368 MR. G. J. ROMANES ON PHYSIOLOGICAL SELECTION. 



sanje in kind, in this case I could liave seen that the question 

 would have been an open one as to which was cause and which 

 effect, or which was the conditional and which the conditioned. 

 But, as the case actually stands, on merely antecedent i^rounds it 

 does not appear to me that the question is an open one. Here 

 we have a constant peculiarity or condition of the reproductive 

 system, repeated over and over again millions of times, through- 

 out organic nature past and present ; and we perpetually find 

 that when this peculiar condition of the reproductive system 

 occurs it is associated with structural changes elsewhere, which, 

 however, may affect any part of any organism, and this in any 

 degree. Now, I ask, is it a reasonable view to imagine that the 

 one constant peculiarity is always the result and never the con- 

 dition of any among these millions of inconstant and organically 

 minute changes with which it is found associated ? Even if I 

 had no theory whereby to account for the primary and constant 

 distinction being also the primordial and conditioning distinction, 

 on merely a priori grounds I should feel convinced that in some 

 way or another it onust be so. 



But, secondly, quitting a priori grounds, it is a matter of 

 notorious fact that in the case of nearly all our innumerable 

 artificial productions, organisms admit of being profoundly 

 changed in a great variety of ways, without any reaction on the 

 reproductive system following as a consequence. So seldom, 

 indeed, does any such reaction follow from what may be termed 

 all these innumerable experiments upon the subject, that Mr. 

 Darwin was obliged to explain the discrepancy between the 

 known influence of artificial selection and the supposed influence 

 of natural selection by invoking a wholly indej)endent, an ex- 

 tremely hypothetical, and, to my mind, a most unsatisfactory 

 principle. This principle — i. e. that of prolonged exposure to 

 similar conditions of life — I have already considered, and shown 

 why it appears to me the feeblest suggestion that is to be met 

 with in the whole range of Mr. Darwin's writings. 



Thirdly, as regards wild species, Mr. Darwin shows that " the 

 correspondence between systematic alfinity and the facility of 

 crossing is by no means strict. A multitude of cases could be 

 given of very closely allied species which will not unite, or only 

 with extreme difiiculty ; and, on the other hand, of very distinct 

 species which unite with the utmost facility." And he goes on 

 to show that " within the limits of the same family, or even of 



