4o8 The Living Plant 



itself of the scanty room and food, there results among them a 

 constant struggle for existence. 



Survival of the Fittest. — In this struggle for existence among a 

 great many individuals of which few can survive, what determines 

 which those few are to be? If the young individuals were born 

 all alike the survival would obviously be determined by nothing 

 but chance; but in fact they are all born unlike, and among the 

 differences, or variations, which they exhibit, there must happen 

 to be some which fit their possessors better for the conditions of 

 the particular struggle in hand than do others; and such better- 

 fitted forms will naturally be the ones to succeed. This is the 

 survival of the fittest. Where the seedlings of spruce trees spring 

 up of themselves in fields that are abandoned, it comes finally to 

 pass that a few tower upward in full vigor, while the shade under- 

 neath them is almost like night from the profusion of dead stems 

 of the unsuccessful, — the ones which did not possess the variation 

 of most rapid upward growth to possession of the indispensable 

 light. 



Heredity. — In reproduction, as everybody knows, the main 

 features of the parents are repeated in their offspring, or are 

 hereditary. Now this is true also of at least a part of the varia- 

 tions. Hence, when a plant or an animal survives by virtue of 

 some particular advantageous variation, that variation is likely 

 to be repeated in its offspring. Meantime, of course, the unfit 

 have perished, and left no descendants. The whole tendency, 

 therefore, is towards the production of a race in which the valuable 

 variation is universal. 



It will now be evident to the reader that these five factors acting 

 together must tend to cause a natural selection, and hereditarj'- 

 fixation in each generation, of the fittest, or most advantageous 

 variations, of whatsoever kind. It remains to consider, and this 

 is a point too often overlooked, how a variation can accumulate 

 and become intensified, generation after generation, until it forms 

 a well-marked character of the species. This, also, is easily under- 



