Darwin s Artificial and Natural Selection 159 



Again : " I should be far from maintaining that the mark- 

 ings arose unconformably to law. Here, as elsewhere, the 

 dominance of law is certain. But I take it, that the laws 

 involved, that is, the physiological conditions of the variation, 

 here are without exception subservient to the ends of a higher 

 power — utility; and that it is utility primarily that deter- 

 mines the kind of colors, spots, streaks, and bands that shall 

 originate, as also their place and mode of disposition. The 

 laws come into consideration only to the extent of conditioning 

 the quality of the constructive materials — the variations, out 

 of which selection fashions the designs in question. And this 

 also is subject to important restrictions, as will appear in the 

 sequel." This conclusion contains all that the most ardent 

 Darwinian could ask. 



He rejects the idea that internal laws alone could have pro- 

 duced the result, because : — 



" If internal laws controlled the markings on butterflies' 

 wings, we should expect that some general rule could be es- 

 tablished, requiring that the upper and under surfaces 

 of the wings should be alike or that they should be 

 different, or that the fore wings should be colored the same 

 as or differently from the hind wings, etc. But in reality all 

 possible kinds of combinations occur simultaneously, and no 

 rule holds throughout. Or, it might be supposed that bright 

 colors should occur only on the upper surface or only on the 

 under surface, or on the fore wings or only on the hind wings. 

 But the fact is they occur indiscriminately, now here, now 

 there, and no one method of appearance is uniform throughout 

 all the species. But the fitness of the various distributions of 

 colors is apparent, and the moment we apply the principle of 

 utility we know why in the diurnal butterflies the upper sur- 

 face alone is usually variegated and the under surface pro- 

 tectively colored, or why in the nocturnal butterflies the fore 

 wings have the appearance of bark, of old wood, or of a leaf, 

 whilst the hind wings, which are covered when resting, alone 



