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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