SYMBIONTICISM AND ORGANIC EVOLUTION 143 



is reasonable to suppose that the acquisition of a particular 

 "injurious" microsymbiont by the host organism led to 

 degenerative responses. It is evident that the "destruc- 

 tive" influence does not operate on the germ plasm of the 

 host, but becomes effective when the animal has reached a 

 certain stage in its development and the microsymbiont 

 has asserted its specific influence. 



Paleontological researches, have shown that new species 

 apparently have arisen suddenly. Furthermore, it seems 

 that in certain geologic eras a large number of new species 

 arose simultaneously. On the basis of these observations 

 and the geologic indications, it has been suggested that 

 "cataclysms" have occurred during various periods. It is 

 quite certain that in the origin of species, large numbers of 

 individuals of a given species were modified simultaneously. 

 It is impossible to go back into geologic time and observe 

 Symbionticism in operation. However, we find a possible 

 clue as to the factors operating in Symbionticism, in the 

 behavior of bacteria in some epidemic diseases. While 

 we know some of the factors concerned in a number of 

 disease epidemics (bubonic plague, cholera, typhoid), we 

 have not been able to solve the mystery of the influenza 

 pandemics that periodically have swept the world. This 

 phenomenon illustrates the possibihties of bacterial be- 

 havior. The pecuUar movements and appearances of 

 these epidemics have been so puzzling that many patholo- 

 gists beheve that the organism associated with the disease 

 is a modification of some form that is constantly present 

 but harmless. Such a suggestion implies a response of the 

 microorganism to some unknoiun extrinsic influence. Nu- 

 merous attempts have been made to isolate a distinctive 

 organism associated with the disease. Many claims of 

 discovery have been made, but the concensus of opinion 

 among pathologists appears to be that the organism as- 

 sociated with the disease is normally harmless and present 



