82 THE POPULAR SCIENCE MONTHLY. 



internal law of 'growth, independently of all questions of natural 

 selection. 



There is another class of natural phenomena upon which Mr. 

 Wallace writes much that is deeply interesting, but to which it 

 may possibly be questioned whether the principle of survival by 

 natural selection is applicable — namely, the phenomena of mimic- 

 ry. Of course it is quite intelligible, to take an instance, that a 

 living creature which is very much like a leaf will escape many 

 enemies, and even have such an advantage in the struggle for life 

 that many other living creatures would be like leaves if they 

 could. But when we endeavor to go back in imagination to the 

 commencement of the mimicking process, we must conceive of a 

 creature not at all like a leaf, but among whose offspring there 

 are certain individuals which have a slightly leaf -like appearance, 

 and that these survive in preference to others not having the ap- 

 pearance in question. The conception involves two difficulties : 

 First, the notion of certain individuals having a slightly leaf -like 

 appearance is eccentric and hard to accept. It is different from 

 that of individuals varying by length of leg, or strength of wing, 

 or what not. It is a variation, so to speak, not of degree but of 

 kind. And, secondly, it is difficult to see why a resemblance to a 

 leaf, admitted to be slight, and therefore one would imagine not 

 easily perceived, should be any substantial protection from ene- 

 mies, and so an appreciable advantage in the struggle for life. 



Similar difficulties occur with regard to other cases of mimicry. 

 My space does not permit me to examine them in detail ; but I 

 have come to the conclusion that, while mimicry may probably 

 be always connected with some advantage which it confers on the 

 animal, it is difficult to conceive of the mimicking transformation 

 being originally brought into operation by any process of natural 

 selection. 



This failure of the principle of natural selection to explain 

 much that is connected with the evolution both of men and of 

 inferior creatures may lead us to inquire, to what extent the prin- 

 ciple satisfies etiological requirements even in those cases in 

 which its application appears most complete. The modification 

 and multiplication of species require three conditions to be post- 

 ulated : (1) an original species; (2) the power of multiplying that 

 species by reproduction ; and (3) the occurrence of variations in 

 the successive generations. 



Now (1) the existence of the original living germ or germs 

 must, I suppose, be left by universal consent in mystery. Mr. 

 Darwin treated of the Origin of " Species," not the Origin of " liv- 

 ing tilings" This latter question is not likely ever to come within 

 the reach of human science ; certainly it has not done so yet. 

 Given the existence of the material universe, or the existence of 



