qi CRITICISMS ON “THE ORIGIN OF SPECIES” 103 
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} 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, 
