The Making of Species 



will be no evolution, unless, by some cause or 

 other, portions of the species are isolated, because 

 in the long run the mutations will neutralise one 

 another. 



Let us now suppose that natural selection 

 comes into play. The old method of determining 

 by lot which forms shall persist is replaced by 

 selection on the fixed principle that the fittest 

 shall survive. The mutations appear as before, 

 and as before, of the large number that occur, 

 only a few are permitted to survive. But now 

 the survivors, instead of being a motley crowd, 

 are a selected band, composed of individuals 

 having many characteristics in common a 

 homogeneous company. Thus one result of 

 natural selection is to accelerate evolution, by 

 weeding out certain classes of individuals and 

 preventing them breeding with those it has 

 selected. On the other hand, natural selection 

 will tend to diminish the number of species which 

 have arisen through mutation, inasmuch as it 

 weeds out many mutants which would have 

 perished had their survival been determined by 

 lot 



From this the kind of work performed by 

 natural selection should be obvious. Natural 

 selection does not make new species. These 

 make themselves, or, rather, originate in accord- 

 ance with the laws of variation. 



"You can," runs an old proverb, " bring a 

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