30 DARWIN'S THEORY. 



dent or chance, is, he says, merely to express our 

 ignorance of the law. Natural Selection but preserves 

 and accumulates the variations as they arise, and 

 directs them into favorable lines of growth. "As all the 

 individuals- of each district are struggling together with 

 nicely balanced forces, extremely slight modifications 

 in the structure or habits of one individual often give 

 it an advantage over the others." And (what is part of 

 the same Natural Selection, called Sexual Selection), 

 were the individual varying, a male, the acquired modi- 

 fication would doubtless give it an advantage, in a 

 contest for the most favored, and, perhaps, similarly 

 varying, females; and, thereby, the modification ac- 

 quired, would be the more surely impressed upon the 

 offspring. In "several thousand generations," or a 

 "million of generations," one of the descendants of 

 this offspring would, probably, also vary, adding thus 

 another character to the complexity of its structure. 



As, under domestication, Man's care and choice of 

 those animals and plants, displaying some improve- 

 ment, tends to the preservation and accumulation of 

 the characters presenting themselves, and assures the 

 transmission of those characters to offspring; so, this 

 Selection by Nature, of the favorably modified animals 

 and plants, as among those which are suffered to sur- 

 vive and propagate their kind, represents the same 

 principle. 



"Can it be thought improbable," says Darwin, "see- 

 ing that variations useful to man, have undoubtedly 

 occurred, that other variations, useful in some way to 

 each being in the great and complex battle of life, 



