HOMOLOGY AND ITS INTERPRETATION 55 



semble their parents. Why look for more recondite explana- 

 tions when one so obvious is at hand? The atavistic theory- 

 gratifies his instinct for simplification, and, if he be of a 

 mechanistic turn of mind, the alternative conception of crea- 

 tionism is quite intolerable. Nevertheless, it goes without 

 saying that the "inference" of common descent from the data 

 of homology is not a ratiocination at all, it is only a simple 

 apprehension, a mere abstraction of similarity from similars — 

 ^'Unde quaecumque inveniuntur convenire in aliqua intentione 

 intellecta," says Aquinas, "voluerunt quod convenirent in una 

 re." {In lib. II sent., dist. 17, q. I, a. 1) Philosophy tells us 

 that the oneness of the universal is conceptual and not at all 

 extramental or real, but the transformist insists that the 

 universal types of Zoology and Botany are endowed with real 

 as well as logical unity, that real unity being the unity of the 

 common ancestor. 



Certainly, from the standpoint of practical effectiveness, the 

 evolutionary argument leaves little to be desired. The presen- 

 tation is graphic and the solution simple. But for the critic, 

 to whom logical sequence is of more moment than psychologi- 

 cal appeal, this is not enough. To withstand the gnawing 

 tooth of Time and the remorseless probing of corrosive human 

 reason, theories must rest on something sounder than a mirage 

 of visual imagery! 



Tell me where is fancy bred, 

 Or in the heart or in the head? 

 How begot, how nourished? 



Reply, reply. 

 It is engendered in the eyes, 

 With gazing fed; and fancy dies 

 In the cradle where it lies. 



But is it fair thus to characterize the "common ancestors" of 

 Transformism as figments which, like all other abstractions, 

 have no extramental existence apart from the concrete objects 

 whence they were conceived? To be sure, their claim to be real 

 entities cannot be substantiated by direct observation or ex- 



