October 3, 1913] 



SCIENCE 



467 



appalling unrelated resemblance. Morph- 

 ology had become somewhat intolerant in 

 the application of its canons, especially 

 since it was aided by the phenomenal 

 growth of embryology. You must not com- 

 pare ectodermal with endodermal products. 

 You must not make a likeness out of an- 

 other germinal layer or anything that ap- 

 pertains to it, because if you do that would 

 be a horror, a heresy, a homoplasy. 



Haeckel went so far as to distinguish 

 between a true homology, or homophyly, 

 which depends upon the same origin, and 

 a false homology, which applies to all those 

 organic resemblances which derive from an 

 equivalent adaptation to similar develop- 

 mental conditions. And he stated that the 

 whole art of the morphologist consists in 

 the successful distinction between these 

 two categories. If we were able to draw 

 this distinction in every case, possibly some 

 day the grand tree of each great phylum, 

 may be of the whole kingdom, might be 

 reconstructed. That would indeed be a 

 tree of knowledge, and, paradoxically 

 enough, it would be the deathblow to classi- 

 fication, since in this, the one and only 

 true natural system, every degree of con- 

 sanguinity and relationship throughout all 

 animated nature, past and present, would 

 be accounted for; and to that system no 

 classification would be applicable, since 

 each horizon would require its own group- 

 ing. There could be definable neither 

 classes, orders, families nor species, since 

 each of these conceptions would be bound- 

 less in an upward or downward direction. 



Never mind the ensuing chaos ; we should 

 at least have the pedigree of all our fellow 

 creatures, and of ourselves among them. 

 Not absolute proof, but the nearest possible 

 demonstration that transformation has 

 taken place. Empirically we know this 

 already, since, wherever sufficient material 

 has been studied, be it organs, species or 



larger groups, we find first that these units 

 had ancestors and, secondly, that the an- 

 cestors were at least a little different. 

 Evolution is a fact of experience proved by 

 circumstantial evidence. Nevertheless we 

 are not satisfied with the conviction that 

 life is subject to an unceasing change, not 

 even with the knowledge of the particular 

 adjustments. We now want to understand 

 the motive cause. First What, then How 

 and now Why? 



It is the active search for an answer to 

 this question (Why?) which is character- 

 istic of our time. More and more the or- 

 ganisms and their organs are considered as 

 living, functional things. The mainspring 

 of our science, perhaps of all science, is not 

 its utility, not the desire to do good, but, as 

 an eminently matter-of-fact man, the father 

 of Frederick the Great, told his Royal 

 Academicians (who, of course, were asking 

 for monetary help) in the following shock- 

 ingly homely words: "Der Grund ist derer 

 Leute ihre verfiuchte Curieusiteit. " This 

 blamed curiosity, the beginnings of which 

 can be traced very far back in the lower 

 animals, is most acutely centered in our 

 desire to find out who we are, whence we 

 have come, and whither we shall go. And 

 even if zoology, considering the first and 

 last of these three questions as settled, 

 should some day solve the problem: 

 Whence have we come? there would re- 

 main outside zoology the greater Why? 



Generalizations, conclusions, can be ar- 

 rived at only through comparison. Com- 

 parison leads no further where the objects 

 are alike. If, for instance, we restrict our- 

 selves to the search for true homologies, 

 dealing with homogenes only, all we find is 

 that once upon a time some organism has 

 produced, invented, a certain arrangement 

 of Anlage out of which that organ arose, 

 the various features of which we have com- 

 pared in the descendants. Result: we 



