COLOR-SENSE 89 



in birds there is a very close correlation between the character 

 of their food and their external coloring. It is only those 

 who have adopted a frugivorous diet that have acquired 

 brilliant hues. How important a good sense of color must 

 be to a fruit-eating animal became clearly demonstrated to 

 me while I was on a visit to Norway; the wild strawberries 

 were then ripe, and several of my party began to gather 

 them; one man, however, could not find any, and it was 

 afterward discovered that he was red-green blind. Had 

 he had to depend for his sustenance on such small fruits, 

 which he gathered for himself, he must soon have perished. 

 In both birds and mammals bright coloring is often sex- 

 limited, and most frequently it is the male which is the more 

 resplendent. Physiologists are generally agreed that such 

 secondary sexual characters are dependent on internal 

 secretions of the genital organs testes or ovaries. This 

 point lends considerable support to the Darwinian hypothesis 

 of sexual selection. It is an hypothesis which, if accepted, 

 recognizes the presence of the color-sense in those animals 

 which have acquired sex-limited decorative hues. The theory 

 of sexual selection raised so much controversial discussion 

 that it will be well here to quote what such an authority as 

 Prof. Weissman 47 wrote concerning it fifty years after the 

 publication of The Origin of Species: ' I really see no reason 

 why we should doubt the power of sexual selection, and I 

 myself stand wholly on Darwin's side. Even though we 

 certainly cannot assume that the females exercise a con- 

 scious choice of the handsomest mate and deliberate like 

 the judges in a court of justice over the perfections of their 

 wooers, we have no reason to doubt that distinctive forms 

 (decorative feathers) and colors have a particularly exciting 

 effect upon the female, just as certain odors have among 

 animals of so many different groups, including the butter- 



