Ill 



103 



amidst the gravel in which it first lay with as 

 much precision as if man had "consciously 

 selected " it by the aid of a sieve. Physical 

 Geology is full of such selections of the picking 

 out of the soft from the hard, of the soluble from 

 the insoluble, of the fusible from the infusible, by 

 natural agencies to which we are certainly not in 

 the habit of ascribing consciousness. 



But that which wind and sea are to a sandy 

 beach, the sum of influences, which we term the 

 " conditions of existence," is to living organisms. 

 The weak are sifted out from the strong. A frosty 

 night " selects " the hardy plants in a plantation 

 from among the tender ones as effectually as if it 

 were the wind, and they, the sand and pebbles, of 

 our illustration ; or, on the other hand, as if the 

 intelligence of a gardener had been operative in 

 cutting the weaker organisms down. The thistle, 

 which has spread over the Pampas, to the de- 

 struction of native plants, has been more effectually 

 " selected " by the unconscious operation of natural 

 conditions than if a thousand agriculturists had 

 spent their time in sowing it. 



It is one of Mr. Darwin's many great services 

 to Biological science that he has demonstrated the 

 significance of these facts. He has shown that 

 given variation and given change of conditions 

 the inevitable result is the exercise of such an 

 influence upon organisms that one is helped and 

 another is impeded; one tends to predominate, 

 36 



