THE ORIGIN OF SPECIES 375 



variation were, broadly speaking, equally important he 

 made no sharp distinction between somatic and germinal. 

 The universality of variations established, Darwin empha- 

 sized the fact that the power of reproduction of organisms far 

 exceeds space for them to live in and food for them to eat. 

 Some recent facts will illustrate this point. A single micro- 

 scopic Paramecium possesses the potentiality to eat, grow, 

 and reproduce to transform the materials of its environ- 

 ment into Paramecium protoplasm at the rate of 3000 

 generations in five years. And all the descendants (if they 

 actually existed) would equal 2 raised to the 3000th power, 

 or a volume of protoplasm approximately equal to 10 1000 

 times the volume of the Earth ! 



Something must inhibit the inherent power of each species 

 to overpopulate the Earth, and Darwin emphasized the 

 struggle for existence between the individuals of species. 

 Since the struggle is so keen, a variation, however slight, 

 which fits adapts an individual better to its surroundings 

 than its neighbors are adapted, will, more often than not, give 

 its possessor an advantage in the struggle, and accordingly 

 the latter will survive to pass on the favorable variation to 

 its progeny. Thus is brought about, in Spencer's phraseology, 

 "the survival of the fittest" -the survival of those indi- 

 viduals, and therefore species, which are adapted to the pe- 

 culiar conditions of their environment and mode of life. And 

 note, this offers an explanation of the fact of adaptation itself 

 - the most striking phenomenon which organisms exhibit. 



This is all so simple from one point of view and so confus- 

 ingly complex from others that it may well be restated in a 

 couple of sentences by Darwin himself: "As many more 

 individuals of each species are born than can possibly survive, 

 and as, consequently, there is frequently recurring struggle 

 for existence, it follows that any being, if it vary however 



