VALUE AND ORIGIN OF COLOR VISION 463 



as it is in most cases and possibly in all, it involves differential sensations 

 with respect to frequencies or imitative combinations of frequencies — 

 mixtures which arouse the same sensations as single frequencies or other 

 mixtures (see pp. 81-102). 



In science, questions which begin with the word 'what' are supposed 

 to come first, to be followed by 'how' questions — 'why' queries being 

 left largely to the philosophers. We know a great deal about the 'what' 

 of color vision. But we know exasperatingly little about its 'how'. It is 

 about as profitable, in the present state of knowledge, to spend thought 

 upon its 'why': 



For human beings, color vision has largely aesthetic values. If it is 

 present in lower animals, which certainly cannot appreciate sunsets and 

 old masters, what does it do for those animals? What was the incentive 

 for its evolution? We cannot answer this question simply by comparing 

 our chromatic, daylight vision with our achromatic experiences by 

 moonlight, for too much else besides color is missing in the latter. But 

 if we compare a black-and-white motion picture with one in color, we 

 note at once a great difference in the visibility of things in the two^ The 

 black-and-white cameraman must be ever alert to maintain sufficient 

 contrast. The heroine may report for work wearing a red blouse and a 

 blue skirt. The cameraman may have to order one of them changed, if 

 she is not to appear, on the screen, as if wearing a uniform! There may 

 actually be more contrast in her costume, as far as the black-and-white 

 film is concerned, if she wears two shades of the same color. 



Color vision, then, promotes the perception of contrasts and hence, 

 visibility. It cannot make vision capable of such complete analysis as 

 audition (where every tone is a 'primary') can accomplish. But it does 

 add a hundred and sixty qualities to human vision. To the first animals 

 which developed a system of color vision, it meant the life-saving differ- 

 ence between being sometimes able to discriminate enemies and prey 

 against their backgrounds, and being usually able to do so. 'Conceal- 

 ment coloration' is a counter-adaptation of some animals against the dis- 

 guise-piercing searchlights of other animals' color vision; but if its evolu- 

 tion and perfection had ever caught up with color vision itself, zoologists 

 would probably not be here to worry over either phenomenon. 



The Duplicity Theory (Chapter 3, section C; Chapter 7, section D) 

 expresses the association of color discrimination with cone visual cells. 

 We shall see shortly that there is reason to suspect that this part of the 

 Theory does not hold at all universally; but at least no pure-rod animal 



