“ Factors of Organic Evolution” 103 
I have quoted enough to show that Dr. Erasmus Darwin 
would have protested against the supposition that func- 
tionally produced modifications were an adequate explana- 
tion of all the phenomena of organic modification. He 
declares accident and the chances and changes of this 
mortal life to be potent and frequent causes of variations, 
which, being not infrequently inherited, result in the 
formation of varieties and even species, but considers these 
causes if taken alone as no less insufficient to account for 
observable facts than the theory of functionally produced 
modifications would be if not supplemented by inheritance 
of so-called fortuitous, or spontaneous variations. The 
difference between Dr. Erasmus Darwin and Mr. Spencer 
does not consist in the denial by the first, that a variety 
which happens, no matter how accidentally, to have varied 
in a way that enables it to comply more fully and readily 
with the conditions of its existence, is likely to live longer 
and leave more offspring than one less favoured ; nor in the 
denial by the second of the inheritance and accumulation of 
functionally produced modifications; but in the amount 
of stress which they respectively lay on the relative im- 
portance of the two great factors of organic evolution, the 
existence of which they are alike ready to admit. 
With Erasmus Darwin there is indeed luck, and luck has 
had a great deal to do with organic modification, but no 
amount of luck would have done unless cunning had known 
how to take advantage of it ; whereas if cunning be given, 
a very little luck at a time will accumulate in the course of 
ages and become a mighty heap. Cunning, therefore, is 
the factor on which, having regard to the usage of language 
and the necessity for simplifying facts, he thinks it most 
proper to insist. Surely this is as near as may be the 
opinion which common consent ascribes to Mr. Spencer 
himself. It is certainly the one which, in supporting 
Erasmus Darwin’s system as against his grandson’s, I have 
always intended to support. With Charles Darwin, on 
