336 



THE AMERICAN NATURALIST [Vol. XLIII 



For clear thinking it is of the greatest importance to 

 distinguish variation as a process from variation as an 

 existing static condition of diversity. If this distinction 

 is not made, we may delude ourselves into thinking we 

 have seen evolution occurring, when all we have seen is 

 the complexity that induces us to invent the theory of 

 evolution. The difference is just the difference between 

 seeing a problem, and seeing its solution ; between asking 

 a question and answering it. 



But is there indeed no evidence that actual racial 

 changes occur in unicellular forms ? On this point we have 

 the extremely important work of Barber. 11 Barber was 

 the first to undertake in bacteria and yeasts the study of 

 ''pure lines"— of races derived entirely from a single 

 individual. In general his results were the same as those 

 set forth above for Paramecium. Many races of yeasts 

 and bacteria exist, and these races are constant (with the 

 exceptions to be noted). Environmental effects were not 

 inherited, and long continued selection was of no effect in 

 changing such a race. Barber studied also unusual indi- 

 viduals ; he found, just as I have set forth above for Para- 

 meicum, that their peculiarities were, as a rule, not in- 

 herited. But he did find a few cases of peculiar individ- 

 uals within a pure race, that transmitted their peculiari- 

 ties to their descendants. Here we have then actual 

 changes in a race; variations in the dynamic sense. In 

 this way there were produced races of yeasts having cells 

 of a different form ; races of bacteria composed of longer 

 rods than the parents. But such cases were extremely 

 rare. Variations that perpetuate themselves were found 

 only in one individual among thousands. Barber's work 

 goes as strongly as my own against the significance of the 

 common variations among individuals— such variations 

 as are measured by the coefficient of variation— for hered- 

 ity or evolution. 



To recapitulate, we find that the unicellular organisms 

 are made up of numerous races, differing minutely but 



