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theory. He draws an analogy between the artificial selection 

 employed by breeders in the production and perpetuation 

 of new breeds or varieties, and natural selection, or that 

 process which all organised beings must undergo, whether 

 animal or vegetable, in the "struggle for existence " against 

 not only those other creatures which prey upon them, but 

 to a still greater extent against those which are similarly 

 nourished as themselves. "The struggle for existence 

 inevitably follows from the high geometrical ratio of increase 

 which is common to all organic beings." It is impossible 

 that all should live. "A grain in the balance may determine 

 which individual shall live, and which die which variety or 

 species shall increase in number, and which shall decrease, 

 and finally become extinct." Thus it follows that, as only a 

 fractional part of those which are born shall survive and 

 produce descendants, the weaker, or those least fitted to 

 conquer in the struggle for existence, must succumb and 

 perish, whilst the stronger, more capable of overcoming by 

 reason of their more favourable organisation, alone survive : 

 and so the struggle for existence results in the " survival of 

 the fittest." 



Slight variations may be perpetuated, and those creatures 

 which, owing to natural advantages, possess greater powers 

 of attack and defence, and which are more adapted for the 

 acquisition of nourishment, naturally overcome those less 

 favoured, and eventually displace them. That striking 

 modifications may be produced and perpetuated in the 

 careful cultivation of plants is undeniable, and Darwin asks : 

 " Can it, then, be thought improbable, seeing that variations 

 useful to man have undoubtedly occurred, that other 

 varieties useful in some way to each being in the great and 

 complex battle of life should occur in the course of many 



