CHAPTER SEVENTEEN 



NATURAL SELECTION 

 I. A FIRE, once lighted, burns in all directions until The ex- 



the fuel is exhausted. Life 'similarly extends, flowing 

 into every possible channel until checked by circum- 

 stance. It is possible to imagine a universe which 

 might become completely vitalized, alive in all its 

 parts ; but immediately it would produce non-living 

 waste materials, as the result of its own activity. Burn- 

 ing or living are states which, from their nature, imply 

 the coming and going of material ; hence a house cannot 

 be all on fire, or a person all alive. By the constant 

 addition of fuel, the sacred flame can be kept burning 

 indefinitely ; by a similar process the flame of life has 

 been kept burning these many million years. The 

 activity has been continuous, the materials ever chang- 

 ing. 



2. When we speak of life seeking opportunity for ex- Lifeevery- 

 tension, we need not imply anything more purposeful 

 than the similar activity of the fire. Living beings 

 feed, grow, and reproduce. These processes, un- 

 checked, lead to increase in what is called geometrical 

 progression, like compound interest. It is easy to 

 calculate that any common roadside weed, occupying a 

 square foot of ground and producing 500 seeds in a 

 season, would in a few years cover the whole land sur- 

 face of the earth with its offspring, if all survived. As 

 a matter of fact it does nothing of the sort ; most plants 

 and animals are about as numerous one year as the 

 next, the population remaining constant. Even when 

 there is a rapid increase, as for example when the so- 

 called Russian thistle reached this country, it is tem- 

 porary, and does not go nearly to the theoretical limits. 



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