38 THE DARWINIAN THEORY 



'will hand down their peculiarities. Just as man 

 selects artificially the forms best suited for his pur- 

 pose, and by breeding from them produces great 

 changes in structure and habit, so in Nature the best 

 and fittest of each generation have an advantage and 

 the best chance of survival. 



f. Change of environment, rendering old charac- 

 ters of less value and bringing new ones to the fore. 



From this follow — Structural modifications. 



Causes are always at work which must lead to 

 change in structure, and this to an apparently un- 

 limited extent. 



Let us now examine the argument more closely. 



A. Rapid Increase of Organisms. — "There is no 

 exception to the rule that every organic being, animal 

 or plant, naturally increases at so high a rate that, 

 if not destroyed, the earth would soon be covered by 

 the progeny of a single pair." Man himself has 

 doubled his numbers in the United States in the 

 course of twenty-five years, and at this rate in less 

 than iooo years there literally would not be standing- 

 room on the earth for his progeny. Linnaeus showed 

 that an annual plant producing two seeds only — and 

 there is no plant so unproductive as this — and these 

 each producing two in the following year, and so on, 

 would in twenty-one years produce over a million 

 plants, as shown in the following table : — 



