136 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 



appearing except in cases where their presence may be explained by 

 the hypothesis of hereditary descent; while in thousands of such cases 

 we find these structures undergoing every conceivable variety of 

 adaptive modification. 



Consequently, special creationists must fall back upon another 

 position and say, Well, but it may have pleased the Deity to form 

 a certain number of ideal types, and never to have allowed the 

 structures occurring in one type to appear in any of the others. We 

 'answer, Undoubtedly such may have been the case; but, if so, it is 

 a most unfortunate thing for your theory, because the fact implies 

 that the Deity has planned his types in such a way as to suggest the 

 counter-theory of descent. For instance, it would seem most capri- 

 cious on the part of the Deity to have made the eyes of an innumerable 

 number of fish on exactly the same ideal type, ; nd then to have made 

 the eye of the octopus so exactly like these other eyes in superficial 

 appearance as to deceive so accomplished a naturalist as Mr. Mivart, 

 and yet to have taken scrupulous care that in no one ideal particular, 

 should the one type resemble the other. However, adopting for the 

 sake of argument this great assumption, let us suppose that God did 

 lay down these arbitrary rules for his own guidance in creation, and 

 then let us see to what the assumption leads. If the Deity formed a 

 certain number of ideal types, and determined that on no account 

 should he allow any part of one type to appear in any part of another, 

 surely we should expect that within the limits of the same type the 

 same typical structures should always be present. Thus, remember 

 what efforts, so to speak, have been made to maintain the uniformity 

 of type in the case of the fore-limb as previously explained, and should 

 we not expect that in other and similar cases a similar method should 

 have been followed ? Yet we repeatedly find that this is not the case. 

 Even in the whale, as we have seen, the hind-limbs are either alto- 

 gether absent or dwindled almost to nothing; and it is impossible to see 

 in what respects the hind-limbs are of any less ideal value than the 

 fore-limbs which are carefully preserved in all vertebrated animals 

 except the snake, and the extinct Dinornis, where again we meet in 

 this particular with a sudden and sublime indifference to the main- 

 tenance of a typical structure (Fig. 15). Now I say that if the theory 

 of ideal types is true, we have in these facts evidence of a most unrea- 

 sonable inconsistency. But the theory of descent with continued 

 adaptive modification fully explains all the known cases; for in every 

 case the degree of divergence from the typical structure which an 



