may be worked out in terms of them to the last detail. 

 All along the line, through the whole course of the 



