THEORY OF EVOLUTION 13 



color are now maintained in our cultures. 

 Some of them are so similar that they can 

 scarcely be separated from each other. It is 

 easily possible beginning with the darkest eye 

 color, sepia, which is deep brown, to pick out a 

 perfectly graded series ending with pure white 

 eyes. But such a serial arrangement would 

 give a totally false idea of the way the different 

 types have arisen; and any conclusion based 

 on the existence of such a series might very 

 well be entirely erroneous, for the fact that such 

 a series exists bears no relation to the order in 

 which its members have appeared. 



Suppose that evolution "in the open" had 

 taken place in the same way, by means of dis- 

 continuous variation. What value then would 

 the evidence from comparative anatomy have 

 in so far as it is based on a continuous series of 

 variants of any organ? 



No one familiar with the entire evidence will 

 doubt for a moment that these 12.5 races of 

 Drosophila ampelophila belong to the same 

 species and have had a common origin, for while 

 they may differ mainly in one thing they are 

 extremely alike in a hundred other things, and 



