COSMIC PHILOSOPHY 



require a large volume. Pigs, . rabbits, cows, 

 fowl, silk-moths, and hive-bees furnish no less 

 instructive evidence ; and the development of 

 the peach and the almond from a common 

 stock, and of countless varieties of apple from 

 the sour crab, may be cited, out of a hundred 

 examples, to show what prodigies artificial se- 

 lection has accomplished in the modification of 

 vegetal organisms. 



Now Mr. Darwin's great achievement has 

 been to show that a similar process of selection, 

 going on throughout the organic world without 

 the knowledge or intervention of man, tends 

 not only to maintain but to produce adaptive 

 alterations in plants and animals. The process 

 is a simple one, when once we have the clew to 

 it. All plants and animals tend to increase in 

 a high geometrical ratio. The old problem of 

 the nails in the horse's shoe teaches us what an 

 astounding affair is a geometrical rate of in- 

 crease ; but when we consider the reproductive 

 capacity of insects and plants, the nails in the 

 horse's shoe are left nowhere. When Arctic 

 travellers tell us that the minute protococcus 

 multiplies so fast as to colour blood-red many 

 acres of snow in a single night, such a rate of 

 increase appears astonishing. But It is a mere 

 trifle compared to what would happen if repro- 

 duction were to go on unchecked. Let us take 

 the ^ase of a plant which yields one hundred 



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