158 Evolution and Adaptation 



account of the accomplishments of the theory of natural se- 

 lection than this, by one of the leaders of the modern school : 

 " Discouraging, therefore, as it may be that the control of 

 nature in her minutest details is here gainsaid us, yet it were 

 equivalent to sacrificing the gold to the dross, if simply from 

 our inability to follow out the details of the individual case 

 we should renounce altogether the principle of selection, or 

 should proclaim it as only subsidiary, on the ground that we 

 believe the protective coloring of the butterfly is not a pro- 

 tective coloring, but a combination of colors inevitably result- 

 ing from internal causes. The protective coloring remains a 

 protective coloring whether at the time in question it is or is 

 not necessary for the species ; and it arose as protective col- 

 oring — arose not because it was a constitutional necessity of 

 the animal's organism that here a red and there a white, 

 black, or yellow spot should be produced, but because it was 

 advantageous, because it was necessary for the animal. 

 There is only one explanation possible for such patent adap- 

 tations, and that is selection. What is more, no other natural 

 way of their originating is conceivable, for we have no right 

 to assume teleological forces in the domain of natural phe- 

 nomena." 



Weismann states that he does not accept Eimers's view that 

 the markings of the wings of the butterflies of the genus 

 Papilio are due to a process of evolution in a direct line, in- 

 dependent of external causes. 



"On the contrary, I believe it can be clearly proved that 

 the wing of the butterfly is a tablet on which Nature has in- 

 scribed everything she has deemed advantageous to the pres- 

 ervation and welfare of her creatures, and nothing else ; or, to 

 abandon the simile, that these color patterns have not pro- 

 ceeded from inward evolutional forces but are the result of 

 selection. At least in all places where we do understand 

 their biological significance these patterns are constituted and 

 distributed over the wing exactly as utility would require." 



