9 
occupies several pages of his Darwin and After-Darwin 
with correcting what he regards as the mistakes and falla 
cies concerning Natural Selection of which its advocates 
no less than its opponents are guilty. Certainly, it must 
be admitted that some very shrewd and clever persons 
have engaged in this interesting enquiry, and it is therefore 
startling to find that it is so easy to fall into error as to 
what the theory means or implies. 
This liability to misapprehension, however, is not alto 
gether the fault of the critic or of the student ; for putting 
on one side those points in which one expert differs from 
another, such as whether Natural Selection is the sole 
method of the transmutation of species, or only one among 
many, we have to take note of the fact that one writer 
sometimes contradicts himself on questions of very great 
importance :—such as the nature of the variations from 
which selection is made ; the strictness or laxity of the 
selection; the result of the selection; whether it be the 
survival of the fittest, or only the elimination of the least 
fit; the constancy or occasional occurrence of Natural Selec 
tion ; and the severity or mildness which characterises the 
struggle for existence. 
The materials on which Natural Selection works are 
the variations which occur necessarily and inevitably in 
connection with the phenomenon of sexual reproduction ; 
and obviously the nature attributed to them will largely 
influence the a priori credibility of the theory. If the 
variations are very slight, if they diverge in all directions, 
and if, therefore, only a few favourable variations occur, 
it is obvious that a stricter selection will be required than 
if the variations are considerable in quantity and if many 
favourable variations occur. 
Mr. Darwin says that variations are slight. And yet 
he says that monstrosities graduate so insensibly into