“ Factors of Organic Evolution” ror 
though less, which must be ascribed to this cause.” (Italics 
mine.) 
Mr. Spencer does not here say expressly that Erasmus 
Darwin and Lamarck considered inheritance of function- 
ally produced modifications to be the sole explanation 
of the facts of organic life ; modern writers on evolution 
for the most part avoid saying anything expressly ; this 
nevertheless is the conclusion which the reader naturally 
draws—and was doubtless intended to draw—from Mr. 
Spencer’s words. He gathers that these writers put for- 
ward an “ utterly inadequate ”’ theory, which cannot for a 
moment be entertained in the form in which they left it, 
but which, nevertheless, contains contributions to the 
formation of a just opinion which of late years have been 
too much neglected. 
This inference would be, as Mr. Spencer ought to know, 
a mistaken one. Erasmus Darwin, who was the first to 
depend mainly on functionally produced modifications, 
attributes, if not as much importance to variations induced 
either by what we must call chance, or by causes having no 
connection with use and disuse, as Mr. Spencer does, still 
so nearly as much that there is little to choose between 
them. Mr. Spencer’s words show that he attributes, if not 
half, still not far off half the modification that has actually 
been produced, to use and disuse. Erasmus Darwin does 
not say whether he considers use and disuse to have 
brought about more than half or less than half; he only 
says that animal and vegetable modification is “ in part 
produced ” by the exertions of the animals and vegetables 
themselves ; the impression I have derived is, that just as 
Mr. Spencer considers rather less than half to be due to use 
and disuse, so Erasmus Darwin considers decidedly more 
than half—so much more, in fact, than half as to make 
function unquestionably the factor most proper to be 
insisted on if only one can be given. Further than this 
he did not go. I will quote enough of Dr. Erasmus 
