Method of Origin of New Species and Structures 409 



stood on reflection. For not only do the offspring of the parents 

 preserved by possessing a fit variation inherit that variation, but 

 they vary in regard to that variation itself. Therefore in any 

 generation, while some of the individuals will inherit the variation 

 about like the parents, a few will vary towards a greater intensity 

 thereof; and in the struggle for existence in this generation, 

 these more extreme individuals will survive. Their offspring, 

 in turn, will tend to resemble them in possessing the greater 

 degree of the variation, but the offspring will include some that 

 vary towards an even higher degree, and these will survive, and 

 so on. Thus a variation, by its continued selection in one direc- 

 tion generation after generation, can pile up until it produces a 

 large and visible change in that feature of the plant. But the 

 different features of the organism are so closely tied together that 

 a change in any one always involves some others, while, moreover, 

 selection may be operating upon more than one feature of a plant 

 at a time. Thus the accumulation of variations gradually make 

 their possessor look distinctly different from the original ancestors; 

 and when that point is reached we call it a new species, especially 

 if, as usually but not invariably happens, the intermediate and 

 less well adapted forms have died out in competition with the 

 better. The process is represented in operation, with increase 

 in size assumed as the advantageous variation, in the accom- 

 panying diagram (figure 172). This process of progressive adapta- 

 tion would continue until the species theoretically has become as 

 perfectly adapted as possible to the selective conditions; but in 

 fact such stability would never be reached since the conditions 

 themselves, like all the rest of the world, are in continual altera- 

 tion. And such is the origin of species by means of natural 



SELECTION, OR THE PRESERVATION OF FAVORED RACES IN THE 



STRUGGLE FOR LIFE, in the words of the title-page of Darwin's 

 greatest book. 



The theory of Natural Selection explains very perfectly not 

 only the origin of new structures and new species, but also the 



