COMMENTS ON THE EVOLUTION AND 

 CLASSIFICATION OF BACTERIA 



R. S. BREED, H. J. CONN and J. C. BAKER 

 From the New York Agricultural Experiment Station, Geneva, New York 



Received for publication, November 12, 1917 



The incompleteness of our present knowledge as to the species 

 of bacteria and their relationships makes it very easy to criticise 

 what others have written upon their evolution and to propose 

 modifications in the classification of the group which in their 

 turn are open to equal criticism. There has been so much 

 speculation along this Hne recently^ that a certain amount of 

 confusion has resulted, and there is danger of increasing this 

 confusion by discussing the subject from a new point of view. 

 There would be little justification, indeed, for doing so, were 

 it not for the fact that Jensen (1909) has already drawn up a 

 detailed ancestral tree for the known groups of bacteria which 

 has considerable merit and that the committee on classification 

 appointed by the Society of American Bacteriologists (Winslow, 

 et al., 1917 b) has accepted many of Jensen's suggestions. This 

 committee has given the matter so much thought and has drawn 

 up such a well formulated report that there is danger of their 

 recommendations being accepted in toto without sufficient 

 scrutiny. Underlying their classification are certain assumptions 

 as to the evolution and relationships of bacteria that should be 

 thoroughly discussed before the report is adopted by the society. 



In discussing the relationships of bacteria, it is necessary to 

 keep in mind — just as when deahng with higher forms of hfe — 

 that the Uving species represent only the ends of evolutionary 

 lines, and that one modern form must not be considered the 

 ancestor of another. It is probably true that there has been a 

 greater persistence of primitive types among bacteria than in 

 any other group of animals or plants, because the environment 



1 See Jensen (1909), Buchanan (1917) and Kligler (1917). 



445 



