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Natural Selection must have been at work to produce some 
of those changes by which the transmutation of species has 
been effected. It should be remembered that the theory of 
Mixed Darwinism implies that transmutation of species 
can take place either with or without Natural Selection ; 
that, in the phraseology of Semper, nature works by 
transforming influences alone, by means of selective 
influences alone, or through the co-operation of both these 
agencies. This being so, the logical mode of procedure 
would surely be first to show all that can be done by 
nature through transforming influences before we introduce 
the principle of Natural Selection. We must be quite sure 
that we know all the factors of Organic Evolution before 
we venture to say that because certain results have not 
been brought about by the transforming influences with 
which we are acquainted, it must have been brought about 
by Natural Selection. And even then we must be quite 
sure that all the logical demands of the theory are capable 
of being realised in nature. But Mr. Spencer has not 
followed this method of demonstration. P'irst of all he 
proves that the inherited effects of use and disuse is a law 
of nature which amply accounts for certain phenomena, 
but not for all; and then ignoring his third factor of “the 
direct action of environing matters and forces,” he 
proceeds to argue as if the choice lay between the inherited 
effects of use and disuse and Natural Selection, and to 
infer that what cannot be produced by the one must be 
produced by the other. 
Having thus introduced the principle of Natural Selec 
tion, he proceeds to show that there are certain instances 
of transmutation for which Natural Selection cannot 
account, and then, without asking whether the inherited 
effects of use or disuse will account for these phenomena, 
he proceeds to deduce the necessity for his third factor.