5i4 THE POPULAR SCIENCE MONTHLY 



changes of form in cattle. Add to these the differences we daily see produced 

 in smaller animals by our domestication of them, as rabbits or pidgeons, or 

 from the differences of climate or even of seasons. . . . Add to these the various 

 changes produced in the forms of mankind by their early modes of exertion, or 

 the diseases occasioned by their habits of life, both of which become hereditary, 

 and that through many generations. 24 



The argument had often been repeated in the nineteenth century; 



and in the period under consideration we find Spencer observing that 



The supporters of the Development Hypothesis . . . can show that the 

 degrees of difference so produced [through structural changes under altered 

 conditions] are often, as in dogs, greater than those on which distinctions 

 of species are in other cases founded. They can show that it is a matter of 

 dispute whether some of these modified forms are varieties or separate species. 26 



This argument, it is true, if taken by itself, suffered from two 

 serious limitations. One has already been adverted to, in another con- 

 nection: the absence of evidence that variation can produce varieties 

 sterile inter se, as species are sterile. But we have already seen that 

 this difficulty, upon the testimony of Huxley himself, was not removed 

 in 1859. The other limitation of the argument was that, before the 

 promulgation of the hypothesis of natural selection, it was commonly 

 associated with a belief in the inheritance of acquired characters. But 

 this association was not logically necessary ; and in any case, the whole- 

 sale denial of such inheritance is a doctrine of neo-Darwinism unknown 

 to the pre-Darwinian period and to Darwin himself; and was in that 

 period, therefore, not a ground of difficulty. 



In a subsequent instalment of this inquiry it will remain to con- 

 sider, somewhat more minutely, four more of the principal general 

 arguments for evolutionism, three of these being, in 1844, of a much 

 less venerable age than the two last mentioned. 



{To be concluded) 



24 " Zoonomia," 1794, pp. 500-501. The elder Darwin, it will be noted, 

 believed in the inheritance of acquired characters; he might be called an 

 eo-Lamarckian. 



25 " The Development Hypothesis," 1852. 



