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to admit that Natural Selection could have had no part 
whatever in relation to a species whose typical form 
remained the same throughout long periods of time. But 
it is not so. It is confidently asserted that the stability of 
species itself is largely due to the action of Natural 
Selection, for it is contended that it not only produces the 
adaptation of the organism to the conditions, but main 
tains it after it has been produced. Mr. Fiske says :— 
“We see that Natural Selection, like a power that slumbers not 
nor sleeps, is ever preserving the stability of species, by seizing all 
individual peculiarities that oscillate within narrow limits on either 
side of the mean that is most advantageous to the species, while 
cutting off all such peculiarities as transgress these limits.”— 
(.Darwinism and other Essays, p. /5.) 
Mr. Herbert Spencer recognises 
“Natural Selection as a means of preserving an already estab 
lished balance between the powers of a species and the forces to 
which it is subject.”—(Principles of Biology, vol. i., p. 44p.) 
Now the first objection to this view is that the inter 
position of Natural Selection is not required to maintain 
the stability of a species which has become adapted 
to new conditions. We have seen that variations neces 
sarily associated with sexual reproduction are swallowed 
up in the average of the race ; so that, in spite of con 
stantly emerging variety, the specific type is preserved 
essentially unchanged. Now by the law of parsimony we 
are forbidden to assume the existence of another cause, 
when one which is sufficient to produce all the phenomena 
is already in the field. The principle of regression to 
mediocrity, about whose action there is no doubt, will 
account for the stability of species, and we need not there 
fore look for another cause ; and we must not, if the law 
of parsimony is to be obeyed.