524 THE POPULAR SCIENCE MONTHLY 



conditions. Concerning the fate of any individual we can say nothing. 

 The problem is,, therefore, a statistical one; evolution, as it occurs in 

 nature, is not a problem of " individuals " but of " populations." 



A. The Protective Value of Color 

 For a century field naturalists have observed the close similarity 

 between the colors of organisms and their environment, and have seen 

 in this resemblance an adaptation for protection. Since the advent of 

 the selection theory protective and aggressive resemblance, warning 

 colors, recognition characters and mimicry have been prominent in 

 biological literature, and are conceptions associated with some of the 

 most honored names in biology. Yet almost all the evidence has been 

 comparative, and attempts to determine empirically whether given color 

 patterns are in the long run of vital significance are discouragingly 

 few, and some biologists are now questioning whether the so-called 

 protective adaptations have any value at all. 



One of the simplest and most direct tests of the value of any char- 

 acter in determining the chances of survival of an individual is that of 

 Di Cesnola for the protective value of color in Mantis religiosa. 1 In 

 Italy the green individuals of this species are found on green grass, the 

 brown ones upon grass burnt by the sun. If the color has any protective 

 value there should be a higher death rate from enemies when the in- 

 sects are exposed on vegetation of a color unlike their own. 



Altogether 110 insects, 45 green and 65 brown were secured and 

 were exposed on separate plants as follows : 



Green insects on green plants 20 



Green insects on brown plants 25 



Brown insects on brown plants 20 



Brown insects on green plants 45 



The experiment began August 15' and observations were made daily 

 for seventeen days. Of the forty individuals exposed on vegetation of 

 similar color, every one survived throughout the entire experiment. 

 All the green individuals exposed on brown grass were killed in eleven 

 days; of the forty-five brown individuals exposed on green grass, ten 

 survived to September 1, when a severe gale destroyed the experiment. 

 This is all made clear by Fig. 1. 



The biometrician would like to see this experiment carried out on 

 a much larger scale, but when we consider that not one of the forty in- 

 sects exposed on similarly colored vegetation was killed at the end of 

 seventeen days, while sixty of the seventy exposed on dissimilarly col- 

 ored vegetation were eliminated 2 by the end of the first eleven days, I 



1 Di Cesnola, A. P., "Preliminary Note on the Protective Colour in Mantis 

 religiosa," Biometrika, Vol. III., pp. 58-59, 1909. 



2 Most of the insects were destroyed by birds ; five were known to have been 

 killed by ants. 



